Electrode reaction of catecholamines on a calix[6]arene monolayer electrode and its application to a doapmine sensor

Self-assembled monolayer (SAM) electrodes were prepared using calix[6]arene provided with thiols, and electrode reactions of catecholamines on bare gold electrodes and the SAM electrodes were investigated. It was found that the calixarene adlayer partly blocked the electrode reaction of dopamine in the solution phase. This blocking effect was also observed in the case of 3,4-dihydroxy-DL-alanine (DOPA), but only slightly. In contrast, the electrode reaction of 3,4-dihydroxyphenylacetic acid (DOPAC) was suppressed almost completely. These results suggested that cationic substrates (dopamine and DOPA) bound with the calixarene molecules on the electrode surface and made Faradaic reaction with the underlying gold electrode. The calixarene molecular-pore was expected to contribute as a spatial pass for electron transfer, leading to a feasible electrode reaction. Mathematical simulations of the cyclic voltammetric i-E responses were made, and the parameters for the electrode reaction were considered. A possible application to an electrochemical dopamine sensor is also described.