Spectroscopy, Structure, Biomacromolecular Interactions, and Antiproliferation Activity of a Fe(II) Complex With DPA-Bpy as Pentadentate Ligand.

An Fe(II) complex with DPA-Bpy (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6 -methanamine) as the ligand was synthesized and characterized to mimic bleomycin. The binding constants (K b) of the complex with calf thymus DNA and human serum albumin (HSA) were quantitatively evaluated using fluorescence spectroscopy, with K b as 5.53×105 and 2.40×104 M-1, respectively; the number of the average binding site (n) is close to 1. The thermodynamic analyses suggested that the electrostatic interactions exist between the complex and DNA, and the hydrogen bonding and Van der Waals force exist for the complex and HSA. The Fe complex exhibits cleavage ability toward pBR322 DNA, and the crystal structure of the HSA Fe complex adduct at 2.4 Å resolution clearly shows that His288 serves as the axial ligand of the Fe center complexed with a pentadentate DPA-Bpy ligand. Furthermore, the cytotoxicity of the complex was evaluated against HeLa cells. Both the Fe complex and HSA Fe complex adduct show obvious effect on cell proliferation with an IC50 of 1.18 and 0.82 µM, respectively; they induced cell apoptosis and arrested cell cycles at S phase. This study provides insight into the plausible mechanism underlying their metabolism and pharmacological activity.

Electronic effects on a mononuclear Co complex with a pentadentate ligand for catalytic H2 evolution.

Previous studies of Co catalysts for H2 evolution have shown opposite effects between the redox potentials of Co centers and their catalytic properties such as the overpotential and turnover frequency: Co catalysts with more positive reduction potentials from structural modification display insignificant changes in the overpotential for H2 evolution and require stronger acid for catalysis, and Co catalysts with lower overpotentials show decreased turnover frequency for H2 evolution. In order to explore the electronic effects of a ligand scaffold on the catalytic properties for H2 evolution by a Co complex with a pentadentate ligand, N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy), we replaced the pyridyls in DPA-Bpy with more basic isoquinoline groups. In contrast to data from previously reported studies, in the current study, a Co complex with a more positive reduction potential, resulting from the replacement of pyridyls with isoquinoline groups, leads to a lower overpotential and higher turnover frequency for both electro- and photocatalytic H2 production in neutral aqueous solution.