Electroactive poly(amino acids). Part 5. Poly(Nδ-4-nitrobenzoyl-L-ornithine) coated on platinum: activity corrections applied to the behaviour of thin films

Abstract

Poly(N^δ-4-nitrobenzoyl-L-ornithine) was obtained with average molecular weight 8.0 × 10⁴ by reaction between the monomer N-carboxyanhydride and sodium hydride. The material was dipcoated onto platinum from dimethylacetamide solution and the behaviour of the coating examined in acetonitrile by cyclic voltammetry. Surface coverages in the range of 13.8 to 1.4 mmol cm^–2 4-nitrobenzoyl residues were obtained by dipping from 0.6–0.07% solution, corresponding to from 20 to 2 layers of close-packed α-helices. The coated electrodes showed i_pc proportional to scan rate. They do not show the severe ageing phenomena on repeated cyclic voltammetry that was associated with poly(N^ε-4-nitrobenzoyl-L-lysine). Expressions are developed which simulate the voltammograms by introducing activity coefficients for reduced and oxidised species within these multilayer films.