Stability constant determinations of alitame with H(I) and Cu(II) under physiological conditions using potentiometric measurements

Stability constant determinations of the new artificial sweetener alitame ( L-alpha-aspartyl-N-(2,2,4,4-tetramethyl-3-thietanyl)-D-alaninamide), an HL type ligand (L- = the deprotonated form of the ligand), was carried out wit h H(I) and Cu(II) under physiological conditions (I = 0.15(NaCl) in water, 37 degrees C) using potentiometric titration. The molar concentration stabi lity constants of H(I) and Cu(II) complexes with alitame, together with a d istribution diagram of the Cu(II)-alitame complex species as a function of pH, are obtained. Cu(II) is able to form binary complex species (CuL+, CuL2 ) with alitame in solution. Those species are further deprotonated to form the corresponding CuLH-1, CuLH-2- and CuL2H-1- species. The neutral Cu(II)- alitame complex, CuL2, is the major species between pH = 6.5 and 7.5 follow ed by CuLH-1. A comparison with the less-stable artificial sweetener, aspar tame (N-L-alpha-aspartyl-L-phenylalanine 1-methyl ester), is considered. Pr eliminary stability tests for alitame and Cu(II)-alitame solutions, using p H and stability constant methods, are reported. (C) 1998 Elsevier Science L td. All rights reserved.