The synthesis and structural characterization of N-(ferrocenyl)2 and N-(ferrocenoyl)2 cystine dimethyl ester derivatives: Potential anion sensing agents

Standard peptide coupling reactions were use to prepare the N-(ferrocenyl)2 and N-(ferrocenoyl)2 cystine dimethyl ester derivatives 4–11. The ferrocene carboxylic acids 1 and 3 were treated with 1-hydroxybenzotriazole (HOBt), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), l-cystine methyl ester hydrochloride and triethylamine in dichloromethane at 0 °C to furnish compounds 4–9. The preparation of compounds 10 and 11 employed the dipeptide derivatives (glycine)2-l-cystine dimethyl ester and (β-alanine)2-l-cystine dimethyl ester respectively. The N-(ferrocenyl)2 and N-(ferrocenoyl)2 cystine dimethyl ester derivatives 4–11, which are potential anion sensing agents, were spectroscopically characterized by a combination of 1H NMR, 13C NMR, IR, UV, DEPT-135 and 1H–13C COSY (HMQC) spectroscopy, mass spectrometry and cyclic voltammetry. ectrochemical detection of dihydrogen phosphate and adenosine nucleotide anions in aqueous electrolyte by monolayers of {N-(ferrocenoyl)-β-alanine}2-l-cystine dimethyl ester 11 immobilized on gold electrodes using cyclic voltammetry is described. Immobilization of this receptor on a gold electrode surface enabled the recognition process to be detected in aqueous media. The recognition process is as a result of electrostatic interactions between the ferricenium cation and the anion, and hydrogen bonding interactions between the peptide amide bonds and the anion. The complexation process was amperometrically sensed via a reduction in the peak current of the ferrocene/ferricenium redox couple. A linear relationship (R2 = c. 0.99) was observed between anion concentration and change in peak current in both cases.