Revisiting the role of π acceptor character of polypyridinc ligands in the redox behavior of tris and bis Fe(II) complexes and in the electron transfer with glucose oxidase

Abstract In this work we revisit the role of π-acceptor character of polypyridinc ligands in the electrochemical behavior of bis and tris Fe(II) complexes [FeL 3 ] 2+ and [FeĹ 2 ] 2+ and in the electron transfer with a representative redox enzyme, glucose oxidase GOD; (L = 1,10-phen, 5-chloro-1,10-phen, 5-nitro-1,10-phen, 5-methyl-1,10-phen, 4-methyl-1,10-phen, 5,6-dimethyl-1,10-phen, 4,7-dimethyl-1,10-phen, 2,2’-bipy, 5,5’-dimethyl-2,2’-bipy, 4,4’-dimethyl-2,2’-bipy, Ĺ = 2,2:6,6-terpy and 4-chloro-2,2:6,6-terpy). The compounds presented a reversible electron transfer [Fe(II)L n ] 2+ →[Fe(III)L n ] 3+ 1e, (n=1,2) followed by an unexpected coupled chemical reaction, EC i mechanism. It was established that the redox potential (E°) and the rate constant ( k f ) of couple reaction are tuned by the pKa of non-coordinated ligand (π acceptor character descriptor). Using UV-vis spectroelectrochemistry different products are proposed for the ECi mechanism. DFT calculations, allow us to state that changes in E°, and pKa are related to HOMO energies. Linear relationships among the electrochemical and kinetic values E°, k f , with the pKa of the ligands were obtained. Using Foot of the Wave Analysis (FOWA) the homogenous electron transfer rate constant ( k s ) for GOD mediation was calculated. From data obtained in this work and choosing similar complexes from literature, it was explored the role of redox potential in this redox mediation.