Abstract
The hydrolysis of amino acid esters is catalysed by the palladium(II) complex [Pd(Pic)](2+) (Pic = 2-picolylamine). The reaction has been studied by the pH-stat technique. The overall Pd-II chelate-promoted hydrolysis of the ethyl esters of glycine and alanine may be accounted by inter- and intramolecular mechanisms depicted in Eqns (1) and (2) respectively.
[Pd(Pic)(NH2CH(R)CO2R'](2+) + OH- -->k(1) [Pd(Pic)(NH2CH(R)CO2](+) + R'OH (1)
[Pd(Pic)(NH2CH(R)CO2R')(OH)](+) -->k(2) [Pd(Pic)(NH2CH(R)CO2)(+) + R'OH (2)
The kinetic data for histidine and methionine methyl esters are fitted assuming that hydrolysis proceeds solely by the intermolecular mechanism [Eqn (1)]. The rate enhancement compared with the free ester is discussed in terms of the structure of the complex. Activation parameters associated with the hydrolysis have been determined and discussed.