13907-45-4Relevant academic research and scientific papers
Hydrolytic and redox transformations of chromium(III) bis-oxalato complexes with glutaminic acid and glutamine: A kinetic, UV-Vis and EPR, study
Kiersikowska, Emilia,Kita, Ewa,Kita, Przemys?aw,Wrzeszcz, Grzegorz
, p. 435 - 445 (2016/04/19)
The title complexes have been synthesized, chromatographically isolated and characterized by their ligands to metal ratio determinations and spectroscopic analyses. The kinetics of the first aquation stage, i.e., the amino acid chelate ring opening via the Cr-N bond cleavage, has been studied spectrophotometrically in acidic and alkaline media. Hydrogen peroxide oxidizes the complexes in alkaline media to CrO 42- anion and a relatively stable Cr(V) complex. Consecutive biphasic kinetics through two first-order steps were observed for the base hydrolysis and the oxidation process, whereas the acid-catalyzed aquation obeys a simple first-order pattern. Based on the kinetic and spectroscopic data, mechanisms of the coordinated amino acid liberation and chromium(III) oxidation are discussed.
Characterization and oxidation of chromium(III) by sodium hypochlorite in alkaline solutions
Jiang, Huijian,Rao, Linfeng,Zhang, Zhicheng,Rai, Dhanpat
, p. 3237 - 3242 (2008/10/09)
Chromium exists in nuclear waste sludges and is a problematic element in the vitrification process of high-level nuclear wastes. It is therefore necessary to treat the waste sludges to remove chromium prior to vitrification, by caustic leaching or oxidation of Cr(III) to Cr(VI). The objective of this study is to investigate the effect of oligomerization of Cr(III) on its oxidation by hypochlorite in alkaline solutions. Monomeric, dimeric and trimeric Cr(III) species in solution were separated by ion exchange. The kinetics of the oxidation of the separated species by hypochlorite in alkaline solutions was studied by UV/Vis absorption spectroscopy, and compared with the oxidation by hydrogen peroxide previously studied. Results indicate that hypochlorite can oxidize Cr(III) to Cr(VI) in alkaline solutions, but the rate of oxidation by hypochlorite is slower than that by hydrogen peroxide at the same alkalinity and concentrations of oxidants. The rate of oxidation of Cr(III) by both oxidants decreases as the concentration of sodium hydroxide is increased, but the oxidation by hypochlorite seems less affected by the degree of oligomerization of Cr(III) than that by peroxide. Compared with the oxidation by hydrogen peroxide where the major reaction pathway has an inverse order with respect to CNaOH, the oxidation by hypochlorite has a significant reaction pathway independent of [OH-].
Chromium(V) peptide complexes: Synthesis and spectroscopic characterization
Barnard, Peter J.,Levina, Aviva,Lay, Peter A.
, p. 1044 - 1053 (2008/10/09)
A series of stable Cr(V) model complexes that mimic the binding of Cr(V) to peptide backbones at the C-terminus of proteins have been prepared for N,N-dimethylurea derivatives of the tripeptides Aib3-DMF, AibLAlaAib-DMF, and AibDAlaAib-DMF (Aib = 2-amino-2-methylpropanoic acid, DMF = N,N-dimethylformamide). The Cr(II) precursor complexes were synthesized by the initial deprotonation of the amide and acid groups of the peptide ligands in DMF with potassium tert-butoxide in the presence of CrCl2. The Cr(II) intermediates thus formed were then immediately oxidized to Cr(V) using tert-butyl hydroperoxide. Spectroscopic and mass-spectrometric analyses of the Cr(V) complexes showed that a new metal-directed organic transformation of the ligand had occurred. This involved a DMF solvent molecule becoming covalently bound to the amine group of the peptide ligand, yielding a urea group, and a third coordinated deprotonated urea nitrogen donor. A metal-directed oxidative coupling has been proposed as a possible mechanism for the organic transformation. The Cr(V/IV) reduction potential was determined for the three Cr(V) complexes using cyclic voltammetry, and in all cases it was quasi-reversible. These are the first isolated and fully characterized Cr(V) complexes with non-sulfur-containing peptide ligands.
Chromium(V) complexes of hydroxamic acids: Formation, structures, and reactivities
Gez, Swetlana,Luxenhofer, Robert,Levina, Aviva,Codd, Rachel,Lay, Peter A.
, p. 2934 - 2943 (2008/10/09)
A new family of relatively stable Cr(V) complexes, [CrVO(L) 2]- (LH2 = RC(O)NHOH, R = Me, Ph, 2-HO-Ph, or HONHC(O)(CH2)6), has been obtained by the reactions of hydroxamic acids with Cr(VI) in polar aprotic solvents. Similar reactions in aqueous solutions led to the formation of transient Cr(V) species. All complexes have been characterized by electron paramagnetic resonance spectroscopy and electrospray mass spectrometry. A Cr(V) complex of benzohydroxamic acid (1, R = Ph) was isolated in a pure form (as a K+ salt) and was characterized by X-ray absorption spectroscopy and analytical techniques. Multiple-scattering analysis of X-ray absorption fine structure spectroscopic data for 1 (solid, 10 K) point to a distorted trigonal-bipyramidal structure with trans-oriented Ph groups and Cr-ligand bond lengths of 1.58 A (Cr-O), 1.88 A (Cr-O(C)), and 1.98 A (Cr-O(N)). Under ambient conditions, 1 is stable for days in aprotic solvents but decomposes within minutes in aqueous solutions (maximal stability at pH ～ 7), which leads predominantly to the formation of Cr(III) complexes. Complex 1 readily undergoes ligand-exchange reactions with biological 1,2-diols, including D-glucose and mucin, in neutral aqueous solutions. It differs from most other types of Cr(V) complexes in its biological activity, since no oxidative cleavage of plasmid DNA in vitro and no significant bacterial mutagenicity (in the TA 102 strain of Salmonella typhimurium) was observed for 1. In natural systems, stabilization of Cr(V) by hydroxamato ligands from bacterial-derived siderophores (followed by ligand-exchange reactions with more abundant carbohydrate ligands) may occur during the biological reduction of Cr(VI) in contaminated soils.
