Determination of pKa of dyes by electrical impedance spectroscopy |
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Authors: | HP de Oliveira |
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Institution: | Colegiado de Pós-Graduação em Ciência dos Materiais, Universidade Federal do Vale do São Francisco, 48909-810, Juazeiro, BA, Brazil |
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Abstract: | In this work, we analyze the electrical response of aqueous solutions of dyes as a function of pH. When the acid-base equilibrium is reached, it is possible to detect structural transitions related with changes in molecular conformation. To this, it is necessary the introduction of parallel plates into the solution and from analysis of Nyquist diagrams of samples, it is possible to determine the values of pKa. The advantage is the absence of redox markers in solution, thus avoiding charge transfer stimulated by the diffusion processes. The effects measured on the electrical response are function of the dye molecular aggregation state, which is structurally dependent on the solution protonation conditions. The detection of aggregated molecules such as dimers, trimers, and oligomers defines Electrical Impedance Spectroscopy (EIS) as a fundamental tool for the analysis of pKa of dyes. |
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Keywords: | Electrical impedance spectroscopy pKa Aggregational processes Nyquist diagrams |
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