Departamento de Quimica Fisica, Facultad de Quimica, Universidad de Barcelona, Marti i Franques, Spain.
J Phys Chem A. 2011 Sep 8;115(35):9876-85. doi: 10.1021/jp2043174. Epub 2011 Aug 12.
The reactions of permanganate ion with seven α-amino acids in aqueous KH(2)PO(4)/K(2)HPO(4) buffers have been followed spectrophotometrically at two different wavelengths: 526 nm (decay of MnO(4)(-)) and 418 nm (formation of colloidal MnO(2)). All of the reactions studied were autocatalyzed by colloidal MnO(2), with the contribution of the autocatalytic reaction pathway decreasing in the order glycine > l-threonine > l-alanine > l-glutamic acid > l-leucine > l-isoleucine > l-valine. The rate constants corresponding to the nonautocatalytic and autocatalytic pathways were obtained by means of either a differential rate law or an integrated one, the latter requiring the use of an iterative method for its implementation. The activation parameters for the two pathways were determined and analyzed to obtain statistically significant correlations for the series of reactions studied. The activation enthalpy of the nonautocatalytic pathway showed a strong, positive dependence on the standard Gibbs energy for the dissociation of the protonated amino group of the α-amino acid. Linear enthalpy-entropy correlations were found for both pathways, leading to isokinetic temperatures of 370 ± 21 K (nonautocatalytic) and 364 ± 28 K (autocatalytic). Mechanisms in agreement with the experimental data are proposed for the two reaction pathways.
高锰酸根离子与七种α-氨基酸在 KH(2)PO(4)/K(2)HPO(4)缓冲水溶液中的反应，在两个不同波长：526nm（MnO(4)(-))衰减和 418nm（胶体 MnO(2)生成）下进行了光谱跟踪。所有研究的反应均被胶体 MnO(2)自动催化，自动催化反应途径的贡献按甘氨酸>l-苏氨酸>l-丙氨酸>l-谷氨酸>l-亮氨酸>l-异亮氨酸>l-缬氨酸的顺序递减。通过微分速率定律或积分方法获得非自动催化和自动催化途径的速率常数，后者需要使用迭代方法来实现。确定了两条途径的活化参数，并对其进行了分析，以获得所研究反应系列的统计学上显著的相关性。非自动催化途径的活化焓强烈地、正依赖于α-氨基酸质子化氨基的离解的标准吉布斯能量。对于两条途径都发现了线性焓熵相关性，导致非自动催化的等动力学温度为 370±21K，自动催化的为 364±28K。为两条反应途径提出了与实验数据一致的机制。
