Metal-bipyridine complexes, cyclic

For the investigation of interaction mechanism of some compounds as metal coordination complexes with DNA, Bard et al. [76] reported comprehensive electrochemical studies using cobalt/ferrum phenanthroline or cobalt/ferrum bipyridine. In that paper, they evaluated limiting shifts and binding constants of mediator compounds by cyclic voltammetry in the absence and presence of DNA in solution phase experiments. As a result of their report, they found those forms (oxidized or reduced form) of mediator compounds which bind to the DNA molecule with a high affinity. 

The results obtained by cyclic voltammetry clearly show that upon oxidation or reduction of the central metal copper, the macrocycle is set in motion. Upon oxidation of 6(4)+, the resulting tetrahedrally coordinated Cu(II) is unstable as Cu(II) forms stable square planar complexes or higher coordination (five or six). Therefore, the macrocycle pirouettes around the axle permitting the restoration of a stable coordination, that is pentacoordination by the 2,2, 6 2"-terpyridine and 2, 2 -bipyridine... 

The cyclic voltammograms (CV) of the bipyridine nitrosyl ruthenium complexes may reveal multiple couples resulting from redox processes centered at the metal, the nitrosyl ligand, and the bpy ligands. Two couples are evident in the CV electrochemical potential range of +1.0 to —1.0 V vs. Ag/AgCl of a 5/ira s-[Ru(bpy)2L(NO)] complexes in organic solvent or aqueous solution. The reduction peak at the more positive value is chemically reversible, whereas the second reduction peak is practically irreversible in the CV time scale such peaks correspond to the NO "° and pro-... 

Pseudocrown ethers, whose structures are maintained by coordination bonds instead of covalent bonds like typical crown ethers, are among the most suitable candidates for allosteric regulation of ion binding. A linear podand 2 possessing bipyridine moieties at the ends of the polyether chain was converted easily to the corresponding pseudocrown ether quantitatively by complexation with Cu+ (Scheme 1.1). The pseudocrown ether shows a positive allosteric effect on alkali metal ion selectivity in ion transport. The drastic conformational change from a linear to cyclic structure results in a significant macrocyclic effect favorable for ion selectivity. 

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