Search

Highly branched low-density polyethylene (HB-LDPE) synthesized from solely ethylene monomer through Brookhart-type α-diimine nickel or palladium catalysts have unique microstructure, low melting temperature and thermal plastic elastomer (TPE) properties. With the increasing demand for recyclable material, synthesis of HB-LDPE has been extensively studied. However, details of its microstructure and the impact of the microstructure on solid structure as well as mechanical/thermal properties have not been fully understood. In this study, various characterizations and mechanical testing are conducted on HB-LDPE entries synthesized by original Brookhart catalyst, 8-p-tolylnaphthylimino substituted sandwich catalyst, and a multinuclear heterogeneous crosslinked catalyst. First, 13C solution-state NMR spectroscopy was employed to obtain detailed insights into their branch structure, including branch density, identity and localization. Using chemical superposition methods, detailed localization structure of the branches were revealed. Formation mechanisms of several localization structures are proposed in supplementary for existing chain walking mechanisms. Second, the solid structure of HB-LDPEs was investigated by using differential Scanning calorimetry (DSC), X-ray diffraction (XRD) and solid-state NMR spectroscopy. The formers are no longer capable of quantitative characterization due to the low crystallinity. Through solid-state 13C NMR analysis, it was found that some entries are entirely amorphous, while the others are semi-crystalline entries which range between 1 and 5 %. The molecular dynamics in the crystalline phase is characterized through 13C spin-lattice relaxation time (T1C), which ranges from 4s to 80s, implying a variable crystalline size. By examining the combination of microstructure and crystalline structure, it is revealed that only those entries with both low levels of long chain branching (LCB) below 10 b/1kC and short chain branching (SCB) below 85 1kC are semi-crystalline. Finally, I have examined how their mechanical properties correlate with their structural characteristics. Various factors including branch density, branch distribution, crystallinity and crystalline size influence the yielding, strain hardening, strength and strain recovery behaviors of the material. Based on the findings from these experiments, a potential overview of the HB-LDPE-TPE system is discussed.

Virus capsids have the function to protect the genetic material from destructive influences in the in- and outside of the host and are usually determinant for the shape of the virus, e.g. icosahedral or helical. Drug design (antivirals, vaccines, and gene therapy), virus evolution and classification, and understanding of the viral life-cycle are all research areas that potentially benefit from structural data on virus capsids. In this thesis, capsid proteins were studied by solid-state nuclear magnetic resonance (NMR), a structural investigation tool profiting from recent developments in proton-detection at magic-angle spinning (MAS) frequencies of 100 and more kHz, but also relying on carbon detection experiments at MAS frequencies around 20 kHz. Additionally, cryo-electron microscopy (EM), a structural biology technique also growing in popularity in the field of viral capsids, was utilized. In Chapter 2 the newly obtained cryo-EM molecular structure of the African cichlid nackednavirus (ACNDV) capsid is presented. ACNDV belongs to a recently discovered non-enveloped fish virus family related to the enveloped human Hepatitis B virus (HBV). The obtained structure shows that the fold of the monomeric unit of the capsid remained surprisingly similar throughout the evolution despite the fact that the lineages of ACNDV and HBV have separated already more than 400 million years ago. Nevertheless, a number of differences are identified: first, the N-terminus of ACNDV capsid protein (Cp) is directed towards the capsid exterior instead of being oriented in parallel with the capsid shell, as in HBV Cp. Second, the dynamic region at the spike tip comprises more residues in ACNDV Cp compared to HBV Cp. Some of these ACNDV Cp spike residues were only visible by solid-state NMR. Third, the ACNDV capsid seems to be statically more disordered than the HBV capsid. The capsid of duck hepatitis B virus (DHBV), a further, though more closely related relative of human HBV, is examined by solid-state NMR in Chapter 3. Here, unlike for the ACNDV Cp, the NMR assignment remains largely incomplete, probably because the extension domain persisted in a disordered state. On the hunt for more easily assignable DHBV Cp variants, an unexpected morphology of DHBV Cp truncated after position 190 was discovered. The truncation variant forms tubes instead of spherical particles, but more resolved spectra were not obtained. At last, Chapter 4 describes the solid-state investigations on two variants of an artificially produced nanocontainer, whereas one of the protein variants (spNC-4) is the split version of the other (NC-4). The two protein spectra differ only in a few instances; a few residues nearby the spNC-4 split were not visible in the NC-4 spectra, likely due to different dynamics. Additionally, small chemical-shift changes in a segment spatially close to the split were detected, indicative of small structural differences. Furthermore, solid-state NMR spin-lock relaxation measurements indicate that microsecond timescale dynamics in NC-4 are within a similar range as in HBV Cp.

Over the last decades solid-state nuclear magnetic resonance (NMR) has emerged as a powerful tool for structural, functional and dynamic studies of biomolecules and materials. In this context protons may provide particularly valuable information due to their potential of forming hydrogen bonds, contributing to thermodynamic stability, supramolecular assembling or molecular recognition (e.g. protein-DNA/RNA interactions). The incomplete averaging of large 1H-1H dipolar couplings under magic-angle spinning (MAS) typically leads to broad spectral lines in proton-detected spectra. However, significant advances in spinning technology and access to spinning frequencies exceeding 100 kHz provide nowadays sufficient spectral resolution even in molecular systems with dense proton dipolar networks like fully protonated proteins, enabling practical applications. In this thesis we investigate both methodological and application aspects of proton-detected solid-state NMR in a spinning regime ranging from 60-170 kHz. Thereby, we will discuss the challenges and possibilities of this technique, whose constant evolution is driven by the access to ever faster spinning frequencies. In the first part of this work we focus on the factors influencing resolution in proton-detected spectra and how it can be improved by going to faster MAS frequencies and higher magnetic field strengths. We report remarkable proton linewidth narrowing in the spectra of a series of fully protonated proteins when pushing with an 0.5 mm probe-head prototype the sample rotation frequency to 150 kHz compared to the more routinely used 100 kHz. Furthermore, we find an improvement in mass sensitivity by comparison with spectra recorded in an 0.7 mm rotor operating at 100 kHz, despite the reduction in sample volume by a factor of 0.52 (from 0.59μL to 0.31μL). We attribute this observation to higher coil efficiency, linewidth narrowing and improvements in polarization-transfer efficiency. Systematic experimental studies monitoring the homogeneous linewidths in fully protonated molecules over the MAS range 60-170kHz reveal that the CH2 resonances in the small drug molecule Meldonium and in two phosphorylated amino acids profit the most from an increase in spinning frequency. To rationalize these findings we developed an alternative simulation method based on second-moment calculations to estimate the portion of the experimental linewidth that originates from the homonuclear dipolar network. Compared to conventional Liouville- von Neumann-based simulation programs, this second-moment approach is much less expensive and allows for performing calculations until convergence is reached also in large multi-spin systems. We established it on the model protein Ubiquitin and used it to prove that the Meldonium linewidth is indeed dominated by coherent dipolar effects and can thereby be improved significantly by faster spinning. Using this simulation approach we also illustrate how the proximity to CH2 groups can be particularly detrimental, due to the typically small spatial and spectral distances between the ethyl protons generating large residual linewidth contributions. In light of these results we also understand the experimental linewidth differences observed for two H2-splitting products of Frustrated Lewis Pairs that we present as an example to illustrate the great potential of proton-detected solid-state NMR for structural studies of functionalized catalytic materials. Our linewidth simulations predict an additional coherent linewidth narrowing effect, when increasing the external magnetic field strength. We verify this prediction experimentally by comparing homogeneous proton linewidths in spectra of proteins and phosphorylated amino acids recorded at 20.0T (850MHz) and 28.2T (1.2GHz). Finally, we show how it is possible to obtain unprecedented resolution and almost baseline separation for the CH2 resonances in o-phospho-L-serine, using a combination of 160 kHz MAS and 28.2 T. In the second part of this thesis we use the strength of solid-state NMR to experimen- tally investigate protein dynamics. Measuring longitudinal and rotating-frame relaxation rate constants and using a detectors approach for data analysis, we obtain information on residue-specific amplitudes of motion over the nanosecond, hundreds of nanoseconds and microsecond timescales. In a first study we characterize the dynamics of the hepatitis B virus capsid. In particular we find that it shows larger amplitudes of microsecond motion within the capsid spike. Thanks to the detectors approach we were able to extract similar information from a recently published 1 μs molecular dynamics (MD) trajectory. A comparison between NMR and MD data reveals overall good agreement for the faster nanosecond motions thereby experimentally validating the MD results, but larger discrepancies for the slower motions on the timescales approaching the end of the trajectory. For these timescales it is therefore advisable to mostly rely on the NMR results. We also investigated the temperature dependence of the dynamics of the archaeal RNA polymerase subunit complex Rpo4-7 over the temperature range from 17 °C to 60°. In addition to proving the stability of the molecule under these conditions we observed in particular rather small differences for the nanosecond motions but a large thermal activation of the slower microsecond motions with increasing temperature. In a third part we explore different possibilities of using proton-detected solid-state NMR to study hydrogen bonding. We characterize asparagine ladder formation in HET-s(218-289) fibrils by using different spectral and relaxation properties of the NH2 proton sidechain resonances. We use a 1H-31P correlation experiment to generate protein-nucleotide correlation signals, proving spatial proximity and describing on a local level the nucleotide binding modes of the ATP-hydrolysis transition state in the bacterial DnaB helicase in complex with DNA. Finally, we use the temperature dependence of the proton chemical shifts as a direct proof for hydrogen bond formation. We extend this approach known from solution-state NMR to the solid-state using o-phospho-L-serine and ubiquitin as model compounds and apply it to further elucidate the protein-nucleotide interactions of the DnaB helicase. In the remaining chapters we characterize the performance of basic polarization transfer steps like spin-diffusion, INEPT and cross polarization and comment on the feasibility and potential of five-dimensional SO-APSY in the fast MAS regime. We show how a specific arginine labeling scheme can be used in combination with spin diffusion and non-refocused INEPT transfers to investigate the highly flexible C-terminal domain of the full-length HBV capsid, which has so far always escaped detection in conventional carbon and proton- detected NMR. Finally, we show some additional biomolecular applications of state-of the art proton-detected NMR. In particular we show techniques that can be used to probe protein side-chain-DNA contacts in the archaeal primase pRN1 and discuss preliminary fingerprint spectra of the prion sup35 and the hepatitis D virus antigen proteins.

