Hydrolysis of methionine-containing peptides in binuclear and mononuclear palladium(II) complexes

Abstract

The diaqua complexes of trans-[Pd(py) 2Cl 2] (Py-pyridine), cis-[Pd(edta)Cl 2] (edta-ethylene diamine tetraacetic acid) (complex A), cis-[Pd(temed)Cl 2] (temed-N,N,N′,N′-tetramethylethylene diamine) and cis-1,2-bis-(2-formylglycinebenzenesulfenyl)ethane (Pd(II) dichloride (complex C) react with methionine-containing dipeptides (AcMet-aa) (aa-amino acid) via the thioether group in the methionyl side chain. The trans-Pd(py) 2(H 2O) 2] 2+ and cis-[Pd(temed)(H 2O) 2] 2+ yield binuclear complex [Pd 2(μ-AcMet-aa) 2(H 2O) 4] 4+, the diaqua complexes of complex A and complex C yield mononuclear complexes, [PdL(AcMet-aa)(H 2O)] 2+ (L-edta, 1,2-bis(2-formylglycinebenzenesulfenyl)ethane). These reactions and hydrolytic cleavage of the Met-aa amide bond in the coordinated AcMet-aa are conveniently monitored by 1H NMR spectroscop. The trans-Pd(py) 2(H 2O) 2] 2+ is a very efficient promoter. The hydrolytic rate promoted by it is almost equal to that promoted by [Pd(H 2O) 3(OH)] +, the fastest one up to now. Although reaction of rans-[Pd(py) 2(H 2O) 2] 2+ and cis-[Pd(temed)(H 2O) 2] 2+ with AcMet-aa yield the same binuclear complex, [Pd 2(μ-AcMet-aa) 2(H 2O) 4] 4+, the kinetic data showed that the hydrolytic rate promoted by cis-[Pd(temed)(H 2O) 2] 2+ was actually controlled by temed release. The new mononuclear complexes, [PdL(AcMet-aa)H 2O] 2+, observed for the first time, are also hydrolytically active. It is of interest because they are closely associated with protein cleavage promoted by simple mononuclear Pd(II) complexes.