Thermodynamics of pyrimethamine and sulfadiazine binding to a chitosan derivative

A thermodynamic investigation of the interaction of pyrimethamine (PYR) and sulfadiazine (SDZ) with immobilized copper on chitosan (chit-Cu) was done by heat-conduction calorimetry at 298.15 K. Langmuir isotherm describes the adsorption equilibrium behaviour in the entire concentration range studied. The molar enthalpies for formation of a monolayer of drug, ΔmonHm, from linear and (non-linear) data analysis methods were found to be −40.2 ± 1.2 (−42.1 ± 1.5) and −69.0 ± 2.2 (−68.5 ± 1.9) kJ mol−1 for PYR and SDZ, respectively.