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Rapid, solution-phase hydrogen/deuterium exchange (HDX) coupled with mass spectrometry (MS) is demonstrated as a means for distinguishing small-molecule metabolites. HDX is achieved using capillary vibrating sharp-edge spray ionization (cVSSI) to allow sufficient time for reagent mixing and exchange in micrometer-sized droplets. Different compounds are observed to incorporate deuterium with varying efficiencies resulting in unique isotopic patterns as revealed in the MS spectra. Using linear regression techniques, parameters representing contribution to exchange by different hydrogen types can be computed. In this proof-of-concept study, the exchange parameters are shown to be useful in the retrodiction of the amount of deuterium incorporated within different compounds. On average, the exchange parameters retrodict the exchange level with ~ 2.2-fold greater accuracy than treating all exchangeable hydrogens equally. The parameters can be used to produce hypothetical isotopic distributions that agree (± 16% RMSD) with experimental measurements. These initial studies are discussed in light of their potential value for identifying challenging metabolite species. [ABSTRACT FROM AUTHOR]

Ion mobility spectrometry (IMS) has become popular to characterize biomolecule folding. Numerous studies have shown that proteins that are folded in solution remain folded in the gas phase, whereas proteins that are unfolded in solution adopt more extended conformations in the gas phase. Here, we discuss how general this tenet is. We studied single-stranded DNAs (human telomeric cytosine-rich sequences with CCCTAA repeats), which fold into an intercalated motif (i-motif) structure in a pH-dependent manner, thanks to the formation of C–H+–C base pairs. As i-motif formation is favored at low ionic strength, we could investigate the ESI-IMS-MS behavior of i-motif structures at pH ~ 5.5 over a wide range of ammonium acetate concentrations (15 to 100 mM). The control experiments consisted of either the same sequence at pH ~ 7.5, wherein the sequence is unfolded, or sequence variants that cannot form i-motifs (CTCTAA repeats). The surprising results came from the control experiments. We found that the ionic strength of the solution had a greater effect on the compactness of the gas-phase structures than the solution folding state. This means that electrosprayed ions keep a memory of the charging process, which is influenced by the electrolyte concentration. We discuss these results in light of the analyte partitioning between the droplet interior and the droplet surface, which in turn influences the probability of being ionized via a charged residue-type pathway or a chain extrusion-type pathway. [ABSTRACT FROM AUTHOR]

We report ion mobility spectrometry and mass spectrometry studies of the non-enzymatic step-by-step degradation of substance P (subP), an 11-residue neuropeptide, with the sequence Arg1-Pro2-Lys3-Pro4-Gln5-Gln6-Phe7-Phe8-Gly9-Leu10-Met11-NH2, in ethanol. At elevated solution temperatures (55 to 75 °C), several reactions are observed, including a protonation event, i.e., [subP+2H]2+ + H+ → [subP+3H]3+, that appears to be regulated by a configurational change and two sequential bond cleavages (the Pro2-Lys3 peptide bond is cleaved to form the smaller nonapeptide Lys3-Met11-NH2 [subP(3–11)], and subsequently, subP(3–11) is cleaved at the Pro4-Gln5 peptide bond to yield the heptapeptide Gln5-Met11-NH2 [subP(5–11)]). Each of the product peptides [subP(3–11) and subP(5–11)] is accompanied by a complementary diketopiperazine (DKP): cyclo-Arg1-Pro2 (cRP) for the first cleavage, and cyclo-Lys3-Pro4 (cKP) for the second. Insight about the mechanism of degradation is obtained by comparing kinetics calculations of trial model mechanisms with experimental data. The best model of our experimental data indicates that the initial cleavage of subP is regulated by a conformational change, likely a trans→cis isomerization of the Arg1-Pro2 peptide bond. The subP(3–11) product has a long lifetime (t1/2 ~ 30 h at 55 °C) and appears to transition through several structural intermediates prior to dissociation, suggesting that subP(3–11) is initially formed with a Lys3-trans-Pro4 peptide bond configuration and that slow trans→cis isomerization regulates the second bond cleavage event as well. From these data and our model mechanisms, we obtain transition state thermochemistry ranging from ΔH‡ = 41 to 85 kJ mol−1 and ΔS‡ = − 43 to – 157 J mol−1 K−1 for each step in the reaction. [ABSTRACT FROM AUTHOR]

Recent studies show that reactions inside micron-sized compartments (e.g., droplets, emulsions) can proceed at significantly accelerated rates and with different mechanisms compared to the same reactions in a macroscopic container. Many of these studies use electrospray ionization (ESI) to both generate droplets and to quantify, via mass spectrometry (MS), droplet reaction kinetics. The highly charged and rapidly evaporating droplets produced in ESI make it difficult to examine precisely the underlying cause for droplet-induced rate enhancements. Additionally, interpretation of the spectra from ESI-MS can be complicated by gas-phase ion-molecule and clustering reactions. Here, we use an approach where droplet generation is separated from ionization, in order to decouple the multiple possible sources of acceleration and to examine more closely the potential role of gas-phase chemistry. The production of sugar phosphates from the reaction of phosphoric acid with simple sugars (a reaction that does not occur in bulk solution but has recently been reported to occur in droplets) is measured using this approach to compare reactivity in droplets (i.e., with compartments) with that in the gas phase (i.e., without compartments). The same product ions that have been previously assigned to in droplet reactions are observed with and without compartmentalization. These results suggest that in some cases, gas-phase processes in the ionization region can potentially complicate the quantification and interpretation of accelerated reactions in droplets using ESI-MS (or one of its variants). In such cases, contributions from in-droplet chemistry cannot be ruled out, but we demonstrate that gas-phase processes can be a significant (and possibly dominant) reaction pathway. We suggest that future studies of rate acceleration in droplets be modified to better assess the potential for non-droplet-related processes.ᅟ [ABSTRACT FROM AUTHOR]

Native mass spectrometry is applied for the investigation of proteins and protein complexes worldwide. The challenge in native mass spectrometry is maintaining the features of the proteins of interest, such as oligomeric state, bound ligands, or the conformation of the protein complex, during transfer from solution to gas phase. This is an essential prerequisite to allow conclusions about the solution state protein complex, based on the gas phase measurements. Therefore, soft ionization techniques are required. Widely used for the analysis of protein complexes are nanoelectro spray ionization (nESI) mass spectrometers. A newer ionization method is laser induced liquid bead ion desorption (LILBID), which is based on the release of protein complexes from solution phase via infrared (IR) laser desorption. We use both methods in our lab, depending on the requirements of the biological system we are interested in. Here we benchmark the performance of our LILBID mass spectrometer in comparison to a nESI instrument, regarding sample conditions, buffer and additive tolerances, dissociation mechanism and applicability towards soluble and membrane protein complexes.ᅟ [ABSTRACT FROM AUTHOR]

