DNA-Induced Reorganization of Water at Model Membrane Interfaces Investigated by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy

Lipid-DNA complexes are important nonviral vectors to be used in gene therapy, which is one of the promising strategies for the cure of many diseases. Although interfacial water is expected to play a significant role in lipid-DNA complexation, a molecular-level understanding about the role of interfacial water in the DNA-lipid complexation is still sparse. In this study, the structure and orientation of water at cationic and zwitterionic lipid monolayer/water interfaces in the presence of DNA are studied by the use of interface-selective heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. It is found that the adsorption of DNA at a cationic lipid interface drastically decreases the orientation of interfacial water reflecting the neutralization of the positively charged interface, whereas the adsorption of DNA at a zwitterionic lipid interface makes interfacial water become more "H-up", indicating that the originally zwitterionic interface becomes negatively charged due to the DNA adsorption. Furthermore, interfacial water having relatively strong hydrogen bonds is observed at both the cationic and zwitterionic lipid interfaces in the presence of DNA.