Área Química General, Departamento de Químico-Física, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Santa Fe, Argentina; Instituto de Química de Rosario-CONICET, Suipacha 570, S2002LRK Rosario, Santa Fe, Argentina.
Área Química General, Departamento de Químico-Física, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Santa Fe, Argentina; Instituto de Química de Rosario-CONICET, Suipacha 570, S2002LRK Rosario, Santa Fe, Argentina.
Carbohydr Polym. 2014 Dec 19;114:1-11. doi: 10.1016/j.carbpol.2014.07.065. Epub 2014 Aug 8.
Selective oxidation of carboxylate groups present in alginic acid by Cr(VI) affords CO2, oxidized alginic acid, and Cr(III) as final products. The redox reaction afforded first-order kinetics in [alginic acid], [Cr(VI)], and [H(+)], at fixed ionic strength and temperature. Kinetic studies showed that the redox reaction proceeds through a mechanism which combines Cr(VI)→Cr(IV)→Cr(II) and Cr(VI)→Cr(IV)→Cr(III) pathways. The mechanism was supported by the observation of free radicals, CrO2(2+) and Cr(V) as reaction intermediates. The reduction of Cr(IV) and Cr(V) by alginic acid was independently studied and it was found to occur more than 10(3) times faster than alginic acid/Cr(VI) reaction, in acid media. At pH 1-3, oxo-chromate(V)-alginic acid species remain in solution during several hours at 15°C. The results showed that this abundant structural polysaccharide present on brown seaweeds is able to reduce Cr(VI/V/IV) or stabilize high-valent chromium depending on pH value.
通过 Cr(VI)选择性氧化褐藻酸中存在的羧酸盐基团可得到 CO2、氧化褐藻酸和 Cr(III)作为最终产物。在固定离子强度和温度下，该氧化还原反应在[褐藻酸]、[Cr(VI)]和[H(+)]中表现出一级动力学。动力学研究表明，该氧化还原反应通过 Cr(VI)→Cr(IV)→Cr(II)和 Cr(VI)→Cr(IV)→Cr(III)途径相结合的机制进行。自由基、CrO2(2+)和 Cr(V)作为反应中间体的观察结果支持了该机制。独立研究了 Cr(IV)和 Cr(V)被褐藻酸还原的过程，发现其在酸性介质中的反应速度比褐藻酸/Cr(VI)反应快 10(3)倍以上。在 pH 值为 1-3 时，在 15°C 下，氧代铬(V)-褐藻酸物种在溶液中可保持数小时。结果表明，这种存在于褐藻中的丰富结构多糖能够根据 pH 值还原 Cr(VI/V/IV)或稳定高价铬。
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