화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.116, No.5, 1687-1699, 2012
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.