The co-solvency and thermodynamic properties of camptothecin in mixtures of (ethyl acetate + methanol/ethanol)

Abstract

The solubility profile, molecular interactions and apparent dissolution thermodynamic properties of camptothecin in mixtures of (ethyl acetate + methanol) and (ethyl acetate + ethanol) was studied at the temperature range from T = (273.15 to 318.15) K under 101.3 kPa. In two mixtures, the solubility profile increased firstly and then decreased with the increasing mass fraction of ethyl acetate. In mixture of (ethyl acetate + methanol) at 318.15 K, it reached a maximum (9.176 × 10-5) in mole fraction when the mass fraction of ethyl acetate (w) = 0.80, and 7.554 × 10-5 in mixture of (ethyl acetate + ethanol) at w = 0.60. The Jouyban-Acree model and CNIBS/R-K model were applied to evaluate the solubility profile. The relative average deviation (RAD) data of Jouyban-Acree model in mixture of (ethyl acetate + methanol) was 3.81%, and 5.50% in mixture of (ethyl acetate + ethanol). However, it was no more than 3.59% for CNIBS/R-K model. The CNIBS/R-K model was more consistent than Jouyban-Acree model. In addition, the KAT-LSER model was used to analyse the effect of the solute–solvent intermolecular interactions on solubility profile. Furthermore, apparent dissolution thermodynamic analysis of camptothecin in mixtures of (ethyl acetate + methanol) and (ethyl acetate + ethanol) at the mean harmonic temperature was also performed. The results indicated that the dissolution process was endothermic and entropy-increasing, and the enthalpy is the main contributor to standard free energy of solution process.