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In the present work, acid dissociation constant (pK a ) values of muscimol derivatives were calculated using the Density Functional Theory (DFT) method. In this regard, free energy values of neutral, protonated and deprotonated species of muscimol were calculated in water at the B3LYP/6-31G(d) basis sets. The hydrogen bond formation of all species had been analyzed using the Tomasi's method. It was revealed that the theoretically calculated pK a values were in a good agreement with the existing experimental pK a values, which were determined from capillary electrophoresis, potentiometric titration and UV-visible spectrophotometric measurements.Uniterms: Nanodrug. Muscimol. Acid/dissociation constants. Computational chemistry. Density Functional Theory.No presente trabalho, calculou-se a constante de dissociação do ácido (pK a ) dos derivados de muscimol, utilizando-se o método da teoria do funcional de densidade (DFT). Com esse objetivo, calcularam-se os valores das espécies neutra, protonada e desprotonada do muscimol em água em base B3LYP/6-31G(d). A formação da ligação de hidrogênio de todas as espécies foi analisada utilizando o método de Tomasi. Demonstrou-se que os valores de pKa calculados teoricamente estavam em boa concordância com os valores experimentais disponíveis, determinados por eletroforese capilar, titulação potenciométrica e medidas por espectrofotometria UV-visível.Unitermos: Nanofármaco. Muscimol. Ácido/constantes de dissociação. Química computacional. Teoria do funcional de densidade.

The protonation constants of adenosine 5'-monophosphate, guanosine 5'-monophosphate, and inosine 5'-monophosphate were determined in binary mixtures of H 2 O containing 0,10,15,20,25,30, 35, 40, 45, and 50% MeOH, using a combination of potentiometric and spectrophotometric methods at a constant temperature (258) and constant ionic strength (0.1 mol · dm À3 NaClO 4 ). The protonation constants were analyzed using the normalized polarity parameter (E N T ), and Kamlet, Abboud, and Taft (KAT) parameters. A linear correlation of log K vs. the normalized polarity parameter was obtained. Dual-parameter correlation of log K vs. p* (dipolarity/polarizability) and a (H-bond-donor acidity), as well as p* and b (H-bond-acceptor basicity) also gives good results in various aqueous organic solvent mixtures. Finally, the results are discussed in terms of the effect of solvent on the protonation equilibria.

Background and Objective : In this work, dissociation of nano drug 5-Fluorouracil derivatives was studied theoretically.Methodology : For this purpose, Gibbs free energy values for neutral and deprotonated forms of 5-Fluorouracil were calculated atgas and aqueous phases by using density functional theory (DFT) method. Solvent effects are taken into account by means ofpolarizable continuum model (PCM). Result : It was shown that, theoretically calculated pKa values are in good agreement withthe existing experimental pKa values, which are determined from capillary electrophoresis, potentiometric titration and UV–visiblespectrophotometric measurements. Conclusion : In summary, cluster continuum method with implicit-explicit solvent moleculeswas used for calculation of pKa values. Total energies and molecular parameters were obtained for 5-FUra nanoscale drug systems,at B3LYP/6-31G(d) level of theory for the anion, cation, and neutral species.