Molecular recognition mechanism on biomembrane surface in primary biological functioning

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Microscopic structure and thermodynamic approach is quite important to investigate biological functioning on biomembrane surface. From this point of view, we developed a method to perform simultaneous X-ray diffraction and differential scanning calorimetry measurements. We applied this method to studies on aqueous dispersions of phospholipid and phospholipid/phosphatidylglycerol. In the former, we obtained the results that the X-ray diffraction intensity is proportional to the transition enthalpy. In the latter, we found the existence of H_<II> structure that plays an important role in biological functioning. As examples for interaction between a phospholipid molecule and a small molecule, we studied systems of phospholipid/alcohol and phospholipid/sugar. In the former, we analyzed the interdigitated structure and proposed a micro-structural model. In the latter, depending on sugars the condition that stabilizes liquid-crystalline phase was revealed. Furthermore, as an example of interaction between a phospholipid molecule and a small molecule, we studied a system of phospholipid/water by thermal analysis and X-ray diffraction. From this study, we found the number of water molecule incorporated in the interbilayer. Furthermore, we studied the structure of a monolayer of fatty acids formed on a graphite surface by scanning tunneling microscopy with atomic resolution and this method offers possibility to carry out a study on interaction at atomic scale.