Short pieces of fused silica capillary tubing were used to support an electrified liquid-liquid interface. A methyl deactivated silica capillary having a diameter of 25 μm was filled with 1,2-dichloroethane solution and served as the organic part of the liquid-liquid interface. A nondeactivated fused silica capillary having a diameter of 5, 10, or 25 μm was filled with an aqueous HCl solution and served as the aqueous part of the electrochemical cell. For the latter, silanization of the capillary interior with chlorotrimethylsilane allowed for a successful phase reversal. All capillaries were characterized by ion transfer voltammetry using tetramethylammonium cation as a model ion. This simple, fast, and low-cost miniaturization technique was successfully applied for detection of the antibiotic ofloxacin. [ABSTRACT FROM AUTHOR]

The uncalcined but highly dispersive oxide-supported metal catalyst for liquid phase reactions may suffer from the agglomeration of metal nanoparticles and the drop of metal catalyst in solution, which will decrease the activity and shorten their life in catalysis. Here, a one-pot successive polyol reaction was developed to prepare M-ExOy colloidal particles as heterogeneous nanocatalysts, which merge the controlled synthesis of metal catalysts and oxide supports, the in situ loading of catalyst, and even the mesopore amplification into a highly integrated process. Unlike the traditional surface-deposited catalysts, the noble metal nanoparticles even with a large amount of loading are internally dispersed in the mesoporous oxide particles, which show higher activity and stability in the hydrogenation of nitroaromatics compared to the isolated nanocatalysts or surface-deposited catalysts. The improved activity and stability comes from the physical confinement of metal nanoparticles and good mass transportation of substrate/product within the support particles. This work proposed a novel method to prepare highly dispersed metal catalysts, which could be potentially useful to heterogeneous catalytic reactions with high-throughput and long-life demands. [ABSTRACT FROM AUTHOR]

Total internal reflection fluorescence correlation spectroscopy (TIR-FCS) is applied to study the self-diffusion of poly(ethylene glycol) solutions in the presence of weakly attractive interfaces. Glass coverslips modified with aminopropyl- and propyl-terminated silanes are used to study the influence of solid surfaces on polymer diffusion. A model of three phases of polymer diffusion allows to describe the experimental fluorescence autocorrelation functions. Besides the two-dimensional diffusion of adsorbed polymer on the substrate and three-dimensional free diffusion in bulk solution, a third diffusion time scale is observed with intermediate diffusion times. This retarded three-dimensional diffusion in the solution is assigned to the long-range effects of solid surfaces on diffusional dynamics of polymers. The respective diffusion constants show Rouse scaling (D ~ N-1), indicating a screening of hydrodynamic interactions by the presence of the surface. Hence, the presented TIR-FCS method proves to be a valuable tool to investigate the effect of surfaces on polymer diffusion beyond the first adsorbed polymer layer on the 100 nm length scale. [ABSTRACT FROM AUTHOR]

The interfacial free energy of a solid, which determines its adsorption properties, depends on interactions between the surface and the fluid. A change in surface composition can completely change the behavior of the solid. Decades of work have explored adsorption and its effects at solid-fluid interfaces from the macroscopic perspective and using molecular modeling, so the concept of the electric double layer (EDL) is well established in the community. However, direct, molecular level, experimental observations of the composition within the interface region, and its change with time and conditions, are not abundant. We used cryogenic X-ray photoelectron spectroscopy (cryoXPS) to observe the composition in the clay mineral-solution interface region as a function of bulk solution composition, on illite and chlorite in MgCl2 and CaCl2 electrolytes, over a range of concentrations (1-125 mM), in situ, on vitrified samples. These samples were prepared from very thin smears of centrifuged wet paste that were instantaneously chilled to liquid N2 temperature. They preserved the adsorbed solution in its amorphous state, maintaining the location of the ions and water with respect to the solid, without the disruption that occurs during drying or the rearrangement that results as water crystallizes during freezing. With decreasing ionic strength, we could directly monitor the loss of negative charge in the interface region, producing an anion deficiency, as predicted by theory. The Cl-/Me2+ ratio dropped below 1 for chlorite at 12-25 mM MeCl2 and for illite at 75-100 mM. In addition to better understanding of clay mineral behavior in solution, this work demonstrates that only those clay minerals where surface charge density is the same or lower than that for chlorite contribute to a low salinity enhanced oil recovery response (LS EOR). This explains many of the contradictory results from studies about the role of clay minerals in LS EOR. [ABSTRACT FROM AUTHOR]

Molecular wires are functional molecules applicable in the field of transfer processes in technological and biochemical applications. Besides molecular wires with the ability to transfer electrons, research is currently focused on molecular wires with high proton affinity and proton transfer ability. Recently, proposed peptidic proton wires (H wires) are one example. Their ability to mediate the transport of protons from aqueous solutions onto the surface of a Hg electrode in a catalytic hydrogen evolution reaction was investigated by constant-current chronopotentiometric stripping. However, elucidating the structure of H wires and rationalizing their stability are key requirements for their further research and application. In this article, we focus on the His (H) and Ala (A)-containing peptidic H wire A3-(H-A2)6 in solution and after its immobilization onto the electrode surface in the presence of the secondary structure stabilizer 2,2,2-trifluoroethanol (TFE). We found that the solvent containing more than 25% of TFE stabilizes the helical structure of A3-(H-A2)6 not only in solution but also in the adsorbed state. The TFE efficacy to stabilize α-helical structure was confirmed using high-resolution nuclear magnetic resonance, circular dichroism, and molecular dynamics simulation. Experimental and theoretical results indicated A3-(H-A2)6 to be a high proton-affinity peptidic H wire with an α-helical structure stabilized by TFE, which was confirmed in a comparative study with hexahistidine as an example of a peptide with a definitely disordered and random coil structure. The results presented here could be used for further investigation of the peptidic H wires and for the application of electrochemical methods in the research of proton transfer phenomena in general. [ABSTRACT FROM AUTHOR]

Plastic crystals are a promising candidate for solid state ionic conductors. In this work, quasielastic neutron scattering is employed to investigate the center of mass diffusive motions in two types of plastic crystalline cyclic alcohols: cyclohexanol and cyclooctanol. Two separate motions are observed which are attributed to long-range translational diffusion (a-process) and cage rattling (fast ß-process). Residence times and diffusion coefficients are calculated for both processes, along with the confinement distances for the cage rattling. In addition, a binary mixture of these two materials is measured to understand how the dynamics change when a second type of molecule is added to the matrix. It is observed that, upon the addition of the larger cyclooctanol molecules into the cyclohexanol solution, the cage size decreases, which causes a decrease in the observed diffusion rates for both the a- and fast ß-processes. [ABSTRACT FROM AUTHOR]

Here we show how to design organic redox-active solutions for use in redox-flow batteries, with an emphasis on attaining high volumetric capacity electrodes that minimize active-material crossover through the flow cell’s membrane. Specifically, we advance oligoethylene oxides as versatile core motifs that grant access to liquid redox-active oligomers having infinite miscibility with organic electrolytes. The resulting solutions exhibit order-of-magnitude increases in volumetric capacity and obviate deleterious effects on redox stability. The design is broadly applicable, allowing both low potential and high potential redox centers to be appended to these core motifs, as demonstrated by benzofurazan, nitrobenzene, 2,2,6,6-tetramethylpiperidin-1-yl)oxyl, and 2,5-di-tert-butyl-1-methoxy-4-(2′-methoxy)benzene pendants, whose reduction potentials range from −1.87 to 0.76 V vs Ag/Ag+ in acetonitrile. Notably, the oligoethylene oxide scaffold minimizes membrane crossover relative to redox-active small molecules, while also providing mass- and electron-transfer kinetic advantages over other macromolecular architectures. These characteristics collectively point toward new opportunities in grid-scale energy storage using all-organic redox-flow batteries. [ABSTRACT FROM AUTHOR]

