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.

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

Poly[[tetra-aquabis-(µ-hydroxy-acetato-κO,O:O,O)-µ(2)-sulfato-κO:O'-dicadmium(II)] monohydrate].

The title compound, {[Cd(2)(C(2)H(3)O(3))(2)(SO(4))(H(2)O)(4)]·H(2)O}(n), was obtained unintentionally in a transmetallation reaction. The crystal structure contains a two-dimensional metal-organic framework based on Cd(II)-(µ-hydroxy-acetato-κ(4)O(1),O(2):O(1),O(1'))-Cd(II) zigzag chains joined together by bridging SO(4) anions. The resulting layers are shifted with respect to each other and are stacked along the c axis. Their construction is supported by hydrogen bonds between water molecules and between water molecules and carboxylate or sulfate groups. Neighbouring layers are bridged by hydrogen bonds between the hydroxyl substituent and a sulfate anion. The sulfate anion and solvent water mol-ecule are located on twofold axes. The results demonstrate that care must be taken when preparing ethyl-enediamine-tetra-acetic acid-type complexes by transmetallation, in order to avoid precipitation of metal complexes with the α-hydroxy-acetate ligand.