Hydration Dynamics of Probes and Peptides in Captivity

Abstract

Water confined on nanometer-length scales is found in many physical and biological environments. Confinement induces special dynamics in liquids, different from that of their bulk counterparts. Reverse micelles, formed by the self-assembly of amphiphilic surfactants in nonpolar solvents, have emerged as an appropriate molecular assembly to monitor the property of water upon confinement due to a number of reasons. A unique advantage of reverse micelles is that molecular dynamics can be monitored with varying states of hydration that is difficult to achieve with assemblies, such as membranes. In this article, we focus on the change in confined hydration dynamics accompanied with increasing hydration, monitored by red edge excitation shift (REES). REES can be effectively used to directly monitor the environment and dynamics around a fluorophore in a molecular assembly utilizing slow solvent relaxation around an excited state fluorophore. It is apparent from the examples discussed that change in solvent relaxation with hydration is complicated and could depend on a number of factors, such as the location of the probe in the reverse micelle and the structure and compactness of the fluorophore involved. We conclude that care should be exercised in interpreting such results.