Mixed chromium(III) complexes with pyridinedicarboxylato and oxalato ligands: kinetic studies in HClO4 solutions

Muzioł

et al. 2010

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], 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.

Section: Introductionmentioning

confidence: 99%

Kinetic studies on chromium-glycinato complexes in acidic and alkaline media

Muzioł

et al. 2010

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“…Thus, the hydroxyl anion in the inner sphere destabilises the bidentate bonded oxalato ligand regardless of the fact that quin is already one-end bonded. Our studies on acid-catalysed aquation of complexes with picolinato-like ligands, showed that the chelate-ring opening takes place at the Cr-N bond [7,[17][18][19] and produces a relatively inert aqua-form intermediate stabilised by the intramolecular hydrogen bond between pyridine nitrogen and 2-carboxylate oxygen atoms. This process is reversible, and the amount of the intermediate decreases with an increase in pH.…”

Section: Resultsmentioning

confidence: 87%

“…Further processes obscure, to some extent, the spectroscopic scans registered after the fast period and the results obtained are mainly of qualitative importance. Comparison of the results obtained for the acid [19] and base hydrolysis led to the establishment of the pH effect on the complex reactivities. However, because in acidic media the parallel ligands dissociation (at ca.…”

Section: Resultsmentioning

confidence: 99%

“…4 ] 2? complexes were prepared as described in [19] and [7]. However, it was found that during elution of [Cr(ox) 2 (quinH)] 2-in 0.2 M HClO 4 from the anionic exchanger, Sephadex DEAE, the complex undergoes a slow acid-catalysed aquation, presumably promoted by the resin.…”

Section: Analysesmentioning

confidence: 99%

“…Recently, chromium(III)-quinolinato product, of the Cr:quin molar ratio of 1:2, was recommended as a supplement helping in controlling body mass and treating diseases caused by chromium deficiency [16]. Previously, we have described synthesis and acid-catalysed aquation of complexes of general formulas [Cr(pdaH) 3 ] 0 and [Cr(ox) 2 (pdaH)] 2-(where pdaH -= 2,3-, 2,4-or 2,5-pyridinedicarboxylic acid anion) [7,[17][18][19]. Studies on base hydrolysis of [Cr(pda) 3 ] 3-were also performed [18,20]; however, due to new data obtained by our group, we need to reinterpret the previous kinetic results.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and mechanism of base hydrolysis of chromium(III) complexes with oxalates and quinolinic acid

2009

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Base hydrolysis of [Cr(ox) 2 (quin)] 3-(where quin 2-is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through [Cr(ox)(quin)(OH) 2 ] 3-and [Cr(quin)(OH) 4 ] 3-formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr-N bond. The kinetics of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy d-d band region at 0.4-1.0 M NaOH. The pseudofirst-order rate constants (k obs0 and k obs1 ) were calculated using SPECFIT software for an A ? B ? C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)-(quin)(OH) 2 ] 3-and cis-[Cr(ox) 2 (OH) 2 ] 3-were studied. The determined pseudo-first-order rate constants were independent of [OH -]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, [Cr(ox) 2 (O-quin)(OH)] 4-, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined.

Mixed-ligand chromium(III)-oxalate-pirydinedicarboxylate complexes: potential biochromium sources: kinetic studies in NaOH solutions and effect on 3T3 fibroblasts proliferation

Michał

et al. 2009

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Base hydrolysis of [Cr(ox) 2 (pda)] 3-(where pda is N,O-bonded 2,4-and 2,5-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through [Cr(ox)(pda)(OH) 2 ] 3-and [Cr(pda)(OH) 4 ] 3-complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d-d band region, at 0.4-1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first order rate constants (k obs0 and k obs1 ) were calculated using SPECFIT software for an A ? B ? C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox) 3 ] 3-were studied. The calculated rate constants were independent of [OH 2 ]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox) 2 (pda)] 3-and [Cr(2,4-pda) 3 ] 3-complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which makes them promising candidates for dietary supplements.