Heteronuclear Fe(III)/Mn(III) salen complex as electron transfer mediator for laccase-based biocathodes: Structural investigations, molecular docking, and electrochemical studies

A novel hetero-trinuclear Fe(III)/Mn(III) complex derived from a salen ligand has been investigated using elemental analysis, infrared spectroscopy, and single-crystal X-ray crystallography. The studied complex crystallized as orthorhombic with the Mn(III) ion coordinated in the equatorial plane by the phenolate O and imine N atoms of the ligand. Two axial positions are taken up by an O atom from water and a N atom from the cyanide group. The [Fe(CN) 6 ] core in the crystal structure links the two [Mn(salen)(H 2 O)] moieties together. In addition, the isolated complexes have been utilized as mediators for the electron transfer between the laccase and the electrode. Moreover, using structural data for the laccase, computational docking simulations were also performed towards the hydrophobic pocket on the surface of the laccase to determine how the complex behaved in the vicinity of a so-called hydrophobic pocket on the surface outside of the Type-1 site. Additionally, the parameters of mediator concentration, temperature, and electrode conditions (CNT, MXene) were used to investigate the electron transfer mechanism.