Magnesium Ion Responses of Zwitterionic Phosphatidylethanolamine Head and Tail Groups Elucidated by Frequency-Resolved SFG-VS.

In the present study, the effects of magnesium ions on the conformational changes of the deuterated 1,2-dimyristoyl- sn -glycero-3-phosphoethanolamine (D 54 -DMPE) monolayer were elucidated by frequency-resolved sum frequency generation vibrational spectroscopy (SFG-VS) and surface pressure-area isotherm measurements. It is found that the tilt angles of the methyl in tail groups decrease, while the tilt angles of the phosphate and methylene in head groups increase during the compression of the DMPE monolayers at both the air/water interface and the air/MgCl 2 solution interfaces. It is also shown that the tilt angle of the methyl in the tail groups slightly decreases, while the tilt angles of the phosphate and methylene in the head groups significantly increase as the MgCl 2 concentration increases from 0 to 1.0 M. These results indicate that both the tail groups and the head groups of the DMPE molecules become closer to the surface normal, as the MgCl 2 concentration increases in the subphase.