[Raman spectroscopy study on the interaction of ginsenoside Rb1 with DPPC bilayers]

In the present work, the authors studied the interaction of ginsenoside Rh1 with lipid bilayers composed of DPPC using Raman spectroscopy. The conformational changes of DPPC molecule were further revealed by analyzing its vibrational modes such as the C--N stretching mode in the polar head-group region (650-850 cm(-1)), C--C stretching (1000-1200 cm(-1)), and C--H stretching (2750-3000 cm(-1)). The results indicated that there was little influence of Rb1 on the conformation of O--C--C--N+ backbone in the choline group of DPPC bilayers. The polar head group is still extending parallel to the bilayer sur face. The intensity ratios I1096/I1126 and I1096/I1062 represent the gauche/trans ratio. Both of them increased with adding the concentration of Rb1 to DPPC bilayers. The increment of gauche/trans ratio indicates that the disorder/order proportion of the alkyl chains arises. The ordering conformations in lipid chains decreased while the interchain disorder increased. The intensity ratio I2848/I2880 in the region of hydrocarbon chain C--H stretching mode reflects phase transition and has been demonstrated as a sensitive parameter of both inter-chain and intra-chain disorder/order intensity ratio in bilayer alkyl chains. The higher the ratio, the more disordered the hydrocarbon chains. Therefore, the increasing ratio I2848/I2880 with increasing amount of Rb1 indicates that this drug decreases the intermolecular ordering of the lipid lattice, and simultaneously increases the membrane lipid fluidity. In addition, previous study showed that an electrostatic interaction exists between sphingomyelin bilayers and drugs like scopolamine and anisodamine. Compared with those results, the action mode of ginsenoside Rb1 on DPPC bilayers may be because of hydrogen bonds that can be easily formed for the sugar moieties and the hydroxyls in Rb1 molecule. Therefore, the mechanism of drug action on DPPC bilayers may be resulting from the intra or inter hydrogen bonds and the head-group hydrophilic region of the DPPC membrane.