Solute-solvent contact by intermolecular cross relaxation. I. The nature of the water-hydrophobic interface.

J Chem Phys

Division of Physical Chemistry and Industrial NMR Center, Department of Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden.

Published: August 2006

Intermolecular cross-relaxation rates between solute and solvent were measured by {1H} 19F nuclear magnetic resonance experiments in aqueous molecular solutions of ammonium perfluoro-octanoate and sodium trifluoroacetate. The experiments performed at three different magnetic fields provide frequency-dependent cross-relaxation rates which demonstrate clearly the lack of extreme narrowing for nuclear spin relaxation by diffusionally modulated intermolecular interactions. Supplemented by suitable intramolecular cross-relaxation, longitudinal relaxation, and self-diffusion data, the obtained cross-relaxation rates are evaluated within the framework of recent relaxation models and provide information about the hydrophobic hydration. In particular, water dynamics around the trifluoromethyl group in ammonium perfluoro-octanoate are more retarded than that in the smaller trifluoroacetate.

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http://dx.doi.org/10.1063/1.2336199DOI Listing

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