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| - Identification of Lipid Aggregate Structures on TiO2 Surface Using Headgroup IR Bands
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| - Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was used to study the natureof the dipalmitoylphosphatidylcholine (DPPC) aggregated structures adsorbed on TiO2. DPPC molecules wereassembled on TiO2 using Langmuir−Blodgett (LB) deposition methods or by directly flowing the DPPCliposome solution across the TiO2-coated ATR crystal. We found that there is a direct correlation betweenthe intensity and frequency position of the zwitterionic headgroup IR bands and the nature of LB films.Specifically, we have shown that the bands due to PO2- modes are sensitive to changes in the degree ofhydration of the LB films and that the symmetric deformation vibrational mode (δs+N−CH3) is sensitive tointeraction with oppositely charged surface sites. Using this information, we found that the liposomes adsorbedon TiO2 remain intact as vesicles and that the vesicles are stable and not removed in flowing water. We havealso shown that the antisymmetric deformation vibrational (δas+N−CH3) modes are sensitive to changes inlateral−lateral DPPC interactions. This information was used to show that there is a lateral interaction betweeneach positively charged +N(CH3)3 headgroup and negatively charged PO2- headgroup of the adjacent DPPCmolecule in the adsorbed vesicles and LB films. This study provides a framework for the use of this IRtechnique in studies of adsorption and transport of molecules across membrane interfaces.
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