Impact of Structural Differences in Galactocerebrosides on the Behavior of 2D Monolayers

Abstract

The molecular interactions of three biologically important galactocerebrosides have been studied in monolayers formed at the soft air/water interface as 2D model membranes. Highly surface-sensitive techniques as GIXD (grazing incidence X-ray diffraction), IRRAS (infrared reflection absorption spectroscopy), and BAM (Brewster angle microscopy) have been used. The study reveals that small differences in the chemical structure have a relevant impact on the physical chemical properties and intermolecular interactions. The presence of a 2-D-hydroxyl group in the fatty acid favored for GalCer C24:0 (2-0H) monolayers a higher hydration state of the headgroup at low lateral pressures (<25 mN/m) and a higher condensation effect above 30 mN/m. An opposite behavior was recorded for GalCer 024:0 and GalCer C24:1, for which the intermolecular interactions are defined by the weakly hydrated but strong H-bonded interconnected head groups. Additionally, the 15-cis-double bond in the fatty acid chain (nervonic acid) of GalCer C24:1 stabilized the LE phase but did not disturb the packing parameters of the LC phase as compared with the saturated compound GalCer C24:0.