Photoinduced Electron Transfer in Eosin-Modified Co(II)-Protoporphyrin IX Reconstituted Myoglobin and α- or β-Hemoglobin Subunits: Photocatalytic Transformations by the Reconstituted Photoenzymes1

Abstract

A series of hemo-protein-derived photocatalysts, prepared by reconstitution of the respective apo-proteins with Co(II)-protoporphyrin IX and chemical modification of the protein with the eosin chromophore, is presented. Apo-myoglobin, Apo-Mb, was reconstituted with Co(II)-protoporphyrin IX and further modified with eosin-isothiocyanate (3) to yield the photocatalyst Eo2--Mb-Co(II). The protein is loaded by two eosin chromophore units. Photoexcitation of Eo2--Mb-Co(II) yields the electron transfer species Eo•--Mb-Co(I) formed by direct oxidative quenching of TEo2--Mb-Co(II), kq = 5.2 × 104 s-1, and via an indirect path where self-quenching of the eosin-chromophore units yields the intermediate redox products (Eo•3- + Eo•-)-Mb-Co(II) that, in the presence of Na2EDTA, generate the Eo•--Mb-Co(I) in a secondary dark electron transfer, kr = 330 s-1. The reconstituted protein Eo2--Mb-Co(II) reveals photocatalytic features and its steady-state illumination in the presence of Na2EDTA yields hydrogen evolution, φ =...