Hirshfeld surface and electrostatic potential surface analysis of clozapine and its solubility and molecular interactions in aqueous blends

Abstract

Solubility and relevant thermodynamic properties as well as molecular interactions of clozapine in aqueous systems of protic cosolvent, e.g. isopropanol, and aprotic cosolvents such as acetonitrile, dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidinone (NMP) are focus of this paper. The intermolecular interactions and overall charge distribution of clozapine were respectively investigated by using Hirshfeld surface analysis and molecular electrostatic potential surface. All experimentations were executed using a shake-flask approach under p = 101.2 kPa (local pressure) from 278.15 (293.15) to 323.15 (333.15) K. The minimum solubility data of clozapine appeared in neat water for each aqueous system at 278.15 K; and the maximum one, in neat cosolvent at 328.15 K. Correlation of the solubility data (mole fraction) through Jouyban–Acree and MRS models acquired acceptable results with relative average deviations (RAD) of no>9.15 %. The solvent descriptors of hydrogen-bonding basicity, solubility parameter and dipolarity-polarizability predominantly controlled the clozapine solubility variation through the quantitative analysis of linear solvation energy relationships in terms of the solubility data at 298.15 K. The extended Hildebrand solubility approach was also employed here to correlate the solubility and study the solvation behavior of solutions. Quantitatively analysis of preferential solvation of clozapine by solvent species in solutions was conducted by the method of inverse Kirkwood–Buff integrals. In the solutions with middle and cosolvent-rich compositions, the parameters of preferential solvation for DMSO, NMP, acetonitrile or isopropanol were positive, which specified that preferential solvation of clozapine was made by co-solvent. In addition, the thermodynamic properties of dissolution of clozapine along with enthalpy–entropy compensation were derived and deeply discussed.