Preparation, Reactivity, and Stereochemistry of Cobalt(III) Complexes with Sulfur- or Selenium-containing Peptide

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In this work, we obtained the following results (1)-(5):1) The cobalt(III) complexes with sexidentate ligands, S,S'-ethylenebis(L-homocysteinate) and S,S'-trimethylenebis(L-homocysteinate), were prepared and chromatographically separated into two geometrical isomers. All isomers were characterized by their electronic absorption, CD, and NMR spectra, and their stereo- and spectrochemical features were investigated.2) Each of the two isomers of bis[[tris(L-cysteinato-N,S)cobaltate(III)-<mu>-S,<mu>-S', <mu>S"]] cobaltate(III) was selectively prepared by the reaction of -fac(S)-tris(L-cysteinato-N,S) cobaltate(III) with Co(II) or Co(III). The crystal structure of one isomer was established by the X-ray diffraction study. The absolute configuration of the two [[Co(L-cys-N,S)3]] moieties and the siz sulfur donor atoms were determined. The electronic absorption, CD, and NMR spectra of the two isomers were discussed in relation to their geometrical and absolute configurations.3) The cobalt(III … More ) complex with D- and/or L-selenomethioninate was prepared and separated into the five geometrical isomers. For the four isomers, the optical resolutions were achieved by the column chromatographic method. For the trans(N) and cis,cis,cis isomers which exhibited the electronic absorption, CD, and NMR spectral changes with time in an agueous solution, and inversion on the asymmetric selenium donor atom was investigated by the spectrophotometric method. Their CD spectra were also discussed in relation to the absolute configuration of the asymmetric selenium donor atom.4) The cobalt(III) complexes with 1,3-propanedithiolate and 1,3-propanedisulfinate were prepared and resolved. The crystal structure of one isomer was established by the X-ray diffraction study. The absolute configurations of their isomers were discussed in relation to the CD spectral behavior in the sulfur-to-metal charge transfer and d-d transistion band regions.5) The cobalt(III) complexes with dipeptides, L-methionyl-glycine and glycyl-L-methionine, were prepared and they were characterized by their electronic absorption, CD, and NMR spectra. The stereochemical properties were discussed. Less