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51.
The hypothesis of the classical chemistry about bond dipoles resulting from shifts of separate pairs of electrons is proved using the non-canonical method of molecular orbitals (MOs). To this end, a relation is sought between the total charge distribution inside an individual chemical bond of a polyatomic molecule and the square of the respective single localized MO (LMO). General expressions for these MOs are obtained directly on the basis of the Brillouin theorem without invoking additional localization criteria. The two characteristics under comparison are presented in an explicit algebraic form in terms of meaningful components. Reshaping of square of the ‘own’ LMO of the given bond is shown to play the decisive role in the formation of secondary dipoles of initially homopolar bonds (e.g. of C–C and C–H bonds in substituted alkanes), as well as of bonds of relatively low initial polarity. Thus, representability of these dipoles by shifts of the ‘own’ pairs of electrons of respective bonds is supported. For bonds of a high initial polarity, the secondary dipoles are shown to originate mainly from contributions of LMOs of other bonds extending over the antibonding basis orbital of the given bond. Moreover, the actual secondary bond dipole takes an opposite direction vs. that predicted by the shift of the respective ‘own’ pair of electrons in this case. The latter result serves to account for the known low nucleofugality of highly electronegative heteroatoms in the SN2 reactions. 相似文献
52.
Summary A capillary zone electrophoresis method for identification and determination of aesculin and aesculetin has been established
using borate-phosphate buffer containing 30% ethanol with on-column UV detection. A detailed investigation of the influence
of changes in borate concentration, pH, applied voltage, temperature and organic modifier was then carried out. For both aesculin
and aesculetin, a linear plot of migration time (MT) against borate concentration was obtained, and ln[measured peak area
(MA)] and lnMT both gave linear plots against ln(applied voltage) with correlation coefficient r>0.999, which also resulted
in a linear correlation between MA and MT (r≥0.9998) under varied voltage. Ethanol as organic modifier to the background electrolytes
helped in separating aesculin and aesculetin from other components in ash barks. The reproducibility with relative standard
deviation in MT and in normalized peak area(NA) and linearity based on NA against concentration were evaluated. Finally, the
method was successfully applied to monitor the quality of different ash barks and to compare the effect of sample preparation
on content of bioactive components in ash bark. Results indicate that CZE promises to be applicable to quality control of
traditional Chinese medicines containing aesculin and aesculetin. 相似文献
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56.
Summary A simple and rapid capillary zone electrophoretic method with UV detection has been developed for determination of tosufloxacin
and trovafloxacin. The separation was performed in fused-silica capillaries (57 cm length × 75μm i.d.); the running buffer
was 35mm borate + 35mm phosphate buffer solution, pH 8.6, containing 6% (v/v) acetonitrile. The applied potential was 15 kV, the temperature 30°C, and detection was at 262 nm. Piromidic acid was used
as the internal standard. Response was linearly dependent on concentration in the range 1.0–120.0 μg mL−1 and the detection limit was 0.2 μg mL−1 for both compounds. The analysis was highly reproducible (RSD between 3.41 and 1.25%). The method was applied to the determination of tosufloxacin and trovafloxacin in human and rat urine.
The method was validated by using HPLC as a reference method. Recovery was between 96.8 and 102%. 相似文献
57.
