Sum frequency generation vibrational spectroscopy(SFG-VS)has been demonstrated to be a powerful technique to study the interfacial structures and interactions of biomolecules at the molecular level.Yet most previous studies mainly collected the SFG spectra in the frequency range of 1500–4000 cm-1,which is not always sufficient to describe the detailed interactions at surface and interface.Thorough knowledge of the complex biophysicochemical interactions between biomolecules and surface requires new ideas and advanced experimental methods for collecting SFG vibrational spectra.We introduced some advanced methods recently exploited by our group and others,including(1)detection of vibration modes in the fingerprint region;(2)combination of chiral and achiral polarization measurements;(3)SFG coupled with surface plasmon polaritons(SPPs);(4)imaging and microscopy approaches;and(5)ultrafast time-resolved SFG measurements.The technique that we integrated with these advanced methods may help to give a detailed and high-spatial-resolution 3D picture of interfacial biomolecules.
Dehydration of a surface is the first step for the interaction between biomolecules and the surface. In this study, we systematically investigated the influence of cholesterol analog 6-ketocholestanol(6-KC) on the dehydration of model cell membrane, using sum frequency generation vibrational spectroscopy. In pure DI water environment, two separate dehydration dynamic components were observed in neutrally charged and isotopically labeled 1,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPC) and positively charged 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine(chloride salt)(DMEPC) bilayer: a large-amplitude fast component and a small-amplitude slow component, which originated from the water molecules with a weak and a strong water-membrane bound strengths, respectively. Dehydration of a negatively charged mixed DMPC/DMPG bilayer lead to the membrane-bound water being reorganized to ordered structures quickly. It is evident that the water-membrane bound strengths depend largely on the charge status of the lipid and has an order of neutrally charged membrane<
