• Nikhil Guchhait

      Articles written in Journal of Chemical Sciences

    • Some spectroscopic studies on cold isolated molecules

      Mihir Chowdhury Nikhil Guchhait

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      Cold isolated molecules produced in seeded supersonic jets are ideal systems for obtaining information on the nature of potential energy surfaces of excited states. The power of the technique is illustrated with examples of molecules having one or two out-of-plane low-frequency vibrations.

    • Benzyl alcohol-ammonia (1:1) cluster structure investigated by combined IR-UV double resonance spectroscopy in jet andab initio calculation

      Nikhil Guchhait

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      Laser-induced fluorescence excitation and IR-UV double resonance spectroscopy have been used to determine the hydrogen-bonded structure of benzyl alcohol-ammonia (1:1) cluster in a jet-cooled molecular beam. In addition,ab initio quantum chemical calculations have been performed at HF/6-31G and HF/6-31G(d,p) levels for different ground state equilibrium structures of the cluster to correlate the calculated OH and NH frequencies and their intensities with experimental results. The broad red-shifted OH-stretching mode in the IR-UV double resonance spectrum suggests strong hydrogen bonding between the hydroxyl hydrogen and the lone pair of the ammonia nitrogen. The position and intensity distribution of the calculated NH and OH modes for the minimum-energy gauche form at HF/6-31G level have better correlation with the experimental results compared to other calculated ground state equilibrium conformers. These results lead to the conclusion that the minimum energy gauche form of the cluster is populated in the jet-cooled condition.

    • Partitioning of methyl internal rotational barrier energy of thioacetaldehyde

      Nikhil Guchhait

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      The nature of methyl internal rotational barrier in thioacetaldehyde has been investigated by relaxation effect, natural bond orbital (NBO) analysis and Pauling exchange interactions. The true experimental barrier can be obtained by considering fully relaxed rotation. Nuclear-electron attraction term is a barrier forming term in the fully relaxed rotation, but it appears as an antibarrier for rigid rotation. It is seen that during methyl rotation, the torsional mode is coupled with the aldehydic hydrogen out-of-plane wagging motion. Natural bond orbital analysis shows that the principal barrier forming term originates from the C-C bond. The lengthening of the C-C bond is explained by considering charge transfer interaction between several bonding and antibonding orbitals in the C-C bond region, which leads to higher bonding overlap for the eclipsed conformer compared to the staggered conformer. S-C(σ)/Cme-Hp and C-Hald/Cme-Hop interactions appear to be the main barrier-forming Pauling exchange terms but have less contribution to make to the barrier compared to the C-C bond interaction.

    • Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensedphase and jet-cooled molecular beams

      Amrita Chakraborty Samiran Kar D N Nath Nikhil Guchhait

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      Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge transfer emission. Laser-induced fluorescence excitation spectra show the presence of two low-energy conformers in jet-cooled molecular beams. Theoretical calculations using density functional theory help to determine structure, vibrational modes, potential energy surface, transition energy and oscillator strength for correlating experimental findings with theoretical results.

    • How does fatty acid influence anti-thyroid drugs binding and specificity toward protein human serum albumin? A blind docking simulation study

      Bijan K Paul Nikhil Guchhait

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      This study reports an AutoDock-based blind docking simulation investigation to characterize the binding interaction of a series of anti-thyroid drugs (2-mercapto-1-methylimidazole (MMI), 2-thiouracil (TU), 6-methyl-2-thiouracil (MTU), 6-𝑛-propyl-2-thiouracil (PTU) with a model plasma protein Human SerumAlbumin (HSA) in the presence and absence of fatty acid (FA). The drug-protein binding efficiency is characterized in terms of binding free energy and the association constant (Ka, which is estimated as the reciprocal of the inhibition constant, Ki) of the drugs to the transport protein. The study also unveils the substantial impact of the presence of fatty acid (FA) on the binding interaction process. It is shown that in the presence of FA the drug-protein binding efficiency is markedly enhanced (except for MTU) and the binding location is changed. Hydrogen bonding interaction appears to play a governing role in the process of FA-induced modifications of binding efficiency and location.

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