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131.
Stanislav S. Stoyko Andrew J. Craig Joshua W. Kotchey Jennifer A. Aitken 《Acta Crystallographica. Section C, Structural Chemistry》2021,77(1):1-10
The new quaternary thiosilicate, Li2PbSiS4 (dilithium lead silicon tetrasulfide), was prepared in an evacuated fused‐silica tube via high‐temperature, solid‐state synthesis at 800 °C, followed by slow cooling. The crystal structure was solved and refined using single‐crystal X‐ray diffraction data. By strict definition, the title compound crystallizes in the stannite structure type; however, this type of structure can also be described as a compressed chalcopyrite‐like structure. The Li+ cation lies on a crystallographic fourfold rotoinversion axis, while the Pb2+ and Si4+ cations reside at the intersection of the fourfold rotoinversion axis with a twofold axis and a mirror plane. The Li+ and Si4+ cations in this structure are tetrahedrally coordinated, while the larger Pb2+ cation adopts a distorted eight‐coordinate dodecahedral coordination. These units join together via corner‐ and edge‐sharing to create a dense, three‐dimensional structure. Powder X‐ray diffraction indicates that the title compound is the major phase of the reaction product. Electronic structure calculations, performed using the full potential linearized augmented plane wave method within density functional theory (DFT), indicate that Li2PbSiS4 is a semiconductor with an indirect bandgap of 2.22 eV, which compares well with the measured optical bandgap of 2.51 eV. The noncentrosymmetric crystal structure and relatively wide bandgap designate this compound to be of interest for IR nonlinear optics. 相似文献
132.
Our sense of smell relies on sensitive, selective atomic-scale processes that occur when a scent molecule meets specific receptors in the nose. The physical mechanisms of detection are unclear: odorant shape and size are important, but experiment shows them insufficient. One novel proposal suggests receptors are actuated by inelastic electron tunneling from a donor to an acceptor mediated by the odorant, and provides critical discrimination. We test the physical viability of this mechanism using a simple but general model. With parameter values appropriate for biomolecular systems, we find the proposal consistent both with the underlying physics and with observed features of smell. This mechanism suggests a distinct paradigm for selective molecular interactions at receptors (the swipe card model): recognition and actuation involve size and shape, but also exploit other processes. 相似文献
133.
The correlation properties of speckle fields are studied for general paraxial systems. The previous studies on lateral and longitudinal speckle size for the case of free-space propagation (Fresnel transform) are generalized to the case of the linear canonical transform. These results have implications for the control of speckle size, through appropriate design of optical systems, with particular relevance for speckle interferometry. 相似文献
134.
We explored plasmon resonant nanorods of gold as a contrast agent for optical coherence tomography (OCT). Nanorod suspensions were generated through wet chemical synthesis and characterized with spectrophotometry, transmission electron microscopy, and OCT. Polyacrylamide-based phantoms were generated with appropriate scattering and anisotropy coefficients (30 cm(-1) and 0.89, respectively) to image distribution of the contrast agent in an environment similar to that of tissue. The observed signal was dependent on whether the plasmon resonance peak overlapped the source bandwidth of the OCT, confirming the resonant character of enhancement. Gold nanorods with plasmon resonance wavelengths overlapping the OCT source yielded a signal-to-background ratio of 4.5 dB, relative to the tissue phantom. Strategies for OCT imaging with nanorods are discussed. 相似文献
135.
Capillary sieving electrophoresis utilizing SDS (CE(SDS)) is one of the most applied methods for the analysis of antibody (mAb) size heterogeneity in the biopharmaceutical industry. Inadequate peak identification of observed protein fragments is still a major issue. In a recent publication, we introduced an electrophoretic 2D system, enabling online mass spectrometric detection of generic CE(SDS) separated peaks and identification of several mAb fragments. However, an improvement regarding system stability and handling of the approach was desired. Here, we introduce a novel 8-port valve in conjunction with an optimized decomplexation strategy. The valve contains four sample loops with increased distances between the separation dimensions. Thus, successively coinjection of solvent and cationic surfactant without any additional detector in the second dimension is enabled, simplifying the decomplexation strategy. Removal efficiency was optimized by testing different volumes of solvents as presample and cationic surfactant as postsample zone. 2D measurements of the light and heavy chain of the reduced NIST mAb with the 8-port valve and the optimized decomplexation strategy demonstrates the increased robustness of the system. The presented novel set-up is a step toward routine application of CE(SDS)-CZE-MS for impurity characterization of proteins in the biopharmaceutical field. 相似文献
136.
