Behaviors of H2TPP and CoTPPCl in Nafion((R)) film and the catalytic activity for nitric oxide oxidation

The behavior of meso-tetraphenylporphyrin (H2TPP) and its Co(III)-complex ( CoTPPCl) in Nafion((R)) film has been studied by cyclic voltammetry and vis ible spectroscopy. Buffer titration of H4TPP2+ in the film showed only the dication-free-base equilibrium (H4TPP2+ reversible arrow H2PP + 2H(+)) and the apparent equilibrium constant, pK(3.4), was determined to be 4.12. Inse rtion of cobalt(III) into the H2TPP core in the film has been realized at r oom temperature by immersion of H2TPP-containing Nafion((R)) film into CoCl 2 solution. The electrocatalytic activity of the resulting film toward NO o xidation at a glassy carbon (GC) electrode has been monitored in comparison with other Nafion((R)) films doped with H2TPP or free CoCl2 A GC electrode coated with Nafion((R)) film doped with CoTPPCl exhibited the highest cata lytic activity, confirming the involvement of the Co site in a catalytic cy cle of NO oxidation. In amperometric detection of NO in phosphate buffer so lution at pH 7.4 this electrode demonstrated a linear response to the NO co ncentration increment. The detection limit at a signal-to-noise ratio of 3 was 1.2 nM. (C) 2001 Elsevier Science B.V. All rights reserved.