Throughout most of the world’s oceans, the bioavailability of marine dissolved organic nitrogen (DON) acts to limit marine primary production and thus is a key control on marine biogeochemical cycles and carbon sequestration. Understanding the processes that control marine DON cycling and availability, and by extension long-term carbon storage in the ocean, are thus of vital importance. Nevertheless, despite significant research, the mechanisms that lead to the accumulation of refractory DON (RDON) largely remain an enigma. In this thesis, I address this knowledge gap by investigating the source and degradation processes of traditionally studied younger, high molecular weight (HMW) DON and, for the first time, directly isolated older, low molecular weight (LMW) solid phase extracted (SPE) DON. I used a range of novel proxies and analytical approaches, including a new suite of D-amino acids and the first compound-specific specific amino acid measurements across the DON age/size spectrum. These powerful molecular level proxies for proteinaceous marine DON source and cycling allowed me to posit a new theory for bacterial control of RDON production. Finally, I pair these analyses with broader advanced solid state NMR techniques to present new information regarding overall marine DON chemical composition. Together, I use these data to propose a novel theory regarding production of the most refractory nitrogen containing molecules in the ocean, suggesting a fundamental paradigm shift in our understanding of the marine DON pool.

Magnesium stearate (MgSt) is the most commonly used pharmaceutical excipient and is present in over half the tablet formulations on the market. In spite of its popularity as an effective lubricant, it has been repeatedly recognized that there is significant variability between MgSt samples, which can cause inconsistent lubrication between batches of MgSt. The hypothesis of this research is that the batch-to-batch variability in tablet lubrication and dissolution observed in tablet formulations containing different MgSt samples can be correlated with differences in MgSt physicochemical properties (fatty acid salt composition, crystal hydrate form, particle size and surface area). Developing correlations between MgSt properties has been challenging in part because there has not been a reliable method for determining crystal form. Recently, 13C solid-state nuclear magnetic resonance (SSNMR) has been used to clearly identifying the MgSt crystal forms. 13C SSNMR is used extensively throughout this work to identify the crystal forms of samples of MgSt. Thermogravimetric analysis and dynamic scanning calorimetry were used as complimentary techniques to understand thermal behavior of the samples. MgSt is typically used in tablets at low levels (0.2-5%), leading to challenges with detection of MgSt in formulations. To enhance detection in SSNMR, samples of MgSt have been synthesized in the lab using 13C-labeled stearic acid. Specific surface area (SSA) results were determined using N2 and Kr adsorption with BET calculations, and samples were dried using nitrogen flow for various times. A discriminating dissolution method was developed to differentiate between MgSt samples with varying properties. Lubrication efficiency was performed using a Presster compaction simulator and tensile strength determination using diametrical compression. Synthesis studies showed that the fatty acid composition and synthesis method affects the crystal form of MgSt produced, with higher stearic content preferring the dihydrate form. Temperature and humidity affect the form of MgSt and facilitate interconversion between forms. Drying MgSt was found to affect surface area results, with the dihydrate converting to the disordered form. Dissolution of indomethacin tablets containing various types of MgSt showed a strong dependence on particle size and surface area, with smaller particle size and higher SSA samples having slower dissolution rates. Fatty acid composition and hydrate form were investigated as secondary variables influencing dissolution, with fatty acid showing no correlation with dissolution. Lubrication efficiency and tabletability studies showed an effect of crystal form, with monohydrate and dihydrate forms showing good lubrication efficiency compared to the disordered form, but also poorer tabletability. In conclusion, the potential for variability in the crystal form of MgSt was found to be an important property of MgSt. There is variability in the form produced from synthesis, as well as interconversion between forms. Temperature, humidity and drying conditions are particularly important in controlling the crystal form of MgSt, as this can impact formulation stability and storage conditions. The primary variable affecting dissolution is particle size and surface area, but crystal form is a potential secondary variable. The physicochemical properties of MgSt, particularly crystal form and surface area, showed trends with lubrication and dissolution. This highlights the importance of choosing a MgSt material with the desired crystal form and surface area properties to match the lubrication and dissolution requirements for the formulation.

Industry often prefers heterogeneous catalysts because solids are easier to remove from the reaction mixture, less likely to foul the reactor, easier to recycle, and produce unique products. However, establishing structure-activity relationships for heterogeneous catalysts is often challenging. Surface organometallic chemistry utilizes techniques similar to homogeneous chemistry to synthesize and characterize heterogeneous catalysts. Ion pairs are common catalysts for chemical transformations and in solution there is a vast library to choose from. Heterogeneous ion pairs are equally important but have been examined in far less detail. The copolymerization of ethylene and polar monomers to yield copolymers with high molecular weights and narrow polydispersities is a challenge that has not been approached by heterogeneous catalysts. Part of this work presents the synthesis of a single-site (α-diimine)PdMe+ catalyst on the surface of sulfated zirconium oxide (SZO) for the copolymerization of methyl acrylate and ethylene. Heterogeneous Lewis acids are commonly used in catalytic transformations; however, the concentration of active sites is usually very low, and the structure is ambiguous. This work approaches this challenge by synthesizing a well-defined silylium-like ion on the surface of SZO ([iPr3Si][SZO]), the first example on an oxide. [iPr3Si][SZO] hydrodefluorinates several inert sp3 C-F bonds in the presence of excess triethylsilane. This study showed that SZO is not as weakly coordinating as common homogeneous weakly coordinating anions, such as carborane and BArF4- anions. Therefore, we wanted to design a weaker coordinating heterogeneous anion on the surface of an oxide. The strong Lewis acid PhF-Al(OC(CF3)3)3 coordinates to -OH sites on the surface of partially dehydroxylated silica forming -O(H)-Al(OC(CF3)3)3 which upon deprotonation forms weakly coordinating ion pairs. One of the ion pairs [iPr3Si][-OAl(OC(CF3)3)3] has a 29Si NMR chemical shift 17 ppm downfield of [iPr3Si][SZO], supporting that the -OAl(OC(CF3)3)3- anion is weaker coordinating than the sulfate anions on SZO. The last part of this work examines the structure of the active site in the ternary catalyst: Cpb2ZrCl2 + iBu3Al + Al2O3, a Ziegler-Natta type ethylene polymerization catalyst. Model catalysts, activity studies, and solid-state 2H NMR studies show that the active catalyst structure is a Cpb2Zr-H+ cation on the surface of Al2O3.

Amongst other applications, solid-state nuclear magnetic resonance (NMR) spectroscopy can provide atomic-resolution data for the determination of protein structures and dynamics. This is true in particular for protein assemblies that cannot be crystallised or are too large for solution-state NMR. While understanding the dynamics of a protein is of great importance for a full appreciation of its molecular machinery, this thesis has a focus on the structural aspects of a number of large protein assemblies. The first study, presented in Chapter 2, builds on previously determined chemical shifts of a mutant form of amyloid-β, which is compared to a brain-seeded form of the wild-type. This comparison suggests that the determined mutant fold can also be adopted by the wild-type, with small conformational adaptations which accommodate the E22 deletion in the Osaka mutant. In addition, this chapter illustrates how other mutants could conform to this model. The stabilisation of the N-terminal part of the protein via an intermolecular salt bridge to K28 may represent a common structural motif for the mutants that are related to early-onset Alzheimer’s disease. This feature may connect to the observed increased toxicity of the mutant forms compared to wild-type Amyloid-β1-40, where the salt bridge involving K28 is intramolecular instead of intermolecular. A continuation of amyloid studies follows in Chapter 3, but for a different kind of amyloid: in recent years the idea that a number of peptide hormones and neuropeptides are transiently stored in aggregated form has accumulated support. These reversible, functional amyloids are believed to be packed into dense-core vesicles, which function as temporary depots of messenger peptides in secretory cells. Somatostatin (SST) is such a peptide hormone that occurs physiologically both aggregated and as a soluble monomer. The structure of human SST-14 in the context of a fibril was determined to atomic resolution using magic-angle spinning (MAS) solid-state NMR spectroscopy. In addition to scanning transmission electron microscopy data, the complete backbone resonance assignment is presented in this chapter. Subsequently, dipolar-based experiments that provide spectrally unambiguous long-range distance restraints are combined with a prediction of secondary-structure elements by secondary chemical-shift calculations and dihedral-angle restraints. The collective data culminate in the molecular structure presented in this chapter. In Chapter 4, both 13C- and 1H-detected experiments are presented. Both approaches are compared in general, and more specifically in the context of several proteins related to the hepatitis B virus (HBV). HBV is a small enveloped DNA virus whose genomic information encodes only a few genes: the envelope proteins S, M and L (collectively known as hepatitis B surface antigen/HBsAg), the core protein (Cp), the polymerase (P), and the X protein (HBx). This chapter presents structural studies of the envelope protein S and the core protein Cp in its full-length (including C-terminal domain (CTD)) and reduced (without CTD) forms. Proton detection is applied to probe interactions between protein and nucleic acids (ATP analogues and the deoxyribonucleotides of DNA) in combination with phosphorus-detected experiments in Chapter 5. Protein-nucleic acid interactions play important roles not only in energy-providing reactions such as ATP hydrolysis, but also in reading, extending, packaging or repairing genomes. While they can often be analysed in detail with X-ray crystallography, complementary methods are necessary to visualise these interactions in complexes which are not crystalline. This chapter describes how solid-state NMR can detect and classify protein-nucleic acid interactions via site-specific 1H- and 31P-detected spectroscopy. The sensitivity of 1H chemical-shift values for non-covalent interactions involved in these molecular recognition processes is exploited to directly probe the chemical bonding state, a characteristic that cannot be directly obtained from an X-ray structure. Despite its rather challenging size, the method is applied to study interactions in the 669 kDa dodecameric DnaB helicase in complex with ADP:AlF4-:DNA. Finally, Chapter 6 investigates proton-detection in solid-state NMR rather from a more methodological point of view in the context of MAS and resolution. Spectral resolution is key to unleash the structural and dynamic information contained in NMR spectra. The advent of ever faster MAS, today exceeding 100 kHz, is what enabled proton detection in solid-state NMR. In this respect, it is valuable to evaluate the benefit of a continued investment in faster spinning. To address this question, MAS up to 150 kHz is used to investigate a protein complex of archaeal RNA polymerase subunits 4 and 7. Using a rotor with an outer diameter of 0.5 mm and a sample content of approximately 170 µg, the total linewidth of Rpo4/7 improves by a factor of 1.23 ± 0.05 by going from 100 to 150 kHz, and signal intensity increases by a factor 1.48 ± 0.13 in the same MAS range. With some further considerations demonstrated in this chapter, the conclusion is that continued investment in faster MAS is indeed meaningful.

