Blue copper protein analogue: synthesis and characterization of copper complexes of the N2S2 macrocycle 1,8-dithia-4,11-diazacyclotetradecane

Abstract

To improve understanding of copper at the active site of Type 1 copper proteins, Cu^I and Cu^II complexes of 1,8-dithia-4,11-diazacyclotetradecane, shown in Fig. 1, have been successfully isolated and structurally characterized by X-ray crystallography. In these compounds, both Cu^I and Cu^II are centered in the plane of the macrocycle containing two sulphur and two nitrogen heteroatoms comprising the distorted tetrahedral/square planar coordination geometry. The UV/VIS spectra, electrochemistry and EPR properties have been obtained for the Cu^II complex 2. Three absorption bands at 295 nm, 354 nm, and 545 nm are observed in aqueous solution at a pH of 5. These bands have been assigned to the N → Cu^II and S → Cu^II charge transfer bands and the d–d transitions respectively. The Cu^I/II redox midpoint potential of complex 2 in CH₃CN is +403 mV versus NHE.