Study of intra- and intermolecular hydrogen-bonding interaction and excited state proton transfer reaction has been carried out in 4-hydroxyacridine (4-HA) and its hydrated clusters theoretically. Density functional theory [B3LYP/6-311++G(d,p)] has been exploited to calculate structural parameters and relative energies of different conformers of 4-HA and its hydrates. The substantial impact of solvent reaction field on hydrogenbond energies, conformational equilibrium, and tautomerization reaction in aqueous medium have been realized by employing Onsager and PCM reaction field methods, and the stability of the conformers of 4-HA is found to be profusely modulated by the electrostatic influence of the solvent. A deeper insight into the nature of H-bonding in 4-HA and its hydrated clusters has been achieved under the provision of natural bond orbital and atoms in molecule analysis. Elucidation of potential energy curves for proton transfer reaction reveals that an intrinsic and two-water-molecule-assisted proton transfer (PT) reaction in 4-HA is hindered by high energy barrier in the Si surface, whereas single-water-assisted PT reaction is practically rendered barrierless. At the same time, the appreciably high barrier height of the ground state potential energy curve in all the cases unambiguously rules out the possibility of ground state proton transfer reaction. © 2010 American Chemical Society.

NIKHIL GUCHHAIT

Chemistry

B K PAUL

S MAHANTA

R B SINGH

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of Physical Chemistry A

Density functional theory based computational study has been performed to characterize intramolecular hydrogen bonding (IMHB) interaction in a series of salicylic acid derivatives varying in chlorine substitution on the benzene ring. The molecular systems studied are salicylic acid, 5-chlorosalicylic acid, 3,5-dichlorosalicylic acid and 3,5,6-tricholorosalicylic acid. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point using atoms-in-molecule theory. Topological features, energy densities based on ρ(r) through perturbing the intramolecular H-bond distances suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of covalent interaction. The interplay between aromaticity and resonance-assisted hydrogen bonding (RAHB) is discussed using both geometrical and magnetic criteria as the descriptors of aromaticity. The optimized geometry features, molecular electrostatic potential map analysis are also found to produce a consensus view in relation with the formation of RAHB in these systems. © 2012 Elsevier B.V. All rights reserved.

Chemical Physics

Geometrical criteria versus quantum chemical criteria for assessment of intramolecular hydrogen bond (IMHB) interaction: A computational comparison into the effect of chlorine substitution on IMHB of salicylic acid in its lowest energy ground state confor

In the present contribution Density Functional Theory (DFT) has been applied to explore molecular dipole moment, frontier molecular orbital (FMO) features, chemical hardness, and the molecular electrostatic potential surface (MEPS) characteristics for optimized molecular geometry of the Green Fluorescent Protein (GFP) chromophore p-hydroxybenzylideneimidazolinone (HBDI) both in its protonated (neutral) and deprotonated (anion) forms. The distribution of atomic charges over the entire molecular framework as obtained from Natural Bond Orbital (NBO) analysis is found to faithfully replicate the predictions from the MEP map in respect of reactivity map of HBDI (neutral and anion) and possible sites for hydrogen bonding interactions etc. The three dimensional MEP map encompassing the entire molecule yields a reliable reactivity map of HBDI molecule also displaying the most probable regions for non-covalent interactions. The differential distribution of the electrostatic potential over the neutral and anionic species of HBDI is authentically reflected on MEP map and NBO charge distribution analysis. Thermodynamic properties such as heat capacity, thermal energy, enthalpy, entropy have been calculated and the correlation of the various thermodynamic functions with temperature has been established for neutral molecule. More importantly, however, the computational approach has been employed to unveil the nonlinear optical (NLO) properties of protonated (neutral) and deprotonated (anion) HBDI. Also in an endeavor to achieve a fuller understanding on this aspect the effect of basis set on the NLO properties of the title molecule has been investigated. Our computations delineate the discernible differences in NLO properties between the neutral and anionic species of HBDI whereby indicating the possibility of development of photoswitchable NLO device. © 2012 Elsevier B.V. All rights reserved.

Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

Looking at the green fluorescent protein (GFP) chromophore from a different perspective: A computational insight

Density functional theory (DFT) based computational study has been performed to characterize intramolecular hydrogen bonding (IMHB) interaction in a series of salicylic acid derivatives having different halogen substitution at the 5-position on the benzene ring. The molecular systems studied are salicylic acid (SA), 5-fluorosalicylic acid (5FSA), 5-chlorosalicylic acid (5ClSA) and 5-bromosalicylic acid (5BrSA). Particular emphasis has been given on the analysis of IMHB interaction by the calculation of electron density ρ(r) and Laplacian ∇;2ρ(r) at the bond critical point using Atoms-In-Molecule (AIM) theory. Topological features and energy densities based on ρ(r) through the perturbation of the IMHB distances suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of a covalent interaction. Concomitantly, the role of charge transfer interaction in the IMHB has been critically addressed under the provision of Natural Bond Orbital (NBO) analysis. The formation of Resonance Assisted Hydrogen Bond (RAHB) in the studied molecular systems is also delineated from quantum chemical calculations. The interplay between aromaticity and RAHB is discussed in this context using both geometrical and magnetic criteria as the aromaticity descriptors. The optimized geometry features, analysis of the molecular electrostatic potential map have also been found to produce a consensus view in relation with the formation of RAHB in the studied systems. The lack of a specific pattern of IMHB energy in the studied molecules with the electronegativity of the substituent has also been attempted to address critically. Another major aspect of the present study is the argument about the superiority of quantum chemical criteria over geometrical criteria for the assessment of IMHB interaction in the studied compounds. © 2013 Elsevier B.V.

Computational and Theoretical Chemistry

A computational acumen into the relative applicability of geometrical and quantum chemical criteria in assessing intramolecular hydrogen bonding (IMHB) interaction: 5-Halosalicylic acids as representative examples

Photophysical properties of an anthracene derivative 9-methyl anthroate (9-MA) have been investigated using absorption and emission spectroscopy, in combination with quantum chemical calculations. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the highly polar character of the excited state, which is also supported by the enhancement of dipole moment of the molecule upon photoexcitation. The emission band has been found to be dependent on polarity and hydrogen-bonding ability of the solvents. Multiple linear regression analysis method has been utilized to rationalize the effect of hydrogen bonding interaction on the emissive state, which was further confirmed by the analysis of the non-radiative decay constants and urea induced H-bonding disruption study. The experimental results correlate well with theoretical predictions obtained via density functional theory (DFT). © 2013 Elsevier B.V. All rights reserved.

Solvent modulated photophysics of 9-methyl anthroate: Exploring the effect of polarity and hydrogen bonding on the emissive state

A Density Functional Theory (DFT)-based quantum chemical computational study has been carried out to characterize the intramolecular hydrogen bonding (IMHB) interaction in a potent bio-active drug molecule viz., 2-acetylindan-1,3-dione (2-AID). The IMHB interaction has been explored by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the Bond Critical Point (BCP) using Atoms-In-Molecule (AIM) theory. Topological features, energy densities provided by AIM theory are calculated with ρ(r) for a number of intramolecular H-bond distances. The results suggest that at equilibrium geometry the IMHB interaction in the molecule develops certain characteristics typical of covalent interaction. The role of hyperconjugative charge transfer interaction in the IMHB has been critically evaluated and addressed under the provision of Natural Bond Orbital (NBO) analysis. The study also pays proper attention to an important feature of IMHB interaction, namely the directional nature, within the NBO framework in a consensus manner. Simulated IR spectra also provide reinforcing evidence for IMHB interaction on the basis of OH stretching frequency shift. The optimized geometry features, molecular electrostatic potential (MEP) map analysis are also found to produce a consensus view in relation with the formation of IMHB in 2-AID. © 2013 Elsevier B.V.

Journal	Journal of Physical Chemistry A
Publisher	AMER CHEMICAL SOC
ISSN	1089-5639
Open Access	No