Simulation and mathematical analysis of L-Cysteine's transfer properties and solvation behavior in mixed water–alcohol solutions

We investigated preferential solvation of L-Cystine (L-Cys) in two aqueous co-solvent systems (methanol (MeOH) and ethanol (EtOH)), utilizing the mole percentage solubility data provided. The inverse Kirkwood-Buff integrals (IKBI) technique was applied over the temperature range of 293.15–323.15 K. In the alcohol (1) + water (2) system, the preference dissolution variables for MeOH/EtOH were negative at all alcohol compositions, indicating that water was the most effective solvent for L-Cys. Across the examined co-solvent mixtures, MeOH systems exhibited the strongest preferential solvation of L-Cys, followed by EtOH solutions. We extensively discussed the enthalpy of dissolution and transfer, alongside entropy and Gibbs free energy. Thermodynamic functions derived from van’t Hoff analysis show that dissolution is endothermic in all mixtures ( Δ s o l H L − C y s o > 0), while the Gibbs energy values ( Δ s o l G L − C y s o > 0) reflect the relatively low affinity of L-Cys for the alcohol-rich media.