Roldán Viviana, Santoro Mabel, González Juan C, Salas-Peregrin Juan Manuel, Signorella Sandra, Sala Luis F
Departamento de Ciencias Básicas, Facultad de Ciencias Veterinarias, UNL, R.P. Kreder 735, Esperanza, Argentina.
J Inorg Biochem. 2004 Feb;98(2):347-57. doi: 10.1016/j.jinorgbio.2003.11.005.
The oxidation of D-lactobionic acid by Cr(VI) yields the 2-ketoaldobionic acid and Cr(3+) as final products when a 20-times or higher excess of the aldobionic acid over Cr(VI) is used. The redox reaction takes place through a complex multistep mechanism, which involves the formation of intermediate Cr(IV) and Cr(V) species. Cr(IV) reacts with lactobionic acid much faster than Cr(V) and Cr(VI) do, and cannot be directly detected. However, the formation of CrO(2)(2+), observed by the first time for an acid saccharide/Cr(VI) system, provides indirect evidence for the intermediacy of Cr(IV) in the reaction path. Cr(VI) and the intermediate Cr(V) react with lactobionic acid at comparable rates, being the complete rate laws for the Cr(VI) and Cr(V) consumption expressed by: -d[Cr(VI)]/dt=[k(I)+k(II)[H(+)]][lactobionicacid][Cr(VI)], where k(I)=(4.1+/-0.1) x 10(-3) M(-1) s(-1) and k(II)=(2.1+/-0.1) x 10(-2) M(-2) s(-1); and -d[Cr(V)]/dt=[k(III)[H(+)]+(k(IV)+k(V)[H(+)])[lactobionicacid]] [Cr(V)], where k(III)=(1.8+/-0.1) x 10(-3) M(-1) s(-1), k(IV)=(1.1+/-0.1) x 10(-2) M(-1) s(-1) and k(V)=(1.0+/-0.1) x 10(-2) M(-2) s(-1), at 33 degrees C. The Electron Paramagnetic Resonance (EPR) spectra show that five-co-ordinate oxo-Cr(V) bischelates are formed at pH 1-5 with the aldobionic acid bound to Cr(V) through the alpha-hydroxyacid group.
当使用的醛糖二酸相对于六价铬过量20倍或更高时，六价铬对D-乳糖酸的氧化反应会生成2-酮醛糖二酸和三价铬作为最终产物。该氧化还原反应通过复杂的多步机制进行，其中涉及中间产物四价铬和五价铬物种的形成。四价铬与乳糖酸的反应速度比五价铬和六价铬快得多，且无法直接检测到。然而，首次在酸性糖/六价铬体系中观察到的二氧化铬二正离子（CrO₂²⁺）的形成，为四价铬在反应路径中作为中间产物提供了间接证据。六价铬和中间产物五价铬与乳糖酸的反应速率相当，六价铬和五价铬消耗的完整速率定律如下：-d[Cr(VI)]/dt = [k(I) + k(II)[H⁺]][乳糖酸][Cr(VI)]，其中k(I) = (4.1 ± 0.1) × 10⁻³ M⁻¹ s⁻¹，k(II) = (2.1 ± 0.1) × 10⁻² M⁻² s⁻¹；以及 -d[Cr(V)]/dt = [k(III)[H⁺] + (k(IV) + k(V)[H⁺])[乳糖酸]][Cr(V)]，其中k(III) = (1.8 ± 0.1) × 10⁻³ M⁻¹ s⁻¹，k(IV) = (1.1 ± 0.1) × 10⁻² M⁻¹ s⁻¹，k(V) = (1.0 ± 0.1) × 10⁻² M⁻² s⁻¹，反应温度为33℃。电子顺磁共振（EPR）光谱表明，在pH值为1 - 5时会形成五配位的氧代铬（V）双螯合物，醛糖二酸通过α-羟基酸基团与铬（V）结合。
