Optimising the synthesis, polymer membrane encapsulation and photoreduction performance of Ru(ii)- and Ir(iii)-bis(terpyridine) cytochrome c bioconjugates

Abstract

Ruthenium(II) and iridium(III) bis(terpyridine) complexes were prepared with maleimide functionalities in order to site-specifically modify yeast iso-1 cytochrome c possessing a single cysteine residue available for modification (CYS102). Single X-ray crystal structures were solved for aniline and maleimide Ru(II) 3 and Ru(II) 4, respectively, providing detailed structural detail of the complexes. Light-activated bioconjugates prepared from Ru(II) 4 in the presence of tris(2-carboxyethyl)-phosphine (TCEP) significantly improved yields from 6% to 27%. Photoinduced electron transfer studies of Ru(II)–cyt c in bulk solution and polymer membrane encapsulated specimens were performed using EDTA as a sacrificial electron donor. It was found that membrane encapsulation of Ru(II)–cyt c in PS₁₄₀-b-PAA₄₈ resulted in a quantum efficiency of 1.1 ± 0.3 × 10⁻³, which was a two-fold increase relative to the bulk. Moreover, Ir(III)–cyt c bioconjugates showed a quantum efficiency of 3.8 ± 1.9 × 10⁻¹, equivalent to a ∼640-fold increase relative to bulk Ru(II)–cyt c.