Control of Interfacial Equilibria by Local Charge Distribution and Average Surface Potential

The incorporation of cadmium ions in porphyrins embedded in matrix monolayers is dominated by head group interactions as opposed to the effect of the average surface potential on interfacial cation concentrations. Similar phenomena are also observed in the adsorption of water-soluble porphyrin complexes to spread monolayers. The influence of such local interactions can be eliminated when the composition of the head group region is kept constant and the interfacial potential is modified by changing dipole layers at distances of about 2.5 nm from the head group interface. Protonation equilibria can be systematically shifted by planned variation of the average potential via such remote dipole layers.