ROTATING-RING-DISK ELECTRODE STUDY OF COPPER(II) COMPLEXES OF THE MODEL PEPTIDES TRIGLYCINE, TETRAGLYCINE, AND PENTAGLYCINE

The reversible electrochemistry of the Cu(II)/Cu(III) couple was inves tigated for the copper(II) complexes of triglycine (G(3)), tetraglycin e (G(4)), and pentaglycine (G(5)) in alkaline solution using a rotatin g ring-disk electrode (RRDE), The study-was motivated by the need to e lucidate electrochemical processes occurring in dual electrode postcol umn detection of peptides, The disk electrode served as the anode and the ring electrode as the cathode, The electrode was used in both line ar sweep voltammetry and constant potential, varied rotation speed mod es, Redox waves for two generic forms of the complexes, Cu(II)-NNNN an d Cu(II)-NNNO, were identified, with respective E(1/2) values of simil ar to 0.45 and 0.7 V. It was found that the G(3) complex underwent an ECE-like process at the anode that magnified the anodic signal and sup pressed the cathodic signal, The G(4) and G(5) complexes were subject to two CE processes, the C reactions being (i) deprotonation of Cu(II) -NNNO to Cu(II)-NNNN and (ii) loss of hydroxide ion by Cu(II)-NNN(OH-) , a variant of Cu(II)-NNNO. An additional C reaction, dissociation of a carbonate variant of Cu(II)-NNNO, occurred in 0.2 M carbonate buffer , Visible absorbance measurements assisted in assignment of these form s, Measurements of diffusion coefficients of the complexes were perfor med by Taylor-A-is laminar now axial dispersion measurements, The anal ytical implications for these findings are discussed.