Inspired by the rapid rise in efficiencies of lead halide perovskite (LHP) solar cells, lead-free alternatives are attracting increasing attention. In this work, we study the photovoltaic potential of solution-processed antimony (Sb)-based compounds with the formula A3Sb2I9 (A = Cs, Rb, and K). We experimentally determine bandgap magnitude and type, structure, carrier lifetime, exciton binding energy, film morphology, and photovoltaic device performance. We use density functional theory to compute the equilibrium structures, band structures, carrier effective masses, and phase stability diagrams. We find the A-site cation governs the structural and optoelectronic properties of these compounds. Cs3Sb2I9 has a 0D structure, the largest exciton binding energy (175 ± 9 meV), an indirect bandgap, and, in a solar cell, low photocurrent (0.13 mA cm–2). Rb3Sb2I9 has a 2D structure, a direct bandgap, and, among the materials investigated, the lowest exciton binding energy (101 ± 6 meV) and highest photocurrent (1.67 mA cm–2). K3Sb2I9 has a 2D structure, intermediate exciton binding energies (129 ± 9 meV), and intermediate photocurrents (0.41 mA cm–2). Despite remarkably long lifetimes in all compounds (54, 9, and 30 ns for Cs-, Rb-, and K-based materials, respectively), low photocurrents limit performance of all devices. We conclude that carrier collection is limited by large exciton binding energies (experimentally observed) and large carrier effective masses (calculated from density functional theory). The highest photocurrent and efficiency (0.76%) were observed in the Rb-based compound with a direct bandgap, relatively lower exciton binding energy, and lower calculated electron effective mass. To reliably screen for candidate lead-free photovoltaic absorbers, we advise that faster and more accurate computational tools are needed to calculate exciton binding energies and effective masses. [ABSTRACT FROM AUTHOR]

Electrospinning of ternary systems containing a nonsolvent is of interest because it can produce fibers that are highly porous on the surface and in the core. Despite the growing interest and applications, electrospinning of such ternary systems is challenging due to their evolving viscoelastic properties prior to electrospinning. In this study, we produce porous/rough poly(lactic acid) (PLA) fibers via electrospinning of binary and ternary systems of PLA, dichloromethane (solvent) and hexane (nonsolvent). We introduce a rheological approach to determine the appropriate time for electrospinning of ternary systems which is within at most 10% of their induction time of crystallization, when incipient crystals are formed within the polymer-rich phase. These incipient crystals act as nucleators for further crystallization during the process leading to higher crystallinity and more a form crystals. Surprisingly, the pore morphology and crystallinity of the as-electrospun fibers are drastically changed after a room temperature solvent exchange. During this process, cold crystallization and a' to a recrystallization occur for all systems. Also, the surface porosity of the fibers is decreased after the solvent exchange, except for the fibers produced from the ternary systems with higher PLA concentrations. Our results indicate that the crystallinity and surface texture of electrospun membranes and thus their performance may change during subsequent analysis and in-service applications, even when a highly volatile solvent is used as a spinning medium. [ABSTRACT FROM AUTHOR]

Copolymer/water interfacial tensions of statistical copolymers of styrene/n-butyl acrylate were estimated by pendant drop tensiometry using an "inverse" configuration according to which a drop of water was formed in toluene/copolymer solutions. The study first involved the precise measurement of copolymer solutions density using pycnometry. Subsequently, interfacial tensions of copolymer solutions against water were plotted as a function of copolymer concentration in toluene. Several methods were explored to fit the experimental data and obtain estimates of copolymer/water interfacial tensions at 100% copolymer concentration in toluene by extrapolation. The Belton-Evans extrapolation resulted in the best fit with the experimental data. When plotted as a function of the styrene composition of the copolymer, the interfacial tensions estimates followed an additivity relationship. This enabled estimation of the copolymer/water interfacial tensions directly from their respective homopolymer/water interfacial tensions values. These results are particularly useful for the prediction of composite particle morphology involving copolymerization of multiple monomers. [ABSTRACT FROM AUTHOR]

Drop profile analysis tensiometry used in the oscillating drop mode provides the dilational viscoelasticity of adsorption layers at liquid interfaces. Applied during the progress of adsorption the dynamic surface rheology can be monitored. For β-casein solutions at the same surface pressure values, the larger the dynamic dilational viscoelasticity the longer the adsorption time, i.e., the smaller the studied protein concentration is. For β-lactoglobulin and human serum albumin, the differences in the viscoelasticity values are less or not dependent on the adsorption time at identical surface pressures. The observed effects are caused by the flexibility of BCS, while the globular proteins BLG and HSA do not change their conformation significantly within the adsorption layer. [ABSTRACT FROM AUTHOR]

In a typical bipolar electrochemistry (BPE) configuration, voltage applied between the two driving electrodes induced a potential drop through solution filled in the microchannel, resulting in an interfacial potential difference between solution and BPE varied along the BPE. In the present work, we employed a recently developed plasmonic imaging technique to map the distribution of surface potential of bipolar electrodes with various geometries including round, triangle, hexagon, star, and rhombus shapes under the nonfaradaic charging process, from which the line of zero potential (LZP) was visualized and determined. We further investigated the dependence of LZP on electrode geometry and the distribution of external electric field and explained the experimental results with a charge balance mechanism. The triangular and star-shaped BPEs show quite different LZP features from the other ones with symmetrical geometry. These experimentally obtained potential distributions are all in good agreement with electromagnetic simulations. Finally, the line of zero overpotential (LZO) of the triangular-shaped BPE under faradaic reactions were investigated. The results confirm the shift of LZO when faradaic reactions occurred at the corresponding ends of BPE. The present work demonstrates the first experimental capability to map the potential distribution of BPE with arbitrary geometry under an arbitrary driving field. It is anticipated to help the design and optimization on the geometry of electrodes and microchannels with implications for boosting their applications in chemical sensing and materials synthesis. [ABSTRACT FROM AUTHOR]

The complexes [MII(acac)2] (M = Cu 1, Pd 2, Pt 3; Hacac = acetylacetone) and 1,4-diiodotetrafluorobenzene (FIB) were cocrystallized in CHCl3–MeOH solutions to form adducts (1–3)·FIB, whose structures were studied by X-ray diffraction. The association leads to unification of the three structures, thus demonstrating the potential of the isostructural Cu/Pd/Pt exchange for construction of supramolecular systems involving [MII(acac)2] complexes. In the crystal structures of (1–3)·FIB, the intermolecular bifurcated halogen bonding I···μ2-(O,O) and noncovalent interactions M···C were identified and then studied by density functional theory calculations and topological analysis of the electron density distribution within the framework of the QTAIM method at the M06/DZP-DKH level of theory. Apart from these unconventional interactions, two types of classic hydrogen bonding, viz. the C–H···I–C and C–H···F–C contacts between Me groups and halogen atoms of FIB, were detected. Collectively all these noncovalent structure-directing interactions provide conversion of one-dimensional arrays of the [MII(acac)2] species into three-dimensional networks. [ABSTRACT FROM AUTHOR]

