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Conventional gas sensors work upon changes in mechanical or conductive properties of sensing materials during a chemical process, which may limit availabilities of size miniaturization and design simplification. However, fabrication of miniaturized sensors with superior sensitivities in real-time and label-free probing of chemical reactions or catalytic processes remains highly challenging, in particular with regard to integration of materials into a desired smaller volume without losing the recyclability of sensing properties. Here, we demonstrate a unique bimetallic nanostructure, the Au-Pd-Au core-shell-frame nanobrick, as a promising archetype for fabrication of miniaturized sensors at nanoscale. Upon analysis of the aqueous synthesis, both ex situ and in situ, the formation of Au frames is consistent with selective deposition and aggregation of NaBH4-reduced Au nanoparticles at the corners and edges of cubic Pd shells, where the {100} surfaces, capped by iodide ions, are growth-limited. By virtue of the thin Pd shell (~3.5 nm) sandwiched in-between the two Au layers of the core and the frame, the Au-Pd-Au nanobrick yields excellent optical sensitivity in hydrogen gas sensing, leading to a large 13 nm spectral shift of light scattering between Pd and PdHx. The composite nanostructure with a size of ~60 nm offers an archetype for miniaturized sensors possessing label-free, real-time, and high-resolution probing abilities and hence paves the way for fabrication of highly efficient nanosensors via sustainable methods. [ABSTRACT FROM AUTHOR]

Although the significance of aqueous interfaces has been recognized in numerous important fields, it can be even more prominent for nanoscaled aqueous aerosols because of their large surface-to-volume ratios and prevalent existence in nature. Also, considering that organic species are often mixed with aqueous aerosols in nature, a fundamental understanding of the electronic and structural properties of organic species in aqueous nanoaerosols is essential to learn the interplay between water and organic solutes under the nanoscaled size regime. Here, we report for the first time the vacuum ultraviolet photoelectron spectroscopy of phenol and three dihydroxybenzene (DHB) isomers including catechol, resorcinol, and hydroquinone in the aqueous nanoaerosol form. By evaluating two photoelectron features of the lowest vertical ionization energies originated from the b1(π) and a2(π) orbitals for phenolic aqueous nanoaerosols, their interfacial solvation characteristics are unraveled. Phenolic species appear to reside primarily on/near the aqueous nanoaerosol interface, where they appear only partially hydrated on the aqueous interface with the hydrophilic hydroxyl group more solvated in water. An appreciable proportion of phenol is found to coexist with phenolate at/near the nanoaerosol interface even under a high bulk pH of 12.0, indicating that the nanoaerosol interface exhibits a composition distribution and pH drastically different from those of the bulk. The surface pH of phenol-containing aqueous nanoaerosols is found to be ∼2.2 ± 0.1 units more acidic than that of the bulk interior, as measured at the bulk pH of 12.0. From the photoelectron spectra of DHB aqueous nanoaerosols, the effects of numbers/arrangements of -OH groups are assessed. This study shows that the hydration extents, pH values, deprotonation status, and numbers/relative arrangements of -OH groups are crucial factors affecting the ionization energies of phenolic aqueous nanoaerosols and thus their redox-based activities. The multifaceted implications of the present study in the aerosol science, atmospheric/marine chemistry, and biological science are also addressed. [ABSTRACT FROM AUTHOR]

High-throughput and sensitive detection of proteins are essential for clinical diagnostics and biomarker discovery. We develop a novel high-throughput, multiplexed, sensitive mass spectrometric (MS) immunoassay method, which utilizes antibody-modified phospholipid bilayer coated gold nanoparticles (PBL-AuNPs) as the detection label and antibody-immobilized magnetic beads as the capture reagent. This method enables magnetic enrichment of the PBL-AuNPs label specific to target protein, allowing sensitive surface enhanced laser desorption ionization (SELDI)-TOF MS detection of the protein via its specific label. AuNPs act as n o t only the support but also the matrix for the phospholipids in SELDI TOF MS detection. Moreover, with phospholipids with varying molecular weights as the encoded MS reporters, this method allows multiplexed detection of multiple proteins. With the use of a predefined phospholipids internal standard, this method also affords excellent reproducibility in protein quantification. We have demonstrated this method using the assays of two tumor biomarkers, and the results reveal that it provides a sensitive platform for multiplexed protein detection with detection limits in the picomolar ranges. This method may provide a useful platform for high-throughput and sensitive detection of protein biomarkers for clinical diagnostics. [ABSTRACT FROM AUTHOR]

C60 and single-layer MoS2 nanocomposites were facilely prepared via a combined solvent transfer and surface deposition (STSD) method by templating C60 aggregates on 2D MoS2 nanosheets to construct hybrid van der Waals heterojunctions. The electronic property of the hybrid nanomaterials was investigated in a direct charge transport diode device configuration of ITO/C60-MoS2 nanocomposites/Al; rewritable nonvolatile resistive switching with low SET/RESET voltage (∼3 V), high ON/OFF resistance ratio (∼4 × 10³), and superior electrical bistability (>104 s) of a flash memory behavior was observed. This particular electrical property of C60-MoS2 nanocomposites, not possessed by either C60 or MoS2 nanosheets, was supposed to be due to the efficiently established C60/MoS2 p-n nanojunction, which controls the electron tunneling via junction barriers modulated by electric-field-induced polarization. Thus, our 2D templating method through STSD is promising to massively allocate van der Waals p-n heterojunctions in 2D nanocomposites, opening a window for important insights into the charge transport across the interface of organic/2D-semiconductors. [ABSTRACT FROM AUTHOR]

Efficient tools for profiling DNA methylation in specific genes are essential for epigenetics and clinical diagnostics. Current DNA methylation profiling techniques have been limited by inconvenient implementation, requirements of specific reagents, and inferior accuracy in quantifying methylation degree. We develop a novel mass spectrometry method, target fragmentation assay (TEA), which enable to profile methylation in specific sequences. This method combines selective capture of DNA target from restricted cleavage of genomic DNA using magnetic separation with MS detection of the nonenzymatic hydrolysates of target DNA. This method is shown to be highly sensitive with a detection limit as low as 0.056 amol, allowing direct profiling of methylation using genome DNA without preamplification. Moreover, this method offers a unique advantage in accurately determining DNA methylation level. The clinical applicability was demonstrated by DNA methylation analysis using prostate tissue samples, implying the potential of this method as a useful tool for DNA methylation profiling in early detection of related diseases. [ABSTRACT FROM AUTHOR]

