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101.
Diastereomers of 18 proteinogenic amino acids were synthesized under microwave irradiation and by vortexing using (S)‐naproxen–benzotriazole as chiral derivatizing reagent. The diastereomers synthesized by two approaches were found to be identical in terms of their characterization and chromatographic data. A linear gradient of triethylammonium phosphate (pH 3.5)–acetonitrile (30–65%, within 35 min) was found to be successful using reversed‐phase high‐performance liquid chromatography for their separation. Detection was carried out at 231 nm and sharp peaks were obtained. The method was validated for accuracy, precision and limit of detection. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
102.
(S)‐Naproxen was used to synthesize a chiral reagent, (S)‐2‐(6‐methoxynaphthalen‐2‐yl)propanehydrazide, by itsreaction with hydrazine hydrate in the presence of dicyclohexylcarbodiimide as coupling agent. The reagent was characterized and its chiral purity was established. It was used as a chiral derivatizing reagent for the synthesis of hydrazone diastereomers, under microwave irradiation, of certain chiral aldehydes and ketones. The respective diastereomers were separated by reversed‐phase high‐performance liquid chromatography using a binary solvent combination containing trifluoroacetic acid. The diastereomers were detected at 231 nm. The method was validated for accuracy, precision, and limit of detection (LOD). For a series of hydrazones the LOD was found to be in the range 1.62–1.65 pmol/mL. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
103.
HPLC enantioseparation of racemic bupropion,baclofen and etodolac: modification of conventional ligand exchange approach by pre‐column formation of chiral ligand exchange complexes
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Separation of racemic mixture of (RS)‐bupropion, (RS)‐baclofen and (RS)‐etodolac, commonly marketed racemic drugs, has been achieved by modifying the conventional ligand exchange approach. The Cu(II) complexes were first prepared with a few l ‐amino acids, namely, l ‐proline, l ‐histidine, l ‐phenylalanine and l ‐tryptophan, and to these was introduced a mixture of the enantiomer pair of (RS)‐bupropion, or (RS)‐baclofen or (RS)‐etodolac. As a result, formation of a pair of diastereomeric complexes occurred by ‘chiral ligand exchange’ via the competition between the chelating l ‐amino acid and each of the two enantiomers from a given pair. The diastereomeric mixture formed in the pre‐column process was loaded onto HPLC column. Thus, both the phases during chromatographic separation process were achiral (i.e. neither the stationary phase had any chiral structural feature of its own nor did the mobile phase have any chiral additive). Separation of diastereomers was successful using a C18 column and a binary mixture of MeCN and TEAP buffer of pH 4.0 (60:40, v/v) as mobile phase at a flow rate of 1 mL/min and UV detection at 230 nm for (RS)‐Bup, 220 nm for (RS)‐Bac and 223 nm for (RS)‐Etd. Baseline separation of the two enantiomers was obtained with a resolution of 6.63 in <15 min. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
104.
105.
K. C. Rao K. G. Bhushan R. Mukund S. M. Rodrigues S. K. Gupta J. V. Yakhmi 《Indian Journal of Physics》2011,85(12):1717-1720
Absolute elastic differential cross sections (DCS) have been measured experimentally for several sulphur containing molecules
such as SF6, CS2, DMS and DMSO using a novel high resolution electron spectrometer. The measured DCS’s were extrapolated in the forward and
backward angles using a tenth order legendre polynomial based least squares fitting technique. Total cross sections (TCS)
were determined by integrating the DCS over all angles for each incident energy. The influence of the sulphur atom on the
molecular TCS is studied by comparing the qualitative behavior of electron impact cross sections for the sulphur containing
molecules against the TCS of the sulphur atom at each incident energy. Theoretical calculations based on independent atom
model are also presented as a guide to understand the nature of the electron-molecule collision processes measured in this
study. 相似文献
106.
We consider the problem of determining the stress intensity factors and the crack energy in an infinitely long isotropic, homogeneous elastic strip containing two coplanar Griffith cracks. We assume that the cracks are opened by an internal pressure and the edges of the strip are rigidly fixed. By the use of Fourier transforms we reduce the problem to solving a set of triple integral equations with cosine kernel and a weight function. The triple integral equations are solved exactly. Exact analytical expressions are derived for the stress intensity factors, shape of the deformed crack and the crack energy. Solutions to some particular problems are derived as limiting cases.This work was supported by the National Research Council of Canada through NRC-Grant No. A4177. 相似文献
107.
A new series of chiral derivatizing reagents (CDRs) consisting of five hydrazino dinitrophenyl (HDNP)-amino acids (CDR 1?C5) was prepared by a two-step synthesis procedure starting from 1,5-difluoro-2,4-dinitrobenzene (DFDNB). In the first step, five fluoro-dinitrophenyl (FDNP)-reagents, namely FDNP-l-Leu, FDNP-l-Val, FDNP-l-Phe, FDNP-l-Ala and FDNP-d-Phg were synthesized by substituting one of the fluorine atoms in DFDNB moiety with amino acids l-Leu, l-Val, l-Phe, l-Ala and d-Phg, respectively. In the following step, the remaining fluorine atom of the FDNP reagents was substituted with hydrazine hydrate to obtain five HDNP reagents (i.e. CDR 1?C5; HDNP-l-Leu, HDNP-l-Val, HDNP-l-Phe, HDNP-l-Ala and HDNP-d-Phg). These five CDRs were used for synthesis of diastereomers of six racemic carbonyl compounds which were resolved by high-performance liquid chromatography using C18 column and gradient eluting mixture of acetonitrile or methanol with triethylammonium phosphate buffer with UV detection at 348 nm. Microwave irradiation was used for synthesis of both the CDRs and the diastereomers. The newly synthesized CDRs were observed to be superior in comparison to their counterparts having amino acid amides as chiral auxiliaries in terms of cost effectiveness and providing better resolution of diastereomers. The method was validated for limit of detection, linearity, accuracy and precision. 相似文献
108.
Bismuth(III) chloride–sodium nitrite was used as a mild and efficient reagent for N-nitrosation of various tetrazoles, secondary amines, and amides under ambient conditions. Nitrosation took place chemoselectively at the nitrogen atom, giving corresponding N-nitroso derivatives in good to excellent yield. 相似文献
109.
Brij Bhushan Tewari 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(9):1564-1568
Removal of p-aminophenol (PAP) and p-nitrophenol (PNP) from aqueous solution have been studied through adsorption on bismuth, lead and manganese ferrocyanides (125 μm British Sieve Standard mesh size) at pH range 1.0–10.0 and room temperature (27 ± 1°C). The progress of adsorption was followed spectrophotometrically by measuring the absorbance of PAP and PNP solutions at their corresponding λmax = 220 and 330 nm, respectively. At neutral pH, PNP was found to more adsorbed than PAP on all three metal ferrocyanides studied. Manganese ferrocyanide and bismuth ferrocyanide were found to have maximum and minimum adsorption, respectively for both adsorbents. The adsorption followed the Langmuir type of adsorption in the concentration range of 10?4 to 10?5 mol/L of PAP and PNP solutions. 相似文献
110.
Brij Bhushan Tewari 《Central European Journal of Chemistry》2005,3(3):441-451
The effects of copper ferrocyanide and light on the dehydrogenation rate of NADH by methylene blue is studied. The results
suggest that the dehydrogenation rate of NADH with methylene blue is enhanced by copper ferrocyanide. Light also affects the
reaction rate. 相似文献