Solubility measurement, solubility behavior analysis and thermodynamic modelling of melatonin in twelve pure solvents from 278.15 K to 323.15 K

Solubility of melatonin in twelve mono-solvents including seven alcohols {methanol (MT), ethanol (ET), npropanol (n-PrA), n-butanol (n-BT), i-butanol (i-BT), n-pentanol (n-PT) and n-hexanol (n-HeA)) and five esters {methyl acetate (MeAC), ethyl acetate (EtAC), n-propyl acetate (n-PrAC), n-butyl acetate (n-BtAC) and n-pentyl acetate (n-PtAC)) was determined by laser monitoring approach from 278.15 K to 323.15 K under 0.1 MPa. The experimental results indicate that the mole solubility of melatonin shows a positive relation with temperature variation. The solubility of melatonin in the twelve pure solvents at 298.15 K has order: MT (0.03570) > ET (0.02536) > n-PrA (0.01965) > n-BT (0.01524) > n-PT (0.01450) > i-BT (0.01267) > n-HeA (0.01136) > MeAC (0.008498) > EtAC (0.006587) > n-PrAC (0.004280) > n-BtAC (0.003410) > n-PlAC (0.02990). Moreover, the miscibility behavior of melatonin was further analyzed by the Hansen solubility parameter (HSP). The solvent effect of melatonin in tested pure solvents was investigated by using the KAT-LSER model. The four thermodynamic models including two-Suffix Margules, NRTL, NRTL-SAC and UNIQUAC models were applied to correlate the experimental solubility data of melatonin. Furthermore, the dissolution thermodynamic properties including the apparent standard dissolution enthalpy (Delta H-dis(0)), the apparent standard dissolution entropy (Delta H-dis(0)) and the apparent standard Gibbs energy change (Delta H-dis(0)) of melatonin in investigated solvents were calculated by van't Hoff equation. (C) 2020 Elsevier B.V. All rights reserved.