Oxidation of D-Gluconic Acid with Vanadium(V). Comparison with related Substrates

DISETTI, M. E.; CERUTI, M. J.; OVIEDO, N.; CEREDA, Y.; SANTORO, M.

BIOCELL

Año: 2008

0327-9545

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Vanadium is a biological-relevant element. High concentrations of V(V) are found in ascidians, some mushrooms and worms. It is active in the oxidation of organic substrates such as carbohydrates and derivatives. The ability of these compounds to reduce the metal ion does not follow a general pattern, it depends on functional groups configuration, and conditions of reaction. Our studies about the reduction of V(V) by a-hidroxyacids show that the relative activity redox is based on the competition of relative  oxidation rate vs the complexation processes substrate-V(V). We decided to evaluate the reduction of V(V) with substrates like D-gluconic and D-lactobionic acids and then compare the results with the studies realised with L(+)tartaric acid. The monitoring of the redox reactions involved kinetic studies at pH=1-2. In  conditions under study, VO2+ is the predominant species of oxidizing agent. The reactions with D-gluconic and D-tartaric acid can be described via the formation of complexes substrate-VO2+, which quickly lead to the reaction products. These complexes  absorb strongly at 350 nm and may superimpose V(V) absorbance. For D-lactobionic acid, the formation and disappearance of complex are very fast, it is necessary the use of stopped-flow technique. The reactions occur through a free radicals mechanism, where V(V) is reduced by one electron. The relative rate of oxidation is: tartaric>D-gluconic>D-lactobionic acids. The characterization of intermediate and reaction products together with the kinetic studies will clarify the mechanisms of oxidation by V(V) and incease the knowledge of the bio-inorganic chemistry of this element.