CrossRef enabled

PAC Archives

Archive →

Pure Appl. Chem., 2013, Vol. 85, No. 1, pp. 53-60

Published online 2012-08-31

Hydrophobicity with atomic resolution: Steady‑state and ultrafast X-ray absorption and molecular dynamics studies

Thomas J. Penfold1,2,3, Christopher J. Milne2, Ivano Tavernelli1 and Majed Chergui2*

1 Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Chimie et Biochimie Computationnelles, ISIC, FSB-BSP, CH-1015 Lausanne, Switzerland
2 Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, ISIC, FSB-BSP, CH-1015 Lausanne, Switzerland
3 Paul-Scherrer-Institut, CH-5232 Villigen, Switzerland

Abstract: Static and time-resolved X-ray absorption spectroscopy (XAS) is used to probe the solvent shell structure around iodide and iodine. In particular, we characterize the changes observed upon electron abstraction of aqueous iodide, which reflects the transition from hydrophilic to hydrophobic solvation after impulsive electron abstraction from iodide. The static spectrum of aqueous iodide, which is analyzed using quantum mechanical/molecular mechanics (QM/MM) molecular dynamics (MD) simulations, indicates that the hydrogens of the closest water molecules point toward the iodide, as expected for hydrophilic solvation. In addition, these simulations demonstrate a small anisotropy in the solvent shell. Following electron abstraction, most of the water molecules move away from iodine, while one comes closer to form a complex with it that survives for 3–4 ps. This lifetime is governed by the reorganization of the main solvation shell, basically the time it takes for the water molecules to reform a hydrogen bond network in the hydrophobic solvation shell.