Designed model transmembrane peptides and oriented 2H and 15N solid-state nuclear magnetic resonance (NMR) spectroscopy were used to analyze how simple sequence modifications can influence peptide structure, behavior and dynamics as well as for determining the pKa of glutamic acid at the membrane interface. The GW5,19ALP23 (acetyl-GGALW(LA)6LWLAGA-amide) peptide framework adopts a well-defined tilted orientation in lipid bilayers (DLPC, DMPC and DOPC) and undergoes low amounts of dynamic motion. The sequence was initially modified by moving the Trp residues outwards to positions 4 and 20. This new sequence GW4,20ALP23 (acetyl-GGAW(AL)7AWAGA-amide) displays high amounts of signal averaging of NMR observables caused by extensive dynamic motion about its average azimuthal rotation. The high dynamics are due to side chain competition induced by the opposing radial locations of the interfacial Trp(W) residues. The GW4,20ALP23 sequence was subsequently modified by introducing Arg(R) residues at either position 14 or 12. The R14 peptide adopts a well-defined tilt in lipid bilayers while completely arresting the high dynamics of the parent framework. In response, the C-terminal Trp causes partial unwinding of the core helix, while the N-terminal residues tighten into the core helix to compensate. R12 pulls the peptide to the membrane surface. A helix discontinuity is observed beginning at residue 11 as well as the formation of a partial N-terminal 310-helix. Modifying the core sequence of GW4,20ALP23 with Leu residues at positions 5 and 19 does not significantly affect the high dynamics, yet causes the peptide to adopt the same tilt as the original GW5,19ALP23 sequence. Removing W4 and replacing it with two Phe residues at positions 4 and 5 not only reduces the dynamics but also causes C-terminal helix distortion. Moving away from helix dynamics, 2H NMR was used to determine the side chain pKa of an interfacial Glu residue in the GW5,19ALP23 framework will oriented in the three lipid bilayers. The pKa increases with lipid bilayer thickness ranging from 4.3 to 11.0. Together, these experiments with model membrane peptides and solid-state NMR can be used to help our understanding of the basic principles that govern protein-lipid interactions.

Atactic-Poly(acrylonitrile)(aPAN) is a precursor for carbon fibers. Chemical reactions of aPAN fibers/films during stabilization process is spatially heterogeneous due to limited oxygen diffusivity. So far, Auger Electron Spectroscopy (AES), Energy-dispersive X-ray spectroscopy (EDS), Near-edge X-ray absorption fine strucutre (NEXAFS), Synchrotoron IR imaging have been applied to investigate depth profiles of elements and functional groups of the aPAN fibers. However, these studies are not sufficient to understand the detailed chemical structures and kinetics of the chemical reactions of the stabilized aPAN fibers/films. Solid-state NMR spectroscopy is one of the powerful characterization tools for structural analysis of organic compounds at the atomic scale, however, cannot be generally applicable to structural studies as a function of depth from the surface.In this work, it is found that both 13C direct polarization magic angle spinning NMR spectra and 1H spin−lattice relaxation time in the laboratory frame (T1H) of the stabilized aPAN films highly depend on the film thickness. These differences are attributed to different chemical reaction mechanisms at the surface and inner cores due to limited oxygen diffusivity. Tunable T1H filtered 2D 13C–13C INADEQUATE NMR for the firsttime selectively observes either the well stabilized aPAN at the surface or poorly stabilized structures at the core region in the films. A relative fraction of the well stabilized aPAN region to the whole films is determined in terms of 13C line-shape analysis. Kinetics of chemical reactions of the stabilized aPAN film as a function of film thickness is also investigated. It is demonstrated that overall stabilization rate is significantly lowered down with increasing film thickness. This novel strategy will be useful for structural study of industrial carbon fiber precursors.

Solid-state NMR is a powerful tool for the study of the structural and dynamic properties of materials and biomolecules. The strength of solid-state NMR lies in the ability to coherently manipulate the system Hamiltonian with the use of radio-frequency pulse sequences and magic-angle spinning. This controlled perturbation is performed by introducing multiple periodic time dependencies and allows for the measurement of the correlation between nuclei and the identification of their local electronic environment. In order to get reliable information and efficient experimental performance, the pulse sequences need to be robust towards experimental uncertainties. Additionally, they need to be highly specific to extract the desired interaction. In this thesis, a variety of widely-used pulse sequences are examined with respect to pulse imperfections and possible approaches based on a theoretical understanding obtained by Floquet theory are presented to tailor the pulse sequences in order to make them more reliably applicable. In the first part of this thesis, the practical compensation of pulse imperfections is studied and previously developed concepts are extended. A published theoretical model of these imperfections, also known as pulse transients, is applied to physically measured pulse shapes to find the origin of pulse imperfections in the spectrometer. Additionally, small adjustments to the experimental setup are presented that ease the implementation of pulse-transient compensation. The second part of this thesis focuses on recoupling sequences, which are pulse sequences designed to reintroduce the dipolar coupling, yielding important information about the spatial proximity of two nuclei. One type of sequence, which includes Radio-Frequency Driven Recoupling or Rotational Echo Double Resonance, uses an isolated pi pulse as a recoupling element. These sequences are widely used due the ease of experimental implementation. Phase cycles are previously proposed modifications to stabilize these sequences. In this thesis, these phase cycles are analysed using the concept of effective Floquet Hamiltonians and numerical simulations to determine their robustness towards pulse imperfections. The advantages and disadvantages of various phase cycles are discussed and the experimental influence of pulse transients is understood using the theoretical concepts developed. A different kind of recoupling sequence uses symmetry-based pulse trains and is known as C or R sequence. A Floquet description of the recoupling sequence of interest, R26, shows inherent flaws in the design of the sequence that are also demonstrated experimentally. The influence of pulse transients is investigated and unexpected results are shown that are in stark contrast to the results found for RFDR and REDOR. A commonly used phase cycle shows great robustness towards any kind of experimental imperfection but calculations of the dipolar scaling coefficient show less recoupling efficiency than the basic sequence. In the third part of this thesis, homo- and heteronuclear decoupling sequences are discussed. Decoupling sequences are designed to remove residual terms in the Hamiltonian that cause line broadening and thus these types of sequences are used to enhance spectral resolution. The homonuclear decoupling sequence frequency-switched Lee-Goldburg for proton-detected experiments is studied. Efficient decoupling is essential for proton detection because without it the lines are too broad to be distinguishable and do not yield reasonable information. This study focuses on the origin of performance degradation of the Lee-Goldburg sequence. Through the use of analytical calculations, numerical simulations, and experimental modifications, the residual line broadening is analysed. A concise conclusion of the origin of the performance degradation is presented for the first time, and it is understood why this sequence is still limited in its use. The heteronuclear decoupling sequence two-pulse phase modulation is investigated with respect to pulse transients. The requirement for the experimental use is a straightforward optimization and the implementation should be robust towards different conditions. Theoretical concepts to describe simple decoupling sequences with discrete phase modulations are presented and extended to understand the influence of pulse transients. The difference between continuous phase modulation and discrete phase jumps as well as a commonly used phase cycle of the basic two-pulse sequence is investigated theoretically and experimentally. In conclusion, this thesis generalises the concepts of pulse transients and the compensation, and draws conclusions on their influence on different kinds of pulse sequences. The removal of pulse imperfections allows the developed theoretical concepts to be validated more accurately and inherent drawbacks of the pulse sequences are found experimentally. This results in suggested modifications and tailoring of the sequence to accommodate the experimental needs of more complex biological systems.

AbstractEnhanced CO2 Capture in Metal-Organic and Covalent-Organic FrameworksbyRobinson W FlaigDoctor of Philosophy in ChemistryUniversity of California, BerkeleyProfessor Omar Yaghi, ChairGlobal atmospheric carbon dioxide (CO2) levels are rising. It is widely acknowledged by the scientific community that this phenomenon is contributing to climate change. Therefore, the need for effective CO2 capture from both point sources (power plants, etc.) and direct air capture is urgent. Despite years of investigation, the development of scalable, cost-effective, and energy-efficient, carbon capture and sequestration (CCS) technologies remains an outstanding challenge. The most widely- employed technique to date is the use of aqueous monoethanolamine (MEA) solutions at CO2 point sources. Flue gas from point sources is pumped through these solutions which capture the CO2 by forming chemical bonds (e.g. ammonium carbamate formation) between the gas and the amine moieties in solution. Although a large amount of CO2 can be captured using this technology, it is energetically inefficient. With one of the highest specific heat capacities among common solvents, water requires a significant amount of energy to bring to temperatures at which the MEA molecules release the previously- captured CO2. The requisite energy is often produced at similar CO2-producing point sources, limiting the effectiveness of this technique when employed.For this reason and others, (e.g. instability of aqueous MEA solutions to other contaminants present in flue gas) many are considering alternative methods of CO2 capture from point sources. One particularly potent method involves the use of amine- functionalized porous adsorbents in an analogous fashion to MEA solutions, as these materials frequently exhibit lower heat capacities, higher selectivities, and greater chemical tunability compared to their liquid-based counterparts.Reticular chemistry, the process of assembling judiciously designed rigid molecular building blocks into predetermined ordered structures (networks) which are held together by strong bonds, has been widely applied to the synthesis of such porous adsorbents, most notably Metal-Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs). Much of the insight on the fundamental science which set the foundation for these materials as a potential next-generation of CO2 adsorbents was gleaned through development of many MOFs which demonstrate some of the highest CO2 uptake capacities of any porous material. Recent work has focused on elucidation of MOF systems with practical CO2 capture applications.Recently, the Yaghi group designed a new MOF, IRMOF-74-III-CH2NH2 that selectively captures CO2 in the presence of water under flue gas conditions. I followed up on this study with an augmented material, IRMOF-74-III-(CH2NH2)2 which exhibited a 133% increase in CO2 uptake in the pressure regime of interest to this application (e.g.