In this work, Cu2O exhibited better synergistic effect with microencapsulated ammonium polyphosphate (MAPP) than other metal oxides, such as CuO, ZnO, SnO, Fe2O3, Ni2O3, and Co2O3, on improving the flame retardancy of epoxy resins (EP). Moreover, the addition of cuprous oxide (Cu2O) could further decrease the total smoke production and carbon monoxide production. The analysis of char residues and evolved gases indicated that Cu2O was beneficial to enhance the formation amount, intumescent degree, and compactness of char. The protective layer of intumescent char residue could hinder the decomposition of EP and diffusion of gaseous products, such as hydrocarbons, aromatic compounds and carbon monoxide (CO). In addition, Cu2O also played a role in conversion of CO to CO2 through a redox cycle, involving the reduction of Cu2+--Cu+--Cu0 by CO and the oxidation of Cu0--Cu+--Cu2+ by O2. The possible flame retardant, smoke suppression, and CO oxidation mechanisms were proposed. [ABSTRACT FROM AUTHOR]

Making use of a tandem free radical cyclization process mediated by Mn(OAc)3 as a key operation, the total synthesis of retrojusticidin B, justicidin E, and helioxanthin has been concisely achieved in four or five steps in an overall yield of 45, 33 and 44%, respectively, from a common starting material 5. [ABSTRACT FROM AUTHOR]

Controlloops widely exist in industrial processes, whose performancedirectly influences the efficiency, safety, and product quality ofproduction plants. Therefore, control performance assessment (CPA)and control system monitoring (CSM) are critically important for industrialprocessing. In consideration of multivariate control systems, thecovariance matrix of closed-loop outputs plays an important role inboth CPA and CSM. Existing methods mainly focus on comparing tracesor determinants of the output covariance matrices, which only utilizepartial information contained in the matrices. As a result, the assessmentand monitoring results may be misleading. In this paper, a multiobjectivescheme is proposed for both CPA and CSM of multivariate control systems,which takes the entire covariance matrices into account by conductinga hypothesis test on the equality of the matrices. To fulfill thepresupposition of such test, autoregressive moving-average (ARMA)filters are established to remove the autocorrelation contained inthe closed-loop output data. The developed scheme can be divided intothree aspects: CPA using a minimum variance (MV) benchmark, CPA usinga user-specified benchmark, and CSM based on historical data. Casestudies show that, compared with the conventional approaches, theproposed method provides more abundant information and achieves betterresults. [ABSTRACT FROM AUTHOR]

We developed a liquid crystal (LC) sensor system for detecting mercuric ion (Hg2+) in aqueous solutions. In this system, 4-cyano-4'-pentyl biphenyl (5CB) was doped with a sulfur- and nitrogen-containing ligand 5-(pyridine-4-yl)-2-(5-(pyridin-4-yl)thiophen-2-yl)thiazole (ZT) as the Hg2+ specific LCs. When the system was immersed in the solution containing Hg2+, the complex of ZT and Hg2+ formed, which disrupted the orientation of LC and lead to a dark-to-bright transition of the image of LCs. From mercuric binding titrations monitored by UV-vis spectroscopy, it was found that 1:1 Hg2+/ZT complexes were formed. The limit of detection (LOD) of the system to Hg2+ is 10 μM, and it did not respond to Cd2+, Zn2+, Cu2+, Pb2+, Fe+, Mg2+, Ca2+, Na+, and K+. Besides, we also demonstrated that this system is capable of detecting Hg2+ in tap water and pond water. Because the signal of this system is colorful under ambient light, which is readily understood by normal users, it can be used as a portable device to monitor the water quality at any location. [ABSTRACT FROM AUTHOR]

Three-layer core--shell plasmonic nanorods (Au/Ag/SiO2--NRs), consisting of a gold nanorod core, a thin silver shell, and a thin silica layer, were synthesized and used as optical imaging probes under a differential interference contrast microscope for single particle orientation and rotational tracking. The localized surface plasmon resonance modes were enhanced upon the addition of the silver shell, and the anisotropic optical properties of gold nanorods were maintained. The silica coating enables surface functionalization with silane coupling agents and provides enhanced stability and biocompatibility. Taking advantage of the longitudinal LSPR enhancement, the orientation and rotational information of the hybrid nanorods on synthetic lipid bilayers and on live cell membranes were obtained with millisecond temporal resolution using a scientific complementary metal-oxide-semiconductor camera. The results demonstrate that the as-synthesized hybrid nanorods are promising imaging probes with improved sensitivity and good biocompatibility for single plasmonic particle tracking experiments in biological systems. [ABSTRACT FROM AUTHOR]

Until now, the expressions of the anisotropic energy barriers Δξ and ΔA, using the uniaxial magnetic anisotropy D, the intrachain coupling strength J, and the high-spin ground state S for single-chain magnets (SCMs) in the intermediate region between the Ising and the Heisenberg limits, were unknown. To explore this relationship, we used density functional theory and ab initio methods to obtain expressions of Δξ and ΔA in terms of D, J, and S of six R4FeII-ReIVCl4(CN)2 (R = diethylformamide (1), dibutylformamide (2), dimethylformamide (3), dimethylbutyramide (4), dimethylpropionamide (5), and diethylacetamide (6)) SCMs in the intermediate region. The ΔA value for compounds 1-3 was very similar to the magnetic anisotropic energy of a single Fe'', while the value of Δξ was predicted using the exchange interaction of FeII with the neighboring ReIV, which could be expressed as 2JSReSFe. Similar to compounds 1-3, the anisotropy energy barrier ΔA of compounds 4 and 5 was also equal to (Di - Ei)SFe², but the correlation energy Δξ was closely equal to 2JSReSFe(cos 98.4 - cos 180) due to the reversal of the spins on the opposite FeII. For compound 6, one unit cell of ReIVFeII was regarded as a domain wall since it had two different ReIV-FeII couplings. Thus, the Δξ of compound 6 was expressed as 4JnSRe1Fe1SRe2Fe2, where Jn was the coupling constant of the neighboring unit cells of Re1Fe1 and Re2Fe2, and ΔA was equal to the anisotropic energy barrier of one domain wall given by DRe1Fe1(S²Re1Fe1 - 1/4). [ABSTRACT FROM AUTHOR]

