• ANUPAM CHATTERJEE

      Articles written in Journal of Chemical Sciences

    • Salting-out of methane in the aqueous solutions of urea and sarcosine

      M K DIXIT ANUPAM CHATTERJEE B L TEMBE

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      Hydrophobic association and solvation of methane molecules in aqueous solutions of urea and sarcosine(sa) have been studied using MD simulations. The potentials of mean force (PMFs) between methanemolecules in water, water-sa, water-urea and water-urea-sa mixtures show an enhancement of methane associationon the addition of these osmolytes. These observations are well supported by calculation of equilibriumconstants. Calculation of thermodynamic parameters shows that the association of methane is stabilized byentropy and favored by enthalpy. The hydrophobic solvation of methane is stabilized by enthalpy and destabilizedby entropy. The calculated solvation free energies of methane in these mixtures show that methane isless soluble in the mixtures of urea and sarcosine than in water. The solubility is the least in the water-urea-samixture. Analysis of distributions of solvent and co-solvent around methane suggests that the local densities ofboth urea and sarcosine are diminished around the methane in the mixtures of these osmolytes. The selectivereduction of both urea and sarcosine from methane surface suggests that both urea and sarcosine push methanemolecules towards water and increase the interaction between methane molecules i.e., salting-out of methane.

    • Na+ Cl- ion pair association in water-DMSO mixtures: Effect of ion pair model potentials

      ATANU SARKAR ANUPAM CHATTERJEE S C TIWARI B L TEMBE

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      Potentials of Mean Force (PMF) for the Na+ Cl- ion pair in water–dimethyl sulfoxide (DMSO)mixtures for three DMSO mole fractions have been computed using constrained Molecular Dynamics (MD)simulations and confirmed by dynamical trajectories and residence times of the ion pair at various inter-ionicseparations. The three ion-ion direct potentials used are 12-6-1, exp-6-1 and exp-8-6-1. The physical picturethat emerges is that there is a strong contact ion pair (CIP) and strong to moderate solvent separated ion pair(SSIP) in these solutions. Analysis of local ion clusters shows that ions are dominantly solvated by watermolecules. The 12-6-1 potential model predicts running coordination numbers closest to experimental data.

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