Solubility of sulfadiazine in (acetonitrile plus methanol) mixtures: Determination, correlation, dissolution thermodynamics and preferential solvation

The equilibrium solubility of sulfadiazine (SD, 3) in {acetonitrile (MeCN, 1) + methanol (MeOH, 2)) mixtures at nine temperatures from 278.15 K to 318.15 K has been determined and correlated by means of some well-known thermodynamic correlation models. Five models including van't Hoff. the mixture response surface (MRS), Jouyban-Acme, Jouyban-Acree-van't Hoff and the modified Wilson models were applied to mathematical solubility data modelling. The accuracy of each model is investigated by the mean relative deviations (MRD%) of the back-calculated solubility. All used models show a low MRD% values ( < 8.0%) for the calculated data indicating a good correlation of sulfadiazine solubility data with the given mathematical models. By using the van't Hoff and Gibbs equations the respective apparent thermodynamic quantities of the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Non-linear enthalpy-entropy relationship was observed for SD in the plot of enthalpy vs. Gibbs energy exhibiting negative slope in the composition region 0.00 < w(1) <0.05 indicating entropy-driving mechanism for this transfer process, and variant but mainly positive slopes in the composition interval 0.05 < w(1) < 0.30, indicating enthalpy-driving mechanism for these transfer processes. From w(1) = 0.30 to neat MeCN a slope near zero is observed. Furthermore, the preferential solvation of SD by Meal or MeOH was analysed by using the inverse Kirkwood-Buff integrals. Thus, SD is preferentially solvated by MeOH molecules in MeOH-rich mixtures. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The equilibrium solubility of sulfadiazine in acetonitrile and methanol mixtures at different temperatures was successfully determined and correlated with various thermodynamic models. The solubility data was well-modeled by the chosen mathematical models, with low MRD% values indicating good correlation. The thermodynamic properties of the dissolution and mixing processes were calculated using van't Hoff and Gibbs equations, revealing different driving mechanisms in different composition ranges. Additionally, the preferential solvation of sulfadiazine by methanol molecules in methanol-rich mixtures was observed.