Fluorescence anisotropy studies on the interaction of the short chain n-alkanols with stratum corneum lipid liposomes (SCLL) and distearoylphosphatidylcholine (DSPC)/distearoylphosphatidic acid (DSPA) liposomes

Abstract

Previously, the action of the short chain n-alkanols (from C1 to C5) and isopropanol as possible enhancers on the transport of lipophilic and polar/ionic permeants across hairless mouse skin was investigated [1–4]. In the present study, the steady-state fluorescence anisotropy was measured as a means of estimating the changes in fluidity caused by the n-alkanols at different depths in the stratum corneum lipid liposomes (SCLL). Some selected experiments with the distearoylphosphatidylcholine (DSPC)/distearoylphosphatidic acid (DSPA) liposomes were performed for relative comparisons. The effects of the n-alkanols on polarity sensitive parameters such as fluorescence lifetimes, fluorescence quantum yield ratios, and emission maxima were studied in the SCLL. The polarity of the bilayer decreased as the fluorescent probe was placed closer to the bilayer center and the n-alkanols did not alter this gradient. Assessment of the depth-dependent effects of the n-alkanols using SCLL showed that most of the significant changes in fluidity induced by the n-alkanols were observed at intermediate depths (C2–C9) and there was little or no increase in fluidity in the deep hydrophobic region close to the bilayer center. These results suggest that the short chain n-alkanols work as effective ‘fluidizing’ agents at the intermediate depths (C2–C9) in the bilayer.