Structure of AcMet‐Gly and its interaction with palladium(II) tetraaqua complex studied by electrospray mass spectrometry and density functional theory

The structure of dipepide AcMet‐Gly was determined by X‐ray crystallographic analysis. It possesses mono‐clinic, space group P2 1 (No. 4). with cell dimensions of α=0.8571(2) nm, b=0.5871(2) nm, c= 1.197(3) nm, β= 99.290(10)°. V=0.5944(15) nm 3 , Z=2, μ=2.74 cm −1 . Mononuclear chelates, described as [Pd(X)(S,N,O‐ AcMet‐Gly)] − , in which Pd(II) is coordinated by thioether, deprotonated amide nitrogen, carbonyl oxygen of me‐thionine and X (AcMetGly or other ligands present in aqueous solution or in mobile phase solution), were detected 5 min after mixing AcMet‐Gly with [Pd(H 2 O) 4 ] 2‐ at room temperature using electrospray ionization mass spectrometry. The geometry of [Pd(H 2 O)( S,N,O ‐AcMet‐Gly)] − is optimized at density functional B3LYP/LanL2DZ level. The fused five‐ and six‐membered chelate is responsible for cleavage of Met‐Gly bond. This is the first time to provide a direct evidence for Pd(II)‐mediated cleavage of dipeptides via external solvent attack.