Molecular interactions between sphingomyelin and phosphatidylcholine in phospholipid vesicles.

The molecular interactions between DPPC and sphingomyelin have been examined using differential scanning calorimetry and Fourier transform infrared spectroscopy (FT-IR). It has been observed using DSC that the mixtures of DPPC and sphingomyelin show a single peak, which indicates that they are very miscible. It has been shown, by means of FT-IR, that the incorporation of sphingomyelin into DPPC does not modify the gauche/all-trans ratio at temperatures either above or below that of the phase transition. However, the librational motion of the fatty acyl chains was affected, although only above the phase transition. Mixing sphingomyelin and DPPC induced a conformational change in the polar region of DPPC, as deduced from the changes observed in the frequencies of the sn-1 and sn-2 C = O groups of DPPC with relation to pure DPPC and also in the polar region of sphingomyelin as deduced from the change in the frequency of the amide band. The phosphate group of sphingomyelin was observed to participate in hydrogen bonds between the molecules of sphingomyelin and, possibly, DPPC. Some possibilities of the interaction between the molecules of DPPC and sphingomyelin are discussed.