Hydrolysis of the amide bond in histidine- and methionine-containing dipeptides promoted by pyrazine and pyridazine palladium(II)-aqua dimers: Comparative study with platinum(II) analogues

Abstract

Two dinuclear palladium(II) complexes, [{Pd(en)Cl}2(μ-pz)](NO3)2 and [{Pd(en)Cl}2(μ-pydz)](NO3)2, have been synthesized and characterized by elemental microanalysis and spectroscopic (1H and 13C NMR, IR and UV–vis) techniques (en is ethylenediamine; pz is pyrazine and pydz is pyridazine). The square planar geometry of palladium(II) metal centers in these complexes has been predicted by DFT calculations. The chlorido complexes were converted into the corresponding aqua complexes, [{Pd(en)(H2O)}2(μ-pz)]4+ and [{Pd(en)(H2O)}2(μ-pydz)]4+, and their reactions with N-acetylated l-histidylglycine (Ac–l–His–Gly) and l-methionylglycine (Ac–l–Met–Gly) were studied by 1H NMR spectroscopy. The palladium(II)-aqua complexes and dipeptides were reacted in 1:1 M ratio, and all reactions performed in the pH range 2.0<pH<2.5 in D2O solvent and at 37°C. In the reactions of these complexes with Ac–l–His–Gly and Ac–l–Met–Gly dipeptides, the hydrolysis of the amide bonds involving the carboxylic group of both histidine and methionine amino acids occurs. The catalytic activities of the palladium(II)-aqua complexes were compared with those previously reported in the literature for the analogues platinum(II)-aqua complexes, [{Pt(en)(H2O)}2(μ-pz)]4+ and [{Pt(en)(H2O)}2(μ-pydz)]4+.