Assessing the molecular structure of alkanethiol monolayers in hybrid bilayer membranes with vibrational spectroscopies

Hybrid bilayer membranes (HBMs), consisting of a lipid monolayer covering a self-assembled alkanethiol monolayer on a metal surface, are useful models for studying the structure and function of cell membranes. Surface-enhanced Raman spectroscopy (SERS) and reflection absorption infrared spectroscopy (RAIRS) are used to study HBMs with various alkanethiol and lipid components. Together, these two techniques clearly indicate that the lipid forms a well-ordered, non-interdigitated layer on the alkanethiol with the head groups of the lipids oriented away from the metal surface. Both techniques reveal that the formation of an HEM produces small changes in the alkanethiols, which are similar to those caused by a reduction in temperature, indicative of an increase in order. The small magnitude of the perturbations in the alkanethiol monolayer upon addition of the lipid layer will simplify the further study of HBMs.