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Stability studies on the SPf66 antimalarial peptide with different pH and temperature conditions were carried out. The degradation mechanism was elucidated by the size-exclusion chromatography (SEC) technique and the experimental data obtained at 37 degrees C and different pH were fitted to a kinetic degradation model that could explain the loss of its immunogenic capacity. At 5, 25, 37, and 70 degrees C and pH 2, changes were detected in the areas of the different species, although the values obtained could not be fitted to any known degradation kinetics.

The effects of 5-fluorouridine (5-FUR, CAS 316-46-1) degradation products, 5-fluorouracil (5-FU, CAS 51-21-8) and D-ribose (CAS 50-69-1), on its degradation rate was investigated following a 2(3) factorial design. The experimental data fitted to the proposed mathematical model which includes two parallel degradation mechanisms: the first one, a second order bimolecular reaction involving both 5-FUR and 5-FU, and the second, a first order one. Experimental data obtained show a high variability. Both graphic and statistical analysis of the experiments for which a full kinetic model was applied manifested that the degradation mechanism included an autocatalytic route and confirmed the role of the 5-FU on the hydrolysis of 5-FUR.