Abstract: Over the last nine years, a new class of materials named lead halide perovskite has made a paradigm shift in the field of optoelectronic solution-processable low-cost and high-efficiency devices, with outstanding accomplishments especially in the ever-growing field of renewable solar energy harvesting. With current state-of-the-art 22.7% efficiency for lab-scale perovskite solar cells, the expectations are high with the potentials of this "magic" material system in being a real driving force for next-generation low-cost and high-efficiency photovoltaics technology. In order to make maximum use of any newly introduced material systems such as halide perovskites for real-life applications, it is essential to carry out fundamental studies which enable better in-depth understanding of the basic material electrical, optical, thermal, mechanical, etc. properties. This understanding is crucial for such a new technology to be able to advance further into actual products in the market. In this work, we tried to shed light on fundamental questions pertaining to important lead halide perovskite material characteristics. We studied the stability of methylamonium lead iodide (MAPbI3) through identifying all possible decomposition products of MAPbI3, which each has a unique fingerprint. Through systematic investigation of potential decomposition pathways under diffierent conditions of humidity and/or heat, we identified a comprehensive understanding of the intrinsic stability of MAPbI3. We hypothesized that the lower stability observed in films is mainly due to the preparation protocols and that the MAPbI3 is more resilient than what was previously thought. Also, we studied two of the main lead halide perovskite materials which are routinely used nowadays in the realization of high-efficiency and relatively-stable perovskite solar cells, namely methylamonium and formamidinium lead mixed halide perovskites. We explored the potential of a new synthetic route (mechanochemical synthesis) to prepare these materials with deffinitive control over stoichiometry. It has been reported earlier in the literature that these systems suffer from halide phase segregation, so we investigated this through adopting a suite of advanced characterization with atomic-scale probing capabilities which confirmed that these systems behave like a solid-solution with atomic scale halide mixing. The significance of the results presented here is vital for future research in this rapidly growing field as these results answer fundamental questions related to the perovskite materials intrinsic properties as well as elaborating on new up-scalable synthesis techniques.

In recent years solid-state NMR has emerged as a valuable tool for elucidating structure and dynamics of large biomolecular systems, especially suited for application in systems ranging from amyloid fibrils, membrane proteins to large protein ligand complexes inaccessible by more traditional structure determination techniques e.g. X-ray crystallography and solution-state NMR. Essential in determination of a biomolecular structure is the acquisition of numerous high quality interatomic distance restraints. However, conventional dipolar coupling based methods lead to significant challenges for accurate determination of critical long range distances. An alternative method to overcome this limitation is the incorporation of paramagnetic centers in proteins and utilization of the very large electron-nucleus couplings. In this dissertation, we combine state of the art proton-detection techniques with development of novel rigid transition metal binding tags, to improve the quality of long range distance restraints generated by measurement of site-specific paramagnetic relaxation enhancements in solid-state NMR.

This thesis describes the design and construction of a three-channel (1H/13C/15N) switched-angle spinning solid-state NMR probe for a 500 MHz (11.7 T) magnet. The probe is designed for studies of membrane-associated proteins in native-like environments. This probe, which is the next generation of the pneumatic SAS probes built in the Martin Lab, keeps the pneumatic angle switching mechanism from the previous generation, while adding the third channel to enable the triple resonance experiments necessary for protein structure work. The channels utilize transmission line segments that act as tunable reactances, with the matching network for each frequency contained within an outer ground plane. The channels are capacitively coupled to the coil to enable smooth switching without bending the leads repeatedly. In order to study proteins with this probe, we will investigate the angular dependence of decoupling sequences. This is necessary because dipolar couplings are partially averaged out depending on the angle at which the sample is spinning. The angular dependence of popular decoupling sequences will be determined in order to assess how they change with the angle of the sample, enabling us to separately optimize for different angles within a single experiment. With SAS-optimized decoupling sequences, structural studies can be performed on membrane-associated proteins at different angles to extract further distance constraints and orientation information.Also described is a high-throughput method for re-equilibrating predicted protein structures and evaluating them to predict their properties in order to search for targets with desired characteristics or other interesting features. This approach allows for the more efficient selection of protein targets for structure determination and biochemical characterization. This method has been used to investigate cocoonases from Heliconius butterflies and aspartic proteases from carnivorous plants, as well as other that are described elsewhere.

Many important material properties are determined by the surface layer (0.5-100 nm); these include optoelectronic properties like conductivity, absorptivity, and reflectance as well as physiochemical properties such as molecular adsorption, hydrophobicity, and surface diffusivity. Furthermore, the crystallization or assembly processes of technologically-important nanomaterials are mediated by surface interactions and influence the surface compositions and properties of the resultant material, including zeolites, colloidal semiconductors, carbon-based electrocatalysts, and mesoporous inorganic oxides. Catalytic reaction properties of diverse porous heterogeneous materials are determined by molecular interactions of adsorbates, reactants, or product species at pore or exterior surface sites. Despite the broad importance of surface interactions in determining material properties, fundamental questions remain regarding the physiochemical interactions at surfaces that determine crystallization, adsorption, optoelectronic, and/or reaction properties. This is because such properties often depend on dilute surface moieties, defect species, and/or molecular adsorbates that occupy distributions that are partially- or non-ordered and are therefore challenging or impossible to characterize by conventional scattering techniques. Developing atomic-level insights into the types, interactions, and distributions of such dilute non-ordered species is crucial to elucidate the molecular-level origins of the properties and synthesis pathways of materials such as zeolites, semiconductor nanoparticles, and mesoporous electrocatalysts. By understanding the crystallization, synthesis, and assembly processes of these materials, as well as the resulting structures and active species, the resulting insights can be applied to develop new synthetic or post-synthetic treatments to generate more effective, stable, and/or active materials with desirable properties. The objective of this dissertation is to measure, understand, and correlate the atomic-scale compositions, structures, and properties of heterogenous materials with diverse applications, including heterogeneous catalysis and solid-state lighting. Recently-developed solid-state nuclear magnetic resonance (NMR) techniques with complementary X-ray diffraction and electron microscopy analyses are applied to elucidate the structures and compositions of dilute surface, defect, or heteroatom species, which are correlated to the macroscopic properties of interest. These techniques are applied to analyze diverse heterogeneous inorganic nanomaterials, including aluminosilicate zeolites, cementitious solids, precious-metal-free electrocatalysts, and nanocrystalline semiconductors. Though the material systems vary in composition and application, in each case the important optical, electronic, and/or catalytic properties arise from dilute partially- or non-ordered defect or heteroatom species in a semi-crystalline lattice. The overall unifying themes are: (1) analysis of order and disorder in semi-crystalline inorganic solids using state-of-the-art diffraction and spectroscopic characterization techniques; (2) determining the distributions and structures of non-stoichiometric species, particularly at surfaces and interfaces; and (3) correlating atomic-level structures and compositions with macroscopic material properties. The insights provided are of broad importance and relevance to diverse material systems of technological interest for sustainable energy storage, conversion, and utilization.

The non-crystalline, nature of supramolecular assemblies makes it difficult to investigate their structures by traditional methods such as X-ray crystallography. On the other hand, solid-state nuclear magnetic resonance (NMR) spectroscopy, a fast-developing technique that mainly detects the local atomic environment, is suitable for this purpose. In this dissertation, we start with a brief introduction in Chapter 1, then focus on the application of solid-state NMR spectroscopy on a few peptide and protein supramolecular assemblies that have biological significance: amyloid fibrils formed by deletion mutants of human prion protein (huPrP) 23-144 in Chapter 2, peptide amphiphile (PA) palmitoyl-VVAAEE-NH2 nanofibers in Chapter 3, and nanofibrils and aggregates of several peptide-chromophore-peptide triblock compounds in Chapter 4. One- and two-dimensional high-resolution magic angle spinning (MAS) solid-state NMR spectroscopy was employed to fast access the conformation and dynamics of these assemblies. Inter-atomic distances were further measured by dipolar recoupling pulse sequences. Other methods, such as transmission electron microscopy (TEM) and atomic force microscopy (AFM) to characterize the morphology of the supramolecular assemblies, X-ray diffraction to measure the interlayer distance, as well as thioflavin T fluorescence assay to monitor the kinetic of amyloid fibril formation, were also largely involved in the dissertation. We have found the shortest fragment of huPrP23-144 that can be expressed at reasonable yield in E. coli and retain the wild-type like amyloid folding. For the PA and peptide-chromophore-peptide triblock compounds we studied, parallel, in-register ß-sheet structure largely exist even for one compound that only forms small, random aggregates. Polymorphism was observed to exist extensively in both PA and the p-conjugated peptides. DRAWS to measure the homo-nuclear distance and TEDOR to measure the hetero-nuclear distance were proven to be two useful experiments to study the stacking in the self- and co-assemblies. Our results can facilitate the understanding of huPrP23-144 amyloid structure and the mechanism of relevant prion diseases, as well as promote more rational design of peptide-based materials that have novel supramolecular structures.

Misfolded prion protein amyloid fibrils are the hallmarks of various transmissible spongiform encephalopathies (TSEs) which affect both human and many animal species. This class of fatal neurodegenerative disease includes bovine spongiform encephalopathy (BSE) or mad cow disease in cattle, Creutzfeldt-Jakob disease (CJD) in human, Scrapie in sheep, and chronic wasting disease in cervids. All these diseases are known to be associated with misfolding and aggregation of prion protein (PrP), undergoing from soluble monomeric cellular form (PrPC) to beta-sheet-rich fibril aggregates (PrPSc). Even though it was once highly debated, growing number of experimental data supports the "protein-only" model, in which the PrPSc prion are identified as the infectious agent. Despite the significant efforts, detailed knowledge of the molecular information of amyloid fibrils, especially the emergence of strain or phenotypes in the same mammalian species and species barrier phenomena between different species. The difficulty with progress in understanding of the intriguing aspects of prion fibrils, also owe it to the difficulties with efficiently propagating the amyloid conversion in vitro. In this work, we used magic-angle spinning solid-state NMR and Y145Stop prion variant (huPrP23-144) as a model to study the fundamental molecular aspect of prion propagation, including the species barrier and strain variation, and to obtain a high-resolution three-dimensional structure of huPrP23-144 fibril.