Levofloxacin, the levo-isomer of the antibiotic ofloxacin, can crystallize into two different hydrate forms, the monohydrate and the hemihydrate. Although these forms are well characterized, little is known about their anhydrous structures besides the study of Singh and Thakur using crystal structure prediction. In order to solve this issue, this paper proposes the use of high-temperature powder X-ray diffraction to determine the anhydrous structures of the levofloxacin forms termed in the literature as α and γ, herein obtained by heating of the levofloxacin monohydrate and hemihydrate, respectively. These are the first levofloxacin anhydrates whose structures could be solved. To support our results, the dehydration process has been also evaluated by means of differential scanning calorimetry, thermogravimetric analysis, and hot-stage polarized microscopy. The resulting X-ray structures differ from the ones reported as the best-predicted solution, although the predicted work had predicted similar structures as lower ranked solutions. [ABSTRACT FROM AUTHOR]

The properties of organic–inorganic hybrid perovskites greatly depend on their compositions. Here, we investigate the crystallization of methylammonium lead mixed halide (MAPbI3–xBrx) from microdroplets by adjusting the molar ratio of iodine to bromine in precursor solution, which helps to control the morphology, crystallinity, and physical properties of the perovskite materials. The composition of the precursor solutions has profound effects on the crystallization and perovskite morphology. It tends to form needle intermediate crystals of MAPbI3−xBrx·DMF from the precursor solution at low bromine concentration, while it tends to form flake or cubic perovskite of MAPbI3−xBrx at high bromine concentration. There is evident composition segregation of bromine when the perovskite and its intermediate grow freely from the solution at low temperature. At a high growing temperature of 100 °C, continuous perovskite films consisting of large crystal domains with sizes up to 100 μm are fabricated from the precursor solution. [ABSTRACT FROM AUTHOR]

Acentric compounds with a layered structure are of current interest owing to their advanced functional properties for technical applications. However, the growth of bulk single crystals of acentric materials with a quasi-two-dimensional structure is challenging, which severely hinders the intrinsic properties investigation and optoelectronic applications of these materials. Herein, we report the controlled growth of bulk CdTeMoO6 single crystals with a layered structure and the investigation of their linear and nonlinear optical properties. High quality CdTeMoO6 single crystals with dimensions of ∼26 × 10 × 9 mm3 were successfully grown through the modified top-seeded solution growth method using TeO2-MoO3 as a flux. The transparent range of CdTeMoO6 single crystals is in the range of 0.345–5.40 μm, and with large birefringence (Δn = no – ne = 0.2868–0.2219 from 514 nm to 1.5467 μm). In addition, the nonlinear optical (NLO) coefficient d36 of CdTeMoO6 single crystals was measured to be 8.5 pm/V using Maker Fringe techniques. We also found CdTeMoO6 is type-I phase-matchable based on the calculated phase-matching curves. Our results indicated that CdTeMoO6 single crystal is an excellent birefringent material combined with a promising NLO material for optoelectronic applications. [ABSTRACT FROM AUTHOR]

NMR crystallographic techniques are used to validate a structure of β-piroxicam determined from powder X-ray diffraction (PXRD) with a relatively poor R-factor. Geometry optimization of PXRD- and single-crystal XRD- derived structures results in convergence to the same energy of the structures, with minimal atomic displacements, and good agreement of gauge-included projector augmented wave (GIPAW) calculated and experimentally determined NMR 1H, 13C, and 15N chemical shifts, and 14N quadrupolar parameters. Calculations on isolated molecules combined with 2D magic-angle spinning (MAS) 1H double-quantum (DQ) and 14N–1H NMR experiments confirm the 3D packing arrangement of β-piroxicam. NMR crystallography is shown to be an effective means of validating crystal structures that might otherwise be considered sceptically on the basis of diffraction data alone. [ABSTRACT FROM AUTHOR]

Seeded growth is one of the most successful and well-studied methods of making nanorods of face-centered cubic (FCC) metals such as Ag, Au, Pt, etc. In this method separately prepared tiny metal seeds (typically smaller than 10 nm) are added to a growth solution containing metal precursor, a weak reducing agent such as ascorbic acid, and a capping agent. The mechanisms that lead to specific shape selection and growth of nanoparticles, in this method, are poorly understood. We propose a mechanism of nanorod growth based on the physical phenomenon of twinning and develop a population balance based model. Briefly, on mixing with growth solution, the seeds start growing isotropically, during which some of the seeds undergo twinning and transform their growth habit to form nanorod nuclei. The nanorod nuclei grow along one dimension to form nanorods, and a mixture of nanorods and nanospheres is obtained after a short aging time (typically < 3 h). The simulations capture the salient features of one-dimensional growth of nanorods, along with the kinetics. The trends in experimental data are reproduced well by this model, and we are able to predict the yield of nanorods. Simulations also reveal that the growth of nanospheres competes with the nucleation and growth of nanorods; their relative magnitudes decide the yield of specific shapes in the system. The model is quite general and will apply to the seeded growth of nanorods of any material that has an FCC crystal structure. [ABSTRACT FROM AUTHOR]

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water and how such structures change while being exposed to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property whereas other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material. [ABSTRACT FROM AUTHOR]

Heavy crude oil has poor solubility and a high density, making recovery and transport much more difficult and expensive than for light crude oil. Emulsifiers can be used to produce low viscosity oil-in-water emulsions for recovery and transport, but subsequent demulsification can be challenging. Here, we develop and implement interfacially active, pH-responsive polymer-coated nanoparticles (PNPs) to reversibly stabilize, recover, and break oil/water emulsions through variation of solution pH. Silica particles with poly(2-(dimethylamino)ethyl methacrylate) (DMAEMA) chains covalently grafted to the surface are prepared although a reversible addition fragmentation chain transfer grafting-through technique. The resulting DMAEMA PNPs can stabilize emulsions of high viscosity Canadian heavy oil at PNP concentrations as low as 0.1 wt % and at neutral pH. The performance of the DMAEMA PNPs exceeds that of DMAEMA homopolymer additives, which we attribute to the larger size and irreversible adsorption of DMAEMA PNPs to the oil/water interface. After recovery, the emulsion can be destabilized by the addition of acid to reduce pH, resulting in separation and settling of the heavy oil from the aqueous phase. Recovery of more than 10 wt % of the crude heavy oil-in-place is achieved by flooding with aqueous solution of 0.1 wt % DMAEMA PNPs without any additional surfactant or chemical. This work demonstrates the applicability of PNPs as surface active materials for enhanced oil recovery processes and for heavy oil transport. [ABSTRACT FROM AUTHOR]

