Browsing by Author "Rohit Kumar Yadav"

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Conformational, structural and vibrational studies of estragole
(Elsevier B.V., 2021) Rohit Kumar Yadav; Bhoopendra Yadav; Gaurav Srivastav; Omkant Jha; R.A. Yadav
Structural and conformational investigations were carried out at the B3LYP/6-311++G** level using the Gaussian 09 software. Vibrational spectra along with other related parameters like molecular geometries; APT charges etc were computed to analyze the experimentally measured Raman and IR spectra. In order to interpret the experimental spectra the potential energy distributions were computed using the GAR2PED software. Barrier heights for the [sbnd]OCH3, [sbnd]CH2CH[dbnd]CH2 and [sbnd]CH[dbnd]CH2 tops were estimated using the DFT and single top rotor theories. Vibrational contributions to the thermodynamic functions, namely, specific heat, entropy and free energy were determined. MEP, ESP plots and HOMO-LUMO energies were calculated using the results of the optimized structures of the three conformers of the estragole molecule. UV-vis spectrum was also investigated and interpreted. Comparative structural, active sites and vibrational investigations were made for all the three conformers. © 2021
DFT studies of molecular structures conformers and vibrational characteristics of sulfanilamide
(Elsevier B.V., 2019) Gaurav Srivastav; Bhoopendra Yadav; Rohit Kumar Yadav; R.A. Yadav
Molecular structures and vibrational parameters for all the four possible conformers of sulfanilamide were studied using Gaussian 09 software and PEDs were calculated using GAR2PED software. MEP and HOMO-LUMO energies were computed and NBO analysis was carried out. Optimized geometries possess Cs symmetry. Out of 51 normal modes, 26 modes are conformer sensitive, out of which 2 modes show frequency variation above 75 cm−1 in going from one conformer to another. Out of the 6 internal modes of NH2, 4 modes were found at lower frequencies for S-NH2 group compared to C-NH2 group, due to presence of intra-molecular O⋯H bonds in the SO2(NH2) group. Strength of nucleophilic attack is stronger with the H atoms of C-NH2 group compared to the H atoms of the S-NH2 group. Intra-molecular O⋯H bonds also lead to difference in corresponding geometrical parameters of S-NH2 and C-NH2 groups and difference in atomic charges at corresponding sites. © 2019 Elsevier B.V.
Experimental IR, Raman, and UV-Vis Spectra DFT Structural and Conformational Studies: Bioactivity and Solvent Effect on Molecular Properties of Methyl-Eugenol
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Rohit Kumar Yadav; Bhoopendra Yadav; R.A. Yadav; Irena Kostova
Highlights: What are the main findings? The ME molecule has 21 stable configurations. For all the tops (except =CH2), the barrier heights are of the same order, while the =CH2 top has a barrier height one order of magnitude higher. Like estragole and eugenol, ME also has the same Fermi doublets for the following modes: νs(–CH2) and 2 (Formula presented.) βs(–CH2); νs(CH3) and 2 (Formula presented.) δs(CH3). The ME molecule has three active sites. Vibrational analysis suggests that the solvents affect the internal modes of both OCH3 moieties strongly. What is the implication of the main finding? The methyl-eugenol molecule could be a good choice for the pharmacological applications The OCH3 moieties of methyl-eugenol play significant role in interaction with other molecules. Structural, conformational, and spectroscopic investigations of methyl-eugenol were made theoretically at the B3LYP-6-311++G**level. Experimental IR, Raman, and UV-vis spectra were investigated and analyzed in light of the computed quantities. Conformational analysis was carried out with the help of total energy vs. dihedral angle curves for different tops, yielding 21 stable conformers, out of which only two have energies below the room temperature relative to the lowest energy conformer. The effect of the solvent on different molecular characteristics was investigated theoretically. MEP and HOMO-LUMO analysis were carried out and barrier heights and bioactivity scores were determined. The present investigation suggests that the molecule has three active sites with moderate bioactivity. The solvent–solute interaction is found to be dominant in the vicinity of the methoxy moieties. © 2023 by the authors.
