Spectroscopic Studies of Model Biological Membranes in Vesicles and Langmuir−Blodgett Films

Fourier transform infrared spectroscopic analyses of egg phosphatidylcholine have been undertaken for the solution state for unilamellar vesicles, for films cast from chloroform, and for Langmuir−Blodgett films. These showed that the phospholipid chains of the vesicles have a high proportion of gauche conformations but that both the chains and the head groups show evidence of alignment in an “ordered” environment. Both the head group and a proportion of the ester carbonyl groups are hydrated and published evidence of a trans/gauche population distribution (at the COC group) has been confirmed. Previous contradictory interpretations of the COC conformation have been reconciled. There is clear evidence of water associated with the lipid when it is cast either from chloroform or from a vesicle solution. The incorporation of alamethicin into (Z-type) LB bilayers has been successfully achieved, and evidence of strong lipid head group/peptide interactions has been found. The peptide conformation appears to be unchanged while the lipid chains retain their essentially all-trans configuration. There is some evidence that the incorporation level is lower than the initial mixture content, at least under some dipping conditions, and that peptide aggregation is not extensive.