Redox and complexation chemistry of the CrVI/CrV/CrIV-d-glucuronic acid system

Abstract

When excess uronic acid over Cr(VI) is used, the oxidation of D-glucuronic acid (Glucur) by Cr(VI) yields D-glucaric acid (Glucar) and Cr(III) as final products. The redox reaction involves the formation of intermediate Cr(IV) and Cr(V) species, with Cr(VI) and Cr(V) reacting with Glucur at comparable rates. The rate of disappearance of Cr(VI), and Cr(V) increases with [H(+)] and [substrate]. The experimental results indicated that Cr(IV) is a very reactive intermediate since its disappearance rate is much faster than Cr(VI)/Cr(V) and decreases when [H(+)] rises. Even at high [H(+)] Cr(IV) intermediate was involved in fast steps and does not accumulate in the reaction. Kinetic studies show that the redox reaction between Glucur and Cr(VI) proceeds through a mechanism combining one- and two-electron pathways for the reduction of intermediate Cr(IV) by the organic substrate: Cr(VI) --> Cr(IV) --> Cr(II) and Cr(VI) --> Cr(IV) --> Cr(III). The mechanism is supported by the observation of free radicals, CrO(2)(2+) (superoxoCr(III) ion) and Cr(V) as reaction intermediates. The EPR spectra show that five-co-ordinate oxo-Cr(V) bischelates are formed at pH < or = 4 with the uronic acid bound to Cr(V) through the carboxylate and the alpha-OH group of the furanose form. Five-co-ordinated oxo-Cr(V) monochelates are observed as minor species in addition to the major five-co-ordinated oxo-Cr(V) bischelates. At pH 7.5 the EPR spectra show the formation of a Cr(V) complex where the cis-diol groups of Glucur participate in the bonding to Cr(V). In vitro, our studies on the chemistry of Cr(V) complexes can provide information on the nature of the species that are likely to be stabilized in vivo. In particular, the EPR pattern of Glucur-Cr(V) species can be used as a finger print to identify Cr(V) complexes formed in biological systems.

Quinic acid and hypervalent chromium: a spectroscopic and kinetic study

“…The intensity ratio between the absorption bands at 245 and 290 nm was 2.2, which conrmed . 18,55,56,63 As occurred with other substrates studied previously, 18,[25][26][27]37 the monotonic growth at 290 nm was found to follow rst-order kinetics (Fig. 6B).…”

“…The UV-vis absorption spectrum of the QA/Cr VI reaction mixture in an acidic medium (HClO 4 ) showed the characteristic behavior of Cr VI in an acidic medium [25][26][27] with a shoulder at 420/450 nm and a band at 350 nm (Fig. 2).…”

“…This observation conrms the formation of Cr II and can be considered to be indirect evidence of the participation of Cr IV in the QA/Cr VI redox mechanism, as has been observed with other saccharides. 18,[25][26][27]37 Taking into account the spectra shown in Fig. 4, the absorbance at 245 nm and 290 nm at any time in these experimental conditions is due to the contributions of CrO 2 2+ and Cr VI .…”

“…11,[13][14][15][16][17] The formation of Cr V and Cr II/IV intermediates during the oxidation of a variety of organic compounds by Cr VI has been observed, [18][19][20][21][22] and their involvement in Cr-induced cancers 1,23 has aroused much curiosity in the chemistry and biochemistry of chromium. 24 In fact, the detection by continuous-wave electron paramagnetic resonance (CW-EPR) or electron spin resonance (ESR) of a long-lived Cr V species [25][26][27][28] is focused on the probable role(s) performed by Cr V species in carcinogenesis brought about by Cr VI . A similar situation has arisen with Cr IV .…”

In Situ Synthesis of Silver Nanoparticles on Cellulose Fibers Using D-Glucuronic Acid and Its Antibacterial Application

“…Most of all, DLA is water soluble and possesses negatively charged carboxyl groups, which might electrostatically interact with Ag + and promote the distribution of Ag + in the cellulose matrix [36,37]. It also has been reported that DLA was able to reduce Cr +5 to Cr +3 [38]. From this point, we can except that the DLA can also be used to reduce silver ions to AgNPs on cellulose fibers.…”