title: Demethylation kinetics of aspartame and L-phenylalanine methyl ester in aqueous solution.
abstract: The kinetics of demethylation of aspartame and L-phenylalanine methyl ester were studied in aqueous solution at 25 degrees C over the pH range 0.27-11.5. The pseudo-first-order rate constant for aspartame was resolved into individual contributions from methyl ester hydrolysis and diketopiperazine formation. pH-rate profiles were quantitatively described by chemically reasonable kinetic schemes. Aspartame is maximally stable at pH 4 (t90 = 53 days at 25 degrees C); phenylalanine methyl ester, at pH 3. The potentiometrically measured pKa values were pKa1 3.19 and pKa2 7.87 for aspartame and pKa 7.11 for phenylalanine methyl ester.
authors.affiliation: School of Pharmacy, University of Wisconsin, Madison 53706-1508.
authors.forename: R D
authors.initials: RD
authors.lastname: Skwierczynski
authors.forename: K A
authors.initials: KA
authors.lastname: Connors
mesh_terms: D001218:Aspartame / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003640:Dealkylation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry; D011199:Potentiometry; D012996:Solutions; D014867:Water
chemical_list: D012996:Solutions; D014867:Water; C034515:phenylalanine methyl ester; D010649:Phenylalanine; D001218:Aspartame