Cobalt complexes amino acids

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]. 

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... 

McLendon G, MarteU AE (1976) Inorganic oxygen carriers as models for biological systems. Coord Chem Rev 19 1-8 McLendon G, Harris W, MarteU AE (1976) Dioxygen compl-exation by cobalt amino acid and peptide complexes. 1. Stoichiometry and equilibria. J Am Chem Soc 98 8379-8386... 

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 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... 

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... 

Amino Acid Complexes of Copper and Cobalt Ions... 

Cobalt(iii) Complexes.—Two kinetic studies of cis-trans isomerization of cobalt(iii) complexes of simple ligands have been described, for the complexes c/j -[Co(en)2(glycinenitrile)Cl] + and [Co(en)2(OH2)(N3)] +. Possible mechanisms of isomerization and racemization for complexes containing flexible quadridentate ligands have been discussed in general terms, for amino-acid complexes [Co(trien)(LL)] +, and for the specific case of the complex [Co(trien)(N-methyl-S -alaninato)] +. The rearrangement of the a -R- to the aj8-5-form of [Co(tetren)(NCS)] + follows the rate law... 

Cobalt(ll) forms many complexes which can exhibit oxygen-carrying properties (2,19). Reversible oxygen uptake in solutions of cobalt (ll)-histidine (33-36), and cobalt (II) in the presence of a-amino acids and peptides (37—39) has been known for some time. The reaction of cobalt (II) with dipeptide was first observed in enzymic studies involving glycyl-glycine (40). 

Fanali, S., Ossicini, L., Foret, F., and Bocek, R, Resolution of optical isomers by capillary zone electrophoresis study of enantiomeric and distereoisomeric cobalt (III) complexes with ethylenediamine and amino acid ligands, /. Microcol. Sep., 1, 190, 1989. 

The next five transition metals iron, cobalt, nickel, copper and zinc are of undisputed importance in the living world, as we know it. The multiple roles that iron can play will be presented in more detail later in Chapter 13, but we can already point out that, with very few exceptions, iron is essential for almost all living organisms, most probably because of its role in forming the amino acid radicals required for the conversion of ribonucleotides to deoxyribonucleotides in the Fe-dependent ribonucleotide reductases. In those organisms, such as Lactobacilli6, which do not have access to iron, their ribonucleotide reductases use a cobalt-based cofactor, related to vitamin B12. Cobalt is also used in a number of other enzymes, some of which catalyse complex isomerization reactions. Like cobalt, nickel appears to be much more extensively utilized by anaerobic bacteria, in reactions involving chemicals such as CH4, CO and H2, the metabolism of which was important... 

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