2-(6-ethylamino-3-ethylimino-2,7-dimethyl-3h-xanthen-9-yl) Benzoic Acid Phenyl Thiourea - A Rhodamine- Based Fluorescent Probe Has Limited Use For Quantitative Hg(ii) Or Mehg(ii) Determination In Environmental Or Biological Samples

Alessandra Pinto Vargas, Diego Alves, Thais Posser, João Batista T. Da Rocha

Resumo


Introdução: Mercury is a dangerous and widespread global pollutant. The long atmospheric residence time of Hg0 vapor and its oxidation to soluble inorganic Hg(II) provides a pathway for contaminating vast amounts of water and soil. Subsequent ingestion of methylmercury by humans from seafood and other dietary and environmental sources can be connected to serious sensory, motor, and cognitive disorders. Consequently, the interest in the development of chemosensors to study the fate of Hg in the environment and in biological samples is remarkable. Material Métodos: this study synthesized the compound 2-(6-ethylamino-3-ethylimino-2,7-dimethyl-3H-xanthen-9-yl) benzoic acid phenyl thiourea to be used as a probe to detect mercuric ions in biological systems here represented by Salvinia auriculata nutrition media. The detection of mercuric ions were design by fluorescence methods. Resultados e Discussão: The compound 2-(6-ethylamino-3-ethylimino-2,7-dimethyl-3H-xanthen-9-yl) benzoic acid phenyl thiourea does not work well in a quantitative way of analysis because its excess cause a quenching in the fluorescence/absorption response, which was evidenced by a critical decrease in these signals when the stochiometry was different of 1:1. Furthermore, we have also observed that this probe can react with methylmercury (MeHg), but the stochiometry is distinct from that of Hg(II). Additionally, the previously claimed sensitivity of ppb for Hg(II) detection by (1) was found here to be in the ppm range. Thus, we conclude that this probe can be used to detect Hg(II) and MeHg qualitatively in biological or environmentally samples. Conclusões: summary, here demonstrated that the probe 2-(6-ethylamino-3-ethylimino-2,7-dimethyl-3H-xanthen-9-yl) benzoic acid phenyl thiourea (1) does not work very well in a quantitative way for Hg analysis because its excess cause a quenching11 in the fluorescence/absorption response, which was evidenced by an critical decrease in these signals when the molar ratio between probe and mercury is less than 1:1. The mechanism by which this inhibition occurs could be explained by a non-fluorescent intermediate that is easily converted in its fluorescent form with an excess of mercuric ions. The application of this compound in analysis of biological materials could be very difficult, because it will require a titration with probe 1 for a better estimation of the quantity of Hg in the sample. Herein we report that the use of probe 1 for analysis of mercury uptake by S. auriculata is limited even using 3 different concentrations of probe 1. Consequently, the use of probe 1 for quantitative analysis of Hg(II) or MeHg has non-sense from an analytical and practical point of view. However, for qualitative studies this compound can have some limited utility. Orgão de Fomento: Fapergs e Cnpq

Palavras-chave


mercuric ion, methylmercury, probe, macrophytes, salvinia

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