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981.
An 17O-enriched version of the titanosilicate glass, KTS2 (K(2)O.TiO(2).2SiO(2)), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO(5) units. Therefore, the structure must consist of linkages between TiO(5) units and SiO(4) tetrahedra and linkages between SiO(4) tetrahedra. 相似文献
982.
Audra A. Hargett Aaron M. Marcella Huifeng Yu Chao Li Jared Orwenyo Marcos D. Battistel Lai-Xi Wang Darn I. Freedberg 《Molecules (Basel, Switzerland)》2021,26(14)
Protein glycosylation is important in many organisms for proper protein folding, signaling, cell adhesion, protein-protein interactions, and immune responses. Thus, effectively determining the extent of glycosylation in glycoprotein therapeutics is crucial. Up to now, characterizing protein glycosylation has been carried out mostly by liquid chromatography mass spectrometry (LC-MS), which requires careful sample processing, e.g., glycan removal or protein digestion and glycopeptide enrichment. Herein, we introduce an NMR-based method to better characterize intact glycoproteins in natural abundance. This non-destructive method relies on exploiting differences in nuclear relaxation to suppress the NMR signals of the protein while maintaining glycan signals. Using RNase B Man5 and RNase B Man9, we establish reference spectra that can be used to determine the different glycoforms present in heterogeneously glycosylated commercial RNase B. 相似文献
983.
984.
The synthesis and characterization of a deep cavitand bearing a fluorescent benzoquinoxaline wall is reported. Noncovalent host-guest recognition events are exploited to sense small charged molecules including acetylcholine. The cavitand also exhibits an anion dependent change in fluorescence that is used to differentiate halide ions in solution. 相似文献
985.
The trimethylphosphine complex Ta(PMe(3))(2)Me(3)Cl(2) has been synthesized by addition of PMe(3) to TaMe(3)Cl(2). The molecular structures of both TaMe(3)Cl(2) and Ta(PMe(3))(2)Me(3)Cl(2) have been determined by X-ray diffraction thereby demonstrating that, in the solid state, these complexes respectively adopt trigonal bipyramidal and capped trigonal prismatic geometries. 相似文献
986.
Automatic filtration and filter flush for robust online solid-phase extraction liquid chromatography
Svendsen KO Larsen HR Pedersen SA Brenna I Lundanes E Wilson SR 《Journal of separation science》2011,34(21):3020-3022
Online solid-phase extraction-liquid chromatography (SPE-LC) with microbore or capillary columns was significantly improved regarding robustness, as an easily installed automatic filtration and filter flushing (AFFL) procedure was added to avoid system clogging. Specifically, an injected sample is passed through a union containing a stainless steel filter prior to SPE trapping. The filter stops any particulate matter from reaching the SPE. When the SPE is subsequently connected to the LC column by column switching, a separate pump backflushes the filter-union, removing the particulate matter off the filter after each injection. This feature greatly reduced backpressure buildup over the entire system. 相似文献
987.
988.
The exchange of Cs(+) into H(1.22)K(0.84)ZrSi(3)O(9)·2.16H(2)O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2(1)/c with cell dimensions of a = 7.2814(3) ?, b = 10.4201(4) ?, c = 13.4529(7) ?, and β = 90.53(1)°) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K(+) cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H(2)O molecules. The occupancy of the Cs(+) cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs(+) ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2(1)/c to orthorhombic P2(1)2(1)2(1). This structural change occurs when Cs(+) occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H(0.18)K(0.45)Cs(1.37)ZrSi(3)O(9)·0.98H(2)O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) ?, b = 13.5821(11) ?, c = 7.3946(6) ?. Solid state (133)Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 ? contribute to the coordination of the Cs(+) cation. 相似文献
989.
Milne JE Storz T Colyer JT Thiel OR Dilmeghani Seran M Larsen RD Murry JA 《The Journal of organic chemistry》2011,76(22):9519-9524
A new convenient and scalable synthesis of phenylacetic acids has been developed via the iodide catalyzed reduction of mandelic acids. The procedure relies on in situ generation of hydroiodic acid from catalytic sodium iodide, employing phosphorus acid as the stoichiometric reductant. 相似文献
990.
Caldwell MA Albers AE Levy SC Pick TE Cohen BE Helms BA Milliron DJ 《Chemical communications (Cambridge, England)》2011,47(1):556-558
A general, efficient method is demonstrated for exchanging native oxyanionic ligands on inorganic nanocrystals with functional trimethylsilylated (TMS) chalcogenido ligands. In addition, newly synthesized TMS mixed chalcogenides leverage preferential reactivity of TMS-S bonds over TMS-O bonds, enabling efficient transfer of luminescent nanocrystals into aqueous media with retention of their optical properties. 相似文献