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81.
Hünig I Painter AJ Jockusch RA Carçabal P Marzluff EM Snoek LC Gamblin DP Davis BG Simons JP 《Physical chemistry chemical physics : PCCP》2005,7(12):2474-2480
The gas phase structures of phenyl alpha- and beta-d-xylopyranoside (alpha- and beta-pXyl) and their mono-hydrates have been investigated using a combination of resonant two-photon ionization (R2PI), ultra-violet hole-burning and resonant infrared ion dip spectroscopy, coupled with density functional theory (DFT) and ab initio computation. The hole-burning experiments indicate the population of a single conformer only, in each of the two anomers. Their experimental and calculated infrared spectra are both consistent with a conformational assignment corresponding to the computed global minimum configuration. All three OH groups are oriented towards the oxygen atom (O1) on the anomeric carbon atom to form an all trans(ttt) counter-clockwise chain of hydrogen bonds. The mono-hydrates, alpha- and beta-pXyl(H(2)O) each populate two distinct structures in the molecular beam environment, with the water molecule inserted between OH4 and OH3 or between OH3 and OH2 in alpha-pXyl(H2O), and between OH2 and O1 in either of two alternative orientations, in beta-pXyl(H2O). In all of the mono-hydrated xyloside complexes, the water molecule inserts into the weakest link of the sugar molecules' hydrogen-bonded chain of hydroxy groups, creating a single extended chain, strengthened by co-operativity. The all-trans configuration of the xylose moiety is retained and the mono-hydrate structures correspond to those calculated to lie at the lowest relative energies. 相似文献
82.
83.
Low Pass metallic mesh interference filters have been designed and constructed for operation in the region 340 m (880 GHz) to 1.8 mm (165 GHz). These filters have been shown to have excellent edge characteristics and good rejection regions. The results show that the mesh filter can be effectively used in both millimetre and submillimetre regions.Part of this work was performed while this author was at Heriot-Watt University, Edinburgh, U.K. 相似文献
84.
85.
The cubic titanosiloxane [RSiO(3)Ti(OPr(i))](4) (R = 2,6-Pr(2)(i)C(6)H(3)NSiMe(3)) (1) is found to be relatively inert in its attempted reactions with alcohols and other acidic hydrogen containing compounds. The reaction of 1 with silanol (Bu(t)O)(3)SiOH however proceeds over a period of approximately 3 months to result in the hydrolysis of (Bu(t)O)(3)SiOH and yield the transesterification product [RSiO(3)Ti(OBu(t))](4) (2) rather than the expected [RSiO(3)Ti(OSi(OBu(t))(3))](4). Products 1 and 2 have been characterized by elemental analysis, thermal analysis, and spectroscopic techniques (IR, EI-MS, and NMR). The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. Compounds 1 and 2 are isomorphous and crystallize in a cubic space group with a central cubic Ti(4)Si(4)O(12) core. Solid state thermolysis of 1 was carried at 450, 600, 800, 900, 1000, and 1200 degrees C in air, and the resulting titanosilicate materials 1a-f were characterized by spectroscopic (IR and DR UV), powder XRD, and electron microscopic methods. While, the presence of Ti-O-Si linkages appears to be dominant in the samples prepared at lower temperatures (450-800 degrees C), phase separation of anatase and rutile forms of TiO(2) occurs at temperatures above 900 degrees C as revealed by IR spectral and PXRD studies. The presence of octahedral titanium centers was observed by DR UV spectroscopy for the samples heated at higher temperatures. The use of new titanosilicate materials as catalysts for olefin epoxidation has been investigated. The titanosilicate materials produced at temperatures below 800 degrees C with a large number of Ti-O-Si linkages (or tetrahedral titanium centers) were found to be more active catalysts compared to the materials produced above 900 degrees C. The observed conversion in the epoxidation reactions was found to be somewhat low although the selectivity of the epoxide formation over the other possible oxidized products was found to be very good. 相似文献
86.
87.
A quantitative theory of plate number N in capillary electrophoresis was developed for buffers containing neutral cyclodextrins (CDs) capable of forming inclusion complexes. In the theory, N was modeled by longitudinal diffusion, injection extent, width of the detection window, and the detector time constant. The apparent mobility was modeled as a weighted sum of the mobilities of the free-solution analyte and the inclusion complex. The apparent diffusion coefficient was modeled as a similarly weighted sum. Both the apparent mobility and diffusion coefficient were corrected by functions that compensated for increases of buffer temperature caused by Joule heat. The experimental N's and apparent mobilities of neutral thiourea and of the anions, dansyl D- and L-leucine, dansyl D- and L-aspartic acid, benzoate, and 4-nitrophenolate, were determined in buffers containing from 0 to 15 mM beta-CD. The binding constants, and mobilities and diffusion coefficients of the free-solution analyte and inclusion complex, were calculated as regression coefficients by fitting theory to these determinations. The regression coefficients were shown to have physicochemical meaning, as assessed by literature values, independent measurements, and theoretical predictions. The assessment showed the Nernst-Einstein equation does not relate mobilities and diffusion coefficients at the electrolyte concentration used. The interdependence of mobilities, diffusion coefficients, binding constants, and other dispersion sources was interpreted to evaluate the factors affecting the variation of N with CD concentration. From the interpretation, an approximate equation for N in low-concentration CD buffers was derived. The equation depends on free-solution and inclusion-complex mobilities and diffusion coefficients, the binding constant, the potential difference over the effective capillary length, and the number of plates in a CD-free buffer. 相似文献
88.
R.S. Sapienza P.E. Riley R.E. Davis R. Pettit 《Journal of organometallic chemistry》1976,121(2):C35-C40
A general synthesis for the preparation of medium sized cycloalkanes having 1,2-butadienyl substituents is described. The reaction sequence involved acylation of butadiene-iron tricarbonyl with a diacid chloride, reduction of the resultant diketone to a diol derivative and conversion with HBF4 to an acyclic bis-pentadienyl Fe(C0)3 dicationic complex. Upon treatment with zinc the dication undergoes intramolecular ring closure to afford the bis-Fe(C0)3 complex of the 1,2-dibutadienyl cycloalkane. Five-, six- and ten-membered cyclolalkene derivatives have been prepared in this manner. 相似文献
89.
The synthesis of the title compound is described. Pinacol reduction of 2,2′-dibenzoylbiphenyl followed by dehydration of the trans-diol, so formed, with dimethylformamide dimethyl acetal yielded 55% of the oxirane. Irradiation of the oxide in methylene chloride at 254 nm gave 10,10-diphenyl-9-(10H)phenanthrone as the major photoproduct. 相似文献
90.
54Mn is analyzed in complex food ash of high cationic environment. The initial step is an extraction atpH 2.7 with hexane containing di(2-ethylhexyl) phosphoric acid (HDEHP) to complex the54Mn and other nuclides. The manganese is reextracted into an alkaline EDTA buffer which is washed with 1% 8-hydroxyquinoline
in chloroform containing 5% isoamyl alcohol. The54Mn is determined by gamma spectrometry with recoveries ranging from 96.6 to 99.4%. 相似文献