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Ortiz S.,Complutense University of Madrid | Alvarez-Ros M.C.,Complutense University of Madrid | Alcolea Palafox M.,Complutense University of Madrid | Rastogi V.K.,Rd Foundation Group Of Institutions | And 2 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2014

A Raman and IR study of the biomolecule 6-chlorouracil was carried out in the solid state. The unit cell found in the crystal was simulated as a tetramer form by density functional calculations. Specific scale factors and scaling equations deduced from uracil molecule were employed in the predicted wavenumbers of 6-chlorouracil. The scaled wavenumbers were used in the reassignment of the IR and Raman experimental bands. Good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of cases. A comparison between the molecular structure and charge distribution of 6-chlorouracil and 5-chlorouracil molecules was presented. The effect of the hydration with the PCM model in the molecular structure and charges was discussed. The optimum tautomers of 6-chlorouracil were optimized and analyzed. Six of them were related to those of uracil molecule. The effect of the halogen substitution in the sixth position of the pyrimidine ring in the stability of the different tautomers was evaluated. HOMO and LUMO orbital energy analysis were carried out. © 2014 Elsevier B.V. All rights reserved. Source


Beaula T.J.,Womens Christian College | Joe I.H.,Center for Molecular and Biophysics Research | Rastogi V.K.,Indian Spectroscopy Society | Rastogi V.K.,Rd Foundation Engineering College | Jothy V.B.,Womens Christian College
Materials Today: Proceedings | Year: 2015

Density functional theory calculations at B3PW91 with 6-311G(d) level basis set were carried out for 2,3-Pyrazinedicarboxylic acid (PDCA) to study about the equilibrium geometries and vibrational spectra. Calculations reveal that the optimized geometry closely resembles the experimental XRD data. Vibrational spectra were analyzed on the basis of the potential energy distribution (PED) of each vibrational mode, which allowed us to obtain a quantitative as well as qualitative interpretation of IR and Raman spectra. Information about size, shape, charge density distribution and site of chemical reactivity of the molecules were obtained by mapping electron density isosurface with electrostatic potential surface (ESP). Based on optimized ground state geometries, NBO analysis has been performed to study donor-acceptor (bond-antibond) interactions. © 2015 Published by Elsevier Ltd. Source


Kattan D.,Norwegian Institute of Food | Alcolea Palafox M.,Norwegian Institute of Food | Rathor S.K.,Indian Spectroscopy Society | Rastogi V.K.,Applied Technology Internet
Journal of Molecular Structure | Year: 2016

The four unit cells found in the crystals of the biomolecule 5-Nitrouracil were simulated as tetramer forms by density functional calculations. Four tetramer forms were fully optimized. Specific scale factors and scaling equations deduced from uracil molecule were employed in the predicted wavenumbers of 5-nitrouracil. The experimental FT-Raman and FT-IR spectra were recorded in the solid state. Comprehensive interpretation of the experimental FT-IR and FT-Raman spectra of the compound under study in the solid state is based on potential energy distribution. A good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of cases. A complete vibrational assignment in the isolated state was also carried out aided by the theoretical harmonic frequency analysis and the results compared with those reported in Ar matrix. The scaled wavenumbers were used in the reassignment of several experimental bands. A comparison between the molecular structure and charge distribution of 5-Nitrouracil with related 5-uracil derivatives was presented. The effect of the nitro substitution in the 5th position of the pyrimidine ring was evaluated. © 2015 Elsevier B.V. Source


Alcolea Palafox M.,Complutense University of Madrid | Bena Jothy V.,Center for Molecular and Biophysics Research | Bena Jothy V.,Womens Christian College | Singhal S.,University Campus | And 4 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

(Figure Presented) The IR and Raman spectra of 3,5-dichlorobenzonitrile (3,5-DCBN) molecule were recorded at room temperature and then the assignment of the observed fundamental bands were achieved by the aid of the theoretical vibrational spectral data obtained from a quantum chemical study carried out for the free molecule case. In the calculations performed to determine the molecular geometry, vibrational spectral data and thermodynamic parameters, Møller-Plesset second order perturbation theory (MP2) and hybrid Density Functional Theory (DFT) types of electronic structure methods, B3LYP and B3PW91, were used. The overestimations of the calculated harmonic wavenumbers were efficiently corrected by the aid of a specific scaling procedure. This empirical scaling process significantly increased the reliability of our assignments and analyses on the observed bands due to different vibrational normal modes of the molecule. For the majority of the normal modes, the deviations between the corresponding experimental and scaled theoretical wavenumbers have located in the expected range. A correct characterization of the normal modes is of vital importance in the assignment of the observed bands, and this was successfully done by the aid of the Potential Energy Distributions (PEDs) separately calculated for each normal mode of 3,5-DCBN. © 2013 Published by Elsevier B.V. Source


Rastogi V.K.,University Campus | Alcolea Palafox M.,Complutense University of Madrid | Tomar R.,University Campus | Singh U.,Indian Spectroscopy Society
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

The experimental IR and Raman spectra of 2-amino-3,5-dichlorobenzonitrile molecule were recorded, and the results compared with theoretical values. Molecular geometry, vibrational wavenumbers and thermodynamic parameters were calculated using MP2 and DFT quantum chemical methods. With the help of specific scaling procedures for the computed wavenumbers, the experimentally observed FTIR and FT-Raman bands were analyzed and assigned to different normal modes of vibrations of the molecule. Simulations in the dimer form were carried out to improve the assignment of the bands in the solid state experimental spectra. The error obtained was in general very low. Using PED's were determined the contributions of the different modes to each wavenumber. Several general conclusions were also deduced. © 2013 Elsevier B.V. All rights reserved. Source

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