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31.
Garth J Simpson 《Chemphyschem》2004,5(9):1301-1310
Recent observations of remarkably large chiroptical effects in second-harmonic generation (SHG) and sum-frequency generation (SFG) measurements suggest exciting possibilities for the development of new chiral-specific spectroscopies and novel chiral materials for nonlinear optics. Several fundamental studies designed to elucidate the molecular and macromolecular origins of the chiral responses are reviewed to provide a framework for development of this emerging field. In general, the chiral activity in SHG and SFG has the potential to arise from complex interactions between hosts of different competing effects. Fortunately, relatively simple electric dipole-allowed mechanisms routinely dominate the nonlinear optical chiral activities of most practical systemsexpressions can often be generated to link the. This substantial reduction in complexity allows for the development of simple models connecting the macroscopic nonlinear optical response to intuitive molecular and supramolecular properties. 相似文献
32.
P. Jagam J. -X. Wang J. J. Simpson 《Journal of Radioanalytical and Nuclear Chemistry》1993,171(2):277-286
Improvements in the detection limits of thorium and uranium in acrylics by neutron activation analysis are described. The average of results from 10 g samples was found to be higher than the results from 450 g samples taken from the same acrylic sheet. Using eighteen large (450 g) samples from a single sheet of acrylic gave an average value of 3.2±0.3 pg/g thorium and 1.1±0.7 pg/g uranium. Interpretation of the results is discussed. Epithermal neutron activation with Cd shielded irradiations did not improve the detection sensitivity for thorium. 相似文献
33.
The interaction of optically active ethyl(1-naphthyl)phenylgermyllithium, R′3-Ge*Li, with alkyl halides, RX, to give optically active R′3Ge*R compounds, occurs with predominant retention of configuration at germanium in the case of MeBr, i-PrCl, i-PrBr, n-BuCl, n-BuBr, t-BuCl, t-BuBr, CH2CHCH2Cl, CH2CHCH2Br and PhCH2Cl, but with predominant inversion in the case of MeI, i-PrI, CH2CHCH2I, PhCH2I, and PhCH2Br. It is suggested that the retention reactions involve direct coupling between R′3Ge*Li and RX, in a four-centre process, while the inversion reactions involve halogen—lithium exchange, to give R′3GeX and RLi, also in a four-centre retentive process, followed by coupling between R′3GeX and RLi in an invertive process. 相似文献
34.
Reversed-phase microbore high-performance liquid chromatography was investigated for high-sensitivity analysis of phenylthiohydantoin (PTH) amino acids. A mixed nitrile alkylsilane bonded phase was developed and ternary gradient elution conditions were devised for resolution of the common PTH amino acids. Elution conditions were developed with a conventional 150 X 4.6 mm I.D. column and transferred to a 150 X 1 mm I.D. microbore column. The performance of these columns was evaluated in terms of PTH amino acid resolution, enhanced sample detectability, and retention time precision. For this work a general purpose high-performance liquid chromatograph was modified to reduce extra column band broadening and a preformed gradient elution technique was developed to achieve rapid analysis times at microbore flow-rates. The microbore high-performance liquid chromatographic system is useful for high-sensitivity analysis of PTH amino acids in micro-sequencing applications. 相似文献
35.
Stephen B. Colbran Brian H. Robinson Jim Simpson 《Journal of organometallic chemistry》1984,265(2):199-204
The nitrosyl clusters PPN[YCCo3(CO)7(NO)] (Y = Me, Ph, COOH, (C5H5)Fe(C5H4)) have been prepared in high yield from the reaction of YCCo3(CO)9 with PPN(NO2) in THF, acetone or acetonitrile. Spectroscopic evidence indicates the structure of the nitrosyl anions is derived from that of YCCo3(CO)9 by the replacement of two CO ligands on one cobalt atom by a linear, terminal nitrosyl group. The nitrosyl metallates are extremely sensitive to oxidation and attempts to protonate the anions resulted in the reformation of the parent YCCo3(CO)9, molecules. The oxidative electrochemistry of the ferrocene complex, PPN[(C5H5)Fe(C5H4CCo3(CO)7(NO)] is also discussed. 相似文献
36.
A continuous gradient elution method for capillary column (less than 0.32 mm I.D.) liquid chromatography was developed. Gradient eluent from a microbore liquid chromatograph was split ahead of the injector so that an accurate percentage (2-3%) of the mobile phase delivered by the pump flowed through the capillary column. The outlet of the column was connected to a length of 0.075 mm I.D. fused-silica capillary tubing which, in turn, was connected to a 6-mm optical path length longitudinal capillary flow cell. Fused-silica capillary columns of 0.32 mm I.D. were slurry-packed efficiently with 7-microns spherical, 300 A pore size, C8 bonded-phase particles, and evaluated in terms of their ability to resolve mixtures of proteins, peptides or phenylthiohydantoin (PTH)-amino acid derivatives. The gradient elution profiles agreed with those obtained using microbore (less than 2.1 mm I.D.) and larger bore columns. The minimum detectable amounts for proteins and PTH-amino acids on 0.32 mm I.D. capillary columns were 50 pg and 25 fmol, respectively. At a flow-rate of 3.6 microliters/min, proteins and peptides were recovered from the capillary columns in volumes of about 2-8 microliters. The use of a multiple-wavelength, forward-optics detector for identifying tryptophan- and tyrosine-containing peptides is discussed. 相似文献
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