Fabricationof nanostructures with great complexity and regularity is a topicof intense current interest because of their importance both in fundamentaltheories and applications. Here we report an interesting finding ofthe formation of ordered polymeric double helices with precise structuresand high stability. These uniform double helices are hierarchicallyself-assembling results of undulated multicompartment cylinders whichformed from primary amphiphilic mixed-shell nanoparticles. Diblockcopolymers of P2VN-b-PAA (poly(vinylnaphthalene)-block-poly(acrylic acid) and PEO-b-PAA(poly(ethylene oxide)-block-poly(acrylic acid)) werenoncovalently/electrostatically cross-linked into amphiphilic PEO/P2VN-shellednanoparticles by 1,6-hexyldiamine in a common solvent DMF. When thecommon solvent changed into selective ones (water), undulated cylinderswere facilely obtained due to their hydrophobic interparticles interactions.After a certain time aging, these undulated cylinders self-organizedinto finally thermodynamic-stable double helices with complex butregular superstructures. The conditions and processes of assemblingwere carefully examined through extensive experiments. [ABSTRACT FROM AUTHOR]

The silver carbonate promoted reaction of [60]fullerene with (Z)-N-arylbenzamidines afforded the unprecedented C60-fused imidazoline derivatives in high yields. Substrates with both electron-donating and -withdrawing groups on aromatic rings could be employed. In addition, the electrochemistry and further selective functionalization of the obtained C60-fused imidazolines were investigated. [ABSTRACT FROM AUTHOR]

A simple and practical approach has been developed for conducting direct, homoallylic alcohol forming allylation reactions of nitroalkenes in water. Employing the new method, various arylmethyl-homoallylic alcohols can be produced from the corresponding, readily prepared β-nitrostyrenes. [ABSTRACT FROM AUTHOR]

In this paper, the design and control of an improved process for the manufacture of a fuel additive (glycerol tertiary butyl ethers, GTBE) from glycerol and isobutylene is developed. The improved process redirects one recycle stream, uses a stripping column instead of a flash tank to recover isobutylene, and uses a rectifying column instead of a distillation column to purify the product. Economic analysis shows that the improved process has a 22% lower total annual cost (TAC) than the best known process published in the literature. Significant increases in the selectivity of the overall process from 84.7% to 99.3% can also be realized by comparing the optimized improved design versus the original design. Dynamic simulations were also conducted and indicated that stringent product specification can be met with a simple decentralized feedback control structure despite impurities in the feed streams and also changes in the throughput. [ABSTRACT FROM AUTHOR]

Formation of isoaspartic acid (isoAsp) is a common modification of aspartic acid (Asp) or asparagine (Asn) residue in proteins. Differentiation of isoAsp and Asp residues is a challenging task owing to their similar properties and identical molecular mass. It was recently shown that they can be differentiated using ion-electron or ion-ion interaction fragmentation methods (ExD) because these methods provide diagnostic fragments c + 57 and z• - 57 specific to the isoAsp residue. To date, however, the presence of such fragments has not been explored on peptides with an N-terminal isoAsp residue. To address this question, several N-terminal isoAsp-containing peptides were analyzed using ExD methods alone or combined with chromatography. A diagnostic fragment [M + 2H - 74]+• was observed for the doubly charged precursor ions with N-terminal isoAsp residues. For some peptides, identification of the N-terminal isoAsp residue was challenging because of the low diagnostic ion peak intensity and the presence of interfering peaks. Supplemental activation was used to improve diagnostic ion detection. Further, N-terminal acetylation was offered as a means to overcome the interference problem by shifting the diagnostic frag ment peak to [M + 2H - 116]+•. [ABSTRACT FROM AUTHOR]

The development of an expedient synthesis toward quinoxaline ring-embedded polyacenoquinone esters with the generic structure A is demonstrated by the synthesis of penta- and hexacenoquinone esters. They are potential n-type small molecules, capable of undergoing successive reductions and self-assembling in face-to-face π-stacks. [ABSTRACT FROM AUTHOR]

A density functional theory (DFT) study of the magnetic coupling interactions and magnetic anisotropy in a family of experimentally synthesized Ni9MoV and Ni9WV systems is presented. Our calculations show that for all of our selected Ni9M6 systems, the intramolecular magnetic coupling interactions are ferromagnetic, and the ground-state spins are 12. All of the D values of Ni9W6 systems come mainly from the contribution of the Di of W6(CN)48Ni extracted from Ni9W6, and the influence of the eight surrounding Ni including the ligands on their magnetic anisotropy is very small. Although the surrounding Ni bounded by different ligands have a small influence on all D values for our selected complexes, they decide on the core structures of W6(CN)48Ni, which dominate their magnetic anisotropy. Thus, to obtain a Ni9W6 system having a large negative D, we can use different ligands bound to Ni to obtain a good core structure of W6(CN)48Ni with a large negative D value. All D values of Ni9Mo6 systems also come mainly from the contribution of Di of the Mo6(CN)48Ni, which is positive or negative but very small; most of these systems do not behave as single-molecule magnets. [ABSTRACT FROM AUTHOR]

Due to its much slower deamidalion rate compared to that of asparagine (Asn), studies on glutamine (Gin) deamidation have been scarce, especially on the differentiation of its isomeric deamidation products: α- and γ-glutamic acid (Glu). It has been shown previously that electron capture dissociation (ECD) can be used to generate diagnostic ions for the deamidalion products of Asn: aspartic acid (Asp) and isoaspartic acid (isoAsp). The current study explores the possibility of an extension of this ECD based method to the differentiation of the α- and γ-Glu residues, using three human Crystallin peptides (αA (1-11), βB2 (4-14), and γS (52-71)) and their potentially deamidated forms as model peptides. it was found that the Z∙-72 ions can be used to both identify the existence and locate the position of the γ-Glu residues. When the peptide contains a charge carrier near its N- terminus, the c+57 and c+59 ions may also be generated at the γ-Glu residue. It was unclear whether formation of these N-terminal diagnostic ions is specific to the Pro-γ-Glu sequence. Unlike the Asp containing peptides, the Glu containing peptides generally do not produce diagnostic side chain loss ions, due to the instability of the resulting radical. The presence of Glu residue(s) may be inferred from the observation of a series of zn∙-59 ions, although it was neither site specific nor without interference from the γ-Glu residues. Finally, several interference peaks exist in the ECD spectra, which highlights the importance of the use of high performance mass spectrometers for confident identification of γ-Glu residues. [ABSTRACT FROM AUTHOR]

Amyloid β peptides are the major components of the vascular and plaque amyloid filaments in individuals with Alzheimer's disease (AD). Although it is still unclear what initiates the disease, isomerization of aspartic acid residues in Aβ peptides is directly related to the pathology of AD. The detection of isomerization products is analytically challenging, due to their similar chemical properties and identical molecular mass. Different methods have been applied to differentiate and quantify the isomers, including immunology, chromatography, and mass spectrometry. Typically, those methods require comparative analysis with the standard peptides and involve many sample preparation steps. To understand the role of Aβ isomerization in AD progression, a fast, simple, accurate, and reproducible method is necessary. In this work, electron capture dissociation (ECD) Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) was applied to detect isomerization in Aβ peptides. ECD generated diagnostic fragment ions for the two isomers of Aβ17-28, [M + 2H - 60]+• and z6• - 44 when aspartic acid was present and z6• - 57 when isoaspartic acid was present. Additionally, the zn - 57 diagnostic ion was also observed in the electron ionization dissociation (EID) spectra of the modified Aβ17-28 fragment. ECD was further applied toward Aβ1-40 and Aβ1-42. The diagnostic ion c6 + 57 was observed in the ECD spectra of the Aβ1-42 peptide, demonstrating isomerization at residue 7. In conclusion, both ECD and EID can clearly determine the presence and the position of isoaspartic acid residues in amyloid β peptides. The next step, therefore, is to apply this method to analyze samples of Alzheimer's patients and healthy individuals in order to generate a better understanding of the disease. [ABSTRACT FROM AUTHOR]

Electrical properties, including electrophoretic mobility, zeta potential, total surface charge density, and surface charge density resulting from primary amino groups, of cationic solid lipid nanoparticles (CSLNs) were investigated in the present study. Cationic lipids including stearylamine (SA) and dioctadecyldimethyl ammonium bromide (DODAB) were covered on the external cores of CSLNs. The influences of glutamate concentration in the medium, composition of cationic lipids, and surfactant species were especially analyzed. The results indicated that an increase in the mole ratio of SA in the cationic lipid caused an increase in the average diameter of CSLNs. Also, the average diameter of Span 20-stabilized CSLNs was larger than that of Tween 80-stabilized CSLNs. The electrostatic traits of CSLNs were reduced as the mole ratio of SA increased, and the electricity of Span 20-stabilized CSLNs was weaker than that of Tween 80-stabilized CSLNs. An increase in the glutamate concentration in the medium led to a decrease in electrophoretic mobility, zeta potential, and total surface charge density of CSLNs. As the glutamate concentration increased, surface charge density resulting from primary amino groups increased, and that from quaternary amino groups decreased as a result of the adsorption of negatively charged glutamate on CSLN surfaces. Ohshima's soft particle theory was adopted to describe the electrical behavior of CSLNs, and the deviations of zeta potential predicted by the Smoluchowski, Happel, and Kuwabara models were normally greater than 10%. [ABSTRACT FROM AUTHOR]

This study identifies submicrometer hematite (α-Fe 2O 3) powder as a cost-effective and efficient starting material for the synthesis of monodisperse magnetic iron oxide nanoparticles (MMIONPs). The feature of this process is the slow dissolution of hematite powder in a mixture of unsaturated fatty acids and organic solvents. The hematite particles are dissolved by the complexation of their iron with the unsaturated fatty acid ligands to give iron acid salt as a soluble compound. This method presents an interesting example for the production of monodisperse oxide NPs from bulk oxide powder with a moderate solubility in fatty acids. Conceptually, it can be simply viewed as a controlled dissolution−recrystallization process. The relatively low solubility of magnetic iron oxides (maghemite and magnetite) in the reaction condition determines their appearance in the recrystallization process. Moreover, the monodispersity of the formed NPs is sustained during the whole process, which results from the slow supply and the fast consumption of growing units by the slow dissolution of hematite and the fast enough growth rate of magnetic iron oxide NPs. The compositions of the MMIONPs were determined by Mössbauer spectroscopy. It appears that γ-Fe 2O 3is preferentially precipitated out at lower ligand concentrations, while the Fe 3O 4appears along with γ-Fe 2O 3at higher ligand concentrations. [ABSTRACT FROM AUTHOR]

A theoretical density functional study of the relationship between the nearest-neighbor constants and the number of peripheral complexes in the cyano-bridged CrCNMn(salen)(H2O)63and (5-Brsalen)2(H2O)2Mn2Cr(CN)6clusters is presented. Two approaches show that the antiferromagnetic coupling interactions between nearest neighbors decrease with the increase of the number of peripheral complexes, although the second approach provides better results using several exchange-correlation functionals. The first approach consisted of evaluating the exchange coupling constant Jijbetween two paramagnetic metal centers iand jin the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for iand jare substituted by diamagnetic Zn(II) cations, while the second consisted of calculating the different spin-state energies of hexanuclear complexes and using the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers. Moreover, Kahn's qualitative theory succeeded in being applied to interpret the trend. [ABSTRACT FROM AUTHOR]

