Preparation and isomerization of Six Isomers of (L-or D-Aspartato) (L-ornithinato)cobalt(III) Complexes

Abstract

Three geometrical isomers of the [Co(L-asp) (L-orn)] complex and three geometrical isomers of the [Co(D-asp) (L-orn)] complex have been prepared (asp =aspartate ion and orn=ornithinate ion), and their configurations are determined from the visible absorption and proton magnetic resonance spectra. The absorption spectrum of trans 05 trans N5 isomer of No(D-asp) (L-orn) is of particular interest since there is a clear shoulder in the second absorption band region which may be due to the splitting of that band. The isomerization of these six isomers was observed in the aqueous solution containing active carbon. After an equilibrium, the isomer ratio was found to be cis 05 cis N5: trans N5 trans IT, fac = 50: 14: 29. The ratio for the isomers containing L--asp could not been obtained because of their low solubilities. The rates of these isomerization were dependent on the pH of the solution, slow at low pH and rapid at high pH. The addition of the organic material decreased the rates of isomerization. Pyridine and anilin showed a more pronounced effect than ethanol, tetrahydrofuran and dimethyl sulfoxide. It is found that the Co(D-asp) (L-orn) and Co(L-asp) (D-orn) complexes are formed by the isomerization of the mixture of the ECo(D-asp) (D-orn) and Co(L-asp) (L-orn) complexes in the aqueous solution containing active carbon. This fact shows that the isomerization occurs via intermolecular as well as intramolecular mechanisms.