This thesis describes a quadruple-resonance 1H/13C/2H/15N magic-angle spinning nuclear magnetic resonance probe for the study of structure and dynamics of biological macro- molecules. The probe utilizes tuning-tube components as discrete circuit elements. A coaxial design allows specialization, with the high-frequency 1H circuit on a low-voltage modified Alderman-Grant coil and the 13C/2H/15N circuit on a solenoid coil for more efficient detection. The mechanical and circuit design of the probe is presented with a description of the benchtop characterization and some initial experimental results.

This thesis describes a quadruple-resonance 1H/13C/2H/15N magic-angle spinning nuclear magnetic resonance probe for the study of structure and dynamics of biological macro- molecules. The probe utilizes tuning-tube components for discrete circuit elements. A coax- ial design allows specialization, with the high-frequency 1H circuit on a low-voltage modified Alderman-Grant coil and the 13C/2H/15N circuit on a solenoid coil for more efficient detec- tion. The mechanical and circuit design of the probe is presented with a description of the benchtop characterization and some initial experimental results.

This dissertation aims to investigate and correlate structure, dynamics and transport properties of several novel soft materials systems using multiple Nuclear Magnetic Resonance (NMR) methodologies, including solid-state NMR (SSNMR), diffusometry, and imaging, and with the help of X-ray scattering. First, we report the investigation of structure and dynamics of three polymeric membranes: hydroxyalkyl-containing imidazolium homopolymers, poly(arylene ether sulfone) segmented copolymers, and disulfonated poly(arylene ether sulfone) random copolymers using a wide array of SSNMR techniques, including: 1) ¹³C cross-polarization magic angle spinning (CPMAS) with varying cross-polarization (CP) contact time, 2) ¹³C single-pulse magic angle spinning (MAS) with varying delay time, 3) ²³Na single-pulse MAS, 4) two dimensional phaseadjusted spinning sideband (2D PASS), 5) proton spin−lattice relaxation (T₁), 6) rotating frame spin−lattice relaxation (T₁ρ), and 7) center-band-only detection of exchange (CODEX). These various types of SSNMR spectroscopic methods provide a wealth of structural and dynamic information over a wide range of time scales from a few nanoseconds to seconds. We further present a picture of rich structural and transport behaviors in supramolecular assemblies formed by amphiphilic wedge molecules using a combination of ²³Na solid-state NMR, ¹H/²H PFG NMR diffusion, relaxation and grazing-incidence small-angle X-ray scattering. Our results show that the liquid crystalline domains in these materials undergo a transition from columnar to bicontinuous cubic phases with a simple increase in humidity, while the amorphous domain boundaries consist of individual wedge molecules with a significant fraction (~ 10%) of total wedge molecules. Multiple-component diffusion of both wedges and water further confirms the structural and dynamic heterogeneity, with the bicontinous cubic phase being able to facilitate much faster water and ion transport than the columnar phase. We then develop a quantitative approach to probe the migration of two novel “theranostic” polymeric agents (combining “therapeutic” and “diagnostic” functions) into bulk hydrogels using two distinct time-resolved magnetic resonance imaging (MRI) methods. To the best of our knowledge, this is the first work that combines time-resolved MRI experiments to reliably quantify diffusivity of paramagnetic and superparamagnetic nanoparticles in bulk biological media. Our results agree closely with those obtained from fluorescence techniques, yet the capability of our approach allows the analysis of actual nanoparticles diffusion through biogels on mm to cm scales during a range of time periods. Finally, we employ a combination of NMR techniques to obtain a comprehensive understanding of ion clustering and transport behaviors of ionic liquids inside the benchmark ionic polymer Nafion. Spin relaxation shows that anion relaxation is more influenced by the fixed sulfonate groups than cation relaxation. 2D ¹H-¹⁹F heteronuclear Overhauser effect spectroscopy (HOESY) and 1D ¹⁹F¹⁹F selective nuclear Overhauser effect (NOE) spectroscopy confirm our assumption of the formation of ion clusters at low water content in the ionomer. While we observe non-restricted diffusion behavior for cations, anion diffusion is strongly restricted both between domain boundaries and within domains in the absence of water. The restricted anion diffusion can serve as a reliable probe for detailed multiscale structures of the ionomer.

Carbon fiber is a kind of material with outstanding properties and low density, which has tremendous applications such as aircraft, automobile industry, and so on. Polyacrylonitrile (PAN) is generally used as precursor to produce carbon fiber. From PAN to carbon fiber, several heat treatment processes including stabilization, carbonization and graphitization are involved, among which stabilization is the most important step. By heat treatment in air at 250oC – 400oC, linear polymeric structure is believed to be converted to ladder structure, which makes it more heat resistant in order to undergo further heat treatment at even higher temperature. For the past decades, several experimental approaches including FT-IR, Raman, TGA, etc, have been applied to characterize chemical and secondary structures of stabilized PAN. However, due to experimental limitations, stabilization structures and processes are still not well-understood at the molecular level. In our research, we developed a novel strategy to characterize PAN stabilized at various temperatures. By applying two dimensional 13C-13C and 1H-13C correlation NMR techniques combined with 13C isotopic labeling, through-bond 13C-13C correlations of stabilized PAN was successfully obtained. Improved spectral resolutions of 1D and 2D NMR data for the first time reveals intramolecular reaction pathways for PAN stabilized under air and nitrogen, respectively.

Many pharmaceutical compounds being developed in recent years are poorly soluble in water. This has led to insufficient oral bioavailability of many compounds in vitro. The amorphous formulation is one of the promising techniques to increase the oral bioavailability of these poorly water-soluble compounds. However, an amorphous drug substance is inherently unstable because it is a high energy form. In order to increase the physical stability, the amorphous drug is often formulated with a suitable polymer to form an amorphous solid dispersion. Previous research has suggested that the formation of an intimately mixed drug-polymer mixture contributes to the stabilization of the amorphous drug compound. The goal of this research is to better understand the role of miscibility, molecular interactions and mobility on the physical stability of amorphous solid dispersions. Methods were developed to detect different degrees of miscibility on nanometer scale and to quantify the extent of hydrogen-bonding interactions between the drug and the polymer. Miscibility, hydrogen-bonding interactions and molecular mobility were correlated with physical stability during a six-month period using three model systems. Overall, this research provides molecular-level insights into many factors that govern the physical stability of amorphous solid dispersions which can lead to a more effective design of stable amorphous formulations.

The ability to successfully sequester and separate trivalent lanthanides and actinides has applications to the nuclear fuel cycle, processing of irradiated target materials, and nuclear forensics. The challenge in separating the trivalent lanthanides and actinides is their similar size and charge. As a result of this, standard size exclusion or ion exchange techniques become much more challenging. Instead of focusing on size or charge for separation, their differences in interactions with complexing ligands can be utilized. Another challenge in trivalent lanthanide and actinide separations is that these metals are often dissolved in highly acidic matrices. Thus, the stability of the extractant ligand used to complex the metal is at risk of degradation. The most common sequestration and separation routes based on complex formation for lanthanides and actinides use liquid-liquid separations, which can generate large volumes of hazardous organic waste. By moving to solid-liquid separations, in which the organic phase is replaced by a solid-phase extractant (SPE), the production of large volumes of waste can be minimized. The most common method of making SPEs for lanthanide and actinide separations is coating an organic extractant ligand on either a silica or polymer support. As a result of only coating the ligand rather than bonding it to the solid support, these materials can suffer from ligand degradation and detachment. Chapter 5 focuses on trivalent lanthanide and actinide interactions with a commercially available SPE. While those materials were found to have use for certain applications, their limitations motivated the organically-modified mesoporous silica (OMMS) development presented in Chapter 7.The work presented here is a study on solid-phase extractants for lanthanide and actinide separations, particularly focused on OMMS. The OMMS materials are made by covalently binding the extractant ligand to the mesoporous silica, to increase the stability of these SPEs in the presence of acidic media. Chapters 6 and 7 discuss the synthesis and characterization of two types of OMMS materials as well as macroscopic and molecular level studies of these materials with trivalent lanthanides and actinides. Additionally, the stability of the OMMS materials in the presence of acid was probed using nuclear magnetic resonance (NMR) spectroscopy. The first OMMS material discussed is a caprolactam (CA)-modified mesoporous silica. The behavior of Eu(III), Sc(III), and Al(III) was studied with the CA-modified mesoporous silica. Al and Sc were studied as comparative trivalent metals that had smaller ionic radii than Eu. The results of batch sorption experiments and mainly solid-state NMR spectroscopy studies are presented. The acid stability studies showed that the CA-modified mesoporous silica degraded in two ways in the presence of acid: 1) the 7-membered ring of the ligand opened, and 2) a portion of the isolated ligands on the surface were cleaved at the silane anchor. It was determined that while the CA materials were not effective sorbents for Eu(III) from acidic matrices, they did bind Al(III) and Sc(III). Through the NMR studies, both Al and Sc were found to complex to the CA ligand and the surface silanols simultaneously. This work was the first time solid-state NMR had been used to study the surface, ligand, and metals directly of OMMS materials via their NMR active nuclei (29Si, 13C, 1H, 27Al, and 45Sc).The second OMMS material studied was a diglycolamide (DGA)-modified mesoporous silica. The main focus of this work was the interactions of the DGA-modified mesoporous silica with Eu(III) and Am(III), but also touched on other trivalent species such as La(III), Lu(III), and Y(III). Again, the stability of this material in the presence of acid was investigated using NMR spectroscopy and while the DGA ligand was found to withstand acid treatment, the isolated ligand cleavage at the silane anchor still occurred. The DGA-modified mesoporous silica was found to efficiently bind the trivalent species at high acid concentrations, particularly below pH 1. As a result of the mesoporous substrate and subsequently high ligand loading for the associated mass, the sorption capacity for Eu(III) (379 umol/g) was found to be higher than other diglycolamide SPEs. Through infrared spectroscopy and NMR spectroscopy experiments, the trivalent metals were found to bind to the carbonyl and ether oxygens of the DGA ligand. Fluorescence spectroscopy of Eu(III) and X-ray absorption spectroscopy studies elucidated that the trivalent metals are complexing as three ligands per metal center. Proof-of-concept column experiments demonstrate the use of DGA-modified mesoporous silica as a stationary phase to which Eu was both sorbed and then eluted. A major focus of this work was the interplay of macroscopic and molecular level studies to best characterize metal interactions with OMMS materials. While both the bulk and molecular level investigations can provide information about these systems, neither gives the full picture in itself. In designing materials for separations, knowledge of the complete picture is necessary in order to best optimize methodologies and predict separation behavior.

