Disparate behavior of pyrazine and pyridazine platinum(II) dimers in the hydrolysis of histidine- and methionine-containing peptides and unique crystal structure of {[Pt(en)Cl]2(μ-pydz)}Cl2 with a pair of NH⋯Cl−⋯HN hydrogen bonds supporting the pyridazine bridge

Synthesis, spectroscopic and X-ray characterization of various pyrazine-bridged platinum(II) complexes: 1H NMR comparative study of their catalytic abilities in the hydrolysis of methionine- and histidine-containing dipeptides

“…Our recent interest in the study of the reactions between dinuclear platinum(II) complexes with bridging diazine ligands and methionine-and histidine-containing peptides stems from the findings that these complexes can be an effective catalytic reagents for the regioselective amide bond hydrolysis in these peptides [1][2][3]. In accordance to this, the 1 even when the hydrolytic reaction was performed with an excess of [Pt(en)(H 2 O) 2 ] 2+ complex [1].…”

“…In accordance to this, the 1 even when the hydrolytic reaction was performed with an excess of [Pt(en)(H 2 O) 2 ] 2+ complex [1]. Moreover, reactions of two dinuclear diazine-bridged Pt(II) aqua complexes, [{Pt(en)(H 2 O)} 2 (l-pz)] 4+ and [{Pt(en)(H 2 O)} 2 (l-pydz)] 4+ (pydz is pyridazine), with Ac-L-Met-Gly and Ac-L-His-Gly indicated that the [{Pt(en) (H 2 O)} 2 (l-pydz)] 4+ complex reacts only with methionine sulfur atom and promotes the sole cleavage of the amide bond involving the carboxylic group of this anchoring amino acid, while the analogous pyrazine Pt(II) aqua dimer reacts with both residues, promoting cleavage of the amide bonds involving the carboxylic groups of both amino acids, methionine and histidine [2]. The catalytic disparity of these two diazine-bridged Pt(II) aqua dimers was explained by the X-ray analysis of their chlorido analogues, [{Pt (en)Cl} 2 (l-pydz)]Cl 2 and [{Pt(en)Cl} 2 (l-pz)]Cl 2 .…”

“…The X-ray data for the two complexes confirmed the presence of a hidden position of the Pt(II) centers in the [{Pt(en)Cl} 2 (l-pydz)]Cl 2 complex caused by their close proximity due to the ortho-substitution (the two Pt (II) centers are only 3.2535(4) Å apart), compared to the separation of 6.7890(3) Å in [{Pt(en)Cl} 2 (l-pz)]Cl 2 ), and an additional steric hindrance from the amine ligand, which in [{Pt(en)Cl} 2 (l-pydz)] Cl 2 is hydrogen bonded to the chlorido ligand belonging to the other Pt(II) center. Also, it was proposed that displacement of this chlorido ligand by a water molecule would make this hydrogen bond shorter due to the shortening of the metal-ligand bond distance [2].…”

Metal assisted peptide bond hydrolysis: Chemistry, biotechnology and toxicological implications

“…In addition to mononuclear Pt(II) complexes, dinuclear ones containing different bridging diazine ligands, such as pyrazine and pyridazine, were tested for their hydrolytic activities, at 2.0 < pH > 2.5 [57][58][59][60]. The complex {[Pt(en)(H 2 O)] 2 ( -pz)} 4+ with two Pt(II) ions bridged by pyrazine was more efficient than the corresponding mononuclear complex in the hydrolysis of Ac-Met-Gly.…”

“…As a consequence, the pyridazine Pt(II) dimer promotes the cleavage of the peptide bond involving the Met but not the His residue. In contrast, the pyrazine Pt(II) dimer cleaves peptide bonds next to Met and His residues [58].…”