Femtosecond study of the effects of ions and hydrophobes on the dynamics of water

被引:1
作者
van der Post, Sietse T. [1 ]
Tielrooij, Klaas-Jan [1 ]
Hunger, Johannes [1 ]
Backus, Ellen H. G. [1 ]
Bakker, Huib J. [1 ]
机构
[1] FOM Inst AMOLF, Amsterdam, Netherlands
关键词
HYDROGEN-BOND DYNAMICS; ULTRAFAST INFRARED-SPECTROSCOPY; DILUTE AQUEOUS-SOLUTIONS; LIQUID WATER; DIELECTRIC-SPECTROSCOPY; GUANIDINE-HYDROCHLORIDE; PROTEIN DENATURATION; HYDRATION SHELL; REORIENTATION; UREA;
D O I
10.1039/c2fd20097j
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We study the effects of ions and hydrophobic molecular groups on the orientational dynamics of water using THz dielectric relaxation (THz-DR) and polarization-resolved femtosecond infrared (fs-IR) pump-probe spectroscopy. We measure the dynamics of water in solutions of NaI, NaCl, CsCl, guanidinium chloride (GndCl) and tetramethyl guanidinium chloride (TMGndCl) of different concentrations. With THz-DR we observe that strongly hydrated cations align the static dipoles of their surrounding water molecules. With fs-IR we find that the OD groups that form hydrogen bonds to halide anions reorient with two distinct time constants of 2 +/- 0.3 ps and 9 +/- 1 ps. The fast process is assigned to a wobbling motion of the OD group that keeps the hydrogen bond with the anion intact. The amplitude of this wobbling motion depends on the nature of both the anion and the counter cation. The replacement of four of the six hydrogen atoms of the weakly hydrated cation guanidinium by hydrophobic methyl groups leads to an exceptionally strong slowing down of the water dynamics. Hydrophobic groups thus appear to have a much stronger effect on the dynamics of water than ions. These findings give new insights in the mechanism of protein denaturation by GndCl and TMGndCl.
引用
收藏
页码:171 / 189
页数:19
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