A nonenzymatic posttranslational modification of proteins and peptides is the spontaneous deamidation of asparaginyl residues via a succinimide intermediate to form a varying mixture of aspartyl and isoaspartyl residues. The isoaspartyl residue is generally difficult to detect particularly using mass spectrometry because isoaspartic acid is isomeric with aspartic acid so that there is no mass difference. However, electron capture dissociation has demonstrated the ability to differentiate the two isoforms in synthetic peptides using unique diagnostic ions for each form; the cr... + 58 and Zl-r - 57 fragment ions for the isoAsp form and the Asp side chain loss ((M + nH)(n-1)+... - 60) for the Asp form. Shown here are three examples of isoaspartyl detection in peptides from proteins; a deamidated tryptic peptide of cytochrome c, a tryptic peptide from unfolded and deamidated ribonuclease A, and a tryptic peptide from calmodulin deamidated in its native state. In all cases, the cr... + 58 and Zl-r - 57 ions allowed the detection and localization of isoaspartyl residues to positions previously occupied by asparaginyl residues. The (M + nH)(n-1)+... - 60 ions were also detected, indicating the presence of aspartyl residues. Observation of these diagnostic ions in peptides from proteins shows that the method is applicable to defining the isomerization state of deamidated proteins. [ABSTRACT FROM AUTHOR]

Previous gas-phase methods for infrared photodissociation spectroscopy (IRPD) require sample volatility. Our method instead uses electrospray ionization to introduce even large nonvolatile molecules into a Fourier transform mass spectrometer, where extended (>15 s) ion storage makes possible high sensitivity spectral measurements with an OPO laser over a range of 3050-3800 cm-1. The spectra of 22 gaseous proton-bound amino acid complexes are generally correlated with the H-stretching frequencies established for O-H and N-H functional groups in solution. For theoretical structure predictions of the Gly2H+ and N-acylated Asp2H+ dimers, IRPO spectra clearly differentiate between the predicted lowest energy conformers. In contrast to solution, in the gas phase the glycine zwitterion is ∼20 kcal/mol less stable than the neutral; however, glycine is clearly zwitterionic in the gaseous GlyLysH+ dimer. The level of theory is inadequate for the larger Lys2H+ dimer, as all low energy predicted structures have free carboxyl O-H groups, in contrast to the IR spectrum. IRPD appears to be a promising new technique for providing unique information on a broad range of biomolecular and other gaseous ions, especially on noncovalent bonding involving O-H and N-H groups. [ABSTRACT FROM AUTHOR]

Describes the implications of the reactive thiol and the proximal non-proline cis-peptide bond of Vibrio harveyi luciferase. Location of the phosphate binding site of flavin mononucleotide; Reduction of molecular oxygen to water; Role of non-proly cis-peptide bonds.

Describes the dimerization of an oxindole on good yield at C-3 form from a benzylic quaternary carbon-carbon bond. Application of the oxindole in the synthesis of folicanthine; Proposal of a radical anion chain mechanism; Characteristics of the dimeric indole alkaloids; Determination of the molecular structure of folicanthine by X-ray crystallography.

Our calculations show that the substitution of metal ions using CoII is not the main reason that CoII9M6 (M = MoV or WV) exhibits single- molecule-magnet behavior, whereas the unsymmetrical distribution of three CH3OH ligands surrounding each CoII is the main one. [ABSTRACT FROM AUTHOR]

Analyzes the selective binding of mannose-encapsulated gold nanoparticles to Type 1 Pili in Escherichia coli. Interaction between antibody conjugated gold nanoparticles and the antigens; Advantages of applying gold nanoparticles in the biological systems; Characterization of mannose-encapsulated gold nanoparticles.

A mechanisticstudy of three-component reactions of various aromaticamines with a number of aldehydes and 1,3-diones was achieved. Theunprecedented reaction involved a nucleophilic attack of an aromaticamine on the in situ generated Michael adduct intermediate followedby six-electron ring cyclizations. It is contrary to the common beliefthat advocates involvement of coupling reactions between a Knoevenageladduct and an aromatic amine to deliver substituted tetrahydroacridinones. [ABSTRACT FROM AUTHOR]

We successfully demonstrate the first solid-state sensor to have reliable responses to breath ammonia of rat. For thioacetamide (TAA)-induced hepatopathy rats, we observe that the proposed sensor can detect liver that undergoes acute-moderate hepatopathy with a p-value less than 0.05. The proposed sensor is an organic diode with vertical nanojunctions produced by using low-cost colloidal lithography. Its simple structure and low production cost facilitates the development of point-of-care technology. We also anticipate that the study is a starting point for investigating sophisticated breath-ammonia-related disease models. [ABSTRACT FROM AUTHOR]

The effects of varying the electron energy and cationizing agents on electron activated dissociation (ExD) of metal-adducted oligosaccharides were explored, using permethylated maltoheptaose as the model system. Across the examined range of electron energy, the metal-adducted oligosaccharide exhibited several fragmentation processes, including electron capture dissociation (ECD) at low energies, hot-ECD at intermediate energies, and electronic excitation dissociation (EED) at high energies. The dissociation threshold depended on the metal charge carrier(s), whereas the types and sequence spans of product ions were influenced by the metal-oligosaccharide binding pattern. Theoretical modeling contributed insight into the metal-dependent behavior of carbohydrates during low-energy ECD. When ExD was applied to a permethylated high mannose N-linked glycan, EED provided more structural information than either collision-induced dissociation (CID) or low-energy ECD, thus demonstrating its potential for oligosaccharide linkage analysis. [ABSTRACT FROM AUTHOR]

In this study, we investigated the interplay of three-dimensional morphologies and the photocarrier dynamics of polymer/inorganic nanocrystal hybrid photoactive layers consisting of TiO2 nanoparticles and nanorods. Electron tomography based on scanning transmission electron microscopy using high-angle annular dark-field imaging was performed to analyze the morphological organization of TiO2 nanocrystals in poly(3-hexylthiophene) (P3HT) in optimal solar cell devices. The Three-dimensional (3D) morphologies of these hybrid films were correlated with the photocarrier dynamics of charge separation, transport, and recombination, which were comprehensively probed by various transient techniques. Visualization of these 3D bulk heterojunction morphologies clearly reveals that elongated and anisotropic TiO2 nanorods in P3HT not only can significantly reduce the probability of the interparticle hopping transport of electrons by providing better connectivity with respect to the TiO2 nanoparticles, but also tend to form a large-scale donor-acceptor phase-separated morphology, which was found to enhance hole transport. The results support the establishment of a favorable morphology for polymer/inorganic hybrid solar cells due to the presence of the dimensionality of TiO2 nanocrystals as a result of more effective mobile carrier generation and more efficient and balanced transport of carriers. [ABSTRACT FROM AUTHOR]