Experimental Raman, FTIR and UV-vis spectra, DFT studies of molecular structures and barrier heights, thermodynamic functions and bioactivity of kaempferol
(Elsevier B.V., 2022) Bhoopendra Yadav; Rohit Kumar Yadav; Gaurav Srivastav; R.A. Yadav
Molecular structures and vibrational parameters for the all the four possible conformers of kaempferol were investigated using Gaussian 09 and GAR2PED software. Raman and FTIR spectra of kaempferol were recorded in the regions 50–4000 cm−1 and 400–4000 cm−1, respectively and interpreted in the light of the computed quantities. Some of the modes were found to have conformer dependent frequencies, IR and Raman intensities and depolarisation ratios. The complex, broad and intense IR band in the range 2900–3500 cm−1 is explained to arise due to the four OH stretching and an overtone modes. The barrier heights for the OH tops against internal rotations have been determined. The UV–vis absorption spectrum was measured in the range 220–800 nm. MEP and HOMO-LUMO energies were computed for all the four conformers and NBO analysis was carried out. Thermodynamic functions of title compound have been carried out. Different bioactivity scores for this molecule were computed. © 2022
Experimental Raman, FTIR and UV-Vis Spectra, DFT Studies of Molecular Structures and Conformations, Barrier Heights Against Internal Rotations, Thermodynamic Functions and Bioactivity of Biologically Active Compound - Isorhamnetin
(Taylor and Francis Ltd., 2024) Bhoopendra Yadav; Rohit Kumar Yadav; Gaurav Srivastav; R.A. Yadav
Molecular structural, conformational and spectroscopic investigations on the isorhamnetin molecule have been carried out at the B3LYP/6-311++G(d,p) level. Experimental FTIR, Raman and UV–vis spectra have been recorded and analyzed in light of the computed quantities and potential energy distributions (PEDs). In addition, MEP, Iso-surface plot of ESP and HOMO-LUMO energies, the barrier heights for the internal rotations about different axes and different thermodynamic functions were computed. Moreover, the wavefunction properties like reduced density gradient and electron localization function were computed. To investigate the biological properties, the bioactivity scores were computed and the molecular docking was also performed. The planarity of the flavone skeleton was stabilized by intramolecular interactions of O16.H24, and O26…H22. The barrier heights for bound OH tops were three times than the free OH tops. The bond length of the C-C linkage was found to be the longest among all the C-C bonds. Out of 99 normal modes, only 66 normal modes were seen to be conformer dependent. The sites near the H and O-atoms of free OH groups are more effective for nucleophilic and electrophilic attacks. The HOMO-LUMO analysis suggests that the molecule is chemically soft. From the observed UV-Vis spectral analysis bathochromic shift was noticed. Thermodynamic functions varied non-linearly with temperature. The bioactivity scores and molecular docking suggest that the molecule is a bioactive molecule. The results of the present investigations made on the isorhamnetin molecule are reported for the first time. © 2023 Taylor & Francis Group, LLC.
Spectroscopic, structural and conformational investigations of the major constituent of the clove oil: Eugenol
(Elsevier B.V., 2023) Rohit Kumar Yadav; Bhoopendra Yadav; R.A. Yadav
Molecular structures of the 12 possible conformers of eugenol were optimized at the B3LYP/6–311++G** level available with the Gaussian 09 software. IR and Raman spectra of eugenol were measured and analysed in light of the computed quantities. The interpretation of the IR spectrum in the OH stretching region suggested the existence of eugenol in the dimeric form. Five dimeric structures of the lowest energy monomeric conformer (C-I) were found to have energy difference below 300K. The complete observed IR and Raman spectra could be explained in terms of the computed spectra of the five lowest energy dimers of C-I. UV–vis absorption spectrum was measured in the range 200–600 nm and analysed with the help of computed parameters. Moreover, MEP plots and HOMO-LUMO analysis were carried out. Different computed quantities/ parameters for C-I and its 5 dimers are compared. In addition, barrier heights for different tops, thermodynamic functions and bioactive scores of the eugenol molecule were determined. © 2023 Elsevier B.V.
