Copper tripeptide complexes

Nucleophilic substitution reactions of trien with copper-(II)-tripeptide complexes. I have long been fascinated by... 

It has been known for many years that the rate of hydrolysis of a-amino acid esters is enhanced by a variety of metal ions such as copper(II), nickel(II), magnesium(H), manganese(II), cobalt(II) and zinc(II).338 Early studies showed that glycine ester hydrolysis can be promoted by a tridentate copper(II) complex coupled by coordination of the amino group and hydrolysis by external hydroxide ion (Scheme 88).339 Also, bis(salicylaldehyde)copper(II) promotes terminal hydrolysis of the tripeptide glycylglycylglycine (equation 73).340 In this case the iV-terminal dipeptide fragment... 

The structure of [Cu(H 2Aib3) -2H20-1.5NaC104 (452) is important as the first structure of a copper(III) complex of a tripeptide which coordinates in the deprotonated state of the ligand." The structure involves a square planar CuNsO chromophore with some of the shortest Cu—N distances known, even for copper(II). The closest axial approach is a (CIO4)" oxygen atom at a distance of 2.91 A and the copper(III) ion lies in the plane of the N3O ligands. 

Tervalent copper and nickel are involved in the autoxidation reactions of [Cu(H 3G4)] and [Ni(H 3G4)] respectively. In the case of nickel, decomposition of [Ni(H 3G4)] proceeds by decarboxylation of the terminal carboxy-group adjacent to the peptide nitrogen. - With copper, decomposition of [Cu-(H sG4)] proceeds through a carbon-centred free radical produced by abstraction of a hydrogen atom from the peptide backbone. Bulky carbon substituents assist the stabilization of the higher-oxidation state ions, and a study of the stabilities of leucyl tripeptide complexes with copper(ii) and nickel(u) has been reported. Copper(iii) and nickel(iii) tripeptide complexes of a-aminoisobutyric acid are thermally stable but are readily decomposed by photochemical pathways. Resonance Raman and other studies with copper(iii) peptide complexes have also been reported. ... 

The kinetics and mechanisms of substitution reactions of metal complexes are discussed with emphasis on factors affecting the reactions of chelates and multidentate ligands. Evidence for associative mechanisms is reviewed. The substitution behavior of copper(III) and nickel(III) complexes is presented. Factors affecting the formation and dissociation rates of chelates are considered along with proton-transfer and nucleophilic substitution reactions of metal peptide complexes. The rate constants for the replacement of tripeptides from copper(II) by triethylene-... 

Cangul IT, Gul NY, Topal A, et al. Evaluation of the effects of topical tripeptide-copper complex and zinc oxide on open-wound healing in rabbits. Vet Dermatol 2006 17 417-23. 

Xiang, Q., Xiang, Y, Nan, Z., Zeng, X., Xie, J. Hydrolysis of p-nitrophenyl picolinate catalyzed by copper(II) and zinc(II) binuclear complexes coordinating tripeptide in micellar solution. J. Dispersion Sci. Technol. 2001, 22(1), 103-109. 

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