We have successfully designed and synthesized two oxetane-functionalized fullerene derivatives, [6,6]-phenyl-C61-butyric oxetane ester (PCBO) and [6,6]-phenyl-C61-butyric oxetane dendron ester (PCBOD). We demonstrated that the oxetane functionality with neutral nature can anchor onto the TiOxsurface via cationic ring-opening reaction under thermal and UV treatment, as evidenced by contact angle measurement and X-ray photoelectron spectroscopy. The self-assembly of PCBO, functionalized with one oxetane group, on the TiOxsurface forms an adhesive monolayer with intimate contact. Inverted bulk-heterojunction device B [ITO/TiOx/SA-PCBO/P3HT:PCBM (1:1 w/w)/MoO3/Ag, where ITO is indium tin oxide, SA is self-assembled, P3HT is poly(3-hexylthiophene), and PCBM is [6,6]-phenyl-C61-butyric acid methyl ester] with this self-assembled PCBO (SA-PCBO) modifier showed an impressive power conversion efficiency (PCE) of 4.1%, which outperforms the reference device A (PCE = 3.6%) without this monolayer [ITO/TiOx/P3HT:PCBM (1:1 w/w)/MoO3/Ag]. This SA-PCBO modifier exerts multipositive effects on the interface, including improvement of exciton dissociation efficiency, reduction of charge recombination, decrease of the interface contact resistance, and passivation of the surface electron traps at the interface of TiOx. Furthermore, PCBOD, containing two oxetane groups, is capable of self-assembling on the TiOxsurface and simultaneously undergoing cross-linking, generating a dense, robust, and pinhole-free multimolecular interlayer to further strengthen the interface characteristics. Device C [ITO/TiOx/C-PCBOD/P3HT:PCBM(1:1, in wt%)/MoO3/Ag] incorporating this cross-linked PCBOD (C-PCBOD) interlayer delivered the highest PCE of 4.5% which represents 26% enhancement over device A. This simple and easy strategy smartly integrates the advantages of self-assembly and cross-linking in a single fullerene-based molecule, showing promise in producing highly efficient inverted PSCs. [ABSTRACT FROM AUTHOR]

In this study, molecular simulation techniques were used to investigate the residual solvent effects on the free volume and performance of 6FDA-mPDA polyimide (PI) membranes. A molecular dynamics (MD) simulation was used to analyze how the residual solvent in the 6FDA-mPDA PI membrane affects the fluctuation and flexibility of the polymer segment and the free volume. The gas sorption in the membrane was analyzed by a Monte Carlo (MC) technique. The energy analysis of the MD simulation indicates that the presence of solvent molecules tends to favor the fluctuation, and flexibility of polymer segments tended to be encouraged due to the presence of solvent molecules through the energy analysis by MD simulation. The free volume analysis revealed that the free space in the membrane would be enlarged by extracting the solvent from the membrane. The gas sorption behavior, analyzed by the MC technique, showed that gas solubility increased in the lower residual solvent membranes. This was caused by the free volume released by extracting the solvent, thus providing more suitable sites for gas sorption. The sorption ability was also affected by the intermolecular attractive energy, while the free volumes inside the membranes were similar. In addition, the residual solvent effect on gas sorption would be eliminated at higher pressure. From the thermal motion analysis of gas molecules, it was found that the effective thermal motion of gaseous molecules improved as residual solvent molecules remained in the membrane matrix, but this did not have an effective influence on gas permeation. [ABSTRACT FROM AUTHOR]

Electron capture dissociation (ECD) studies of two modified amyloid β peptides (20–29 and 25–35) were performed to investigate the role of H• radicals in the ECD of peptide ions and the free-radical cascade (FRC) mechanism. 2,4,6-Trimethylpyridinium (TMP) was used as the fixed charge tag, which is postulated to both trap the originally formed radical upon electron capture and inhibit the H• generation. It was found that both the number and locations of the fixed charge groups influenced the backbone and side-chain cleavages of these peptides in ECD. In general, the frequency and extent of backbone cleavages decreased and those of side-chain cleavages increased with the addition of fixed charge tags. A singly labeled peptide with the tag group farther away from the protonated site experienced a smaller abundance decrease in backbone cleavage fragments than the one with the tag group closer to the protonated site. Despite the nonprotonated nature of all charge carriers in doubly labeled peptide ions, several c and z• ions were still observed in their ECD spectra. Thus, although H• transfer may be important for the N-Cα bond cleavage, there also exist other pathways, which would require a radical migration via H• abstraction through space or via an amide superbase mechanism. Finally, internal fragment ions were observed in the ECD of these linear peptides, indicating that the important role of the FRC in backbone cleavages is not limited to the ECD of cyclic peptides. [Copyright &y& Elsevier]

A protocol that uses moist magnesium monoperoxyphthalate (MMPP) as an oxidant under microwave irradiation rapidly yields a variety of glycosyl sulfoxides from corresponding sulfides in high yields with high selectivity. [ABSTRACT FROM AUTHOR]

Examines the stereoselective synthesis of sialic acid dimer derivative. Use of allyl alcohol to achieve α-sialylation product; Aims to provide subsequent coupling with neuraminate in minimal protection-deprotection manipulations; Identification on the polysialic acid chains.

