Enantioselectivity of resolved Δ and Λ orthoruthenated 2-phenylpyridine complexes [Ru( o-C 6H 4-2-py)(LL) 2]PF 6 (LL = bpy and phen) toward glucose oxidase

Abstract

Cyclometalated 2-phenylpyridine complexes [Ru II( o-C 6H 4-2-py)(LL) 2]PF 6, LL = 2,2′-bipyridine ( 1) and 1,10-phenanthroline ( 2) were resolved into Δ and Λ enantiomers using column chromatography on SP Sephadex C-25 in the presence of (+)-2,3-dibenzoyl- D-tartrate. The absolute configuration of enantiomers was established using circular dichroism spectroscopy. The rate constants k et for the electron transfer from reduced glucose oxidase (GO from Aspergillus niger) and PQQ-dependent glucose dehydrogenase (GDH) at the generated Ru III species were measured by cyclic voltammetry and UV–vis spectroscopy. The electron transfer shows enantioselectivity. In the case of GO, the bell-shaped pH profile for the ratio k Λ/ k Δ has a maximum at pH 7 ( k Λ/ k Δ equals 3.4 and 3.9 for 1 and 2, respectively), but its inversion is observed at pH around 5 and 9. The k Λ/ k Δ ratio equals 2.0 for 2 and GDH at pH 7. The results of theoretical modeling of biological electron transfer for GO using functional docking Monte-Carlo simulations are presented and analyzed together with the experimental observations.