Metal peptide complexes: preparations and proton and carbon-13 NMR spectra of cobalt(III) tripeptide complexes

Abstract

The preparations of cobalt(II1) complexes of a series of tripeptides are reported in which the peptides are coordinated as quadridentate chelates through the terminal NH,, two peptide N-and terminal CO, groups. The 'H and I3C N M R spectra are given for the free peptides in the anionic, zwitterionic, and cationic forms and for the cobalt(II1) complexes. The chemical shift data are analyzed in terms of the effects of protonation and coordination, and the coupling constants for the a-CH-P-CH2 fragments of the leucyl, phenylalanyl, and tyrosyl residues are analyzed in terms of the possible rotamers for the side groups. In [Co(NH3),(g1y-gly-~-phe)], the phenyl group adopts a conformation that results in an adjacent NH3 ligand resonating at the very unusual position of 6 0.77. IntroductionAs part of an investigation into the reactions of metal peptide complexes, a series of diammine(tripeptide)cobalt(III) complexes has been prepared with the peptide coordinated as a quadridentate chelate (structure 1). Although the prepa-

Synthesis and Structure of Tris(alkyl- and silyl-tetramethylcyclopentadienyl) Complexes of Lanthanum

“…(C 5 Me 4 R) 3 La Syntheses. In the first step of the synthesis, eq 6, formation of the (C 5 Me 4 R) 2 LaCl 2 K(THF) 2 “ate” salts from LaCl 3 and KC 5 Me 4 R was accomplished following the traditional procedure for introducing a C 5 R 5 ligand into a lanthanide ion coordination sphere. ,, The synthesis of the (C 5 Me 4 R) 2 LaCl 2 K(THF) 2 complexes was nearly identical to the route used for formation of (C 5 Me 5 ) 2 LaCl 2 Li(Et 2 O) 2 , except that heating the reaction mixture at reflux was found to be unnecessary. The use of the KC 5 Me 4 R salts rather than LiC 5 Me 4 R gave slightly better yields (53−62%) than those previously reported for (C 5 Me 5 ) 2 LaCl 2 Li(Et 2 O) 2 (49%).…”

Chemistry of Tris(pentamethylcyclopentadienyl) f-Element Complexes, (C5Me5)3M

“…The C 5 Me 5 ligand , was introduced into lanthanide chemistry in 1980. − This ligand has all the favorable aspects of the C 5 H 5 group plus a larger size and enhanced solubilizing capacity. Its introduction into organolanthanide chemistry had a significant impact on the chemistry of both trivalent and divalent ions.…”

Coordinating properties of the amide bond. Stability and structure of metal ion complexes of peptides and related ligands

“…126 Triglycine yields Co2+ and Co3+ complexes similar to those of diglycine with the coordinating groups of the two ligands being amino and deprotonated amide nitrogens and either the carboxylate oxygen of the dipeptide or the carbonyl oxygen of the central glycyl residue of the tripeptide.127 By a different procedure quadridentate triglycine complexes with the ligand chelated in a plane about hexacoordinate Co3+ with amino nitrogen, two deprotonated peptide nitrogens, and a carboxylate oxygen may be prepared. 128 The preceding outline of the formation of the irreversible, wine-red mononuclear Co3+ complex by oxygenation of the Co2+ complex does not admit difficulties that have arisen in establishing release of peroxide.…”