We report the formation of crack patterns in drying films of Laponite-NaCl solution. Crack patterns that develop upon drying aqueous Laponite-NaCl solution change drastically as the amount of NaCl is varied in the solution. In this work, we have investigated the effect of NaCl on drying films of aqueous solution of Laponite under two conditions: (i) when the film is bounded by a wall, as in Petri dish experiments and (ii) when the film does not have any boundary, as in experiments with droplets. In order to obtain insights into the effect of the substrate, the experiments have been done with two different substrates of different hydrophobicities, polypropylene and glass. The formation of crack patterns has been explained on the basis of the wetting and spreading properties of the solution on these substrates and the effect of salt on colloidal aggregation. In this work, we have shown that the presence of salt in aqueous Laponite solution can induce crack patterns depending on the nature of the substrate. Another important aspect of this work is the role of NaCl in crack inhibition in desiccating films of aqueous Laponite, in the presence of static electric field. This effect can be utilized to suppress undesirable crack formation in many applications. [ABSTRACT FROM AUTHOR]

The size distribution and the rheological properties of dispersions of biological colloids are relevant quality attributes for a variety of industrial applications, including pharmaceutical, food, and cosmetic products. For instance, the biophysical properties of monoclonal antibodies and therapeutic proteins, which represent an important class of drugs in the pharmaceutical market, are important for their safety and efficacy. In this work, we apply a microfluidic diffusion platform to analyze protein sizes and interactions in high-concentration antibody solutions directly in the liquid state with minimal perturbation of the sample. We show that this method provides size distributions in a size range scaling from a few angstroms to hundreds of nanometers. The detection sensitivity of the technique is independent of the particle size, and the method provides number-average distributions, enabling the simultaneous detection of both monomeric species and soluble aggregates. We further show that the same platform can be applied to measure viscosity-scaling effects in crowded environments by probing the Brownian motion of several tracers with different sizes. Such tracers experience a shift from the microviscosity to the macroviscosity of the sample at a critical probe size that is equal to the characteristic dimension of the main components of the dispersions. The technique simultaneously provides quantitative measurement of the microrheological properties and the macroviscosity of the sample, as well as information on the characteristic size of the components of the solution. Overall, these methods represent attractive tools in the context of the analysis of sizes and interactions of proteins in both diluted and high-concentration solutions during development, manufacturing, and formulation. [ABSTRACT FROM AUTHOR]

Oxidized corn starch-gelatin (OCS-Gel) was successfully synthesized by the electrochemical-assisted oxidation method. The introduction of spray-drying technology, as an advanced method for the postprocessing of sample solution, also has greatly improved the application property of blend. The corn starch was gelatinized first, and then mixed with gelatin solution to prepare the blend solution in the electrolyzer with current (120 mA) and 0.5% sodium chloride. Finally, the prepared OCS-Gel solution was dehydrated and granulated using the spray-drying process to obtain the powder particles of OCS-Gel. The spray-dried OCS-Gel was characterized by FT-IR, XRD and SEM. The introduction of active groups (amino, carboxyl, carbonyl) promoted OCS-Gel hydration and swelling. In addition, compared with CS the crystallinity of spray-dried OCS-Gel decreased obviously. The OCS-Gel formed a hollow or deflated spherical structure. The electrochemical-assisted oxidation and spray-drying technology were masterfully combined to prepare the OCS-Gel, which can dramatically improve the application performance of biomaterials. [ABSTRACT FROM AUTHOR]

A new light-switchable azo-surfactant arylazopyrazole tetraethylene glycol carboxylic acid (AAP-E4) was used as a molecular building block to functionalize macroscopic foams. AAP-E4 was studied in the bulk solution with UV/vis spectroscopy and at the interface with sum-frequency generation (SFG) as well as tensiometry. Additional foaming experiments were performed with a dynamic foam analyzer to study the role of AAP-E4 surfactants at the ubiquitous air-water interface as well as within macroscopic foam. In the bulk, it is possible to switch the AAP-E4 surfactant reversibly from trans to cis configurations and vice versa using 380 nm UV and 520 nm green light, respectively. At the interface, we demonstrate the excellent switching ability of AAP-E4 surfactants and a substantial modification of the surface tension. In addition, we show that the response of the interface is strongly influenced by lateral electrostatic interactions, which can be tuned by the charging state of AAP-E4. Consequently, the electrostatic disjoining pressure and thus the foam stability are highly dependent on the bulk pH and the charging state of the interface. For that reason, we have studied both the surface net charge (SFG) and the surface excess (tensiometry) as important parameters that determine foam stability in this system and show that neutral pH conditions lead to the optimal compromise between switching ability, surface excess, and surface charging. Measurements on the foam stability demonstrated that foams under irradiation with green light are more stable than foams irradiated with UV light. [ABSTRACT FROM AUTHOR]

Hydroperoxides are important oxidants in epoxidation processes and play a central role in the industrial hydrocarbon autoxidation. This paper presents a new and water-free/low-water iodometric titration technique that can be utilized to quantify organic hydroperoxides. In this protocol, the aqueous thiosulfate titrant used in the conventional iodometric titration method was replaced with a new titrant (triphenylphosphine solution) in order to prevent the need for aqueous solutions. In addition, a comparison of two methods showed that titration time in this new method is shorter than that of thiosulfate titrant based one. It is predicted that a colorless charge-transfer complex is formed from interaction between triphenylphosphine and iodine. The proposed protocol can be utilized in the industrial processes that go through hydroperoxide intermediates. [ABSTRACT FROM AUTHOR]

The artificiality of the actual amount adsorbed (AAA) estimated from the experimentally measured Gibbsian surface excess (GSE) of a gas is discussed. The use of AAA for calculation of isosteric heat of adsorption or mixed gas adsorption isotherms using ideal adsorbed solution theory can be misleading and incorrect. The GSE, on the other hand, can be unambiguously used to describe all practical aspects of adsorption science and technology. [ABSTRACT FROM AUTHOR]

The large and sparsely hydrated thiocyanate anion, SCN-, plays a prominent role in the study of specific ion effects in biological, colloid, and atmospheric chemistry due to its extreme position in the Hofmeister series. Using atomistic modeling of aqueous SCN- solutions, we provide novel insight at the molecular scale into the experimentally observed differences in ion pairing, clustering, reorientation dynamics, mutual diffusion, and solubility between the sodium, Na+, and the potassium, K+, salt. Compared to KSCN, NaSCN has a less pronounced tendency to ion pairing; nevertheless, at high salt concentrations, we observe a strong attraction between Na+ cations and the nitrogen end of SCN-, resulting in larger and more closely packed ion clusters. To accurately model aqueous SCN- solutions in computer simulations, we develop a thermodynamically consistent force field rooted in quantum-chemical calculations and refined using the Kirkwood-Buff theory. The force field is compatible with the extended simple point charge and three-point optimal point charge classical water models and reproduces experimental activity derivatives and air-water surface tension for a wide range of salt concentrations. [ABSTRACT FROM AUTHOR]