A novel iminoxyl radical-promoted dichotomous regioselective 5-exo-trig cyclization onto vinylic halogen/1,2-halogen radical shift sequence is developed for the synthesis of halomethyl isoxazoles/cyclic nitrones using β-halo-β,γ- and γ-halo-γ,δ-unsaturated ketoximes as the substrates and PhI(OAc)2/TEMPO as the oxidation system. DFT calculations reveal that a halogen-bridged three-membered ring transition state is involved in the 1,2-Cl-/Br-atom shift, while the 1,2-I atom migration can be taken into account with an elimination/readdition mechanism. The migration ability was indicated to be ranked in the following order: I > Br > Cl. [ABSTRACT FROM AUTHOR]

Detailed glycan structural characterization is frequently achieved by collisionally activated dissociation (CAD) based sequential tandem mass spectrometry (MSn) analysis of permethylated glycans. However, it is challenging to implement MSn (n > 2) during online glycan separation, and this has limited its application to analysis of complex glycan mixtures from biological samples. Further, permethylation can reduce liquid chromatographic (LC) resolution of isomeric glycans. Here, we studied the electronic excitation dissociation (EED) fragmentation behavior of native glycans with a reducing-end fixed charge tag and identified key spectral features that are useful for topology and linkage determination. We also developed a de novo glycan sequencing software that showed remarkable accuracy in glycan topology elucidation based on the EED spectra of fixed charge-derivatized glycans. The ability to obtain glycan structural details at the MS2 level, without permethylation, via a combination of fixed charge derivatization, EED, and de novo spectral interpretation, makes the present approach a promising tool for comprehensive and rapid characterization of glycan mixtures. [ABSTRACT FROM AUTHOR]

The first Pd-catalyzed multisite-selective acetoxylation reactions are disclosed at an unactivated alkene sp² C-H bond versus secondary allylic sp³ C-H bond in cyclic olefins via the modulation of directing groups. The different directing groups overcome the key challenge in differentiating C-H bonds and provide a new controlling approach for site-specific C-H activation. A wide variety of substrates are readily acetoxylated under operationally simple conditions. Mechanistic studies suggest that different Pd (IV) intermediates were involved in the multisite-selective acetoxylation reactions. [ABSTRACT FROM AUTHOR]

Glutathione (GSH), the most abundant nonenzymatic antioxidant in living systems, actively scavenges various exogenous/endogenous oxidizing species, defending important biomolecules against oxidative damages. Although it is well established that the antioxidant activity of GSH originates from the cysteinyl thiol (−SH) group, the molecular origin that makes the thiol group of GSH a stronger reducing agent than other thiol-containing proteins is unclear. To gain insights into the molecular basis underlying GSH's superior antioxidant capability, here we report, for the first time, the valence electronic structures of solvated GSH in the aqueous aerosol form via the aerosol vacuum ultraviolet photoelectron spectroscopy technique. The pH-dependent electronic evolution of GSH is obtained, and the possible correlations between GSH and its constituting amino acids are interrogated. The valence band maxima (VBMs) for GSH aqueous aerosols are found at 7.81, 7.61, 7.52, and 5.51 ± 0.10 eV at a pH of 1.00, 2.74, 7.00, and 12.00, respectively, which appear to be lower than the values of their corresponding hybrid counterparts collectively contributed from the three isolated constituting amino acids of GSH. An additional photoelectron feature is observed for GSH aqueous aerosols at pH = 12.00, where the thiol group on its Cys residue becomes deprotonated and the relatively well-separated feature allows its vertical ionization energy (VIE) to be determined as 6.70 ± 0.05 eV. Compared to a VIE of 6.97 ± 0.05 eV obtained for a similar thiolate feature observed previously for isolated Cys aqueous aerosols, a 0.27 eV reduction in the VIE is found for GSH, indicating that the outermost electron corresponding to the nonbonding electron on the thiolate group can be removed more readily from the GSH tripeptide than that from Cys alone. The possible origins underlying the decrease in the VBM of GSH with respect to that of each corresponding hybrid counterpart and the decrease in the VIE of the thiolate feature of GSH with respect to that of the isolated Cys are discussed, providing hints to understand the superior antioxidant capability of GSH from a molecular level. [ABSTRACT FROM AUTHOR]

One of the major challenges in structural characterization of oligosaccharides is the presence of many structural isomers in most naturally occurring glycan mixtures. Although ion mobility spectrometry (IMS) has shown great promise in glycan isomer separation, conventional IMS separation occurs on the millisecond time scale, largely restricting its implementation to fast time-of-flight (TOF) analyzers which often lack the capability to perform electron activated dissociation (ExD) tandem MS analysis and the resolving power needed to resolve isobaric fragments. The recent development of trapped ion mobility spectrometry (TIMS) provides a promising new tool that offers high mobility resolution and compatibility with high-performance Fourier transform ion cyclotron resonance (FTICR) mass spectrometers when operated under the selected accumulation-TIMS (SA-TIMS) mode. Here, we present our initial results on the application of SA-TIMS-ExD-FTICR MS to the separation and identification of glycan linkage isomers. [ABSTRACT FROM AUTHOR]

Bottom-up proteomics is a powerful tool for characterization of protein post-translational modifications (PTMs), where PTMs are identified at the peptide level by mass spectrometry (MS) following protein digestion. However, enzymatic digestion is associated with additional sample processing steps that may potentially introduce artifactual modifications. Here, during an MS study of the PTMs of the regulator of G-protein signaling 4, we discovered that the use of ProteaseMAX, which is an acid-labile surfactant commonly used to improve protein solubilization and digestion efficiency, can lead to in vitro modifications on cysteine residues. These hydrophobic modifications resemble S-palmitoylation and hydroxyfarnesylation, thus discouraging the use of ProteaseMAX in studies of lipid modifications of proteins. Furthermore, since they target the cysteine thiol group, the presence of these artifacts will inevitably lead to inaccuracies in quantitative analysis of cysteine modifications. [ABSTRACT FROM AUTHOR]

Heparan sulfate (HS) 3-O-sulfation determines the binding specificity of HS/heparin for antithrombin III and plays a key role in herpes simplex virus (HSV) infection. However, the low natural abundance of HS 3-O-sulfation poses a serious challenge for functional studies other than the two cases mentioned above. By contrast, multiple distinct isoforms of 3-O-sulfotranserases exist in mammals (up to seven isoenzymes). Here we describe a novel peeling reaction that specifically degrades HS chains with 3-O-sulfated glucosamine at the reducing-end. When HS/heparin is enzymatically depolymerized for compositional analysis, 3-O-sulfated glucosamine at the reducing ends appears to be susceptible to degradation under mildly basic conditions. We propose a 3-O-desulfation initiated peeling reaction mechanism based on the intermediate and side-reaction products observed. Our discovery calls for the re-evaluation of the natural abundance and functions of HS 3-O-sulfation by taking into consideration the negative impact of this novel peeling reaction. [ABSTRACT FROM AUTHOR]

