Metal-peptides

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-... 

Modified Marcus Parameters for Proton-Transfer Reactions with Deprotonated Metal Peptide Complexes... 

Crystal Structures of Metal-Peptide Complexes Hans C. Freeman... 

Table 8 Logarithmic Equilibrium Constants of Some Metal-Peptide Complexes in Aqueous Media ... 

Table 9 Structures of some Metal-Peptide Complexes from X-Ray Crystallography...

Fig. I Two principally different alternatives for the chemical synthesis of metal-peptide bioconjugates (a) On the resin (top) and post-SPPS (b) (bottom). Functionalization can be N-terminal or on one of the amino acid side chains...

Applications of metal-peptide conjugates in general were published in several areas, also extending the range of subjects covered herein. We are restricting the discussion below (1) to metal-peptide conjugates with organometallic compounds and (2) to biomedical applications only. 

Outside Protonation. When metal-peptide complexes are placed in acidic solutions, the complexes dissociate. Metal ions which are sluggish in their substitution reactions, such as Ni(II) (43), Pd (II) (44), and Co (III) (45), add protons to the peptide oxygens prior to the metal-N (peptide) bond dissociation. The Cun(H 2GGhis)" complex is sufficiently sluggish in its reaction with acid to permit outside protonation to be observed kinetically (12). Protonation constants of 104 2 and... 

Early studies on metal-peptide complexes were generally concerned with polyglycines, and there are several reviews on these complexes. In the first part of this article, we will discuss various metal-peptide complexes that have coordinating side chains. Comparison of these metal-peptide complexes will be made with their glycine analogs, and the differences will be noted. The second part of the article will deal with metal-mediated peptide-bond cleavage. 

Copper-peptide complexes have been the most extensively studied of all the metal-peptide complexes. Copper(II) is the most important oxidation state in copper-peptide complexes, although copper(III) can be stabilized by coordination to peptides. The deprotonated peptide nitrogens help stabilize the higher oxidation state of copper therefore the more deprotonated peptide nitrogens, the more stable the copper(III) complex. Copper(III) complexes are generally prepared by electrochemical oxidation of the copper(II) complex at pH 10 or higher. 

The HRE peptide was shown to minerahze a total of seven nanoclusters, ZnS, Au , Ag°, Pt°, Cu , Ti02, and Ag2S. All nanoparticles were formed by mixing appropriate ratios of metal to peptide to form a metal peptide precursor complex. To this solution, sulfide or reductant was added to form the appropriate encapsulated metal nanocluster. Condensation of titanium isopropoxide in the presence of HRE was used for synthesis of Ti02-(HRE) nanoparticles. Once formed, all of the nanoclusters were characterized using UV-vis, IR, powder XRD, transmission electron microscopy, and an antigen capture assay,... 

Other Metal-Peptide and -Protein Interactions.—The determination of protein-bound trace elements in biological material by neutron activation analysis has been described Zn, Hg, Cu, and Se were accurately detected in human liver samples, provided that most of the element concerned was protein bound. An interaction of mercury with a protein or a protein-DNA complex has been invoked to explain the partitioning of the metal in euchromatin over heterochromatin (from mouse liver nuclei) by a 10 1 ratio. " Bovine retinas, isolated rod outer segments and emul-phogene extracts of rod outer segments have been shown to contain appreciable amounts of Zn ", Ca and the zinc levels being light sensitive. 

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