This paper attempts to provide empirical mass and kinetic models for the flash evaporation of sodium chloride (NaCl) aqueous solution based on experimental phenomena. The models have nine parameters and six affecting factors including initial temperature, operation pressure, NaCl mass fraction, solution depth, evaporator diameter and time. On the basis of a large number of flash evaporation experimental data from various literatures, the mass model parameters were optimized and validated. After optimization of the model parameters with 283 sets of literature experimental data, the average relative error between the model values and the experimental data is about 5.7%. And a statistical method proved the mass model is well posed. The verification with other 215 sets of literature experimental data showed the mass model is in good agreement with flash evaporation phenomena, and the average relative error between the model values and the experimental data is about 8.3%. Then, the kinetic model of flash evaporation was obtained according to the empirical mass model. Finally, the analysis of these models indicated that the increase of initial temperature or evaporator diameter and the decrease of operating pressure are in favor of evaporation. Although the increase of solution depth can improve the evaporated mass, the corresponding evaporation efficiency will be slightly reduced. And the increase of salt content is having a detrimental effect on the evaporation of NaCl-water solution. In addition, the influence of salt content on evaporation at higher operating pressure is more obvious than that at lower operating pressure. The above results show that these models proposed in our work have high accuracy, wide practicability, and good rationality. [ABSTRACT FROM AUTHOR]

Electrochemistry serves as a powerful method for generating reactive intermediates, such as organic cations. In general, there are two ways to use reactive intermediates for chemical reactions: (1) generation in the presence of a reaction partner and (2) generation in the absence of a reaction partner with accumulation in solution as a "pool" followed by reaction with a subsequently added reaction partner. The former approach is more popular because reactive intermediates are usually short-lived transient species, but the latter method is more flexible and versatile. This review focuses on the latter approach and provides a concise overview of the current methods for the generation and accumulation of cationic reactive intermediates as a pool using modern techniques of electrochemistry and their reactions with subsequently added nucleophilic reaction partners. [ABSTRACT FROM AUTHOR]

Electrosynthesis has much to offer to the synthetic organic chemist. But in order to be widely accepted as a routine procedure in an organic synthesis laboratory, electrosynthesis needs to be presented in a much more user-friendly way. The literature is largely based on electrolysis in a glass beaker or H-cells that often give poor performance for synthesis with a very slow rate of conversion and, often, low selectivity and reproducibility. Flow cells can lead to much improved performance. Electrolysis is participating in the trend toward continuous flow synthesis, and this has led to a number of innovations in flow cell design that make possible selective syntheses with high conversion of reactant to product with a single passage of the reactant solution through the cell. In addition, the needs of the synthetic organic chemist can often be met by flow cells operating with recycle of the reactant solution. These cells give a high rate of product formation while the reactant concentration is high, but they perform best at low conversion. Both approaches are considered in this review and the important features of each cell design are discussed. Throughout, the application of the cell designs is illustrated with syntheses that have been reported. [ABSTRACT FROM AUTHOR]

The conformational preferences of proteinogenic glutamic acid esterified (GluOMe) and N-acetylated (AcGluOMe) derivatives have been determined in solution for the first time. Theoretical calculations at the ωB97X-D/aug-cc-pVTZ made possible the assignment of six and eight stable conformers for GluOMe and AcGluOMe, respectively. The conformational equilibrium of the studied compounds was evaluated in different organic solvents using a combination of the integral equation formalism polarizable continuum model (IEF-PCM) and ¹H NMR spectroscopy data. The results showed that the conformational equilibrium of both derivatives change in the presence of solvent. According to the quantum theory of atoms in molecules (QTAIM), non-covalent interactions (NCI), and natural bond orbitals (NBO) analyses, the conformational preferences observed for GluOMe and AcGluOMe are not dictated by the presence of a specific interaction but are due to a combination of hyperconjugative and steric effects. [ABSTRACT FROM AUTHOR]

An upper critical solution temperature (UCST) block copolymer, poly(acrylamide-co-acrylonitrile)-b-polyvinylpyrrolidone (P(AAm-co-AN)-b-PVP), was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, assembled in solution, and deposited within functional layer-by-layer (LbL) temperature-responsive films. In aqueous solutions, the polymer formed well-defined block copolymer micelles (BCMs) at ambient temperature and exhibited a reversible micelle-unimer transition within an ~40-50 °C temperature range in a wide range of pH and ionic strengths. Temperature-induced dissociation of BCMs to unimers was completely suppressed, however, when BCMs were assembled with tannic acid (TA) within LbL films. Instead, reversible changes in micellar sizes and film swelling occurred as a result of UCST-driven uptake/release of water within/from the micellar cores. The solution pH modulated strength of hydrogen bonding between TA and PVP in the micellar corona, thus strongly affecting film growth, micelle morphology, and film swelling. Spherical micellar morphology and high film swelling degrees were observed with films at neutral pH values, where hydrogen bonding was counteracted by the negative charge of partially ionized TA. In contrast, strong hydrogen bonding and absence of charge in TA caused crumpling of BCMs and reduced the film swelling degree in acidic solutions. Film swelling was also dependent on number of assembled micellar layers, with thicker films exhibiting larger swelling amplitudes and sharper temperature transitions. The LbL assemblies were stable in phosphate buffer saline up to pH 7.5 at 50 °C and preserved their response after 55 heating/cooling cycles. The robustness of the temperature transitions in these films taken together with their occurrence in an aqueous environment in a wide range of pH and ionic strengths makes these films potentially useful for controlling responses of soft interfaces in biological environments. [ABSTRACT FROM AUTHOR]

High molecular weight water-soluble polymers are widely used as flocculants or thickeners. However, synthesis of such polymers via solution polymerization invariably results in highly viscous fluids, which makes subsequent processing somewhat problematic. Alternatively, such polymers can be prepared as colloidal dispersions; in principle, this is advantageous because the particulate nature of the polymer chains ensures a much lower fluid viscosity. Herein we exemplify the latter approach by reporting the convenient one-pot synthesis of high molecular weight poly(glycerol monomethacrylate) (PGMA) via the reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization of a water-immiscible protected monomer precursor, isopropylideneglycerol methacrylate (IPGMA) at 70 °C, using a water-soluble poly(glycerol monomethacrylate) (PGMA) chain transfer agent as a steric stabilizer. This formulation produces a low-viscosity aqueous dispersion of PGMA-PIPGMA diblock copolymer nanoparticles at 20% solids. Subsequent acid deprotection of the hydrophobic core-forming PIPGMA block leads to particle dissolution and affords a viscous aqueous solution comprising high molecular weight PGMA homopolymer chains with a relatively narrow molecular weight distribution. Moreover, it is shown that this latex precursor route offers an important advantage compared to the RAFT aqueous solution polymerization of glycerol monomethacrylate since it provides a significantly faster rate of polymerization (and hence higher monomer conversion) under comparable conditions. [ABSTRACT FROM AUTHOR]

The colligative property freezing point depression is evaluated as a means for estimating the extent of aggregation for solutions of poly(ethylene oxide) alcohol (C10E6) nonionic surfactant in cyclohexane. Combined with additional measurements of self-diffusion coefficients, it is shown that both unaggregated C10E6 as well as reverse micelles are significantly present for the entire range of measured C10E6 concentration (0.048-2.35 mol kg-1). A change in speciation near 0.2 mol kg-1 is indicated by the results from both freezing point depression and self-diffusion coefficient measurements. It is shown that average reverse micelle radii and aggregation numbers obtained from the ratio of solvent and C10E6 self-diffusion coefficients are consistent with prior reported results. However, unreasonably small radii for the reverse micelles as well as for the cyclohexane were obtained from analysis of the results by the Stokes-Einstein equation using additional measured solution viscosities. The concentration of reverse micelles and unaggregated C10E6 was calculated from the freezing point depression results using the aggregation numbers obtained from ratio of self-diffusion coefficients. These concentrations indicate that the reverse micelles become smaller in average size and increase in number with increasing temperature without an increase in unaggregated C10E6. [ABSTRACT FROM AUTHOR]

