Cytochrome c oxidase models: iron(III) porphyrin-copper(II) complexes with sulfur bridges

Synthetic Models for Heme−Copper Oxidases

“…Trinuclear cyanide-, formate-, imidazolate-, and sulfur-bridged heme−copper model complexes: 33c , 4e , 42 , 33d , 52 , 48 . All structural formulas are supported by X-ray crystallography.…”

“…The use of a mononuclear cyanide−copper(II) complex instead of a cyanide−iron species as a precursor affords highly interesting but not biologically relevant trinuclear species Cu II- NC−Fe III- CN−Cu II (Figure ). ,

17 Trinuclear cyanide-, formate-, imidazolate-, and sulfur-bridged heme−copper model complexes: 33c , 4e , 42 , 33d , 52 , 48 . All structural formulas are supported by X-ray crystallography.

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“…Variable temperature magnetic studies showed a weak antiferromagnetic coupling for all three complexes ( J ∼ −2 cm -1 ). “Weak” EPR signals observed were interpreted as being due to the above-mentioned relaxation broadening mechanism …”

“…As the exchange coupling between the metal ions was found to be weak, they proposed a "relaxation broadening mediated by a small degree of exchange coupling through the bridging sulfur atom" to explain the silent EPR spectra. Furthermore, inspired by the unusual behavior of this and other trinuclear µ-sulfur complexes, 231,274 Elliott and Akabori 275 proposed an alternative mechanism to explain heme a 3 -Cu B oxidase enzyme EPR silence. They suggested that a combination of dipolar coupling and a small exchange coupling between the copper(II) and the rapidly relaxing S ) 3 / 2 iron(III) would cause sufficient EPR broadening so as to make any signal nonobservable.…”

“…"Weak" EPR signals observed were interpreted as being due to the abovementioned relaxation broadening mechanism. 231 Imidazolate-Bridged Complexes. A couple of µ-imidazolate heme-copper complexes with the formula [(L)(TPP)Fe III -Cu II (imidH-DAP)] + (36b, L ) chloride, 36c, L ) triflate) (Figure 19) were prepared by equimolar reaction of the corresponding iron(III)porphyrinate [(TPP)Fe III -(L)] complexes and [Cu II -(imidH 2 DAP)] 2+ , in the presence of 1 equiv of base.…”