title: pKa determinations of xanthene derivates in aqueous solutions by multivariate analysis applied to UV-Vis spectrophotometric data.
abstract: 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.
authors.affiliation: Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5.790, CEP 87.020-900, Maringá, Paraná, Brazil.
authors.forename: Vagner Roberto
authors.initials: VR
authors.lastname: Batistela
authors.forename: Diogo Silva
authors.initials: DS
authors.lastname: Pellosi
authors.forename: Franciane Dutra
authors.initials: FD
authors.lastname: de Souza
authors.forename: Willian Ferreira
authors.initials: WF
authors.lastname: da Costa
authors.forename: Silvana Maria
authors.initials: SM
authors.lastname: de Oliveira Santin
authors.forename: Vagner Roberto
authors.initials: VR
authors.lastname: de Souza
authors.forename: Wilker
authors.initials: W
authors.lastname: Caetano
authors.forename: Hueder Paulo Moisés
authors.initials: HP
authors.lastname: de Oliveira
authors.forename: Ieda Spacino
authors.initials: IS
authors.lastname: Scarminio
authors.forename: Noboru
authors.initials: N
authors.lastname: Hioka
mesh_terms: D004801:Eosine Yellowish-(YS) / Q000737:chemistry*; D004923:Erythrosine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D012395:Rose Bengal / Q000737:chemistry*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*; D014966:Xanthenes / Q000737:chemistry*
chemical_list: D012996:Solutions; D014966:Xanthenes; D014867:Water; D012395:Rose Bengal; D004923:Erythrosine; D004801:Eosine Yellowish-(YS)