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31.
Quantitative ROESY analysis of computational models: structural studies of citalopram and β‐cyclodextrin complexes by 1H‐NMR and computational methods
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Complexation of racemic citalopram with β‐cyclodextrin (β‐CD) in aqueous medium was investigated to determine atom‐accurate structure of the inclusion complexes. 1H‐NMR chemical shift change data of β‐CD cavity protons in the presence of citalopram confirmed the formation of 1 : 1 inclusion complexes. ROESY spectrum confirmed the presence of aromatic ring in the β‐CD cavity but whether one of the two or both rings was not clear. Molecular mechanics and molecular dynamic calculations showed the entry of fluoro‐ring from wider side of β‐CD cavity as the most favored mode of inclusion. Minimum energy computational models were analyzed for their accuracy in atomic coordinates by comparison of calculated and experimental intermolecular ROESY peak intensities, which were not found in agreement. Several least energy computational models were refined and analyzed till calculated and experimental intensities were compatible. The results demonstrate that computational models of CD complexes need to be analyzed for atom‐accuracy and quantitative ROESY analysis is a promising method. Moreover, the study also validates that the quantitative use of ROESY is feasible even with longer mixing times if peak intensity ratios instead of absolute intensities are used. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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This paper reports on the formation of nanostructures produced in soda-lime glass by controlling the irradiation conditions of a single-beam femtosecond laser. Periodic nanoholes are fabricated in the sample with the lowest diameter of 200 nm (approximately one fourth of the incident light wavelength). Self-organized nanogratings with a period of 120 nm are fabricated for the first time on soda-lime glass surface by applying many pulses at the same spot. We discover that the nanogratings’ period decreases with the increase of the applied pulses. We investigate that the direction of the nanogratings is perpendicular to the direction of laser polarization. Further, it is discovered that the microholes, due to the illumination by many pulses, are elliptical in shape with the major axis perpendicular to the direction of laser polarization. Finally, long distance horizontal and vertical gratings are fabricated by scanning a femtosecond laser beam only in the horizontal direction. 相似文献
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35.
Farid Ahmed M. Shamim Ahsan Man Seop Lee Martin B. G. Jun 《Applied Physics A: Materials Science & Processing》2014,114(4):1161-1165
In this paper, a study of the effect of a transparent dielectric medium (soda-lime glass placed after an objective lens) on femtosecond pulse filamentation in Corning Eagle2000 glass is presented. The dielectric medium placed after the objective lens increases the effective numerical aperture of the focusing lens and tightly focuses the beam to elevate the power density in a tiny focal volume. A single-shot narrow filamentary void of diameter 3.8 μm is observed to propagate as long as 700 μm in Corning Eagle2000 glass. Elevated optical intensity confined in the small focal volume and low ionization losses per unit length in the narrow plasma column collectively enhance the filamentary propagation of the ultra-short pulse in bulk glass. The applied technique also offers an approach to control the length and width of a filamentary void structure in a transparent dielectric medium. 相似文献
36.
Stanley N. S. Vasconcelos Anwar Shamim Bakhat Ali Isadora M. de Oliveira Hélio A. Stefani 《Molecular diversity》2016,20(2):469-481
1,2,3-Triazol tyrosines were synthesized from tyrosine alkynes that were in turn prepared via Sonogashira cross-coupling reaction. The tyrosine alkynes were subjected to click-chemistry reaction conditions leading to the corresponding 3-(1,2,3-triazolyl)-tyrosines in yields ranging from moderate to good. 相似文献
37.
M. Iqbal M. Ejaz Shamim A. Chaudhri Zamiruddin 《Journal of Radioanalytical and Nuclear Chemistry》1978,42(2):335-348
Diphenyl-2-pyridylmethane, a high molecular weight substituted pyridine has been examined and found to be a useful solvent
extraction reagent. Its behaviour is similar to amines in that it forms salts with mineral acids. The acid ionization constant
(pKBH
+) determined spectrophotometrically has a value of 4.41±0.06 at 25 °C. A study of the partition behaviour of trace amounts
of gold between mineral acid solutions and 0.1M diphenyl-2-pyridylmethane dissolved in chloroform indicates that the metal
can be quantitatively extracted from dilute mineral acid solutions and also from concentrated hydrochloric acid media in a
single extraction. Attempts have been made to gain an understanding of factors affecting the extraction of gold. Common anions
have little effect on extraction in concentrations upto 1M. Separation factors of a number of metal ions relative to gold
are reported for three mineral acid systems; and gold has been estimated in some synthetic samples using neutron activation
technique by prior extraction with 0.1M solution of diphenyl-2-pyridylmethane dissolved in chloroform. 相似文献
38.
[reaction: see text] An enantioselective total synthesis of (-)-stemonine (1) is reported via a convergent assembly of the acyclic precursor 2. Key transformations include a Staudinger-aza-Wittig reaction to form the central perhydroazepine ring system and an iodine-induced tandem cyclization to construct the pyrrolidino-butyrolactone framework. 相似文献
39.
Metabolism of 7-O-methylnaringenin (sakuranetin) by Cunninghamella elegans NRRL 1392 yielded naringenin and naringenin-4'-sulfate. C. elegans also converted 5, 3', 4'-trihydroxy-7-methoxyflavanone into eriodictyol-4'-sulfate. Furthermore, incubation of 5, 4'-dihydroxy-7, 3'-dimethoxyflavanone with the same fungus gave homoeriodictyol (5, 7, 4'-trihydroxy-3'-methoxyflavanone) and homoeriodicytol-7-sulfate. The structures of the new metabolites were established by spectral analysis including 2D-NMR, HR-ESI-FT-MS beside hydrolysis by acid. 相似文献
40.
Shamim Mahbub Akter Parul Hoque Md. Anamul Rub Malik Abdul 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2019,93(12):2494-2501
Russian Journal of Physical Chemistry A - Interaction of anionic surfactant, sodium dodecyl sulfate (SDS) with antibiotic drug cefradine monohydrate (CFD) were carried out in H2O/low concentration... 相似文献