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Ab initio SCF MO calculations using a contracted double zeta basis set of 168 gaussian type functions were performed on TCNQ+, TCNQ, TCNQ? and TCNQ2?. The ionisation potentials obtained from total energy differences are generally 0.25-0.50 eV higher than the corresponding negative orbital energies from the TCNQ calculation and in satisfactory agreement with experimental results. The energy of the disproportionation reaction 2TCNQ?-TCNQ+TCNQ2? is calculated to be 4.62 eV. The charge distributions as measured by the gross atomic populations generally deviate from those obtained in earlier π-electron calculations as a consequence of taking the σ-electron distribution into account. The atomic charges are in good agreement with the limited experimental data available. 相似文献
95.
Vasbinder E Van der Weken G Vander Heyden Y Baeyens WR Debunne A Remon JP García-Campaña AM 《Biomedical chromatography : BMC》2004,18(1):55-63
An ion-pair high performance liquid chromatographic method was developed for the simultaneous determination of p-aminosalicylic acid (PAS) and its degradation product m-aminophenol (MAP) in a newly developed multiparticular drug delivery system. Owing to the concentration differences of PAS and MAP, acetanilide and sulfanilic acid were used as internal standards, respectively. The separation was performed on a Chromolith SpeedROD RP-18e column, a new packing material consisting of monolithic rods of highly porous silica. The mobile phase composition was of 20 mm phosphate buffer, 20 mm tetrabutylammonium hydrogen sulphate and 16% (v/v) methanol adjusted to pH 6.8, at a flow-rate of 1.0 mL/min, resulting in a run-time of about 6 min. Detection was by UV at 233 nm. The method was validated and proved to be useful for stability testing of the new dosage form. Separation efficiency was compared between the new packing material Chromolith SpeedROD RP-18e and the conventional reversed-phase cartridge LiChroCART 125-4 (5 microm). A robustness test was carried out on both columns and different separation parameters (retention, resolution, run time, temperature) were determined. 相似文献
96.
Two series of amino acid derivatives and phenylamines were used to evaluate the potential of highly sulfated cyclodextrins (HS-CDs) for the screening for chiral separations by capillary electrophoresis (CE). HS-CDs showed to be very versatile and to exhibit very high enantioselectivity. The use of short-end injection allowed to reduce dramatically the analysis time. From the results obtained, a scheme for the rapid screening of enantiomeric molecules was developed and applied to various chiral drugs. Results are very satisfying as almost all compounds (62 out of 67) could be baseline-resolved. Usually, less than three experiments were necessary to obtain very good separation. 相似文献
97.
Haines TJ Bionta RM Blewitt G Bratton CB Casper D Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Jones TW Kielczewska D Kropp WR Learned JG Lehmann E LoSecco JM Matthews J Park HS Price LR Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1986,57(16):1986-1989
98.
Mato-Iglesias M Platas-Iglesias C Djanashvili K Peters JA Tóth E Balogh E Muller RN Vander Elst L de Blas A Rodríguez-Blas T 《Chemical communications (Cambridge, England)》2005,(37):4729-4731
The complex [Gd(L)(H2O)]3- (H(6)L =N,N'-bis(6-carboxy-2-pyridylmethyl)ethylenediamine-N,N'-methylenephosphonic acid) displays the highest water exchange rate ever measured for a Gd(III) chelate (k(298)(ex)= 8.8 x 10(8) s(-1)), which is attributed to the flexibility of the metal coordination environment. 相似文献
99.
Glass/PA 6 composites were manufactured from specially designed hybrid yarns. The hybrid yarns were produced by three different spinning systems: friction spinning, ring twisting and pneumatic texturing. Each of these systems gives a different structure of the yarn and a different level of blending of the reinforcing and thermoplastic fibres. The crystallization and melting behaviour of PA 6 in the yarns and the composites were studied by differential scanning calorimetry.
The different structure of the hybrid yarns leads to differences in the crystallinity of PA 6 in the yarns and the composites. The mechanical properties of the thermoplastic yarns and the composites are influenced, among other factors, by the crystal structure of the polymer. 相似文献
100.
Quantitative structure-retention and retention-activity relationships of beta-blocking agents by micellar liquid chromatography 总被引:1,自引:0,他引:1
Detroyer A Vander Heyden Y Carda-Broch S García-Alvarez-Coque MC Massart DL 《Journal of chromatography. A》2001,912(2):211-221
Sixteen beta-blocking agents (acebutolol, alprenolol, atenolol, bisoprolol, carteolol, celiprolol, esmolol, labetalol, metoprolol, nadolol, oxprenolol, pindolol, practolol, propranolol, sotalol and timolol) showing a large range of hydrophobicity (octanol-water partition coefficients, log P between -0.026 and 2.81) were subjected to micellar liquid chromatography with sodium dodecyl sulfate as micelle forming agent, and n-propanol as organic modifier. The correlation between log P and the retention factor extrapolated to a mobile phase free of micelles and organic modifier was investigated. The use of an interpolated retention factor or the retention factor for specific individual experimental mobile phases was however advantageous since the retention factors of all beta-blocking agents were measurable in the selected mobile phases. Good correlations with log P and with in vitro biological parameters (cellular permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments) were found. 相似文献