Abstract
Temperature-dependent Fourier transform infrared spectra of polyion-complexed synthetic lipid films of dioctadecyl dimethyl ammonium poly(styrene sulfonate), dihexadecylglutamate poly(styrene sulfonate) and two other glutamate-based and diethanolamine-based lipids with a long spacer chain were measured in air and compared with those of liposomal and synthetic bilayer membranes. The antisymmetric CH2 stretching band of the films showed strong phase transition dependence, indicating that the fundamental conformational changes associated with the phase transition of the lipid films are close to those of aqueous bilayer membranes. However, the films displayed some differences in the spectra; the symmetric CH2 stretching and carbonyl(ester) stretching band of the films of the glutamate-based lipids did not exhibit phase transition dependence, in sharp contrast with the results of aqueous bilayer systems. This may be due to the retention of higher ordering in the long alkyl chain even at temperatures above the phase transition.
