Ion transport through a porphyrin-terminated hybrid bilayer membrane

A hybrid bilayer membrane (HBM) has been prepared on a glassy carbon electrode (GCE). The HBM consists of an inner layer of n-hexadecylamine (HDA) covalently attached at the GCE and an out-layer of tetra-(N-hexadecylpyridiniurnyl)porphyrin (TC16PyP). The HDA was covalently bounded on the carbon surfaces through its primary amine under cyclic voltammetric potential scans forming a self-assembled monolayer (SAM). The TC16PyP forms a second layer on top of the HDA layer due to hydrophobic interaction. The TC16PyP/HDA/GCE assembly has been utilized to study ion transport through hybrid bilayer membranes. The ion transport through this porphyrin-terminated HBM has been found to strongly dependent on pH. It allows negatively charged redox ions, Fe(CN)63−, to penetrate at pH <6 while repelling positively charged Ru(NH3)63+. However, no faradaic current has been detected at pH >6 with either ions. We believe that electrostatic interaction between the redox ions and the charged membrane is the main reason for this pH dependent ion transport.