Chromium(III)-isocinchomeronato and quinolinato complexes: kinetic studies in NaOH solutions and effect on 3T3 fibroblast proliferation

Abstract

The aquation of chromium(III)-isocinchomeronato and quinolinato complexes, mer-[Cr(icaH)3]0 and mer-[Cr(quinH)3]0 (where icaH− and quinH− are N,O-bonded isocinchomeronic and quinolinic acid anion, respectively) was studied in NaOH solutions. The process leads to successive ligand liberation in the fully deprotonated species. The kinetics of the first ligand liberation were studied spectrophotometrically in the visible region. A mechanism is proposed in which the rate of the chelate-ring opening at the Cr–N bond is much faster than the rate of the Cr–O bond breaking. The rate-determining step is described by the rate law: kobs1 = kOH(1) + kOQ2 [OH−], where kOH(1) and kO are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and Q2 is an equilibrium constant between these two protolytic forms. The first pseudo-first-order rate constants (kobs1) were calculated using SPECFIT software for an A → B → C reaction pattern. The results are compared with those determined in acidic medium. Kinetics of the second and third ligand liberation were also studied and values of successive pseudo-first-order rate constants (kobs2, kobs3) are [OH−] independent. Effect of chromium(III)-quinolinato and isocinchomeronato complexes on 3T3 fibroblast proliferation was evaluated. Cytotoxicity of these complexes is low, suggesting they may be promising candidates as novel dietary supplements.