Interfacial Complexes between a Protein and Lipophilic Ions at an Oil−Water Interface

Abstract

The interaction between an intact protein and two lipophilic ions at an oil−water interface has been investigated using cyclic voltammetry, impedance based techniques and a newly developed method in which the biphasic oil−water system is analyzed by biphasic electrospray ionization mass spectrometry (BESI-MS), using a dual-channel electrospray emitter. It is found that the protein forms interfacial complexes with the lipophilic ions and that it specifically requires the presence of the oil−water interface to be formed under the experimental conditions. Furthermore, impedance based techniques and BESI-MS with a common ion to polarize the interface indicated that the Galvani potential difference across the oil−water interface significantly influences the interfacial complexation degree. The ability to investigate protein−ligand complexes formed at polarized liquid−liquid interfaces is thus a new analytical method for assessing potential dependent interfacial complexation using a structure elucidating detection principle.