title: Solid state stability studies of model dipeptides: aspartame and aspartylphenylalanine.
abstract: Some solid-state pharmaceutical properties and the solid-state thermal stability of the model dipeptides aspartame (APM) and aspartylphenylalanine (AP), have been investigated. Studies by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), high-performance liquid chromatography, powder X-ray diffraction, and optical microscopy have shown that the dipeptides undergo solid state intramolecular aminolysis of the type, solid --> solid + gas. This reaction was observed for APM at 167-180 degrees C with the liberation of methanol and for AP at 186-202 degrees C with the liberation of water. The exclusive solid product of the degradation reaction of both dipeptides is the cyclic compound 3-(carboxymethyl)-6-benzyl-2,5-dioxopiperazine. The rates of the degradation reactions were monitored by isothermal TGA and by temperature-ramp DSC and were found to follow kinetics based on nucleation control with activation energies of about 266 kJ mol(-1) for APM and 234 kJ mol(-1) for AP.
authors.affiliation: Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis 55455-0343, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Leung
authors.forename: D J
authors.initials: DJ
authors.lastname: Grant
mesh_terms: D001218:Aspartame / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002851:Chromatography, High Pressure Liquid; D004151:Dipeptides / Q000737:chemistry*; D004355:Drug Stability; D007700:Kinetics; D008956:Models, Chemical; D014961:X-Ray Diffraction
chemical_list: D004151:Dipeptides; C045207:aspartyl-phenylalanine; D001218:Aspartame