An elastomer is a polymer material that has the ability to resume its shape afterlarge deformation. Among various types of elastomers, natural rubber (NR) is the most typical one and an indispensable material for many industrial and household applications, such as tires, belts, gaskets, gloves, soles, rubbers, foam mattresses and so on. Because of the limited production of NR, a large amount of synthetic NR is synthesized, isoprene rubber (IR), to fulfill the requirement of industry and human society.The versatility of NR is mainly due to its outstanding tensile properties and the good crack growth resistance, which originates from crystallization under elongation. Many experimental techniques including X-ray diffraction (XRD), Transmission electron microscopy (TEM), birefringence, DSC and nuclear magnetic resonance (NMR) have been applied over the years to investigate the crystallization of NR under external strain.In this study, we designed a new and entire NMR system for characterizing crystallinity of rubber samples and successfully determined crystallinity of NR and IR under various strains. We will further investigate crystallinity of NR nanocomposite with carbon black and blends with other rubbers. Our developed NMR tools will be technique transferred to Bridgestone America for future research.

Polyrotaxane (PR) is consisting of linear polymer chain threading into cyclic molecules, e.g., cyclodextrins (CDs), and endcapped with bulky groups. Chemical modifications of pendant hydroxyl-functional groups on CDs significantly suppresses hydrogen bonding interactions between cyclodextrin molecules and leads to unique viscoelastic properties different from that of unmodified PR (Macromolecules 2010, 43, 4660-4666). The molecular dynamics of PR consisting of poly (ethylene glycol) (PEG) and a-cyclodextrins (CDs), hydroxypropylated polyrotaxane (HyPR) consisting of PEG and a-CDs partially modified by hydroxypropyl (Hy) group with modification ratios of 25 % (HyPR25) and 78 % (HyPR78) are investigated by various solid-state NMR techniques. In three samples, two-dimensional 1H-13C wide-line separation (WISE) NMR demonstrates that PEG segmental motions give much faster dynamics at a frequency more than ca. 50 kHz at near onset temperature of viscoelastic relaxation (317 K), while backbones in CDs do not perform. WISE also directly detects the chemical modification effect by confirming increasing mobility of CD side chains after modification. 13C spin-lattice relaxation time in the rotating frame (T1¿c) measurement indicates that side groups and backbones in CDs of HyPR78 show higher mobility than those of HyPR25 and PR. Center band-only detection of exchange (CODEX) NMR is sensitive to the slow dynamics of molecules whose frequency is directly comparable to macroscopically viscoelastic measurement. CODEX NMR clearly detects the slow backbone dynamics of CDs in HyPR78 in mechanical relaxation temperature range, while other two systems do not. According to all the NMR data, it is concluded that chemical modifications on pendant hydroxyl side groups can dramatically affect not only the hydrogen bonding interactions among CDs but also CDs dynamics and bulk viscoelastic property.

Abstract: Presented herein is a solid-state 71Ga and 69Ga NMR study of several six-coordinate gallium-oxygen compounds: Ga(acac)3, Ga(thd)3, Ga(trop)3, and (NH4)3[Ga(cit)2]·4H2O. Spectra of stationary and magic angle spinning (MAS) samples are reported, and their electric field gradient (EFG) and chemical shift anisotropy (CSA) tensor parameters are determined at the 71Ga and 69Ga sites. Experimental results are complemented with density functional theory (DFT) calculations using CASTEP. Tensor parameters are compared with those of similar compounds containing other group-13 metals including 27Al and 115In, and periodic trends are considered. This work shows that solid-state NMR studies of gallium compounds are worthwhile and practical with modern techniques, as 71Ga and 69Ga NMR spectra of the chosen compounds were successfully acquired and interpreted. The potential for further studies is discussed.

This thesis describes the study of the immobilization of Rh(I) complexes with N,N (bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim), and 4-(pyrazol-1-yl)methyl)-1-H-1,2,3-triazole (PyT)) and N,P (1-[2-(diphenylphosphino)ethyl]pyrazole (dmPyP) ligands onto carbon surfaces (glassy carbon electrode (GC), glassy carbon beads (GCB), carbon black (XC)) via robust carbon-carbon bonds. The immobilized Rh(I) complexes were employed as recoverable catalysts for hydromamination and hydroalkoxylation reactions. A series of aforementioned N,N ligands and one N,P ligand precursor were functionalized with aniline and aniline hydrochloride respectively. The treatment of the aniline-functionalized ligands and aniline hydrochloride-functionalized ligand precursor with HNO2 resulted in the transformation of the NH2 functionality into diazonium one. The electrochemical reduction of the diazonium functionality of the N,N ligands and N,P ligand precursor resulted in the surface attachment of these compounds onto glassy carbon electrode surfaces. The treatment of the surface-bound N,P ligand precursor with LiPPh2 resulted in the formation of the surface-bound N,P ligand (dmPyP). The complexation of [Rh(CO)2(μ-Cl)]2 with the immobilized N,N and N,P ligands led to the formation of immobilized Rh(I) complexes of these ligands. XPS confirmed the surface attachment of the N,N ligands and N,P ligand precursor as well as the success of the synthesis of the N,P ligand on the surface and complexation between immobilized ligands and the Rh precursor. The surface coverage of immobilized Rh(I) complexes was evaluated using CV and was found to be close to being a monolayer. The immobilized Rh(I) complexes were active as catalysts for the intramolecular hydroamination and dihydroalkoxylation reactions with extremely high TONs in comparison with their homogeneous counterparts. Studies of the recovered catalyst samples showed that Rh leached from the surface while the ligand remained intact. The aniline-functionalized N,N ligands were also attached onto glassy carbon electrodes without electrochemical assistance by dipping the electrode into a solution of aryl diazonium salt. Complexation of the ligands immobilized without electrochemical assistance and [Rh(CO)2(μ-Cl)]2 resulted in immobilized Rh(I) complexes with these ligands. XPS confirmed that the immobilized species had the same nature as those immobilized using electrochemical reduction and they were effective catalysts for dihydroalkoxylation. The surface coverage of these complexes was evaluated by means of CV and was found to be close to being a monolayer. The ligand bpm was also immobilized onto carbon powders (GCB and XC) without electrochemical assistance. The immobilized support-[Rh(bpm)(CO)2] complexes were obtained by the treatment of bpm-functionalized supports with [Rh(CO)2(μ-Cl)]2. XPS confirmed the ligand attachment onto the surface of carbon powders and complexation with Rh. TGA also confirmed the covalent immobilization of the ligand and was used to determine the surface coverage of ligand. The immobilized complex XC-[Rh(bpm)(CO)2] was active as a catalyst for the intramolecular hydroamination and dihydroalkoxylation of alkynes reactions. The recovered catalyst XC-[Rh(bpm)(CO)2] had significantly lower activity in the hydroamination and slightly decreased activity in the hydroalkoxylation reaction in comparison with the fresh catalyst. It was found that Rh leached from the surface of XC support during the catalytic reaction due to the cleavage of N-Rh bonds. The structure of a 13CO-labelled complex [Ir(PyP)(13CO)Cl] was examined using a series of solid-state NMR techniques. 1D 1H MAS, 13C and 31P CP MAS NMR spectra provided structural information similar to that obtained using NMR in solution. High resolution 2D solid-state correlation spectroscopy provided information about the dipolar coupling between protons and carbon/phosphorus. The use of the BABA pulse sequence to create and reconvert back double quantum coherences revealed the dipolar coupling contacts between immediately adjacent protons. The internuclear distance 13CO-31P was determined using REDOR. The combination of all of these techniques made it possible to obtain the additional information about the structure of [Ir(PyP(13CO)Cl] in solid state which was similar to that obtained using X-Ray crystallography.

A bulk heterojunction, organic solar cell, composed of a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied to determine the structure at the interface of the two compounds. Films of neat P3HT and the P3HT:PCBM composite where cast and annealed at elevated temperatures in order to determine the impact of sample annealing on the interface structure and interface volume of the blend. The films were characterized with 1D 13C solid-state NMR and 2D 1H-13C heteronuclear correlation (HETCOR) NMR. HETCOR NMR, with Lee-Goldburg cross polarization, was used to observe discrete intermolecular interactions between the alkyl side chain of P3HT and the C60, phenyl ring, and alkyl groups of PCBM. From these intermolecular interactions, a model of the structure at the P3HT:PCBM interface was constructed, which reveals the presence of stabilizing π- stacking between the thiophene ring of the P3HT and the phenyl ring of PCBM. Also, the C60 species interacts extensively with the alkyl groups of P3HT. The data indicates a phase separation after annealing that reduces the volume of the interface without disturbing the interface structure. A HETCOR NMR method using tangent cross polarization was used to confirm the phase separation of the P3HT and PCBM layers after thermal annealing.

