Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5.790, CEP 87.020-900, Maringá, Paraná, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2011 Sep;79(5):889-97. doi: 10.1016/j.saa.2011.03.027. Epub 2011 Apr 2.
Xanthenes form to an important class of dyes which are widely used. Most of them present three acid-base groups: two phenolic sites and one carboxylic site. Therefore, the pKa determination and the attribution of each group to the corresponding pKa value is a very important feature. Attempts to obtain reliable pKa through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pKa values allied to strong UV-Vis spectral overlap, multivariate analysis, a powerful chemometric method, is applied in this work. The determination was performed for eosin Y, erythrosin B, and bengal rose B, and also for other synthesized derivatives such as 2-(3,6-dihydroxy-9-acridinyl) benzoic acid, 2,4,5,7-tetranitrofluorescein, eosin methyl ester, and erythrosin methyl ester in water. These last two compounds (esters) permitted to attribute the pKa of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pKa determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.
吖嗪类化合物形成了一类广泛应用的重要染料。它们大多数呈现出三个酸碱基团：两个酚基位点和一个羧基位点。因此，pKa 值的确定以及每个基团对应于相应的 pKa 值的归属是一个非常重要的特征。通过电位滴定法和使用一阶和二阶导数的电子吸收分光光度法尝试获得可靠的 pKa 值的尝试都失败了。由于与强紫外-可见光谱重叠相关的接近的 pKa 值，多元分析，一种强大的化学计量学方法，被应用于这项工作中。对于曙红 Y、赤藓红 B 和孟加拉玫瑰红 B 进行了测定，并且还对其他合成衍生物如 2-(3,6-二羟基-9-吖啶基)苯甲酸、2,4,5,7-四硝基荧光素、曙红甲酯和赤藓红甲酯在水中进行了测定。后两种化合物（酯）允许归属酚基团的 pKa 值，对于一些研究的染料来说，这是不容易识别的。除了 pKa 值的确定之外，化学计量学还允许估计一些常见的质子化物种的电子光谱和取代基效应的评估。
