Ruchi Kohli - Academia.edu (original) (raw)

Papers by Ruchi Kohli

Research paper thumbnail of Hydrogen bonding ability of hydroxamic acid and its isosteres with water and amino acid side chain groups

Research paper thumbnail of Correlation between proton affinity and conjugation effects in carbamic acid and its higher chalcogenide analogs

Journal of Molecular Structure: THEOCHEM, 2009

The protonation sites and conformations of N-substituted and Y-substituted carbamic acid have bee... more The protonation sites and conformations of N-substituted and Y-substituted carbamic acid have been investigated. The proton affinities of substituted carbamic acid for their chalcogen and nitrogen sites have been evaluated theoretically at the MP2/6-311++G(d,p)//MP2/6-31+G* and B3LYP/6-311++G(d,p)//B3LYP/ 6-31+G* levels. Proton affinity have been correlated with the several contributing factors like charge density, percentage s character and conjugative interactions.

Research paper thumbnail of The role of isomerism and medium effects on stability of anions of formo- and thioformohydroxamic acid

Journal of Molecular Structure: THEOCHEM, 2009

The anionic forms of formo-and thioformohydroxamic acids have been analyzed for their relative st... more The anionic forms of formo-and thioformohydroxamic acids have been analyzed for their relative stabilities and barriers for interconversion between the tautomeric forms employing ab initio and DFT methods. The deprotonation affinities and pK a values are evaluated to differentiate the various deprotonation processes. The effect of medium on deprotonation behavior is analysed using Tomasi's PCM model and examining free energy changes of deprotonation from isolated molecules, molecule-water aggregates and subsequently from anion-water aggregates in the gas phase and aqueous phase respectively. Variation of geometrical parameters, charges, electron delocalizations, intramolecular H-bonding and relative stabilities upon water aggregation of the anions all point towards NAH deprotonation as the most favored process.

Research paper thumbnail of Hydrogen bonding of formo- and thioformohydroxamic acid with methanethiol and methaneselenol as amino acid side chain groups

Structural Chemistry, 2014

Hydrogen (H-) bonding ability of most stable keto and enol tautomers of formo-and thioformohydrox... more Hydrogen (H-) bonding ability of most stable keto and enol tautomers of formo-and thioformohydroxamic acids has been investigated by optimizing their 1:1 aggregates with MeSH and MeSeH as model molecules for sulfur and selenium containing amino acid side chains. Although enol is the most stable conformer of thioformohydroxamic acid, yet the most stable aggregate in both hydroxamic acids (HAs) being formed with keto conformer suggests that H-bonding can influence specific conformational dominance. In the aggregates, HAs preferably act as H-bond donor and S/Se of MeSH and MeSeH act as H-bond acceptor. The SÁÁÁH and SeÁÁÁH H-bonds although disfavored by electrostatics yet are favored by significant charge transfer. H-bonding preference and strength of interaction of HAs with MeSH and MeSeH is remarkably similar but markedly different from MeOH. AIM and NBO analysis have been employed to understand the role of electron delocalization, bond polarizations, charge transfer etc. as contributors to stabilization energy.

Research paper thumbnail of Understanding hydrogen bonding of hydroxamic acids with some amino acid side chain model molecules

Structural Chemistry, 2011

The hydrogen-bonding abilities of a few amino acid side chains have been studied through aggregat... more The hydrogen-bonding abilities of a few amino acid side chains have been studied through aggregation of methylamine, methanol, and acetic acid (as model molecules) with formo- and thioformo- hydroxamic acids using ab initio calculations. Forty six aggregates representing all possible H-bond interactions between these amino acid side chain groups and two most stable keto and enol tautomeric forms of both hydroxamic acids have been optimized. Although participation of conventional H-bond donors and acceptors leads to significant stabilization energies, yet C–H···O, C–H···N, S–H···O, and S–H···N etc. unconventional H-bonds also contribute to stabilize interactions in many aggregates. Strength of H-bonds of the molecules with formo- and thioformo- hydroxamic acid studied follows the order acetic acid > methylamine > methanol. A comparative study of atomic charges and orbital interactions employing NBO analysis has been carried out to explore the role of bond polarizations, charge transfer, and electron delocalizations as contributors to stabilization energy.