The objective of this dissertation is to demonstrate different applications of ssNMR, with particular emphasis on uses in polymeric and biosciences. First, dynamics investigations on two polymers will be discussed: (1) disulfonated poly(arylene ether sulfone)s /poly(ethylene glycol) blends (BPS-20_PEG), which are under development as chlorine-resistant reverse osmosis (RO) membrane alternatives to aromatic polyamide (PA) technology, and (2) poly(arylene ether sulfone)s modified with 1,4-cyclohexyl ring units to improve processability. Simple cross-polarization magic-angle-spinning (CPMAS) experiments compared the chlorine tolerance of BPS-20_PEG and PA. Techniques capable of detecting motional geometries and rates on timescales from nanoseconds to seconds, including relaxation time measurements, were applied. Correlations were established between relaxation time and water permeability for the RO membranes, and between relaxation time and polydispersity in the 1,4- cyclohexyl ring modified polymer. Next, 31P and 2H static ssNMR experiments evidencing the formation of toroidal pores and thinned bilayers in oriented zwitterionic and anionic phospholipid bilayers, (biomembrane mimetic systems), by the antimicrobial peptides (AMPs) magainin-2 and aurein-3.3, will be mentioned. The toroidal pore geometries induced by magainin-2 were different than those produced by aurien-3.3. The most prominent features were observed in 2H spectra, implying greater interaction of the peptides with hydrophobic lipid acyl chains. Following this, a new two-dimensional homonuclear dipolar recoupling MAS experiment, capable of correlating long range 13C-13C spin pairs in a uniformly/ extensively 13C-labeled biomolecule, will be introduced. This technique was demonstrated on 13C-labeled versions of Glutamine and Glycine-Alanine-Leucine. Experiments involving the recoupling of all 13C-13C spin pairs, and experiments with selective recoupling using Gaussian or cosine-modulated Gaussian pulses, were demonstrated. Finally, work using static 1H- 13C CP ssNMR to selectively detect interfacial water around hydrophobic C60 will be recounted. This project exploited the distance limitation of CP, and 1H spin-lattice relaxation times, to separate the influence of bulk and interfacial water on the spectra. Results indicated that the tumbling of interfacial water is slowed by a factor of 105 compared to bulk water, providing it with a solid-like character, and allowing the hydration shell to be stable at temperatures above the freezing point of water.

Designed transmembrane peptides were employed for investigations of protein-lipid interactions by means of oriented solid-state deuterium NMR spectroscopy using isotope-enriched alanine residues. Using the model GWALP23 sequence (GGALW(LA)6LWLAGA) as a host peptide having single interfacial tryptophan anchor residues, the effects of different guest mutations were explored. Replacements of glycine residues 2 and 22 to positively charged lysine or arginine on both termini had little influence on the peptide average orientation. Conversely, glycine to tryptophan substitutions had profound effects, manifested in the increased dynamics and altered tilt direction of the peptide. While the charged residues at the peptide termini did not cause significant changes relative to the GWALP23 sequence, leucine to arginine mutations close to the peptide center led to dramatic consequences. Thus GWALP23-R14 retained a transmembrane topology, with the orientation and dynamics largely governed by the arginine residue, while GWALP23-R12 adopted multistate behavior in DOPC, with both transmembrane and interfacial states being populated. Coarse-grained molecular dynamics simulations, performed by collaborators, yielded substantial agreement concerning the interactions among arginine, tryptophan and lipid bilayers. Further insights into the multistate behavior of GWALP23-R12 were acquired by altering the host sequence to the isomeric GW3,21ALP23, which offers a longer separation between the tryptophan anchor residues. Both the L12R and L14R mutants of this modified sequence retained transmembrane topology, suggesting that the unique arrangement of tryptophan and arginine residues in GWALP23-R12 is responsible for its multistate character. In addition to serving as a host sequence, GWALP23 itself was modified for an investigation of hydrophobic matching, by shifting the tryptophan residues outward toward the termini (GW3,21ALP23) or inward toward the center (GW7,17ALP23), leading to peptide isomers with identical amino acid composition, but different effective hydrophobic (inter-Trp) lengths. In addition to altered tilt angles, tryptophan side chain reorientation was investigated and was found to provide additional response to hydrophobic mismatch conditions. In selected cases the 2H NMR data were analyzed in conjunction with restraints from separated local-field 15N solid-state NMR spectra. The combined analysis of the 2H and 15N NMR data provided multiple constraints and proved advantageous for explicit modeling of the peptide dynamics.

Nuclear magnetic resonance (NMR) is a tool used to probe the physical and chemical environments of specific atoms in molecules. This research explored small molecule analogues to biological materials to determine NMR parameters using ab initio computations, comparing the results with solid-state NMR measurements. Models, such as dimethyl phosphate (DMP) for oligonucleotides or CuCl for the active site of the protein azurin, represented computationally unwieldy macromolecules. 31P chemical shielding tensors were calculated for DMP as a function of torsion angles, as well as for the phosphate salts, ammonium dihydrogen phosphate (ADHP), diammonium hydrogen phosphate, and magnesium dihydrogen phosphate. The computational DMP work indicated a problem with the current standard 31P reference of 85% H3PO4(aq.). Comparison of the calculations and experimental spectra for the phosphate salts indicated ADHP might be a preferable alternative as a solid state NMR reference for 31P. Experimental work included magic angle spinning experiments on powder samples using the UNL chemistry department’s Bruker Avance 600 MHz NMR to collect data to determine chemical shielding anisotropies. For the quadrupolar nuclei of copper and scandium, the electric field gradient was calculated in diatomic univalent metal halides, allowing determination of the minimal level of theory necessary to compute NMR parameters for these nuclei.

Massey and Hemmerich proposed that the different reactivities displayed by different flavoenzymes could be achieved as a result of dominance of different flavin ring resonance structures in different binding sites. Thus, the FMN cofactor would engage in different reactions when it had different electronic structures. To test this proposal and understand how different protein sites could produce different flavin electronic structures, we are developing solid-state NMR as a means of characterizing the electronic state of the flavin ring, via the 15N chemical shift tensors of the ring N atoms. These provide information on the frontier orbitals. We propose that the 15N chemical shift tensors of flavins engaged in different hydrogen bonds will differ from one another. Tetraphenylacetyl riboflavin (TPARF) is soluble in benzene to over 250 mM, so, this flavin alone and in complexes with binding partners provides a system for studying the effects of formation of specific hydrogen bonds. For N5, the redoxactive N atom, one of the chemical shift principle values (CSPVs) changed 10 ppm upon formation of a hydrogen bonded complex, and the results could be replicated computationally. Thus our DFT-derived frontier orbitals are validated by spectroscopy and can be used to understand reactivity. Indeed, our calculations indicate that the electron density in the diazabutadiene system diminishes upon H-bond complex formation, consistent with the observed 100 mV increase in reduction midpoint potential. Thus, the current studies of TPARF and its complexes provide a useful baseline for further SSNMR studies aimed at understanding flavin reactivity in enzymes.

Cadmium sulfide (CdS) nanoparticles (NP) of ~ 4 nm in diameter and a moderate particle size distribution have been synthesized in the presence of 1-thioglycerol (TG) and characterized by TEM, powder XRD, absorption, photoluminescence and 113Cd, 13C and 1H solid-state NMR (SSNMR). The CdS NPs, which are coated with 1-thioglycerol (TG), were dialyzed to remove excess 1-thioglycerol and salt by-products present. The TG that is bound to the surface of the NPs remains after dialysis and SSNMR studies reveal that the molecules have restricted motion. 113Cd NMR shows that the surface sites of the NPs have a structure similar to that of the core and that TG is involved in the NP surface reconstruction. Broad photoluminescence was observed for the NPs, indicating the presence of defect sites on the surface of the NPs. Powder XRD shows that the NPs have the wurtzite crystal structure. The aqueous solubility and stability of the TG coated NPs allowed for the fabrication of polymer-NP composites. Composites were produced by combining CdS-TG-D NPs with polyvinylpyrrolidone (PVP) and sulfonated polystyrene (PSS). 1H-113Cd SSNMR revealed broadening and an upfield shift of the 113Cd resonance suggesting a small modification to the NP surface upon interaction with the polymers. Broadening of the signal from the OH group of TG in the 1H NMR spectrum indicates an interaction between the polymer and TG. 1H-13C SSNMR was used to study the interfacial polymer material in the composites. Changes in T1ρ(1H) indicate a change in the molecular dynamics of TG, consistent with a direct interaction with the polymer. The glycerol portion of TG is proposed to form hydrogen bonds with the carbonyl and amine groups of PVP and the sulfonate group of PSS. The hydrogen bond interaction also leads to a change in the dynamics of PVP, as observed from SSNMR relaxation measurements. In contrast, the interaction between TG and the sulfonate group had little influence on the dynamics of the organic portion of the polymer.CdS nanoparticles, with diameters of 3-7 nm, were also synthesized within a poly(styrene sulfonate) matrix using ion-exchange and precipitation, and the polymer-nanoparticle composite has been cast into films. The material is characterized at both the atomic and molecular levels using high-resolution TEM (HRTEM), powder X-ray diffraction and solid-state NMR (SSNMR). The structure surrounding the Cd2+ sites in the precursor, poly(cadmium 4-styrene sulfonate), is highly disordered upon drying and becomes more ordered with hydration. The increase in order results from water migrating to the Cd2+ sites and the polymer adopting a micellar structure. SSNMR and TEM studies shows that there is nearly quantitative conversion of the Cd2+ to CdS, with only trace amounts of Cd(OH)2 and amorphous CdS interacting with the polymer present, and that the CdS nanoparticles are in the cubic phase, which extends to the particle surface. 113Cd SSNMR shows that the overall structural order of the NPs increases when they are synthesized in the presence of the polymer matrix. Exposure of the composite film to ambient conditions over several months results in the partial oxidation of only the first few outermost layers of the NPs.

Alumina nanofibers, having average diameters of 500 nm, have been fabricated via the electrospinning process. Annealing the as-spun nanofibers at temperatures ranging from 525 °C-1200 °C was found to produce intermediate forms of alumina, transition aluminas before conversion into the thermodynamically stable phase, α-alumina. An in depth characterization of these alumina nanofibers via solid-state nuclear magnetic resonance (SSNMR) and other characterization techniques provide valuable information about the bulk and surface properties of these alumina nanofibers. As the surface of alumina materials have been known to have chemical and catalytic capabilities, the reactive nature of these alumina nanofibers were studied by the adsorption of phosphorus compounds on the surface of the nanofibers. Two phosphorus containing compounds were used; a chemical warfare agent simulant, dimethylmethyl phosphonate (DMMP) and methyl phosphate. The interaction of these materials with the surface of the alumina nanofibers were studied by SSNMR. Protonation (doping) of polyaniline, with a protonic acid renders it conducting, altering its electronic and structural properties. One of the highest reported conductivities of doped polyaniline is when it is doped with camphorsulfonic acid (HCSA) and cast from a m-cresol solution. Several models of the crystal structure of this system have been proposed, however they have not been proven experimentally. Solid-state NMR has been used to investigate the structure and specific interactions that occur between the dopant and/or solvent within the conducting polymer system. The structure of polyaniline synthesized in the presence of a polyacid, poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAAMPSA) was also investigated, by the used of solid-state NMR.

