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

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 dualchannel 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.