Research paper thumbnail of Substituent effect on NH bond dissociation enthalpies of amines and amides: A theoretical study

International Journal of Quantum Chemistry, 2009

NOH bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio-and s... more NOH bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio-and seleno-analogs have been studied employing ab initio and density functional methods. The orbital interactions involving lone pair of electrons on nitrogen and substituent, electrostatic interactions, spin delocalization, and hydrogen bonding are the important factors affecting the stability of the molecule and the radical. The molecule stabilization effect and radical stabilization effect have been calculated using isodesmic reactions in order to analyze the effect of substituent on the stabilization of the molecule and the radical.

Research paper thumbnail of Hydrogen bond cooperativity in dimers of hydroxamic acids

International Journal of Quantum Chemistry, 2010

Research paper thumbnail of A Theoretical Study of Hydrogen-Bonded Complexes of Ethylene Glycol, Thioglycol and Dithioglycol with Water

Asian Journal of Chemistry, 2021

In the present study, a theoretical analysis of hydrogen bond formation of ethylene glycol, thiog... more In the present study, a theoretical analysis of hydrogen bond formation of ethylene glycol, thioglycol, dithioglycol with single water molecule has been performed based on structural parameters of optimized geometries, interaction energies, deformation energies, orbital analysis and charge transfer. ab initio molecular orbital theory (MP2) method in conjunction with 6-31+G* basis set has been employed. Twelve aggregates of the selected molecules with water have been optimized at MP2/6-31+G* level and analyzed for intramolecular and intermolecular hydrogen bond interactions. The evaluated interaction energies suggest aggregates have hydrogen bonds of weak to moderate strength. Although the aggregates are primarily stabilized by conventional hydrogen bond donors and acceptors, yet C-H···O, S-H···O, O-H···S, etc. untraditional hydrogen bonds also contribute to stabilize many aggregates. The hydrogen bonding involving sulfur in the aggregates of thioglycol and dithioglycol is disfavoure...

Research paper thumbnail of Hydrogen bonding ability of hydroxamic acid and its isosteres with water and amino acid side chain groups

Research paper thumbnail of Correlation between proton affinity and conjugation effects in carbamic acid and its higher chalcogenide analogs

Journal of Molecular Structure: THEOCHEM, 2009

The protonation sites and conformations of N-substituted and Y-substituted carbamic acid have bee... more The protonation sites and conformations of N-substituted and Y-substituted carbamic acid have been investigated. The proton affinities of substituted carbamic acid for their chalcogen and nitrogen sites have been evaluated theoretically at the MP2/6-311++G(d,p)//MP2/6-31+G* and B3LYP/6-311++G(d,p)//B3LYP/ 6-31+G* levels. Proton affinity have been correlated with the several contributing factors like charge density, percentage s character and conjugative interactions.

Research paper thumbnail of The role of isomerism and medium effects on stability of anions of formo- and thioformohydroxamic acid

Journal of Molecular Structure: THEOCHEM, 2009

The anionic forms of formo-and thioformohydroxamic acids have been analyzed for their relative st... more The anionic forms of formo-and thioformohydroxamic acids have been analyzed for their relative stabilities and barriers for interconversion between the tautomeric forms employing ab initio and DFT methods. The deprotonation affinities and pK a values are evaluated to differentiate the various deprotonation processes. The effect of medium on deprotonation behavior is analysed using Tomasi's PCM model and examining free energy changes of deprotonation from isolated molecules, molecule-water aggregates and subsequently from anion-water aggregates in the gas phase and aqueous phase respectively. Variation of geometrical parameters, charges, electron delocalizations, intramolecular H-bonding and relative stabilities upon water aggregation of the anions all point towards NAH deprotonation as the most favored process.

