The chromium(III) complexes with a new potential chromium transporting ligand-2,5-pyridinedicarboxylic acid (isocinchomeronic acid, icaH 2 ):[Cr(icaH) 3 ] 0 , [Cr(icaH) 2 (H 2 O) 2 ] + and [Cr(icaH)(H 2 O) 4 ] 2+ (where icaH = N,O-bonded isocinchomeronic acid anion), have been obtained and characterized in solution. The [Cr(icaH) 3 ] 0 complex undergoes aquation in acidic media to the diaquaproduct. Kinetics of this process was studied spectrophotometrically in the 0.1-1.0 M HClO 4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is a much faster than the second one. The rate laws are of the form: k obs = k 1 + k -1 /Q 1 [H + ] and k obs = k 2 Q 2 [H + ]/ (1 + Q 2 [H + ]), where k 1 and k 2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k -1 is the rate constant of the chelate-ring closure, Q 1 and Q 2 are the protonation constants of the pyridine nitrogen and 5-carboxylate group in the one-end bonded intermediate, respectively. The results are discussed in terms of potential pharmaceutical application of the complex.

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,Obonded 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 chelatering 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:where k OH(1) and k O are rate constants of the first ligand liberation from the hydroxo-and oxo-forms of the intermediate, respectively, and Q 2 is an equilibrium constant between these two protolytic forms. The first pseudo-firstorder rate constants (k obs1 ) 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 (k obs2 , k obs3 ) 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.

Chromium(III)-lutidinato complexes of general formula [Cr(lutH) n (H 2 O) 6-2n ] 3-n (where lutH -is N,Obonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH) 3 ] 0 leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1-1.0 M HClO 4 and 0.4-1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were characterized. The dependencies of pseudo-first-order rate constants on [H ? ] are as follows: k obs1 = k 1 ? k -1 /K 1 [H ? ] and k obs2 = k 2 K 2 [H ? ]/(1 ? K 2 [H ? ]), where k 1 and k 2 are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k -1 is the rate constant for the chelate-ring closure, and K 1 and K 2 are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate, respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH -]: k obs1 = k OH(1) ? k O [OH -], where k OH(1) and k O are rate constants of the first ligand liberation from the hydroxo-and oxoforms of the intermediate, respectively, and K 2 is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH) 4 ] 3-were also studied and the values of the pseudo-first-order rate constants are [OH -] independent.

Three chromium(III) complexes of general formula [Cr(ox) 2 (pdaH)] 2-(where ox = C 2 O 4 2-and pdaH -is N,O-bonded 2,3-, 2,4-or 2,5-pyridinedicarboxylic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(ox) 2 (pdaH)] 2-gave two products: [Cr(ox)(pdaH)(H 2 O) 2 ] 0 (P 1 ) and cis-[Cr(ox) 2 (H 2 O) 2 ] 2-(P 2 ). The kinetics of these reactions were studied spectrophotometrically, within the 0.1-1.0 M HClO 4 range, and the pseudo-first-order rate constants for the oxalato (k obs1 ) and pdaH -(k obs2 ) ligands dissociation were calculated based on the determined pseudo-first-order rate constants (k obs ) and P 1 :P 2 molar ratio. The dependencies of the pseudo-first-order rate constants on [H ? ] are as follows: k obs1 = b 1 [H ? ] and k obs2 = b 2 [H ? ], where b 1 and b 2 are the second-order rate constants for the oxalato and pdaH -ligands dissociation, respectively. Kinetic parameters were determined and the mechanism of the pdaHligand dissociation is proposed.

], where k 0 and k 1 are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage, the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case, the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine.