FT infrared and Raman investigation of saccharide-phosphatidylcholine interactions using novel structure probes

Conformational consequences of adduct formation between saccharides (trehalose, glucose, raffinose) and sorbitol with dipalmitoylphosphatidylcholine (DPPC) in multibilayers are revealed by relative intensity changes of the band components corresponding to the nu asN(CH3)3 and nu sC-N(CH3)3 stretching modes of the choline chain terminal and those of the nu C = O band. The conformational sensitivity of those modes was demonstrated previously (J. Grdadolnik et al., Chem. Phys. Lipids 65 (1993) 121) and used to demonstrate the effects of stepwise hydration of phosphatidylcholines. The latter are compared with the effects of saccharide binding and found to be qualitatively similar, but not identical. The same is true of the low frequency shifts of the nu asPO2- vibration: the shifts due to saccharide binding correspond to the binding of six to seven water molecules per phosphate which is about 20 cm-1 less than the shift caused by full hydration. A particularly interesting finding concerns the appearance of two bands in the nu asPO2- region of the DPPC-saccharide adducts. The relative intensities of the two bands (1243 and 1223 cm-1) change on additional hydration; it is the one at 1223 cm-1 that prevails at high hydration levels. Major changes in saccharide conformation are not detectable but minor differences between the DPPC bound and crystal spectra are observed.