Research paper thumbnail of Hydrogen bonding of formo- and thioformohydroxamic acid with methanethiol and methaneselenol as amino acid side chain groups

Structural Chemistry, 2014

Hydrogen (H-) bonding ability of most stable keto and enol tautomers of formo-and thioformohydrox... more Hydrogen (H-) bonding ability of most stable keto and enol tautomers of formo-and thioformohydroxamic acids has been investigated by optimizing their 1:1 aggregates with MeSH and MeSeH as model molecules for sulfur and selenium containing amino acid side chains. Although enol is the most stable conformer of thioformohydroxamic acid, yet the most stable aggregate in both hydroxamic acids (HAs) being formed with keto conformer suggests that H-bonding can influence specific conformational dominance. In the aggregates, HAs preferably act as H-bond donor and S/Se of MeSH and MeSeH act as H-bond acceptor. The SÁÁÁH and SeÁÁÁH H-bonds although disfavored by electrostatics yet are favored by significant charge transfer. H-bonding preference and strength of interaction of HAs with MeSH and MeSeH is remarkably similar but markedly different from MeOH. AIM and NBO analysis have been employed to understand the role of electron delocalization, bond polarizations, charge transfer etc. as contributors to stabilization energy.

Research paper thumbnail of Understanding hydrogen bonding of hydroxamic acids with some amino acid side chain model molecules

Structural Chemistry, 2011

The hydrogen-bonding abilities of a few amino acid side chains have been studied through aggregat... more The hydrogen-bonding abilities of a few amino acid side chains have been studied through aggregation of methylamine, methanol, and acetic acid (as model molecules) with formo- and thioformo- hydroxamic acids using ab initio calculations. Forty six aggregates representing all possible H-bond interactions between these amino acid side chain groups and two most stable keto and enol tautomeric forms of both hydroxamic acids have been optimized. Although participation of conventional H-bond donors and acceptors leads to significant stabilization energies, yet C–H···O, C–H···N, S–H···O, and S–H···N etc. unconventional H-bonds also contribute to stabilize interactions in many aggregates. Strength of H-bonds of the molecules with formo- and thioformo- hydroxamic acid studied follows the order acetic acid > methylamine > methanol. A comparative study of atomic charges and orbital interactions employing NBO analysis has been carried out to explore the role of bond polarizations, charge transfer, and electron delocalizations as contributors to stabilization energy.

Research paper thumbnail of Substituent effect on NH bond dissociation enthalpies of amines and amides: A theoretical study

International Journal of Quantum Chemistry, 2009

NOH bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio-and s... more NOH bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio-and seleno-analogs have been studied employing ab initio and density functional methods. The orbital interactions involving lone pair of electrons on nitrogen and substituent, electrostatic interactions, spin delocalization, and hydrogen bonding are the important factors affecting the stability of the molecule and the radical. The molecule stabilization effect and radical stabilization effect have been calculated using isodesmic reactions in order to analyze the effect of substituent on the stabilization of the molecule and the radical.

Research paper thumbnail of Hydrogen bond cooperativity in dimers of hydroxamic acids

International Journal of Quantum Chemistry, 2010

Research paper thumbnail of A Theoretical Study of Hydrogen-Bonded Complexes of Ethylene Glycol, Thioglycol and Dithioglycol with Water

Asian Journal of Chemistry, 2021

In the present study, a theoretical analysis of hydrogen bond formation of ethylene glycol, thiog... more In the present study, a theoretical analysis of hydrogen bond formation of ethylene glycol, thioglycol, dithioglycol with single water molecule has been performed based on structural parameters of optimized geometries, interaction energies, deformation energies, orbital analysis and charge transfer. ab initio molecular orbital theory (MP2) method in conjunction with 6-31+G* basis set has been employed. Twelve aggregates of the selected molecules with water have been optimized at MP2/6-31+G* level and analyzed for intramolecular and intermolecular hydrogen bond interactions. The evaluated interaction energies suggest aggregates have hydrogen bonds of weak to moderate strength. Although the aggregates are primarily stabilized by conventional hydrogen bond donors and acceptors, yet C-H···O, S-H···O, O-H···S, etc. untraditional hydrogen bonds also contribute to stabilize many aggregates. The hydrogen bonding involving sulfur in the aggregates of thioglycol and dithioglycol is disfavoure...