Institute of Solution Chemistry of Russian Academy of Sciences, 153045, Ivanovo, Academicheskaya str. 1, Russian Federation.
J Phys Chem A. 2012 Nov 8;116(44):10683-94. doi: 10.1021/jp305325e. Epub 2012 Sep 27.
Protonation of a free-base meso-pyrimidinyl-substituted AB(2)-corrole (H(3)AB(2)) in ethanol solution by stepwise addition of sulfuric acid has been studied in the temperature range from 293 to 333 K. The formation rate of protonated species was found to depend profoundly on the temperature at which the titration was undertaken. Two steps in the titration curve were identified at temperatures around 293-298 K, whereas one-step formation of protonated species was found to occur at temperatures above 308 K. The protonation product was the same in both cases, i.e., H(4)AB(2)(+) corrole, protonated at the macrocycle core nitrogen atoms. The two steps in the protonation kinetics at lower temperatures were attributed to protonation of individual tautomers of the free-base H(3)AB(2) corrole. To the best of our knowledge, this is the first well-illustrated (spectrophotometric) observation of individual properties of corrole NH tautomers in fluid solution. Concomitant increase in the NH tautomerization rate with increasing temperature is proposed to account for the one-step protonation. Evidences for the role of individual corrole NH tautomers in the protonation process as well as their optical features are discussed based on spectroscopic results and simulation data.
在 293 至 333 K 的温度范围内，通过逐步添加硫酸研究了游离碱中嘧啶基取代的 AB(2)-卟啉（H(3)AB(2)）在乙醇溶液中的质子化。发现质子化物种的形成速率强烈依赖于进行滴定的温度。在 293-298 K 左右的温度下，在滴定曲线上确定了两个步骤，而在高于 308 K 的温度下，发现质子化物种的形成是一步完成的。在这两种情况下，质子化产物都是相同的，即 H(4)AB(2)(+)卟啉，在大环核氮原子上质子化。在较低温度下的质子化动力学中的两个步骤归因于游离碱 H(3)AB(2)卟啉的各个互变异构体的质子化。据我们所知，这是首次在流体溶液中很好地观察到卟啉 NH 互变异构体的单个性质。提出随着温度的升高，NH 互变异构体速率的同时增加来解释一步质子化。基于光谱结果和模拟数据，讨论了单个卟啉 NH 互变异构体在质子化过程中的作用及其光学特征。
