FTIR spectroscopic analysis of the amide and acid bands of ganglioside G M1, in pure form and in mixtures with DMPC

Abstract

The amide I bands of sphingolipids show complicated patterns due to intra- and intermolecular interactions via hydrogen bonds. In order to assign the amide I absorption bands of the ganglioside G M1 to the different amide groups in the headgroup and back bone, the compounds N-acetylgalactosamine, N-acetylneuraminic acid, glucocerebroside and ceramide III were examined as reference systems. The frequencies of the COOH and COO − bands of the sialic acid-residue of G M1 were determined by pH-titration and were found to absorb at 1729 cm −1 and 1605 cm −1, respectively. In D 2O the three amide groups of G M1 give one broad absorption band at 1627 cm −1, whereas in the glucocerebroside intra- and intermolecular interactions of the amide group give rise to three distinct amide I bands. For a solid sample of G M1 in KBr also one broad band was observed in the amide I region. We also studied the influence of the ganglioside G M1 on model membranes of DMPC as host lipid. The change of the CH 2 stretching vibrational absorption bands as a function of temperature reveal that addition of G M1 to DMPC leads to increased phase transition temperatures T m with increasing ganglioside content. No Ca 2+ binding to the COO − group of G M1 was observed.