Amino acid complexes of cobalt

The cis-isomers of the tris(a-amino acid) complexes of cobalt(III) and chromium(III) have larger extinction coefficients for band maxima of d-d transitions than the corresponding trans-isomers (19-24). Although the difference in the coordination environment between the cis- and trans-tris(hydroxamato)chromi-um(III) complexes is less than that in the amino acid complexes, differences in the absorption spectra of the cis- and trans-isomers of Cr(hydroxamate)3 complexes have been found, especially for the extinction coefficients of the high energy transition... 

Amino Acid Complexes of Copper and Cobalt Ions... 

All these methods have found applications in theoretical considerations of numerous problems more or less directly related to solvent extraction. The MM calculated structures and strain energies of cobalt(III) amino acid complexes have been related to the experimental distribution of isomers, their thermodynamic stability, and some kinetic data connected with transition state energies [15]. The influence of steric strain upon chelate stability, the preference of metal ions for ligands forming five- and six-membered chelate rings, the conformational isomerism of macrocyclic ligands, and the size-match selectivity were analyzed [16] as well as the relation between ligand structures, coordination stereochemistry, and the thermodynamic properties of TM complexes [17]. 

Complexes of other amino acids or their derivatives with cobalt(II) that have been investigated include dipeptides (120) these complexes have long been known to absorb dioxygen. For example, the mononuclear cobalt(II) complex of N, N,N", N "-diglycylethylenediaminete-traacetic acid (121) absorbs one mole of dioxygen per two moles of complex. This system has been proposed as a simple, convenient model system for the study of dioxygen complexes of cobalt(II) peptides in solution because of its relatively slow conversion to the irreversibly formed cobalt(III) dioxygen complex. 

Amino acid complexes are also nucleophilic towards the Vilsmeier reagent. The cobalt(II) glycine complex (36) gives rise initially to an unusually stable iminium complex, which can be hydrolyzed with concentrated sulfuric acid to the complex of formylglycine (Scheme 13). The formyl group... 

Amino-acid Complexes. X-Ray crystal structures have been reported for many cobalt(m) amino-acid complexes. Potassium dinitrobis(P-alaninato)cobaltate(m) has octahedral co-ordination about the cobalt, trans nitro-groups, and a trans arrangement of amino N- and carboxylato O-donors from the bidentate P-alaninates.371 In Ca[Co(aspar-tate)2] there are two isomeric ions the cis(N)trans Os) (64) and cis(lSl)trans 06) (65),... 

Very little is known about the metabolism of metal complexes, though a number of ammine complexes of cobalt(III) were used as nitrogen sources for aspergillus niger nearly forty years ago (150), and much more recently, both tris(ethylenediamine)cobalt(III) ions (757) and amino acid complexes (152) of cobalt(III) have served as nitrogen sources for species of pseudomonas. Correlations through enzymic selectivity are therefore as yet not... 

Because cobalt(III) complexes bind to the N-terminal amino acid residue of peptides, only the N-terminal peptide bond is hydrolyzed. It would be advantageous if the metal complex could coordinate to various parts of a peptide chain, thus allowing for cleavage of other areas of the peptide chain. Recently this has become an active area of research, and there have been several publications on the cleavage of the polypeptide backbone of proteins promoted by metal complexes. The advantage that these complexes have over the cobalt(III) complexes is that they can be selectively introduced on to various amino acid side chains, allowing for cleavage of peptide bonds at locations other than the N-terminus. This is of interest because,... 

O-Donor Ligands. A number of new cobalt(iii) complexes containing a single bi-dentate o-dihydroxy aromatic ligand and amine counter ligands have been prepared by methods similar to those used for cobalt(in) amino-acid complexes. The reduction of polynuclear o-terephthalatocobalt(in) complexes by Cr and has been studied. Kinetic data from the reduction of trisoxalatocobaltate(m) by... 

The compounds studied are the substituted triethylenetetra-aminecobalt(III) amino acid complexes depicted in Figure 1. Formally the A Bj chromophore will be the triethylenetetraamine-cobalt(III) glycinato moiety (compounds 1 and 7, identified in Figure 1) (with an associated configurational effect) and the optically active (Bj) chromophores will be represented by the various R2 substituents at the a-carbon of the chelated glycine... 

This report describes a method of experimentally obtaining the vicinal effects of amino acid anions bound to a tetraamine-cobalt(III) moiety by dealing exclusively with A-B2 complexes of both R and S-amino acids. Additivity of circular dichroism of both the configurational and vicinal effects for - transitions is verified experimentally. It is demonstrated that the vicinal effect not only contains information as to the chirality of the bound amino acid but also as to the mode of binding, i.e., Bi vs. b2-... 

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