Showing papers by "Hirdyesh Mishra published in 2016"
TL;DR: Spectroscopic and structural study of a newly synthesized heteroligand complex of copper with creatinine and urea has been discussed and the complex is found to be rigid and stable in its monomeric form at very low concentrations.
24 citations
TL;DR: The metabolic transformation of antirheumatic fluorescent drug leflunomid into its active metabolite teriflunomide through isoxazole ring opening has been monitored in vitro using steady state and time domain fluorescence spectroscopy and density functional theory to reveal slow conversion of lefl UNO to E and Z forms in aqueous medium, which becomes faster at basic pH.
Abstract: The metabolic transformation of antirheumatic fluorescent drug leflunomide into its active metabolite teriflunomide through isoxazole ring opening has been monitored in vitro using steady state and time domain fluorescence spectroscopy and density functional theory. During metabolic reaction, absorption of leflunomide split into two bands resembling absorption spectra of teriflunomide. The fluorescence spectra reveal slow conversion of leflunomide to E and Z forms of teriflunomide in aqueous medium, which becomes faster at basic pH. The E form, which is more potent as a drug, becomes more stable with an increase in the basicity of the medium. Both molecules are associated with charge transfer due to twisting in the lowest singlet excited state. Excited state charge transfer followed by proton transfer was also observed in the Z form during the ring opening of leflunomide. Quantum yield and radiative decay rates have been observed to decrease for the metabolite because of an increase in nonradiative decay ...
9 citations
TL;DR: In this paper, quantum-chemical calculations based on density functional theory (DFT) have been performed on the diphenyltin(IV) derivative of glycyl-phenylalanine (H2L) at the B3LYP/6-31G(d,p)/LANL2DZ(Sn) level of theory without any symmetry constraint.
Abstract: Abstract The quantum-chemical calculations based on density functional theory (DFT) have been performed on the diphenyltin(IV) derivative of glycyl-phenylalanine (H2L) at the B3LYP/6-31G(d,p)/LANL2DZ(Sn) level of theory without any symmetry constraint. The harmonic vibrational frequencies were computed at the same level of theory to find the true potential energy surface minima. The various geometrical and thermochemical parameters for the studied complex are obtained in the gas phase. The atomic charges at all the atoms were calculated using the Mulliken population analysis, the Hirshfeld population analysis, and the natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, frontier molecular orbital analysis, and conceptual DFT-based reactivity (global and local) descriptors, using the finite difference approximation method. The nature of O-Sn, N-Sn, N→Sn, and C-Sn bonds is discussed in terms of the conceptual DFT-based reactivity descriptors. The structural analysis of the studied complex has been conducted in terms of the selected bond lengths and bond angles. The structural and the atomic charge analyses suggest a distorted trigonal bipyramidal arrangement consisting of negatively charged centers around the positively charged central Sn atom.
6 citations
01 Aug 2016
TL;DR: In this article, the density functional theory calculations in electronic structure studies of n-Bu2SnL2 (where L is the monoanion of chlordiazepoxide (LH), a benzodiazepine derivative with hypnotic action) have been reported using the Gaussian09 software.
Abstract: Density functional theory calculations in electronic structure studies of n-Bu2SnL2 (where L is the monoanion of chlordiazepoxide (LH), a benzodiazepine derivative with hypnotic action) have been reported using the Gaussian09 software. The molecular geometries of LH and tetrahedral n-Bu2SnL2 have been optimized at B3LYP/6-31G(d,p) and B3LYP/ 6-31G(d,p)/Def2-SVP(Sn) level of theory, respectively. Harmonic vibrational frequencies are computed at the same level of theory to find the true potential energy surface minima. The effect of functional, basis set and computational cost is analyzed. The various geometrical and thermochemical parameters have been obtained in gas phase and in the solvent. The atomic charges at all the atoms are calculated using Mulliken population analysis, Hirshfeld population analysis and natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, and conceptual-DFT based global reactivity descriptors using the finite difference approximation method. The calculated parameters suggest a distorted tetrahedral geometry around the central Sn atom. The calculated Sn−O bond lengths reveals different degree of interaction of two chlordiazepoxide units with the di-n-butyltin(IV) moiety. Among the atoms coordinated to the central Sn atom, oxygen from one LH unit is nucleophilic, whereas the second oxygen atom from the other LH unit is electrophilic in nature. The results provide an insight into the efficacy of computational methods in understanding the structure and reactivity of organotin(IV) derivatives of hetero donor atoms.