Abstract
The effect of metal ions on the solution state of phospholipids was investigated by means of an attenuated total reflection fourier transform infrared (ATR-FTIR) spectroscopy. Two peaks corresponding to symmetric and asymmetric stretching vibrations of the methylene groups (hy drophobic groups) in phospholipid molecules were recognized independent of the kind of phospholipids and of solution state (gel and liquid crystal states). When calcium ion was added in L-α-dipalmitoylphosphatidylglycerol (DPPG) systems, the peak corresponding to the asymmetric stretching mode of the methylene groups at 70°C shifted to lower wavenumbers with increasing molar ratios of the metal ion, which is due to the phase transition from liquid crystal state to gel state. Meanwhile, the addition of metal ions resulted in a dehydration of the phosphate groups (hydrophilic groups) in DPPG molecules. Dehydration caused by the addition of metal ions was in the order calcium ion>magnesium ion>barium ion. It is found that the addition of metal ions resialts in an increase in the dehydration of the phosphate groups and the depression of fluidity in the methylene groups in acidic phospholipid (DPPG) molecules.
