Reactivity trends of cobalt(III) complexes towards various amino acids based on the properties of the amino acid alkyl chains

The reactivity of the cobalt(III) complexes dichlorido[tris(2-aminoethyl)amine]cobalt(III) chloride, [CoCl₂(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl₂(trien)]Cl, towards different amino acids (L-proline, L-asparagine, L-histidine and L-aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (L-prolinato-κ²N,O)[tris(2-aminoethyl)amine-κ⁴N,N',N'',N''']cobalt(III) diiodide monohydrate, [Co(C₅H₈NO₂)(C₆H₁₈N₄)]I₂·H₂O, I, (L-asparaginato-κ²N,O)[tris(2-aminoethyl)amine-κ⁴N,N',N'',N''']cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), II, and (L-prolinato-κ²N,O)(triethylenetetramine-κ⁴N,N',N'',N''')cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), V. The syntheses of the complexes were followed by characterization using UV-Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM.

Polymorphism of dinitro[tris(2-aminoethyl)amine]cobalt(III) chloride

Three polymorphs of bis(nitrito-κN)[tris(2-aminoethyl)amine-κ(4)N,N',N'',N''']cobalt(III) chloride, [Co(NO2)2(C6H18N4)]Cl, have been structurally characterized in the 100-300 K temperature range. Two orthorhombic polymorphs are related by a solid-state enantiotropic order-disorder k2 phase transition at ca 152 K. The third, monoclinic, polymorph crystallizes as a nonmerohedral twin. In the structure of the high-temperature (300 K) orthorhombic polymorph, the Co(III) complex cation resides on a crystallographic mirror plane, whereas the Cl(-) anion occupies a crystallographic twofold axis. In the unit cell of the monoclinic polymorph, the cationic Co(III) complex is in a general position, whose charge is balanced by two halves of two Cl(-) anions, each residing on a crystallographic twofold axis.