A density functional theory evaluation of hydrophobic solvation: Ne, Ar and Kr in a 50-water cluster – Implications for the hydrophobic effect

Abstract

The physical explanation for the hydrophobic effect has been the subject of disagreement. Physical organic chemists tend to use a explanation related to pressure, while many biochemists prefer an explanation that involves decreased entropy of the aqueous solvent. We present DFT calculations at the B3LYP/6-31G(d,p) and X3LYP/6-31G(d,p) levels on the solvation of three noble gases (Ne, Ar, and Kr) in clusters of 50 waters. Vibrational analyses show no substantial decreases in the vibrational entropies of the waters in any of the three clusters. The observed positive free energies of transfer from the gas phase or from nonpolar solvents to water appear to be due to the work needed to make a suitable hole in the aqueous solvent. We distinguish between hydrophobic solvations (explicitly studied here) and the hydrophobic effect that occurs when a solute (or transition state) can decrease its volume through conformational change (which is not possible for the noble gases).

The interactions of phenylalanines in β-sheet-like structures from molecular orbital calculations using density functional theory (DFT), MP2, and CCSD(T) methods

“…We note that the methods used do not reflect the importance of the pressure within the solvent due to the hydrophobic effect upon solvation. The hydrophobic effect results from increased pressure within the solvent 25 consistent with the observed result of alkanes preferring conformations that minimize their volumes in aqueous media. 26 Solvation models do not generally include this effect.…”

Aqueous Solvation of Polyalanine α-Helices with Specific Water Molecules and with the CPCM and SM5.2 Aqueous Continuum Models Using Density Functional Theory

“…Unfortunately, the continuum models, as well as MD models such as TIP3P, do not break the solvation free energy into enthalpic and entropic terms. We have recently noted 67 that the work done by making a hole in water is not taken into account in the early work 68 on hydrophobic solvation, resulting in the overestimation of the entropic effect. Nevertheless, we have included the data for the continuum solvent models, as the data will be of general interest.…”

Near infrared overtone (vOH = 2 ← 0) spectroscopy of Ne–H2O clusters

“…9 Furthermore, weak attractive interactions are now thought to play a critical role in stabilizing pre-reactive complexes in the early stages of a chemical reaction. 10 Such interactions have also been speculated to control the degree of solvation for non-polar hydrophobic molecules in water 11 and thus the propensity to produce clathrates under high pressure conditions. 12 Detailed insights into the intermolecular potential energy surfaces (PESs) associated with these interactions can be obtained via high resolution spectroscopy of strong infrared chromophores such as H 2 O complexed with rare gas atoms for which the "supermolecules" are bound non-covalently by combination of (i) van der Waals attraction between two polarizable species and (ii) dipole-induced dipole interaction between a permanent dipole and a polarizable species.…”