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Stability constant determinations of the new artificial sweetener alitame ( l -α-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 with H(I) and Cu(II) under physiological conditions ( I =0.15(NaCl) in water, 37°C) using potentiometric titration. The molar concentration stability constants of H(I) and Cu(II) complexes with alitame, together with a distribution 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 + , CuL 2 ) with alitame in solution. Those species are further deprotonated to form the corresponding CuLH −1 , CuLH −2 − and CuL 2 H −1 − species. The neutral Cu(II)-alitame complex, CuL 2 , is the major species between pH=6.5 and 7.5 followed by CuLH −1 . A comparison with the less-stable artificial sweetener, aspartame ( N - l -α-aspartyl- l -phenylalanine 1-methyl ester), is considered. Preliminary stability tests for alitame and Cu(II)-alitame solutions, using pH and stability constant methods, are reported. |
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