New Au (III), Pt (II) and Pd (II) Complexes with Pentapeptide Glycylglycyl-L-Methyonyl-Glycyl-Glycine and Their Interaction with Calf Thymus DNA

The three new Au (III), Pt (II) and Pd (II) complexes with pentapeptide glycyl-glycyl-L-methyonyl-glycylglycine have been synthesized, isolated, and spectroscopically and structurally elucidated in solution and in the solid-state. Solid-state linear-dichroic infrared (IR-LD) spectroscopy of oriented colloids in a nematic liquid crystal host, 1H- and 13CNMR, TGA and DSC, UV-VIS spectroscopy, EPR, ESI- and FAB- mass spectrometry and HPLC tandem mass spectrometry (HPLC-MS/MS) have been used. Quantum chemical calculations and molecular modelling were carried out in order to determine the structures and spectroscopic properties of the ligand, the newly synthesised metal complexes and their interactions with calf thymus DNA. The pentapeptide coordinates in a tetradentate manner with the metal ions via an S-atom on the methyonyl-side chain, two N-amide nitrogens, (after a deprotonation of gly1 and gly2 residues) and the primary NH2 nitrogen of Ntermini. The MN3S chromophores are distorted to near square planar geometry. Their interaction with calf thymus DNA shows the competitive N7 (G) coordination position, where the pentapeptide residues is coordinated with the metal centers in a tridentate manner through the S- atom and both N-amide centers. This interaction leads to a transfer from a distorted square planar geometry (D4h symmetry) to a pseudo tetrahedral (Td symmetry) of the metal ions with the obtained dihedral angle values of the MN3N7(G) chromophors within 114.67 to 110.92 . The isolated Au (III) complex is stable for about 1.5 months, while the stability of the Au (III) complex/DNA adduct is decreased to 33 days.