Reaction Kinetics and Equilibria of β-Elimination of Some Schiff Base Complexes

Article abstract of DOI:10.1021/ja00410a036

The kinetics of β-elimination of O-phosphoserine, β-chloroalanine, S-ethylcysteine, and β-chloro-α-aminobutyric acid was investigated by NMR in deuterium oxide media at 31.5 +/- 0.5 deg C in the presence of pyridoxal and in the presence and the absence of Ga(III), Al(III), and Zn(II) ions.The reaction rate constants and relevant equilibrium constants are reported for these systems.The specific rate constants for the individual molecular species in solution were determined from the observed reaction rate cobstants and equilibrium constants applicable to these systems.Catalysis by pyridoxal in the absence of metal ions showed an increase in rate as pD was increased, with a rate maximum in the region of pD 8-9, and moderate decrease at higher pH.The first-order rate constants varied with the amino acid moiety in the order β-chloroalanine > O-phosphoserine > β-chloro-α-aminobutyric acid > S-ethylcysteine.The rate constants reported for pyridoxal catalysis in the presence of metal ions show rate enhancements in the order of ten times the values of metal-free systems.Possible mechanisms of these reactions are discussed.