We recently developed a pathway analysis framework (paper 1) for describing single-molecule kinetics for renewal (i.e., memoryless) processes based on the decomposition of a kinetic scheme into generic structures. In our approach, waiting time distribution functions corresponding to such structures are expressed in terms of self-consistent pathway solutions and concatenated to form measurable probability distribution functions (PDFs), affording a simple way to decompose and recombine a network. Here, we extend this framework to nonrenewal processes, which involve correlations between events, and employ it to formulate waiting time PDFs, including the first-passage time PDF, for a general kinetic network model. Our technique does not require the assumption of Poissonian kinetics, permitting a more general kinetic description than the usual rate approach, with minimal topological restrictiveness. To demonstrate the usefulness of this technique, we provide explicit calculations for our general model, which we adapt to two generic schemes for single-enzyme turnover with conformational interconversion. For each generic scheme, wherein the intermediate state(s) need not undergo Poissonian decay, the functional dependence of the mean first-passage time on the concentration of an external substrate is analyzed. When conformational detailed balance is satisfied, the enzyme turnover rate (related to the mean first-passage time) reduces to the celebrated Michaelis-Menten functional form, consistent with our previous work involving a similar scheme with all rate processes, thereby establishing further generality to this intriguing result. Our framework affords a general and intuitive approach for evaluating measurable waiting time PDFs and their moments, making it a potentially useful kinetic tool for a wide variety of single-molecule processes. [ABSTRACT FROM AUTHOR]

The application of protein deuteration and high flux neutron reflectometry has allowed a comparison of the adsorption properties of lysozyme at the air-water interface from dilute solutions in the absence and presence of high concentrations of two strong denaturants: urea and guanidine hydrochloride (GuHCl). The surface excess and adsorption layer thickness were resolved and complemented by images of the mesoscopic lateral morphology from Brewster angle microscopy. It was revealed that the thickness of the adsorption layer in the absence of added denaturants is less than the short axial length of the lysozyme molecule, which indicates deformation of the globules at the interface. Two-dimensional elongated aggregates in the surface layer merge over time to form an extensive network at the approach to steady state. Addition of denaturants in the bulk results in an acceleration of adsorption and an increase of the adsorption layer thickness. These results are attributed to incomplete collapse of the globules in the bulk from the effects of the denaturants as a result of interactions between remote amino acid residues. Both effects may be connected to an increase of the effective total volume of macromolecules due to the changes of their tertiary structure, that is, the formation of molten globules under the influence of urea and the partial unfolding of globules under the influence of GuHCl. In the former case, the increase of globule hydrophobicity leads to cooperative aggregation in the surface layer during adsorption. Unlike in the case of solutions without denaturants, the surface aggregates are short and wormlike, their size does not change with time, and they do not merge to form an extensive network at the approach to steady state. To the best of our knowledge, these are the first observations of cooperative aggregation in lysozyme adsorption layers. [ABSTRACT FROM AUTHOR]

An experimental apparatus was developed for rapid and continuous supercritical CO2 extraction and separation of hydrophobic organic compounds from liquid solution. The mixing of supercritical CO2 and liquid solutions in a micromixer enhances mass transfer, which enables rapid extraction of hydrophobic organic compounds. Near-equilibrium yields were obtained in about 10 s. The separation of supercritical CO2 from liquid was achieved using a newly developed separation system. In this separation system, the liquid level is controlled by the differential pressure between the head pressure and the supercritical CO2 phase. A control bulb at the outlet of the liquid line was regulated to maintain a constant differential pressure. The extraction of aqueous vanillin solution was conducted at 40 °C under pressures of 10, 15, and 20 MPa. Our results suggest that greater than 97% equilibrium was achieved in our system within the extraction time of 10 s. The extraction of a black liquor filtrate, that contains vanillin, its related compounds, and more than 5 wt % salts, was also conducted. More than 80% of the vanillin was successfully extracted to the CO2 phase. [ABSTRACT FROM AUTHOR]

The overarching analytic integrated rate equation for the chemical kinetics of any reversible or irreversible reaction involving an arbitrary number of species and any integral orders is shown to be Πi=1r[1 - fi-1ξ(t)]γi = e(-1)r F0t, where ξ(t) is the extent of reaction variable, the fi are roots of a polynomial of order r, the exponents are determined by γi = Πk(≠i)r(fi - fk)-1, and F0 is a factor involving the stoichiometric coefficients and rate constants (k±). All integrated rate equations of elementary reactions appearing in chemical kinetics are special cases of this universal solution. Not only does the solution provide insight into the analytical form of the exponents γi and F0 that govern the time evolution of the system, but it also provides an elegant framework for the pedagogy and application of kinetics in physical chemistry. [ABSTRACT FROM AUTHOR]

[FeFe] hydrogenases are efficient enzymes that produce hydrogen gas under mild conditions. Synthetic model compounds containing all CO or mixed CO/PMe3 ligands were previously studied by us and others with ultrafast ultraviolet or visible pump-infrared probe spectroscopy in an effort to better understand the function and interactions of the active site with light. Studies of anionic species containing cyano groups, which more closely match the biological active site, have been elusive. In this work, two model compounds dissolved in room-temperature acetonitrile solution were examined: [Fe2(μ-S2C3H6)(CO)4(CN)2]2- (1) and [Fe2(μ-S2C2H4)(CO)4(CN)2]2- (2). These species exhibit long-lived transient signals consistent with loss of one CO ligand with potential isomerization of newly formed ground electronic state photoproducts, as previously observed with all-CO and CO/PMe3-containing models. We find no evidence for fast (ca. 150 ps) relaxation seen in the all-CO and CO/PMe3 compounds because of the absence of the metal-to-metal charge transfer band in the cyano-functionalized models. These results indicate that incorporation of cyano ligands may significantly alter the electronic properties and photoproducts produced immediately after photoexcitation, which may influence the catalytic activity of model compounds when attached to photosensitizers. [ABSTRACT FROM AUTHOR]

Attempts to generate the free bis(N-heterocyclic carbene) vegiR (R = nPr, tBu; vegiR = 2,7-dihydro-2,7-dialkyldiimidazo[1,5-b:5',1'-f]pyridazine-1,8-diylidene) from its imidazolium salts 1 with alkali-metal bases resulted exclusively in the formation of the respective lithium, sodium, and potassium complexes 2-4 due to the strongly chelating properties of the dicarbene. DFT calculations reveal pronounced dispersion interactions in the case of N-tert-butyl substituents as the reason for the formation of the homoleptic lithium species 2b-H in solution. The dynamic behavior of the lithium complexes in equilibrium was studied by NMR techniques. Attempts to liberate the free carbenes by addition of the respective crown ethers failed for the lithium and sodium complexes. Deprotonation of the imidazolium salts 1a,b with the strong metal-free phosphazene base P4-tBu ({(Me2N)3PN}3PNtBu) generated successfully the free dicarbenes vegiR (5) and monocarbene 6b in solution. [ABSTRACT FROM AUTHOR]

