Spectroscopic characterization of different protonation/deprotonation states of Barbaloin in aqueous solution

Autor(es)

Matos, Fernanda Lima ; Duarte, Evandro L. ; Muniz, Gabriel S. V. ; Milan-Garces, Erix Alexander ; Coutinho, Kaline ; Lamy, M. Teresa ; da Cunha, Antonio R.

• Tipo de documento: Artigo Científico
• Fonte: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY; v. 286, p. 11-pg., 2023-02-05.

Resumo

Barbaloin (10-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthraquinone: aloin A), present in Aloe species, is widely used in food, cosmetic and pharmaceutical industries. Here we characterize its optical absorption and emission spectra in aqueous solution at different pH values. Through pH titration, using both absorption and fluorescence spectroscopy, two pKa values for Barbaloin were determined: pKa1 = 9.6 +/- 0.6 and pKa2 = 12.6 +/- 0.8. These acidity constants were found to be higher than those found for Emodin, a similar molecule which lacks the sugar moiety present in Barbaloin. Performing quantum mechanical calculations for non-ionized, singly, doubly, and triply deprotonated forms of Barbaloin in vacuum and in water, we assigned the positions of the site for the first and third deprotonation in the anthraquinone group, and the second deprotonation in the glucose group. The instability of Barbaloin in high pH solutions is discussed here, and the optical absorption and fluorescence spectra due to products resulted from Barbaloin degradation at high pH is well separated from the Barbaloin original spectra. Biological fluids have specific pH values to maintain homeostasis, hence determining the pKa of Barbaloin is important to evaluate the mechanism of action of this drug in different parts of an organism as well as to predict pharmacological relevant parameters, such as absorption, distribution, metabolism, and excretion. (AU)

• Processo FAPESP: 17/25930-1 - Caracterização de dispersões lipídicas de interesse biológico: estruturas e interações
• Beneficiário: Maria Teresa Moura Lamy
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 14/50983-3 - INCT 2014: fluidos complexos
• Beneficiário: Antonio Martins Figueiredo Neto
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 18/20162-9 - Investigando a Patogênese e a Resistência à Drogas em Microrganismos - Caracterização e Controle de Transportadores ABC
• Beneficiário: Andrea Balan Fernandes
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 21/01593-1 - Múltiplas técnicas físicas na caracterização estrutural de membranas lipídicas de interesse biológico
• Beneficiário: Maria Teresa Moura Lamy
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 17/03910-9 - Interação de antraquinonas com modelo de membrana biológica
• Beneficiário: Fernanda Lima Matos
• Modalidade de apoio: Bolsas no Brasil - Iniciação Científica
• Processo FAPESP: 21/09016-3 - Caracterização estrutural e eletrônica de moléculas biogênicas emitidas pela flora amazônica
• Beneficiário: Kaline Rabelo Coutinho
• Modalidade de apoio: Auxílio à Pesquisa - Regular