Dipeptide Complexes

Complexes of cobalt with dipeptides from several laboratories led to confusion about the variety of the species formed and their structure In 1966, Gillard et al. prepar several salts of bis(glycylglycinato)cobaltate(III), [Co(glygly)2], by treating an aqueous solution (pH 6.5 9.0) containing cobalt(II) ion and glycyl- 

Stadtherr and Martin investigated stereoselectivity by proton magnetic resonant spectra of solutions prepared by aerating a 2 1 molar ratio mixture of peptide and cobalt(II) salt the relative percentages of the produced diastereoisomers were evaluated from the peak hights due to methyl or methylene-methin portion. For the product of [Co(gly-L-ala)2] formed over a period of days at pH 9.5, the ratio of the isomers was found to be 58/42, for [Co(L-val-gly)2] and [Co(L-pheala-gly)2] ca. 66/33 

Boas et al. prepared and separated the meridional isomers of the [Co(ai-02)2] type complexes (oti-a2 represents the dianion of the dipeptide H2 i-a2 where ai is the N-terminal residue). Seven methods were used to prepare bis(dipeptidato)-cobaltate(III) complexes (i) by oxygenation of cobalt(II), (ii) from cobalt(II) carbonate, (iii) from sodium tricarbonatocobaltate(III), (iv) from hexaamminecobalt-(III) chloride, (v) from hexakis(urea)cobalt(III) perchlorate, (vi) from cobalt(III) hydroxide oxide, (vii) from triammine(glycylglycinato)cobalt(III). The methods starting from Co gave more minor products, Na3[Co(C03)3] 3 H2O gave less, and cobalt(III) hydroxide oxide gave very little of these products. Thus, the method (vi) was prefered. The peptides used were gly-gly, L-ala-gly, gly-L-ala, L-leu-gly, gly-L-leu, L-phe-gly, gly-L-phe, L-ala-L-ala, L-ala-D-ala, L-leu-L-leu. 

Two diastereoisomers of each bi dipeptidato) complexes were separated by anion-exchange chromatography on QAE-Sephadex A-25, and their absolute configurations were determined by PMR, electronic, circular-dichroism spectroscopy. Referring to the stereoselectivity, the workers said that with optically active peptides the formation is stereoselective, but not stereospecific as had earlier been suspected. 

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E. and Randaccio, L. (1992) Gold(III) glycyl-L-histidine dipeptide complexes. Preparation and x-ray structures of monomeric and cyclic tetrameric species. Inorganic Chemistry, 31, 1983 (b) Carotti, S., Marcon, G., Marussich, M., Mazzei, T., Messori, L., Mini, E. and Orioli, P. (2000) Cytotoxicity and DNA binding properties... 

The synthesis of threonine can be made stereospecific using optically active complexes of the type L-[Co(en)2Gly]2+ but with low asymmetric yield.442 In the case of dipeptide complexes only... 

Coordination-Induced C-13 Chemical Shifts in Vanadium(V) Dipeptide Complexes... 

The chemistry already described is reproduced by numerous ligands that have not specifically been addressed in the previous discussion. The V-salicylidenehydrazides (Scheme 4.18a) and related compounds provide a good example. The structure [76] of a typical complex, represented in Scheme 4.18b, is not very different from that proposed for the solution structures of dipeptide complexes (Scheme 4.17). Interestingly, other similar complexes, based on Schiff base-derived ligands, form dimeric [VO]2 core complexes (Scheme 4.1) via two long ( 2.4 A) VO bonds [2], The cyclic core is not necessary for dimer formation, and a dimer can form via a linear VOV bond [77], These complexes otherwise are not significantly different in their vanadium coordination from that depicted in Scheme 4.18b. 

Buhl, M. 2005. Molecular dynamics of a vanadate-dipeptide complex in aqueous solution. Inorg. Chem. 44 6277-6283. 

Dipeptides complex in a trident fashion to form oxoperoxodipeptido products. The rate of complexation by these ligands is quite slow. Even the vanadium-catalyzed disproportionation of hydrogen peroxide occurs quickly when compared to the rate of complexation by dipeptides. The formation of the dipeptide complex is interesting, in the sense that the ligand is tridentate, and complex formation involves loss of a... 

Chen, L., Rose, J. R, Breslow, E., Yang, D., Chang, W. R., Furey, W. R, Sax, M., and Wang, B.C. (1991). Crystal structure of a bovine neurophysin II dipeptide complex at 2.8 A determined from the single-wavelength anomalous scattering signal of an incorporated iodine atom., Proc. Natl. Acad. Sci. U.S.A., 88, 4240-4244. 

Although the X-ray structure of a Pinl-dipeptide complex implicated covalent catalysis, a lack of nucleophilic assistance in the catalytic pathway can be derived from the covalent modification of parvulins by 5-OH-l,4-naphthoquinone (juglone). A juglone-inactivated E. coli ParlO contains two inhibitor molecules that are covalently bound to the side-chains of Cys41 and Cys69 because of a Michael... 

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