Constrained molecular dynamics simulations have been performed to investigate the structure and t... more Constrained molecular dynamics simulations have been performed to investigate the structure and thermodynamics of Na+ - Cl- ion-pair association in water-methanol mixtures in supercritical and ambient conditions in dilute solutions. From the computed potentials of mean force (PMFs) we find that contact ion pairs (CIPs) are more stable than all other associated states of the ion pairs in both ambient and supercritical conditions. Stabilities of CIPs increase with increase with the mole fraction of methanol. In supercritical conditions, major changes in PMFs occur as we go from xmethanol = 0.00 to xmethanol = 0.50. The stable solvent shared ion pair (SShIP) which occurs in xmethanol = 0.00 and 0.25, vanishes when xmethanol is 0.50 or greater. The stabilities of these ion pairs increase with increasing temperature. Local structures around the ions are studied using the radial distribution functions, density profiles, angular distribution functions, running coordination numbers and excess coordination numbers. Preferential solvation analysis shows that both Na+ and Cl- ions are preferentially solvated by water. From the calculation of enthalpies and entropies, we find that Na+ - Cl- ion-pair association in water-methanol binary mixtures is endothermic and driven by entropy both in ambient as well as in supercritical conditions.
Constrained molecular dynamics (MD) computer simulations are presented for the solvation of Na+-C... more Constrained molecular dynamics (MD) computer simulations are presented for the solvation of Na+-Cl− ion-pair in supercritical methanol in an isothermal–isobaric ensemble (NPT) to understand the changes in the solvation structure of the ion pair as temperatures and pressures change from ambient to supercritical conditions. Potentials of mean force (PMF) of the Na+-Cl− ion-pair are calculated as a function of temperature and pressure. Contact ion-pair (CIP) is found to be the most stable and dominant in supercritical conditions. Over the temperature and pressure ranges investigated, we observe that methanol molecules retain significant hydrogen bonding. From calculations of energies and entropies through temperature derivatives of PMFs, we have found that Na+-Cl− ion-pair association in supercritical methanol is endothermic and is driven by entropy.
Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures h... more Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures have beenperformedas a functionof salt concentrationandthe compositionofmixtures. Temperaturedependence of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.
Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs... more Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs) of Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs) are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially solvated by DMSO, unlike the water–DMSO mixtures
Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile - dimethyl sulfoxide mixtures... more Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile - dimethyl sulfoxide mixtures have been performed as a function of salt concentration and the composition of mixtures. Temperature dependence of the potential of mean force (PMF) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.
Constrained molecular dynamics simulations have been performed to investigate the structure and t... more Constrained molecular dynamics simulations have been performed to investigate the structure and thermodynamics of Na+ - Cl- ion-pair association in water-methanol mixtures in supercritical and ambient conditions in dilute solutions. From the computed potentials of mean force (PMFs) we find that contact ion pairs (CIPs) are more stable than all other associated states of the ion pairs in both ambient and supercritical conditions. Stabilities of CIPs increase with increase with the mole fraction of methanol. In supercritical conditions, major changes in PMFs occur as we go from xmethanol = 0.00 to xmethanol = 0.50. The stable solvent shared ion pair (SShIP) which occurs in xmethanol = 0.00 and 0.25, vanishes when xmethanol is 0.50 or greater. The stabilities of these ion pairs increase with increasing temperature. Local structures around the ions are studied using the radial distribution functions, density profiles, angular distribution functions, running coordination numbers and excess coordination numbers. Preferential solvation analysis shows that both Na+ and Cl- ions are preferentially solvated by water. From the calculation of enthalpies and entropies, we find that Na+ - Cl- ion-pair association in water-methanol binary mixtures is endothermic and driven by entropy both in ambient as well as in supercritical conditions.
Constrained molecular dynamics (MD) computer simulations are presented for the solvation of Na+-C... more Constrained molecular dynamics (MD) computer simulations are presented for the solvation of Na+-Cl− ion-pair in supercritical methanol in an isothermal–isobaric ensemble (NPT) to understand the changes in the solvation structure of the ion pair as temperatures and pressures change from ambient to supercritical conditions. Potentials of mean force (PMF) of the Na+-Cl− ion-pair are calculated as a function of temperature and pressure. Contact ion-pair (CIP) is found to be the most stable and dominant in supercritical conditions. Over the temperature and pressure ranges investigated, we observe that methanol molecules retain significant hydrogen bonding. From calculations of energies and entropies through temperature derivatives of PMFs, we have found that Na+-Cl− ion-pair association in supercritical methanol is endothermic and is driven by entropy.
Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures h... more Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures have beenperformedas a functionof salt concentrationandthe compositionofmixtures. Temperaturedependence of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.
Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs... more Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs) of Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs) are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially solvated by DMSO, unlike the water–DMSO mixtures
Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile - dimethyl sulfoxide mixtures... more Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile - dimethyl sulfoxide mixtures have been performed as a function of salt concentration and the composition of mixtures. Temperature dependence of the potential of mean force (PMF) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.
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Papers by Sonanki Keshri
ion-pair in supercritical methanol in an isothermal–isobaric ensemble (NPT) to understand the changes
in the solvation structure of the ion pair as temperatures and pressures change from ambient to supercritical conditions. Potentials of mean force (PMF) of the Na+-Cl− ion-pair are calculated as a function of
temperature and pressure. Contact ion-pair (CIP) is found to be the most stable and dominant in supercritical conditions. Over the temperature and pressure ranges investigated, we observe that methanol
molecules retain significant hydrogen bonding. From calculations of energies and entropies through temperature derivatives of PMFs, we have found that Na+-Cl− ion-pair association in supercritical methanol
is endothermic and is driven by entropy.
beenperformedas a functionof salt concentrationandthe compositionofmixtures. Temperaturedependence
of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to
the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt
concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach
a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of
salt and mixture compositions.
Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by
calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs)
are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase
with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination
number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential
solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially
solvated by DMSO, unlike the water–DMSO mixtures
ion-pair in supercritical methanol in an isothermal–isobaric ensemble (NPT) to understand the changes
in the solvation structure of the ion pair as temperatures and pressures change from ambient to supercritical conditions. Potentials of mean force (PMF) of the Na+-Cl− ion-pair are calculated as a function of
temperature and pressure. Contact ion-pair (CIP) is found to be the most stable and dominant in supercritical conditions. Over the temperature and pressure ranges investigated, we observe that methanol
molecules retain significant hydrogen bonding. From calculations of energies and entropies through temperature derivatives of PMFs, we have found that Na+-Cl− ion-pair association in supercritical methanol
is endothermic and is driven by entropy.
beenperformedas a functionof salt concentrationandthe compositionofmixtures. Temperaturedependence
of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to
the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt
concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach
a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of
salt and mixture compositions.
Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by
calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs)
are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase
with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination
number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential
solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially
solvated by DMSO, unlike the water–DMSO mixtures