N,N-Butyl-decamethylferrocenyl-amine reactivity at liquid vertical bar liquid interfaces: electrochemically driven anion transfer vs. pH driven proton transfer

We have developed a permethylated ferrocene redox system with a butylamine substituent for application in liquid vertical bar liquid ion sensors. The steric hindrance associated with the methyl groups results in an electrochemical system where the ferricenium derivative is chemically inert and the redox system remains chemically reversible, even for applications in aqueous or biphasic media. N,N-Butyl-decamethylferrocenyl-amine is soluble in hydrophobic organic solvents, such as 4-(3-phenylpropyl) pyridine (PPP) and N-octyl-pyrrolidone (NOP), and is employed here under "microphase'' conditions, deposited in the form of microdroplets onto an electrode and immersed in aqueous buffer solutions. It is shown that under these conditions, electron transfer and proton transfer are only weakly coupled, and that anion transfer dominates the microphase redox process over the entire pH range. The corresponding biphasic Pourbaix diagram is discussed.