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

Article abstract of DOI:10.1016/s0277-5387(98)00010-2

The diaqua complexes of trans-[Pd(py)₂Cl₂] (Py-pyridine), cis-[Pd(edta)Cl₂] (edta-ethylene diamine tetraacetic acid) (complex A), cis-[Pd(temed)Cl₂] (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(H₂O)₂]²⁺ and cis-[Pd(temed)(H₂O)₂]₂₊ yield binuclear complex [Pd₂(μ-AcMet-aa)₂(H₂O)₄] ⁴⁺, the diagua complexes of complex A and complex C yield mononuclear complexes, [PdL(AcMet-aa)(H₂O)]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 spectroscopy. The trans-Pd(py)₂(H₂O)₂]^2- is a very efficient promoter. The hydrolytic rate promoted by it is almost equal to that promoted by [Pd(H₂O)₃(OH)⁺, the fast one up to now. Although reaction of trans-[Pd(py)₂(H₂O)₂)²⁺ and cis-[Pd(temed)(H₂O)₂]¹²⁺ with AcMet-aa yield the sam binuclear complex, [Pd₂(μ-AcMet-aa)₂(H₂O)₄] ⁴⁺, the kinetic data showed that the hydrolytic rate promoted by cis-[Pd(temed)(H₂O)₂]²⁺ was actually controlled by temed release. The new mononuclear complexes, [PdL(AcMet-aa)(H₂O]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.