Structural characterization of highly sulfated glycosaminoglycans (GAGs) by collisionally activated dissociation (CAD) is challenging because of the extensive sulfate losses mediated by free protons. While removal of trie free protons may be achieved through the use of derivatization, metal cation adducts, and/or electrospray supercharging reagents, these steps add complexity to the experimental workflow. It is therefore desirable to develop an analytical approach for GAG sequencing that does not require derivatization or addition of reagents to the electrospray solution. Electron detachment dissociation (EDD) can produce extensive and informative fragmentation for GAGs without the need to remove free protons from the precursor ions. However, EDD is an inefficient process, often requiring consumption of large sample quantities (typically several micrograms), particularly for highly sulfated GAG ions. Here, we report that with improved instrumentation, optimization of the ionization and ion transfer parameters, and enhanced EDD efficiency, it is possible to generate highly informative EDD spectra of highly sulfated GAGs on the liquid chromatography (LC) timescale, with consumption of only a few nanograms of sample. We further show that negative electron transfer dissociation (NETD) is an even more effective fragmentation technique for GAG sequencing, producing fewer sulfate losses while consuming smaller amount of samples. Finally, a simple algorithm was developed for de novo HS sequencing based on their high-resolution tandem mass spectra. These results demonstrate the potential of EDD and NETD as sensitive analytical tools for detailed, high-throughput, de novo structural analyses of highly sulfated GAGs. [ABSTRACT FROM AUTHOR]

Direct detection and quantification of protein/ peptide palmitoylation by mass spectrometry (MS) is a challenging task because of the tendency of palmitoyl loss during sample preparation and tandem MS analysis. In addition, the large difference in hydrophobidty between the palmitoyi peptides and their unmodified counterparts could prevent their simultaneous analysis in a single liquid chromatography--MS experi-ment Here, the stability of palmitoylation in several model palmitoyl peptides under different incubation and fragmentation conditions was investigated. It was found that the usual trypsin digestion protocol using dithiothreitol as the reducing agent in ammonium bicarbonate buffer could result in significant palmitoyl losses. Instead, it is recommended that sample preparation be performed in neutral tris buffer with tris(2-carboxyethyl)phosphine as the reducing agent, conditions under which palmitoylation was largely preserved. For tandem MS analysis, collision-induced dissociation often led to facile palmitoyl loss, and electron capture dissociation frequendy produced secondary side-chain losses remote from the backbone deavage site, thus discouraging their use for accurate palmitoylation site determination. In contrast, the palmitoyl group was mostly preserved during electron transfer dissociation, which produced extensive inter-residue cleavage coverage, making it the ideal fragmentation method for palmitoyl peptide analysis. Finally, derivatization of the unmodified peptides with a perfluoroalkyl tag, N-[(3-perfluorooctyl)propyl] iodoacetamide, significandy increased their hydrophobicity, allowing them to be simultaneously analyzed with palmitoyl peptides for relative quantification of palmitoylation. [ABSTRACT FROM AUTHOR]

The structural complexity and diversity of glycans parallel their multilateral functions in living systems. To better understand the vital roles glycans play in biological processes, it is imperative to develop analytical tools that can provide detailed glycan structural information. This was conventionally achieved by multistage tandem mass spectrometry (MSn) analysis using collision-induced dissociation (CID) as the fragmentation method. However, the MSn approach lacks the sensitivity and throughput needed to analyze complex glycan mixtures from biological sources, often available in limited quantities. We define herein the critical parameters for a recently developed fragmentation technique, electronic excitation dissociation (EED), which can yield rich structurally informative fragment ions during liquid chromatographic (LC)-MS/MS analysis of glycans. We further demonstrate that permethylation, reducing end labeling and judicious selection of the metal charge carrier, can greatly facilitate spectral interpretation. With its high sensitivity, throughput, and compatibility with online chromatographic separation techniques, EED appears to hold great promise for large-scale glycomics studies. [ABSTRACT FROM AUTHOR]

The weak and variable binding affinities exhibited by lectin-carbohydrate interactions have often compromised the practical utility of lectin in capturing glycoproteins for glycoproteomic applications. We report here the development and applications of a new type of hybrid biomaterial, namely a boronic acid-decorated lectin (BAD-lectin), for efficient bifunctional glycoprotein labeling and enrichment. Our binding studies showed an enhanced affinity by BAD-lectin, likely to be mediated via the formation of boronate ester linkages between the lectin and glycan subsequent to the initial recognition process and thus preserving its glycan-specificity. Moreover, when attached to magnetic nanoparticles (BAD-lectin@MNPs), 2 to 60-fold improvement on detection sensitivity and enrichment efficiency for specific glycoproteins was observed over the independent use of either lectin or BA. Tested at the level of whole cell lysates for glycoproteomic applications, three different types of BAD-lectin@MNPs exhibited excellent specificities with only 6% overlapping among the 295 N-linked glycopeptides identified. As many as 236 N-linked glycopeptides (80%) were uniquely identified by one of the BAD-lectin@MNPs. These results indicated that the enhanced glycan-selective recognition and binding affinity of BAD-lectin@MNPs will facilitate a complementary identification of the under-explored glycoproteome. [ABSTRACT FROM AUTHOR]

Novel C60 derivatives of a singly bonded dimer and a 1,4-adduct bearing a sulfonic acid functionality have been prepared via the electroreductive transformation of a [60]fullerosultone. It has been shown that the reaction of the in situ formed dianion with benzyl bromide is initiated by a ring-opening of the [60]fullerosultone via the C60-O bond cleavage upon receiving one electron. The [60]fullerosultone dianion is electrooxidized at 0.40 V to afford the singly bonded dimer species, which can be further electrooxidized at 1.30 V to restore the starting material [60]fullerosultone. The reaction mechanism is studied with the cyclic voltammetry and vis-NIR spectroscopy. [ABSTRACT FROM AUTHOR]