As the [2Fe]H subsite models of [FeFe]-hydrogenases, a series of PNP-chelated and -bridged diiron dithiolate complexes 1a-f and 2a-f together with the three related monophosphine complexes 3a-c were prepared by the selective substitutions of the all-carbonyl complex Fe2(μ-pdt)(CO)6 (A, pdt = SCH2CH2CH2S) with aminodiphosphines (Ph2P)2NR (denoted as PNP) under different reaction conditions. The first UV irradiation of the toluene solutions of A with different PNP ligands (PNP = (Ph2P)2NR; R = (CH2)3Me, (CH2)3NMe2, (CH2)3Si(OEt)3, C6H5, C6H4OMe-p, C6H4CO2Me-p) readily afforded the target PNP-chelated complexes Fe2(μ-pdt)(CO)4{(κ²-Ph2P)2NR} (1a-f), while the reflux of xylene solutions of A with the aforementioned PNP ligands produced the PNP-bridged complexes Fe2(μ-pdt)(CO)4{(μ-Ph2P)2NR} (2a-f). Comparatively, treatments of A and one type of PNP ligand with N-aryl substituents R (R = C6H5, C6H4OMe-p, C6H4CO2Me-p) in MeCN at room temperature in the presence of the decarbonylating agent Me3NO·2H2O formed the unexpected monophosphine complexes Fe2(μ-pdt)(CO)5{κ¹-Ph2P(NHR)} (3a-c) and the minor chelated complexes 1d-f. All of the complexes 1a-f, 2a-f, and 3a-c have been characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1a,b,d-f, 2b,d-f, and 3b by X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes 1a and 2a as a pair of representative isomers have been evaluated and compared by cyclic voltammetry in MeCN as solvent in the absence and presence of HOAc as a proton source. [ABSTRACT FROM AUTHOR]

Polysarcosine (pSar) was one of the first polymers synthesized in a controlled living manner, but it was only recently when it was reconsidered as a promising alternative for poly(ethylene glycol) (PEG) in biomedical applications. Despite receiving more and more attention, very little is known about the solution properties of pSar, such as coil dimensions and thermodynamic interactions. In this article, we report on these properties of pSar with degrees of polymerization 50 < Xn < 400 that were prepared by controlled living ring-opening polymerization. The polymers are characterized by gel permeation chromatography (GPC), MALDI-TOF mass spectrometry, dynamic and static light scattering (SLS), and viscometry. The chain stiffness of pSar in PBS in terms of the Kuhn statistical segment length, lk, was estimated to lk = 1.5 nm by application of the Yamakawa-Fujii wormlike chain theory to the experimentally determined hydrodynamic radii, Rh, thus being higher than lk = 1.1 nm for PEG in PBS. Also, the second virial coefficients, A2, of pSar and PEG in PBS were similar and reflect their good solubility in aqueous solution. While the universal calibration of GPC elution volumes failed for pSar in HFIP utilizing PMMA standards, it worked better in PBS buffer with PEG standards. Alternatively, an Rh-Mw relation is established in the present work, which enables the determination of molar masses of pSar by simple DLS measurements. In addition, it is demonstrated that pSar independent from its chain length (50 < Xn < 400) does not induce any detectable complement activation (C5a) in human serum. [ABSTRACT FROM AUTHOR]

In previous works aiming at understanding the mesoporous network after alkaline treatment in the presence of organic additives, conventional bulk characterization techniques led to the conclusion that the dissolved zeolite does not undergo any kind of recrystallization [Verboekend, D., Cryst. Growth. Des. 2013, 13, 5025-5035]. Here for the first time, we demonstrate using the data obtained from ¹H and 129Xe NMR spectroscopy that such recrystallization does occur, which leads to the formation of a very thin coating of the mesopore walls. This demonstration is done on a beta (BEA) zeolite treated in the presence of TPA+ in an alkaline solution. The formation of a small amount of nanosized crystals or embryonic phases of silicalite-1 (MFI) zeolite is evidenced, as well as their homogeneous dispersion on the mesoporous surface of the beta zeolite. We think that these results may explain why a homogeneous mesopore size distribution is obtained, when organic pore-directing agents are used in the zeolite hierarchization process performed in an alkaline medium. [ABSTRACT FROM AUTHOR]

In this study, paper-based microfluidic devices (μPADs) capable of K+ quantification in aqueous samples, as well as in human serum, using both colorimetric and distance-based methods are described. A lipophilic phase containing potassium ionophore I (valinomycin) was utilized to achieve highly selective quantification of K+ in the presence of Na+, Li+, and Mg2+ ions. Successful addition of a suspended lipophilic phase to a wax printed paper-based device is described and offers a solution to current approaches that rely on organic solvents, which damage wax barriers. The approach provides an avenue for future alkali/ alkaline quantification utilizing μPADs. Colorimetric spot tests allowed for K+ quantification from 0.1-5.0 mM using only 3.00 μL of sample solution. Selective distance-based quantification required small sample volumes (6.00 μL) and gave responses sensitive enough to distinguish between 1.0 and 2.5 mM of sample K+. μPADs using distance-based methods were also capable of differentiating between 4.3 and 6.9 mM K+ in human serum samples. Distance-based methods required no digital analysis, electronic hardware, or pumps; any steps required for quantification could be carried out using the naked eye. [ABSTRACT FROM AUTHOR]

Recombinase polymerase amplification (RPA) has been combined with electrochemical detection for simple and rapid point-of-care testing. However, there are two major hindrances to this simple and rapid testing: (i) washing or purification steps are required to remove unbound labeled probes and interfering species in the sample; (ii) it is difficult to quantify double-stranded DNA (dsDNA) electrochemically by using biospecific affinity binding without dsDNA denaturation. In the present study, we describe a washfree and rapid electrochemical method to detect RPA-amplified dsDNAs using a zinc finger protein, Zif268. Electrochemical detection is achieved using proximity-dependent electron mediation of ferrocenemethanol between a glucose-oxidase (GOx) label and an electrode, which differentiates the specifically electrode-bound and -unbound labels without a washing or purification step. RPA-amplified dsDNA containing a biotinterminated forward primer is specifically bound to a neutravidin-modified electrode, and GOx-conjugated Zif268 is specifically bound to the dsDNA. The whole detection is performed within 17 min (15 min for the RPA reaction and <2 min for the electrochemical measurement). Electrochemical detection is carried out without an additional incubation period, because the specific binding between Zif268 and the dsDNA occurs during the RPA reaction. The detection method could discriminate between target template DNA of Piscirickettsia salmonis and nontarget DNAs (random sequence and calf thymus DNA). The detection limit for the target DNA is approximately 300 copies in 13.2 μL, indicating that the detection method is ultrasensitive. We believe that the method could offer a promising solution for simple and rapid point-of-care testing. [ABSTRACT FROM AUTHOR]