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Thermal signature of hydrophobic hydration dynamics

Qvist, Johan LU and Halle, Bertil LU (2008) In Journal of the American Chemical Society 130(31). p.10345-10353
Abstract
Hydrophobic hydration, the perturbation of the aqueous solvent near an apolar solute or interface, is a fundamental ingredient in many chemical and biological processes. Both bulk water and aqueous solutions of apolar solutes behave anomalously at low temperatures for reasons that are not fully understood. Here, we use 2H NMR relaxation to characterize the rotational dynamics in hydrophobic hydration shells over a wide temperature range, extending down to 243 K. We examine four partly hydrophobic solutes: the peptides N-acetyl-glycine-N′-methylamide and N-acetyl-leucine-N′-methylamide, and the osmolytes trimethylamine N-oxide and tetramethylurea. For all four solutes, we find that water rotates with lower activation energy in the hydration... (More)
Hydrophobic hydration, the perturbation of the aqueous solvent near an apolar solute or interface, is a fundamental ingredient in many chemical and biological processes. Both bulk water and aqueous solutions of apolar solutes behave anomalously at low temperatures for reasons that are not fully understood. Here, we use 2H NMR relaxation to characterize the rotational dynamics in hydrophobic hydration shells over a wide temperature range, extending down to 243 K. We examine four partly hydrophobic solutes: the peptides N-acetyl-glycine-N′-methylamide and N-acetyl-leucine-N′-methylamide, and the osmolytes trimethylamine N-oxide and tetramethylurea. For all four solutes, we find that water rotates with lower activation energy in the hydration shell than in bulk water below 255 2 K. At still lower temperatures, water rotation is predicted to be faster in the shell than in bulk. We rationalize this behavior in terms of the geometric constraints imposed by the solute. These findings reverse the classical “iceberg” view of hydrophobic hydration by indicating that hydrophobic hydration water is less ice-like than bulk water. Our results also challenge the “structural temperature” concept. The two investigated osmolytes have opposite effects on protein stability but have virtually the same effect on water dynamics, suggesting that they do not act indirectly via solvent perturbations. The NMR-derived picture of hydrophobic hydration dynamics differs substantially from views emerging from recent quasielastic neutron scattering and pump−probe infrared spectroscopy studies of the same solutes. We discuss the possible reasons for these discrepancies. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of the American Chemical Society
volume
130
issue
31
pages
10345 - 10353
publisher
The American Chemical Society
external identifiers
  • wos:000258080600057
  • scopus:48749129145
ISSN
1520-5126
DOI
10.1021/ja802668w
language
English
LU publication?
yes
id
5a683876-b9de-4247-8019-b649bafc6471 (old id 1227836)
alternative location
http://dx.doi.org/10.1021/ja802668w
date added to LUP
2008-09-05 11:19:47
date last changed
2017-11-19 03:42:30
@article{5a683876-b9de-4247-8019-b649bafc6471,
  abstract     = {Hydrophobic hydration, the perturbation of the aqueous solvent near an apolar solute or interface, is a fundamental ingredient in many chemical and biological processes. Both bulk water and aqueous solutions of apolar solutes behave anomalously at low temperatures for reasons that are not fully understood. Here, we use 2H NMR relaxation to characterize the rotational dynamics in hydrophobic hydration shells over a wide temperature range, extending down to 243 K. We examine four partly hydrophobic solutes: the peptides N-acetyl-glycine-N′-methylamide and N-acetyl-leucine-N′-methylamide, and the osmolytes trimethylamine N-oxide and tetramethylurea. For all four solutes, we find that water rotates with lower activation energy in the hydration shell than in bulk water below 255 2 K. At still lower temperatures, water rotation is predicted to be faster in the shell than in bulk. We rationalize this behavior in terms of the geometric constraints imposed by the solute. These findings reverse the classical “iceberg” view of hydrophobic hydration by indicating that hydrophobic hydration water is less ice-like than bulk water. Our results also challenge the “structural temperature” concept. The two investigated osmolytes have opposite effects on protein stability but have virtually the same effect on water dynamics, suggesting that they do not act indirectly via solvent perturbations. The NMR-derived picture of hydrophobic hydration dynamics differs substantially from views emerging from recent quasielastic neutron scattering and pump−probe infrared spectroscopy studies of the same solutes. We discuss the possible reasons for these discrepancies.},
  author       = {Qvist, Johan and Halle, Bertil},
  issn         = {1520-5126},
  language     = {eng},
  number       = {31},
  pages        = {10345--10353},
  publisher    = {The American Chemical Society},
  series       = {Journal of the American Chemical Society},
  title        = {Thermal signature of hydrophobic hydration dynamics},
  url          = {http://dx.doi.org/10.1021/ja802668w},
  volume       = {130},
  year         = {2008},
}