title: Chromium(V) peptide complexes: synthesis and spectroscopic characterization.
abstract: A series of stable Cr(V) model complexes that mimic the binding of Cr(V) to peptide backbones at the C-terminus of proteins have been prepared for N,N-dimethylurea derivatives of the tripeptides Aib3-DMF, AibLAlaAib-DMF, and AibDAlaAib-DMF (Aib = 2-amino-2-methylpropanoic acid, DMF = N,N-dimethylformamide). The Cr(ll) precursor complexes were synthesized by the initial deprotonation of the amide and acid groups of the peptide ligands in DMF with potassium tert-butoxide in the presence of CrCl2. The Cr(II) intermediates thus formed were then immediately oxidized to Cr(V) using tert-butyl hydroperoxide. Spectroscopic and mass-spectrometric analyses of the Cr(V) complexes showed that a new metal-directed organic transformation of the ligand had occurred. This involved a DMF solvent molecule becoming covalently bound to the amine group of the peptide ligand, yielding a urea group, and a third coordinated deprotonated urea nitrogen donor. A metal-directed oxidative coupling has been proposed as a possible mechanism for the organic transformation. The Cr(V/IV) reduction potential was determined for the three Cr(V) complexes using cyclic voltammetry, and in all cases it was quasi-reversible. These are the first isolated and fully characterized Cr(V) complexes with non-sulfur-containing peptide ligands.
authors.affiliation: Centre for Heavy Metals Research, School of Chemistry, University of Sydney, New South Wales 2006, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Barnard
authors.forename: Aviva
authors.initials: A
authors.lastname: Levina
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lay
mesh_terms: D000577:Amides / Q000737:chemistry; D002857:Chromium / Q000737:chemistry*; D002942:Circular Dichroism; D004563:Electrochemistry; D008024:Ligands; D013058:Mass Spectrometry; D008782:Methylurea Compounds / Q000737:chemistry; D008956:Models, Chemical; D009842:Oligopeptides / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010455:Peptides / Q000138:chemical synthesis*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000577:Amides; D008024:Ligands; D008782:Methylurea Compounds; D009842:Oligopeptides; D009942:Organometallic Compounds; D010455:Peptides; D002857:Chromium