Browsing by Author "Narayan, V"

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    Quantum-chemical (DFT, MP2) and spectroscopic studies (FT-IR and UV) of monomeric and dimeric structures of 2(3H)-Benzothiazolone
    Sinha, L; Prasad, O; Karabacak, M; Mishra, HN; Narayan, V; Asiri, AM
    Molecular geometry and vibrational wavenumbers of 2(3H)-Benzothiazolone (C7H5NSO, HBT) was investigated using density functional (DFT/B3LYP) method with 6-311+G(d,p) basis set. The vibrational wavenumbers are found to be in good agreement with experimental FT-IR spectra. Hydrogen-bonded dimer of HBT, optimized by counterpoise correction, was studied by MP2 and DFT/B3LYP at the 6-311+G(d,p) level and the effects of molecular association through N-H-O hydrogen bonding were discussed. A detailed analysis of the nature of the hydrogen bonding, using topological parameters, such as electronic charge density, Laplacian, kinetic and potential energy density evaluated at bond critical points (BCP) has also been presented. The UV absorption spectra of the compound dissolved in ethanol and chloroform solutions were recorded in the range of 200-600 nm. The UV-vis spectrum of the title molecule was also calculated using TD-DFT method. The calculated energy and oscillator strength almost exactly reproduce the experimental data. Total and partial density of state (TDOS, PDOS) of the HBT in terms of HOMOs and LUMOs and molecular electrostatic potential (MEP) were calculated and analyzed. The electric dipole moment, polarizability and the first static hyper-polarizability values for HBT were calculated at the DFT/B3LYP with 6-311+G(d,p) basis set. The results also show that the HBT molecule may have nonlinear optical (NLO) comportment with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis. (C) 2013 Elsevier B.V. All rights reserved.
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    Molecular structure, electronic properties, NLO, NBO analysis and spectroscopic characterization of Gabapentin with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations
    Sinha, L; Karabacak, M; Narayan, V; Cinar, M; Prasad, O
    Gabapentin (GP), structurally related to the neurotransmitter GABA (gamma-aminobutyric acid), mimics the activity of GABA and is also widely used in neurology for the treatment of peripheral neuropathic pain. It exists in zwitterionic form in solid state. The present communication deals with the quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of GP using density functional (DFT/B3LYP) method with 6-311++G(d,p) basis set. In view of the fact that amino acids exist as zwitterions as well as in the neutral form depending on the environment (solvent, pH, etc.), molecular properties of both the zwitterionic and neutral form of GP have been analyzed. The fundamental vibrational wavenumbers as well as their intensities were calculated and compared with experimental FT-IR and FT-Raman spectra. The fundamental assignments were done on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The electric dipole moment, polarizability and the first hyperpolarizability values of the GP have been calculated at the same level of theory and basis set. The nonlinear optical (NLO) behavior of zwitterionic and neutral form has been compared. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Ultraviolet visible (UV-Vis) spectrum of the title molecule has also been calculated using TD-DFT method. The thermodynamic properties of both the zwitterionic and neutral form of GP at different temperatures have been calculated. (C) 2013 Elsevier B.V. All rights reserved.
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    A combined experimental and theoretical DFT (B3LYP, CAM-B3LYP and M06-2X) study on electronic structure, hydrogen bonding, solvent effects and spectral features of methyl 1H-indol-5-carboxylate
    Srivastava, R; Al-Omary, FAM; El-Emam, AA; Pathak, SK; Karabacak, M; Narayan, V; Chand, S; Prasad, O; Sinha, L
    Investigation of ground state geometry, molecular properties and electronic structure of methyl 1H-indol-5-carboxylate has been reported for the first time using the implements of density functional theory. The two possible conformers of the title compound were first optimized at B3LYP/6-31G(d) and then further at B3LYP, M06-2X and CAM-B3LYP functionals at 6-311++G(d,p) basis set. A comprehensive vibrational analysis has been performed for both the conformers at B3LYP/6-311++G(d,p). Good agreement between theoretical spectral data with experimental spectra has been obtained. Polarizability and first static hyperpolarizability have been compared at different functionals used in the present study. To estimate the intra-molecular delocalization along with the inter-molecular interaction, the NBO analysis has been done for monomer and dimer of the title molecule. Topological parameters at the bond critical point involved in intermolecular hydrogen-bonding have also been calculated using AIM theory to assess the strength of hydrogen bonding. Effects of solvents (water, carbon tetrachloride and chloroform) on the optimized geometry and the inter-molecular hydrogen bonding have been evaluated. UV-Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and their corresponding energy gap have also been calculated by TD-DFT approach.