Biomimetic oxidation of chromium(III): Does the antidiabetic activity of chromium(III) involve carcinogenic chromium(VI)?
Mulyani, Irma,Levina, Aviva,Lay, Peter A.
, p. 4504 - 4507 (2007/10/03)
The insulin-enhancing activities of some CrIII complexes, such as [Cr3O(OCOEt)6-(OH2)3]+ (1), previously attributed to specific interactions of CrIII ions with cellular insulin receptors, are more likely to be caused by the formation of [CrO4]2- (2). Oxidation of 1 to 2 by biologically relevant oxidants, including enzymes (see scheme), and inhibition of an isolated protein tyrosine phosphatase by a CrVI complex are reported.
Selective Recovery of Chromium from Precipitates Containing d Elements and Actinides: I. Effect of H2O2
Fedoseev, A. M.,Shilov, V. P.,Charushnikova, I. A.,Yusov, A. B.,Budantseva, N. A.,Delegard, C. H.
, p. 355 - 360 (2008/10/08)
Oxidation of various Cr(III) hydroxides and mixed Cr(III)-Ni(II) and Cr(III)-Fe(III) hydroxides with hydrogen peroxide was studied. The initial reaction rate increases as the Cr(III) content in the suspension and H2O2 concentration are increased and nonmonotonicaly decreases with increasing NaOH concentration within the 0.2-2.0 M range. The activation energyin 0.5 M NaOH is equal to 82 kJ mol**-1 (30-90°C). The oxidant c onsumption substantially exceeds the stoichiometry.
Selective Recovery of Chromium from Precipitates Containing d Elements and Actinides: I. Effect of O2
Fedoseev, A. M.,Budantseva, N. A.,Yusov, A. B.,Shilov, V. P.,Delegard, C. H.
, p. 347 - 354 (2008/10/08)
Oxidation of Cr(III) hydroxides, double Fe(III)-Cr(III) hydroxides, and some examples of spinel phases NiCr2O4 and Fe(Cr,Fe)2O4 in alkaline suspensions (0.2-0.5 M NaOH) under the action of air and pure oxygen (1-3 atm) was studied. The reaction rate increases with increasing concentration of alkali, temperature, and oxygen pressure. Under these conditions, Pu(IV) sorbed on chromium hydroxides is not oxidized with oxygen and remains in the precipitate.
Oligomerization of chromium(III) and its impact on the oxidation of chromium(III) by hydrogen peroxide in alkaline solutions
Rao, Linfeng,Zhang, Zhicheng,Friese, Judah I.,Ritherdon, Ben,Clark, Sue B.,Hess, Nancy J.,Rai, Dhanpat
, p. 267 - 274 (2008/10/08)
Monomeric, dimeric and trimeric chromium(III) species in solution were separated by ion exchange and characterized with UV/Vis absorption and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). The kinetics of the oxidation of the separated species by hydrogen peroxide in alkaline solutions were studied by conventional and stopped-flow UV/Vis absorption spectroscopy. Results indicate that the intensity of Cr-Cr scattering in the EXAFS spectra (dCr-Cr ～ 2.99 A), a measure of the degree of oligomerization, increases as the solution alkalinity is increased. As the oligomerization proceeds, the rate of oxidation by hydrogen peroxide in alkaline solutions decreases in the order: monomer > dimer > trimer > aged/unseparated alkaline chromium(III) solution where higher oligomers dominate. The dominant redox pathway has an inverse order with respect to CNaOH. The data suggest that the rate-determining step involves the weakening of the bridging bonds in the oligomer and a concomitant release of one hydroxyl group from the chromium(III) moiety upon the attack by hydrogen peroxide.
Kinetics of oxidation of chromium(III) by N-bromosuccinimide in aqueous alkaline medium
Kamble,Hugar,Nandibewoor
, p. 144 - 147 (2007/10/03)
The title reaction is first order in [N-bromosuccinimide] (NBS), fractional order in [chromium(III)] and inverse fractional order in [OH-]. A negative temperature effect is noticed. The active species of chromium(III) and NBS are Cr(OH)4- and HOBr respectively. A mechanism has been proposed and the reaction constants are derived.
Nucleophilic catalysis by HPO42- in the hydrolysis of Cr2O72-. Formation and decay of HO3POCrO32-
Brasch,Buckingham,Clark
, p. 2283 - 2289 (2007/10/02)
The initial reaction of Cr2O7(2-) in phosphate buffer (pH 6.03-8.54, 25.0°C, I = 1.0 M NaClO4) follows the rate law kobs = kK[HPO4(2-)]/(1+K[HPO4(2-)]). This is interpreted as arising from the reversible and rapid formation of a chromium(VI)-phosphato intermediate of increased coordination number (K = 5.5±1.3 M-1), and rate-determining loss of CrO4(2-) from this species (k = 4.4±0.5 s-1) to give HO3POCrO3(2-) (pKac = 6.96). This appears to be the first clear demonstration of an addition-elimination (stepwise) mechanism for substitution at chromium (VI). Subsequent equilibration of HO3POCrO3(2-) to give HCrO4- and H2PO4- (K = 5.95±1.90 M-1) is seen as a separate process which is subject to specific H+ and OH-, and general base (HPO4(2-)) catalysis, in addition to a spontaneous reaction.
