Reduction of vanadium(V) by L-ascorbic acid at low and neutral pH: kinetic, mechanistic, and spectroscopic characterization |
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Authors: | Wilkins Patricia C Johnson Michael D Holder Alvin A Crans Debbie C |
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Institution: | Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, 88003, USA. |
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Abstract: | L-Ascorbic acid interacts with vanadium(V) over the pH range of 0.4-7.0 to form three different coordination complexes. Both inner- and outer-sphere electron-transfer pathways are proposed to form vanadium(IV) complexes with L-ascorbate or dehydroascorbate, respectively. Effects of the pH on the coordination of L-ascorbic acid to the vanadium(V) center were observed and are presumably related to the speciation of the vanadium(V) ion. Three vanadium(IV) complexes were observed using ambient-temperature electron paramagnetic resonance spectroscopy. Two of these complexes are proposed to be vanadium(IV) L-ascorbate complexes, and one is consistent with a vanadium(IV) dehydroascorbic acid complex proposed earlier. These reduction reactions will occur under physiological conditions and could be important to the reduction of vanadium(V)-containing coordination complexes used as insulin-enhancing agents for treatment of diabetes. |
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