Browsing by Author "Sunil Kumar Srivastava"

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Lectotypifications in Millingtonia L.f. (Oroxyleae, Bignoniaceae)
(Magnolia Press, 2016) Virendra K. Madhukar; Sunil Kumar Srivastava; Nawal Kishore Dubey
[No abstract available]
Modeling the weak hydrogen bonding of pyrrole and dichloromethane through Raman and DFT study
(2012) Dheeraj Kumar Singh; Birendra Pratap Asthana; Sunil Kumar Srivastava
Raman spectra of neat pyrrole (C4H5N) and its binary mixtures with dichloromethane (CH2Cl2, DCM) with varying mole fractions of C4H5N from 0.1 to 0.9 were recorded in order to monitor the influence of molecular interaction on spectral features of selected vibrational bands of pyrrole in the region 600-1600 cm-1. Only 1369 cm-1 vibrational band of pyrrole shows a significant change in its peak position in going from neat pyrrole to the complexes. The 1369 cm-1 band shows (∼6 cm-1) blue shift upon dilution and the corresponding linewidth shows the maximum shift at C=0.5 mole fraction of pyrrole upon dilution which clearly indicates that the concentration fluctuation model plays major role. Quantum chemical calculation using density functional theory (DFT) and ab-initio (MP2 and HF) methods were performed employing high level basis set, 6-311++G(d,p) to obtain the ground state geometry of neat pyrrole and its complexes with DCM in gas phase. Basis set superimpose error (BSSE) correction was also introduced by using the counterpoise method. In order to account for the solvent effect on vibrational features and changes in optimized structural parameters of pyrrole, polarizable continuum model (PCM) (bulk solvations) and PCM (specific plus bulk solvations) calculations were performed. Two possible configurations of pyrrole + DCM complex have been predicted by B3LYP and HF methods, whereas the MP2 method gave only single configuration in which H atom of DCM is bonded to π ring of the pyrrole molecule. This affects significantly the ring vibrations of pyrrole molecule, which was also observed in our experimental results. © Springer-Verlag 2012.
Study of structure-activity relationship of enantiomeric, protonated and deprotonated forms of warfarin via vibrational spectroscopy and DFT calculations
(Elsevier B.V., 2013) Alok Mishra; Sunil Kumar Srivastava; D. Swati
(Figure Presented) The structure-activity relationship of the anticoagulant drug warfarin were studied by studying two enantiomeric forms (S-form and R-form) of warfarin and its protonated as well as deprotonated structures in aqueous media using density functional theory (DFT). Theoretically computed Raman and IR spectra of all the computed structures were compared and their specific vibrational spectroscopic signatures were discussed. The percentage contributions of individual normal modes of warfarin, which provides direct evidence of the different molecular activity due to change in relative atomic position of atoms in molecule, were investigated through potential energy distribution (PED). The optimized energy and molecular electrostatic potential (MEP) maps show that the S-form of the drug molecules warfarin is energetically more stable than R-form and provides higher docking opportunity for the molecular binding with the receptors in the bio-systems. © 2013 Elsevier B.V. All rights reserved.
Typification of Bignonia africana Lam. (Bignoniaceae)
(Tsumura Laboratory, 2015) Virendra Kumar Madhukar; Sunil Kumar Srivastava; Nawal Kishore Dubey
The typification of Bignonia africana Lam. is discussed. One of authentic and original specimens from the type locality studied by the authors as cited in the protologue presently housed in the Herbarium of Université Montpellier (MPU) is designated as the holotype.