[2Gp01-04] Soft matter/Biomaterial (SO/BI)

[2Gp03] X-ray absorption spectroscopy in aqueous solution to investigate sodium ion coordination to lipid bilayers

*Yu Kinjo¹, Masanari Nagasaka², Koji Okuwaki³, Yuji Mochizuki³, Ryugo Tero¹ (1. Toyohashi University of Technology, 2. Institute for Molecular Science, 3. Rikkyo University)

We aim to reveal the ion coordination to the lipid molecules in lipid bilayers and its effect on the molecular orientation using X-ray absorption spectroscopy (XAS) in water. The O K-edge XAS spectra of DOPC-SLB were attributed to three components, two derived from the P=O group and one derived from the C=O group of the DOPC molecule. The XAS spectra of DOPC-SLB obtained at [Na⁺] of 2.1 - 510.4 mM showed characteristic high-energy peak shifts and intensity changes of the P=O-derived components at the [Na⁺] regions of <50 mM, 50 - 100 mM, and >100 mM. The calculated inner-shell spectra of oxygen atoms in the P=O group, whose configuration was determined by the FMO-DPD method, showed high-energy shift depending on the distance from Na⁺. These results indicate that the ion coordination on lipid molecules is evaluated by the XAS spectra in water.