Effect of solvent composition on DSC exothermic peak of human serum albumin suspended in pyridine-n-hexane mixtures

Human serum albumin (HSA) immersed in pyridine-n-hexane mixtures was analyz ed using differential scanning calorimetry (DSC). State of the solid HSA in organic solvent mixtures is the non-equilibrium state which is seen as the exothermic peak on the DSC curves. The enthalpy change corresponding to th is exothermic peak approaches zero when going from pure pyridine to pure n- hexane. Dependence of the enthalpy change on the pyridine concentration is suggestive that the non-equilibrium state of the immersed HSA results from the HSA-pyridine interactions 'frozen' at the lower temperature. Most likel y the temperature-initiated exothermic peak observed on the DSC curves refl ects the swelling of HSA by pyridine.