The complex formation of ions with a phospholipid monolayer adsorbed at an aqueous|1,2-dichloroethane interface

Abstract

The complex formation of phosphatidylcholine adsorbed at a water|1,2-dichloroethane, W|DCE, interface with ions was evaluated based on the desorption behavior of lipids at the interface accompanied by an ion transfer and was confirmed by measuring voltammograms for the ion transfer facilitated by the complex formation with lipids. The desorption behavior of lipids was measured according to the Wilhelmy vertical plate method, the cell of which was improved to achieve polarization of the W|DCE interface. Voltammograms for the ion transfer at the W|DCE interface facilitated by the complex formation with lipids were recorded at a micro W|DCE interface in order to avoid the influence of convection caused by the desorption of lipids at the interface. Lipids adsorbed at the W|DCE interface showed complex formation with alkali metal ions, NH 4 + , ( CH 3 ) NH 3 + , ( CH 3 ) 2 NH 2 + or ( CH 3 ) 3 NH + , but not with ( CH 3 ) 4 N + or anions such as SO 4 2 - , CH 3COO −, Cl −, Br −, NO 3 - , I − or ClO 4 - . Lipids also showed strong complex formation with a basic amino acid such as an arginine cation, which has two amino groups in the molecule. The strength of the complex formation with lipids was Arg + > Li + , Na + > K + > NH 4 + > CH 3 NH 3 + > ( CH 3 ) 2 NH 2 + > Cs + > ( CH 3 ) 3 NH + .