title: (133)Cs NMR and molecular dynamics simulation on bilayers of Cs(+) ion binding to aggregates of fatty acid soap at high pH.
abstract: Fatty acid bilayers are usually formed due to the hydrogen bonds between the protonated carboxyl (-COOH) and the deprotonated carboxylate (-COO(-)). Therefore, the formation of the bilayers must be at the pH around the pKa of the fatty acid, which is a narrow pH range (mostly about 7-9). Fatty acid bilayers can be used as cell membrane model but the narrow pH range largely limits their applications. Herein, fatty acid bilayers were first detected at high pH (>13) in the stearic acid (SA)/CsOH/H2O system, which is not consistent with the explanation of the traditional hydrogen bond theory for fatty acid bilayers around pH. Cryogenic transmission electron microscopy (cryo-TEM) images, X-ray diffraction (XRD) patterns, and deuterium nuclear magnetic resonance ((2)H NMR) spectra demonstrate the planar sheet bilayers. The pH, conductivity, and (133)Cs NMR data indicate the strong interaction between Cs(+) and the bilayers. Rheological characterizations reflect the viscoelasticity of the Lα phase sample of bilayers. Molecular dynamics simulation increases the reliability of our observations. The assumed growth process of the aggregates and the detailed arrangement of the Cs(+) on the bilayers were proposed according to the experimental data and the molecular dynamics simulation. This work will promote the application scope of fatty acid bilayers with wide pH range.
authors.affiliation: Key Laboratory of Colloid and Interface Chemistry, Shandong University , Ministry of Education, Jinan 250100, P. R. China.
authors.forename: Wenlong
authors.initials: W
authors.lastname: Xu
authors.forename: Heng
authors.initials: H
authors.lastname: Zhang
authors.forename: Shuli
authors.initials: S
authors.lastname: Dong
authors.forename: Jingcheng
authors.initials: J
authors.lastname: Hao