Novel method for prediction of micro/nanostructures of diphenylalanine dipeptide based on semiempirical thermodynamic study

Diphenylalanine dipeptide, a structural motif of Alzheimer β-amyloid polypeptide, self-assembles in different solvents (especially high purity water) into micro/nanostructures applying in many current and emerging applications. The morphological evolution of the dipeptide into various micro/nanostructures has been predicted by a semi-empirical thermodynamic study. In this study, the thermodynamical properties of the dipeptide (molar enthalpy of fusion and melting point temperature) were measured 45.3 kJ/mol and 310 °C, respectively, by differential scanning calorimetry. The dipeptide solubility in water was determined by high performance liquid chromatography at three different temperatures. These thermodynamical properties were used in a van’t Hoff type expression to calculate the experimental activity coefficients. The activity coefficient has then been correlated by the generalized electrolyte NRTL model with three adjustable parameters. To have a solubility prediction at any temperature, the parameters of the model were regressed from the experimental activity coefficients determined in three different measured solubilities. The solubility of the diphenylalanine dipeptide in water made it possible to predict the morphological evolution of the dipeptide into different micro/nanostructures as a function of supersaturation.