Analysis of Cooperativity and Group Additivity in the Hydration of 1,2-Dimethoxyethane

Abstract

We calculate hydration free energies of 1,2-dimethoxyethane (DME) conformations in water at 298 K and 1 bar. We find that the preference for the two most abundant tgt and tgg conformations derives from favorable nonspecific (i.e., long-range) solute–water interactions that are partially offset by unfavorable free energies of forming cavities in water to accommodate these conformations. The much lower population of the third most abundant tg + g – conformation, the most abundant conformation in the ideal gas at 298 K, is attributed to less favorable long-range solute–water interactions. We also find that long-range methyl/methylene group–water and ether oxygen–water interactions make significant nonadditive contributions to the free energy of DME hydration and propose a method based on quasichemical theory for reducing these nonadditive contributions by identifying constituent groups of DME that minimize the covariance in the long-range methyl/methylene group–water and ether oxygen–water interactions. We apply this method to show that the decomposition of DME into its constituent dimethyl ether groups is a better approximation of group additivity than decompositions based on distinguishing hydrophobic/hydrophilic constituent groups.

Thermodynamics of Hydration from the Perspective of the Molecular Quasichemical Theory of Solutions

“…21,25,27,28,39 These solutes span a diversity of chemical complexity ranging from those that chemically interact with water 5,6,12−14,43−45 to cases where specific chemical bonding may be ignored but one still needs to consider strong short-range interactions, 4,9,16,16,36,37,41,[46][47][48][49]52 to prototypical hydrophobes, 39,40,42 and to solutes which are heterogeneous in terms of their chemical composition. 21−25,27,28,39, 54 The theory has been used to enhance the interpretation of ab initio simulations 6,18,38,41,[44][45][46]50 which are necessarily limited to short time scales, small system sizes, and the inherent limitation of the underlying electron density functionals. The theory has also been used to study nonaqueous systems such as hard-sphere fluids 35,55 and mixed solvents, 56 and for suggesting ways to incorporate multibody effects in the description of associating patchycolloids.…”

“…This cooperativity of hydration can also be seen by analyzing binding energy distributions. 22,24,54 The correlation contributions are relatively constant, and it is this feature that masks the breakdown of additivity! Temperature Dependence of Hydration Free Energies.…”

“…The quasichemical approach sketched above and its further specializations have been used to probe the structure and thermodynamics underlying the hydration of monatomic solutes, − ,,− ,,,− water, ,,,,,− small multiatomic solutes, ,, short peptides, , and longer peptides and macromolecules. ,,,, These solutes span a diversity of chemical complexity ranging from those that chemically interact with water ,,− ,− to cases where specific chemical bonding may be ignored but one still needs to consider strong short-range interactions, ,,,,,,,− , to prototypical hydrophobes, ,, and to solutes which are heterogeneous in terms of their chemical composition. − ,,,, The theory has been used to enhance the interpretation of ab initio simulations ,,,,− , which are necessarily limited to short time scales, small system sizes, and the inherent limitation of the underlying electron density functionals. The theory has also been used to study nonaqueous systems such as hard-sphere fluids , and mixed solvents,…”

Thermodynamics of Hydration from the Perspective of the Molecular Quasi-Chemical Theory of Solutions

“…21,25,27,28,39 These solutes span a diversity of chemical complexity ranging from those that chemically interact with water, 5,6,[12][13][14][43][44][45] to cases where specific chemical bonding may be ignored but one still needs to consider strong short-range interactions, 4,9,16,16,36,37,41,[46][47][48][49]52 to prototypical hydrophobes, 39,40,42 and to solutes which are heterogenous in terms of their chemical composition. [21][22][23][24][25]27,28,39,54 The theory has been used to enhance the interpretation of ab initio simulations 6,18,38,41,[44][45][46]50 which are necessarily limited to short time scales, small system sizes, and the inherent limitation of the underlying electron density functionals. The theory has also been used to study nonaqueous systems such as hard-spher...…”

“…This cooperativity of hydration can also be seen by analysing binding energy distributions. 22,24,54 The correlation contributions are relatively constant, and it is this feature that masks the breakdown of additivity! Table 1: Correlation contributions to the net chemical plus packing contribution.…”