We report a general method, based on intramolecular spin-diffusion, for the measurement and calculation of spin-diffusion coefficients in amorphous polymers and their blends using only NMR data. The basic structural unit that defines 1H polarization density in polymers is the monomer unit. Using appropriately selected internal reference distances calculated from energy-minimized chain dimension simulations, timescales for the redistribution of 1H polarization within amorphous homopolymers may be used to independently calculate maximum values of the spin diffusion coefficients D. This strategy represents an attractive alternative to current methods employed for domain size measurements in polymer blends, which require calibration of spin diffusion coefficients based on comparisons of similar NMR data obtained on model compounds analyzed previously using scattering or microscopy techniques. In this way, many more polymer systems become amenable to study by NMR spin-diffusion methods, since X-ray scattering or microscopy calibrations on representative standards are no longer necessary to define quantitative limits on spin-diffusion coefficients. Experimentally, the fate of proton magnetization is followed with high selectivity using 2D 1H-13C solid-state HETCOR sequences incorporating controlled periods of 1H-1H spin-diffusion.

Solid-state NMR was applied to investigate atomic-level structure in heterogeneous materials that have proven challenging to study by existing physical methods. The ability of solid-state NMR to provide accurate structural information in these materials was demonstrated, and solid-state NMR techniques were applied to study chemical structure in bone tissue and to investigate the interactions of organic guest molecules inside a zeolite framework. It was proven that accurate distances could be reliably obtained using 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning. Distance measurements were made on natural abundance solids for the first time using this technique. The ability to obtain 1H spectra with correct chemical shift values using 2D correlation experiments was demonstrated. The sensitivity of a Frequency-Switched Lee-Goldburg Heteronuclear Correlation experiment was improved by a factor of 2.4, facilitating the investigation of natural abundance materials. Structural changes in apatite minerals upon carbonate substitution were explored. Hydroxide ion changed orientation within the hydroxide channel to hydrogen bond with surrounding phosphate and carbonate ions. Carbonate ion was located within the apatite lattice. Molecular modeling suggests that carbonate oxygens occupy the same O1-O3-O3' oxygen positions as phosphate in hydroxyapatite. An ordered water layer was directly observed for the first time on bone mineral crystallite surfaces. This layer may mediate the interaction between bone mineral and collagen, an interaction responsible for the unique biomechanical properties of bone. Three structural roles for water were discovered in synthetic carbonated apatite, deproteinated bone and unmodified bone mineral. Isolated water molecules occupy hydroxide ion vacancies in the calcium-lined hydroxide channel. Other crystal waters occupy non-channel vacancies. Bone mineral-organic matrix interactions were directly observed in bone tissue using a 1H-31 P chemical shift correlation experiment. Signals observed above 7 ppm were concluded to arise from mineral-H2O-collagen hydrogen-bonding interactions. Spectral differences between model apatites and unmodified bone mineral suggest significant structural differences. A novel method for preparing polyaniline (PANI) nanowires was developed. Guest p-aminobenzoic acid (PABA) molecules were loaded onto porous zeolite hosts from solution. Upon drying, the PABA molecules reacted to form PANI. Oxidized PANI is a semiconductor, and the presence of isolated radicals was evident in NMR spectra.

Milled wood lignin (MWL) is a fraction of the total lignin in wood but is considered the isolated lignin most representative of lignin in its native state. It is useful for lignin studies because it is isolated relatively free of carbohydrates, however structural changes occur during its isolation. This study presents attempts to evaluate the whole lignin structure with the goal of analysis its structure in intact wood. Solution-state and solid-state NMR experiments and degradative techniques were performed on soluble and insoluble lignins to make an estimation of the interunit linkages. MWL and cellulolytic enzyme lignin (CEL) exhibit only minor structural differences. MWL is lower in b-aryl ether content, has a higher degree of condensation, and a slightly higher amount of oxidized end group moieties. MWL may derive from the middle lamella to a larger extent than CEL. MWL and lignins isolated from milled wood and REL (Residual Enzyme Lignin) were dissolved using dimethyl sulfoxide (DMSO)/N-methylimidazole (NMI) for NMR analysis. HMQC showed that these lignins are similar from the standpoint of structural moieties present. Quantitative 13C NMR indicates that MWL has a b-O-4' content lower than that of the wood. Solid-state NMR suggests that MWL had a higher degree of condensation. The milled wood and REL contain a significant portion of high MW material (~55,000 g/mol) which contributes to their insolubility in aqueous dioxane. Solution-state NMR indicates that prolonged rotary ball milling results in more structural changes than the standard milling technique. There are few differences between samples milled in toluene or under N2 in a vibratory ball mill. Milling under N2 results in a higher MWL yield and the isolated lignin contains higher aliphatic and phenolic hydroxyl contents. The DFRC method is inefficient because it does not completely cleave all b-O-4' linkages. Inefficiency increases with molecular weight indicating that the cause is either accessibility or molecular mobility in the reductive cleavage step. Thioacidolysis completely degrades the b-aryl ether linkages in lignin and is therefore preferrable for analysis of these structures.

Phenol-formaldehyde (PF) resole and polymeric diphenylmethane diisocyanate (PMDI) are two commonly used exterior thermosetting adhesives in the wood-based composites industry. There is an interest in combining these two adhesives in order to benefit from their positive attributes while also neutralizing some of the negative ones. Although this novel adhesive system has been reportedly utilized in some limited cases, a fundamental understanding is lacking. This research serves this purpose by investigating some of the important aspects of this novel adhesive system. The adhesive rheological and viscometric properties were investigated with an advanced rheometer. The resole/PMDI blends exhibited non-Newtonian flow behavior. The blend viscosity and stability were dependent on the blend ratio, mixing rate and time. The adhesive penetration into wood was found to be dependent on the blend ratio and correlated with the blend viscosity. By using dynamic mechanical analysis, the blend cure speed was found to increase with the PMDI content. Mode I fracture testing of resole/PMDI hybrid adhesive bonded wood specimens indicated the dependence of bondline fracture energy on the blend ratio. The 75/25 PF/PMDI blend exhibited a high fracture energy with a fast cure speed and processable viscosity. Exposure to water-boil weathering severely deteriorated the fracture energies of the hybrid adhesive bondlines. More detailed chemistry and morphological studies were performed with cross-polarization nuclear magnetic resonance and 13C, 15N-doubly labeled PMDI. A spectral decomposition method was used to obtain information regarding chemical species concentration and relaxation behavior of the contributing components within the major nitrogen resonance. Different urethane concentrations were present in the cured blend bondlines. Water-boil weathering and thermal treatment at elevated temperatures (e.g. > 200°C) caused reduced urethane concentrations in the bondline. Solid-state relaxation parameters revealed a heterogeneous structure in the non-weathered blends. Water boil weathering caused a more uniform relaxation behavior in the blend bondline. By conducting this research, more fundamental information regarding the PF/PMDI hybrid adhesives will become available. This information will aid in the evaluation of, and improve the potential use of PF/PMDI hybrid adhesives for wood-based composites.

This work addresses the morphology of the wood/ Phenol-Formaldehyde (PF) adhesive interphase using yellow-poplar. In this case, morphology refers to the scale or dimension of adhesive penetration into wood. The objective is to develop methods for revealing ever smaller levels of wood/resin morphology. Dynamic techniques that are commonly utilized in polymer blend studies are investigated as potential methods for probing the wood/ adhesive interphase morphology. These are Dynamic Mechanical Analysis (DMA) and solid state NMR using CP/MAS. PF resin molecular weight is manipulated to promote or inhibit resin penetration in wood, using a very low or a very high molecular weight PF resin. With DMA, the influence of PF resin on wood softening is investigated. It is first demonstrated that the cooperativity analysis according to the Ngai coupling model of relaxation successfully applies to the in-situ lignin glass transition of yellow-poplar and spruce woods. No significant difference in intermolecular coupling is detected between the two woods. It is then demonstrated that combining simple DMA measurements with the cooperativity analysis yields ample sensitivity to the interphase morphology. From simple DMA temperature scans, a low molecular weight PF (PF-Low) does not influence lignin glass transition temperature. However, the Ngai coupling model of relaxation indicates that intermolecular coupling is enhanced with the low molecular weight PF. This behavior is ascribed to the low molecular weight PF penetrating lignin on a nanometer scale and polymerizing in-situ. On the other hand, a high molecular weight resin with a broad distribution of olecular weights (PF-High) lowers lignin glass transition temperature dramatically. This plasticizing effect is ascribed to a small fraction of the PF resin being low enough in molecular weight to penetrate lignin on a nanoscale, but being too dispersed for forming a crosslinked network. With CP/MAS NMR, intermolecular cross-polarization experiments are found unsuitable to probe the angstrom scale morphology of the wood adhesive interphase. However, observing the influence of the PF resins on the spin lattice relaxation time in the rotating frame, HT1r, and the cross-polarization time (TCH) is useful for probing the interphase morphology. None of the resins significantly affects the cross-polarization time, suggesting that angstrom scale penetration does not occur with a low nor a high molecular weight PF resin. However, the low molecular weight PF substantially modifies wood polymer HT1r, indicating that the nanometer scale environment of wood polymers is altered. On the other hand, the high molecular weight PF resin has no effect on wood HT1r. On average, the high molecular weight PF does not penetrate wood on a nanometer scale. Interestingly, the low molecular weight PF resin disrupts the spin coupling that is typical among wood components. Spin coupling between wood components is insensitive to the high molecular weight PF. Finally, it is noteworthy that the two PF resins have significantly different T1r 's in-situ. The low molecular weight resin T1r lies within the range of wood relaxations, suggesting some degree of spin coupling. On the other hand, the T1r of the high molecular weight PF appears outside the range of wood relaxations. Spin coupling between the high molecular weight resin and wood components is therefore inefficient. The CP/MAS NMR and DMA studies converge to identify nanometer scale penetration of the low molecular weight PF in wood. On the other hand, the high molecular weight PF resin forms separate domains from wood, although a very small fraction of the PF-High is able to penetrate wood polymers on a nanoscale.