http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Catalysis of [beta]-elimination of amino acids by pyridoxal and metal ions
xiii, 121 leaves : illustrations, graphs ; 28 cm
The kinetics and equilibrium measurements of a-amino acids have been investigated, under β-elimination conditions, in the presence of pyridoxal with and without catalytic metal ions. The nmr technique was applied to several pyridoxal-amino acid systems, β-chloroalanine, β-chloro-αobutyric acid, O-phosphoserine, S-ethylcysteine, β-phenylserine, and β-hydroxyglutamic acid, in order to determine reactivity, equilibria, and reaction kinetics. The order of the reaction rate for β-eliminotion, from the fastest to the slowest, is S-chloroalanine, O-phosphoserine, β- chloro-a-aminobutyric acid, and S-ethylcysteine. The differences in the rate constants showed that the most electronegative group is the best leaving group. The differences in the rate constants between β-chloroalanine and β-chloro- α -aminobutyric acid also showed the β-substituent effect. The experiment with β-phenylserine showed that more than one reaction is possible with β-hydroxy amino acid systems. Both β-elimination and dealdolation reactions were observed for β-phenylserine. The dealdolation reaction was the dominating reaction for this system. The β-hydroxyglutamic acid system not only showed that more than one reaction is possible, but showed that sequential reactions are possible. The main reactions were deaidolation and β -elimination reactions, and sequential reactions are β -elimination followed by decarboxylation. The above reactions point out the necessity of choosing the proper conditions in order to observe a particular reaction. The metal ion catalysis of the β -elimination reaction is very pronounced for ail the amino acids studied. The Ga(III) and Al(III) ions were shown to be more effective catalysts than Zn(II) ion. For the amino acids with more than one reaction, metal ions also showed considerable catalytic effect. The product ratio varied with the charges of the metal ions.
Includes bibliographical references (leaves 112-120).