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Salting-Out of Methane in the Aqueous Solutions of Urea and Glycine-Betaine

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Title Salting-Out of Methane in the Aqueous Solutions of Urea and Glycine-Betaine
 
Creator DIXIT, MK
SIDDIQUE, AK
TEMBE, BL
 
Subject TRIMETHYLAMINE-N-OXIDE
MOLECULAR-DYNAMICS SIMULATIONS
AA FORCE-FIELD
LIQUID-STATE PROPERTIES
HYDROPHOBIC INTERACTIONS
PROTEIN DENATURATION
CONFORMATIONAL-ANALYSIS
ENTROPY CONTRIBUTIONS
UNFOLDED PROTEINS
AMINO-ACIDS
 
Description We have studied the hydrophobic association and solvation of methane molecules in aqueous solutions of urea and glycine betaine (GB). We have calculated the potentials of mean force (PMFs) between methane molecules in water, aqueous GB, aqueous urea and aqueous urea GB mixtures. The PMFs and equilibrium constants indicate that both urea and GB increase the hydrophobic association of methane. Calculation of thermodynamic parameters shows that the association of methane is stabilized by entropy whereas solvation is favored by enthalpy. In the case of the water urea GB mixture, both hydrophobic association and solvation are stabilized by entropy. From the investigation of radial distribution functions, running coordination numbers and excess coordination numbers, we infer that both urea and GB are preferentially excluded from methane surface in the mixtures of osmolytes and methane is preferentially solvated by water molecules in all the mixtures. The favorable exclusion of both urea and GB from the methane surface suggests that both urea and GB increase the interaction between methane molecules, i.e., salting-out of methane. We observe that addition of both urea and GB to water enhances local water structure. The calculated values of diffusion constants of water also suggest enhanced water water interactions in the presence of urea and GB. The calculated free energies of methane in these mixtures show that methane is less soluble in the mixtures of urea and GB than in water. The data on solvation free energies support the observations obtained from the PMFs of methane molecules.
 
Publisher AMER CHEMICAL SOC
 
Date 2016-01-15T06:10:51Z
2016-01-15T06:10:51Z
2015
 
Type Article
 
Identifier JOURNAL OF PHYSICAL CHEMISTRY B, 119(34)10941-10953
1520-6106
http://dx.doi.org/10.1021/acs.jpcb.5b00556
http://dspace.library.iitb.ac.in/jspui/handle/100/17898
 
Language en