Structural, Conformational and Spectroscopic Investigations of a Biologically Active Compound: L-Dopa
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Rohit Kumar Yadav; Ram Anjore Yadav; Irena Kostova
Highlights: What are the main findings? The L-dopa molecule has 108 stable configurations. Vibrational analysis confirms the existence of a dimeric form of L-dopa and a strong IR band peak at 2770 cm−1 suggests its OH forms. L-dopa molecules are found to be chemically soft and biologically active in nature. Strong active sites are near the O and H atoms of the OH and COOH groups. What is the implication of main findings? L-dopa molecule would be a good choice for medicinal application. Multiple active sites play significant role for its chemical activities. Structural, conformational and spectroscopic investigations of the L-dopa molecule were made at the b3lyp/6-311++g** level using the Gaussian 09 software. IR, Raman and UV-vis spectra were measured and analyzed in light of the computed spectral quantities. Total energy vs. dihedral angle scans yielded 108 pairs of stable conformers of L-dopa. All the conformers had energies above 500 K relative to the lowest-energy conformer C-I. The observed spectra could be explained in terms of the computed spectra of the lowest-energy dimer of the C-I monomer. MEP and HOMO-LUMO analysis were carried out, and barrier heights and bioactivity scores were determined. The positive bioactive scores represent its higher medicinal and pharmaceutical applications. The present investigation suggests that the molecule has three active sites with moderate bioactivity. © 2023 by the authors.
Vibrational spectra and molecular structure of sulfanilamide: IR and Low temperature Raman studies and DFT investigation of monomeric and dimeric forms
(Elsevier B.V., 2021) Gaurav Srivastav; Bhoopendra Yadav; Rohit Kumar Yadav; R.A. Yadav
Raman spectra of sulfanilamide were recorded at temperatures 80, 90, 120, 150 and 300 K in the range 50-4000 cm−1. The room temperature FTIR spectrum of this compound was investigated in the range 400−4000 cm−1. The molecular structures and vibrational parameters for the lowest energy conformer of sulfanilamideand its dimer were carried out at the B3LYP/6−311++G** levelusing the Gaussian 09 software and PEDs have been calculated using the GAR2PED software. Low temperature Raman spectra enabled to observe some modes which were not resolved at room temperature.The low temperature Raman spectra show splitting of bands around 1135 and 1595 cm−1 which could be associated with the (C)NH2---SO2(NH2) interaction, which is indicative of the existence of sulfanilamide in dimeric form. Based on the present investigation five Quantum Scaling Factors (QSFs) are proposed.These QSFs provide better agreement between the observed and computed scaled frequencies. © 2020 Elsevier B.V.
Vibrational spectra and molecular structure of sulfanilic acid: IR and low temperature Raman studies and DFT investigation of monomeric and dimeric forms
(Elsevier B.V., 2023) Gaurav Srivastav; Rohit Kumar Yadav; Bhoopendra Yadav; R.A. Yadav
Room temperature IR and Raman spectra, low temperature Raman spectra and UV–vis spectrum of sulfanilic acid (SA) were measured. Molecular structures of monomeric SA in the OH and zwitter-ion (ZI) forms and dimeric SA were optimized at the b3lyp/6-311++g** level using the Gaussian 09 software. Computations of APT charges, IR, Raman and UV–vis spectra and related quantities were also carried out. MEP, ESP plots and pictorial representations of the HOMO-LUMO were drawn using the optimized structures of the different forms of the SA molecule. Barrier heights were calculated for different tops using one dimensional potential energy scan versus dihedral angle at the same level of theory. The IR, Raman and UV–vis spectra were interpreted in light of the computed quantities. Thermodynamic functions were computed in the temperature range 100–600 K. Bioactivity scores of the SA molecule were also determined. The present investigation suggests that the SA molecule exists in the ZI form as a monomer and in the OH form as a dimer. Appearance of the intense and broad IR band in the range 2200 to 3300 cm−1 could be explained only in terms of the O[sbnd]H stretching mode of the dimeric form of SA. © 2022