Water gradient in the membrane-water interface: a time-resolved study of the series of n-(9-anthroyloxy) stearic acids incorporated in AOT/water/iso-octane reverse micelles.
The water radial distribution in AOT/iso-octane/water reverse micelles (RM), used to mimic the membrane-water interface, was examined by excited-state lifetime and transient spectral measurements of the series of n-(9-anthroyloxy) stearic acids (n-AS), with n = 2, 3, 6, 7, 9, 10, and 12. A water gradient in the RM extended from the polar head group region up to the middle of the surfactant carbon chains. A fast intramolecular excited-state relaxation, involving the rotation of the carboxylic group of the ester bond with respect to the anthracene ring, gave rise to a nanosecond time-dependent fluorescence Stokes shifts (TDFSS). In water-filled RMs, we only observed a water-induced TDFSS occurring over subnano- and nanosecond time scales with decreasing amplitudes and rates as a function of depth, according to the decreasing water gradient and the slowing down of the anthroyloxy moiety rotational motion. This water-induced TDFSS is most likely the result of both H-bond formation and general dipolar relaxation, as indirectly showed by measurements with DMF (a nonprotic polar solvent) instead of water in RMs.
Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université Paris-Sud, UMR 8619-CNRS, F-91405 Orsay, France. mevincent94@yahoo.fr
Michel
M
Vincent
Jacques
J
Gallay
D008823:Micelles; D008958:Models, Molecular; D009795:Octanes / Q000737:chemistry*; D013229:Stearic Acids / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
D008823:Micelles; D009795:Octanes; D013229:Stearic Acids; D014867:Water; C026728:octane