137.
Liquid chromatography-electrospray ionization-infrared multiphoton dissociation (IRMPD) mass spectrometry was developed to investigate the distributions of intrastrand crosslinks formed between cisplatin and two oligodeoxynucleotides (ODNs), d(A1T2G3G4G5T6A7C8C9C10A11T12) (G3-D) and its analog d(A1T2G3G4G5T6T7C8C9C10A11T12) (G3-H), which have been reported to adopt different secondary structures in solution. Based on the formation of site-specific fragment ions upon IRMPD, two isobaric crosslink products were differentiated for each ODN. The preferential formation of G3G4 and G4G5 crosslinks was determined as a function of reaction conditions, including incubation temperature and presence of metal ions. G3-D consistently exhibited a greater preference for formation of the G4G5 crosslink compared with the G3-H ODN. The ratio of G3G4:G4G5 crosslinks increased for both G3-D and G3-H at higher incubation temperatures or when metal salts were added. Comparison of the IRMPD fragmentation patterns of the unmodified ODNs and the intramolecular platinated crosslinks indicated that backbone cleavage was significantly suppressed near the crosslink. Figure
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138.
The Direct Synthesis of Hydrogen Peroxide Using Platinum‐Promoted Gold–Palladium Catalysts 下载免费PDF全文
Dr. Jennifer K. Edwards James Pritchard Li Lu Marco Piccinini Greg Shaw Dr. Albert F. Carley David J. Morgan Prof. Christopher J. Kiely Prof. Graham J. Hutchings 《Angewandte Chemie (International ed. in English)》2014,53(9):2381-2384
The direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated. The addition of a small amount of Pt to a CeO2‐supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H2O2 and decreased the non‐desired over‐hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated. 相似文献
139.
Infrared Detection of Criegee Intermediates Formed during the Ozonolysis of β‐Pinene and Their Reactivity towards Sulfur Dioxide 下载免费PDF全文
Jennifer Ahrens Philip T. M. Carlsson Nils Hertl Prof. Dr. Matthias Olzmann Mark Pfeifle Dr. J. Lennard Wolf Dr. Thomas Zeuch 《Angewandte Chemie (International ed. in English)》2014,53(3):715-719
Recently, direct kinetic experiments have shown that the oxidation of sulfur dioxide to sulfur trioxide by reaction with stabilized Criegee intermediates (CIs) is an important source of sulfuric acid in the atmosphere. So far, only small CIs, generated in photolysis experiments, have been directly detected. Herein, it is shown that large, stabilized CIs can be detected in the gas phase by FTIR spectroscopy during the ozonolysis of β‐pinene. Their transient absorption bands between 930 and 830 cm?1 appear only in the initial phase of the ozonolysis reaction when the scavenging of stabilized CIs by the reaction products is slow. The large CIs react with sulfur dioxide to give sulfur trioxide and nopinone with a yield exceeding 80 %. Reactant consumption and product formation in time‐resolved β‐pinene ozonolysis experiments in the presence of sulfur dioxide have been kinetically modeled. The results suggest a fast reaction of sulfur dioxide with CIs arising from β‐pinene ozonolysis. 相似文献
140.
Laura L. Adduci Dr. Matthew P. McLaughlin Trandon A. Bender Dr. Jennifer J. Becker Prof. Dr. Michel R. Gagné 《Angewandte Chemie (International ed. in English)》2014,53(6):1646-1649
The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C? O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6F5)3) is shown to catalyze the metal‐free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products. 相似文献