Fourier transform infrared spectroscopy of aqueous dispersions of phosphatidylserine-cholesterol mixtures.

The effect of cholesterol on vibrational spectra in the non polar and in the polar region of dimyristoyl phosphatidylserine (DMPS) and of phosphatidylserine from bovine spinal cord (PS) has been investigated. The small shifts in the methylene CH stretching frequencies after taking into account the contribution of the cholesterol spectrum were interpreted as a combined effect of cholesterol on the conformation of the chains and of the lesser contributions of the cholesterol methyl groups. Cholesterol also influences the ratio of the trans (1465 cm-1) to the lower wavelength (1457 cm-1) CH2 bending bands. No significant direct effect of cholesterol on the vibration of the polar residues was discerned. The small shift of the carboxylate band observed below the phase transition is probably due to the change in the intermolecular zwitterions when the average distance between the neighboring polar groups increases due to incorporation of cholesterol molecules.