Electrochemical behavior of a dopamine polymer. Dopamine release as a primitive analog of a synapse

A modified polystyrene was synthesized and characterized which held N-(2-(3,4-dihydroxyphenyl)ethyl)isonicotinamide units. This polymer was dissolved in DMF, syringed onto glassy carbon electrodes, and dried; the electrode was then used in aqueous electrolyte solutions. In pH 7 solution, at potentials more negative than -0.9 V (SCE), cathodic current caused cleavage of the amide linkage and release of the neurotransmitter dopamine. The released dopamine was detected at a second electrode by its oxidation or by HPLC. Voltammetric studies of the reduction process as well as the oxidation of the hydroquinone units in the polymer layer were performed. It was shown that only a few equivalent monolayers of polymer units could be oxidized or reduced even if the layer contained many more such units. The oxidation of solution-phase NADH on these electrodes was studied voltammetrically. It was ssown that the polymer acted as an electrocatalyst. Quinone units were formed on the polymer and they in turn oxidized NADH molecules. Maximum catalytic efficiency was obtained with a layer holding approximately one equivalent monolayer of dopamine units.