"Microscopic probing of the size dependence in hydrophobic solvation"

Huang, N.: D. Schlesinger, D. Nordlund, C. Huang, T. Tyliszczak, T.M. Weiss, Y Acremann, L.G. Pettersson, A. Nilsson ; The Journal of Chemical Physics , 02/21/12.

Additional Authors: D. Schlesinger, D. Nordlund, C. Huang, T. Tyliszczak, T.M. Weiss, Y Acremann, L.G. Pettersson, A. Nilsson

Abstract:

We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (C(n)H(2n+1))(4)N(+) (R(4)N(+)) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 Å, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations.