Spectroscopic studies of the interaction of cobalt(II) N,N′,N″,N″′-tetramethyltetra-3,4-pyridinoporphyrazine with amino acids and nitrogen oxides

The interaction of histidine, cysteine, NO and nitrite with cobalt(II) N,N′,N″,N″′-tetramethyltetra-3,4-tetrapyridinoporphyrazine ([Co^IItmtppa]⁴⁺) is reported. Metal-based autoreduction of [Co^IItmtppa]⁴⁺ occurs with the formation of the [Co^Itmtppa(−2)]³⁺ species in the presence of histidine and cysteine. Kinetic data for the auto reduction of [Co^IItmtppa]⁴⁺ in the presence of these amino acids gave the rate constants k_f = 2.1 × 10¹ and 2.8 dm³ mol⁻¹ s⁻¹, for cysteine and histidine, respectively. One molecule of NO or nitrite was found to coordinate to the [Co^IItmtppa]⁴⁺ species. The equilibrium and rate constants for the coordination of the nitric oxide were K = 2.3 × 10⁴ dm³ mol⁻¹ and k_f = 7.5 dm³ mol⁻¹ s⁻¹, respectively. The coordination of nitrite to [Co^IItmtppa]⁴⁺ occurred with an equilibrium constant of K = 2.0 × 10² dm³ mol⁻¹ and a rate constant of k_f = 4.0 × 10⁻³ dm³ mol⁻¹ s⁻¹. There was no evidence for the coordination of two molecules of nitrite to the [Co^IItmtppa]⁴⁺ species. Copyright © 2001 John Wiley & Sons, Ltd.