Kremser L Brückner A Heger A Grunert T Buchacher A Josic D Allmaier G Rizzi A 《Electrophoresis》2003,24(24):4282-4290
The isoforms distribution of the glycoprotein antithrombin III (ATIII) derived from human plasma was investigated by means of isoelectric focusing (IEF) in polyacrylamide gels with immobilized pH gradients (IPG) and two-dimensional gel electrophoresis (2-DE) as well as capillary electrophoretic methods. It turned out that the presence of high concentrations of chaotropics (urea, thiourea) and zwitterionic detergents (3-[(3-cholamidepropyl)dimethylammonio]-1-propanesulfonate (CHAPS)) was decisive for attaining good resolution of the protein isoforms. Resolution by IPG-IEF was obtained with excellent reproducibility and pI differences down to 0.01 pH units could be distinguished. ATIII-alpha and ATIII-beta-fractions preseparated by heparin affinity chromatography showed an analogous but shifted spot pattern consisting each of one major and three minor isoforms. The main isoforms of ATIII-alpha and ATIII-beta exhibit pI values of 5.18 and 5.32, respectively, both values determined in the presence of high concentrations of urea. The pI difference of 0.14 pH units correspond to the effect of two sialic acids absent in ATIII-beta. The formation and occurrence of ATIII dimers and trimers turned out to be dependent on the sample preparation. The results obtained by 2-DE were compared with those of capillary zone electrophoresis (CZE) and capillary IEF (CIEF). Quantitative analysis regarding the CZE separated isoforms of plasma derived ATIII yielded a content of about 70% ATIII-alpha main isoform and about 6.6% of ATIII-beta. The pI values of ATIII determined by CIEF with internal calibration were in fair agreement with the pI values of the main isoforms achieved with 2-DE. 相似文献
58.
The model proteins cytochrome c, myoglobin, ovalbumin, and beta-lactoglobulin were investigated with regard to their adsorption properties on capillaries for electrophoresis. The model compounds were selected to cover a wide range of properties. Cytochrome c is a basic protein (isoelectric point (pI): 9.6; M(r): 11.7 kDa), beta-lactoglobulin is rather acidic (pI: 5.4, M(r): 18.4 kDa), myoglobin was chosen as a neutral reference protein (pI: 6.8-7.4, M(r): 17.8 kDa), and ovalbumin (pI: 5.1, M(r): 45.0 kDa) was selected as a relatively larger analyte. First, the pH dependence of adsorption was investigated for the bare fused silica. A clear correlation to the respective pIs was noted. For myoglobin and ovalbumin, none or negligible adsorption was found above the pI, whereas strong adsorption was noted just below this parameter. Cytochrome c and beta-lactoglobulin already showed distinct adsorption above their pIs. However, none of the proteins showed any significant adsorption more than one pH unit above the pIs. For linear polyacrylamide-coated capillaries, a decreased but not a complete lack of adsorption was observed. Here, pH-dependent adsorption was noted as well. Regeneration of the capillaries by rinsing with buffers containing 200 mM SDS was also investigated. This method was completely successful for myoglobin, but that too for only freshly-adsorbed protein. After a storage time of 24 h and due to the aging of the adsorbate, a sufficient regeneration was no longer possible. 相似文献
59.
PengZHANG JiCunREN ZuoJunSHEN 《中国化学快报》2004,15(9):1091-1094
In this paper, we first presented a novel method for quantification of circulating DNA in human serum based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). The serum was digested by proteinase to release free DNA, and then CZE-LIF system was used for the quantification of total circulating DNA. This method was successfully used to quantify the circulating DNA levels in sera from healthy individuals and certain cancer patients.We found the significantly elevated circulating DNA levels in certain prostate cancer patients. Our results demonstrated that CZE-LIF system has good linearity, excellent sensitivity (0.5 ng/mL DNA),satisfactory reproducibility (RSDs in one day and between days were both less than 5%) and reliability, and is well suitable to the quantification of the circulating DNA in human serum or plasma. 相似文献
60.
M. Drozdowski K. apsa P. Ziobrowski Z. B aszczak E. Andrzejewska M. Andrzejewski 《Journal of Molecular Structure》1998,450(1-3):129-134
In this paper we report a temperature study of Brillouin scattering and optical Kerr effect in the ethane-1,2-diol dimethacrylate, pentane-1,5-diol dimethacrylate and hexane-1,6-diol dimethacrylate belonging to the series of dimethacrylate homologues. Using these methods we have studied the temperature behaviour of the hypersonic velocity, adiabatic compressibility and optical Kerr constant in the temperature range from 283 to 323 K.
The obtained results are compared to those obtained earlier from Brillouin scattering and optical Kerr effect experiments for butane-1,4-diol dimethacrylate and 2,2′-thiodiethyl dimethacrylate (a sulfur-containing monomer). The results are also discussed in terms of changes in the intermolecular interactions and arrangement in the liquid compounds under study. 相似文献