Electron Transfer in a Bio-Photoelectrode Based on Photosystem I Multilayer Immobilized on the Conducting Glass

A film of similar to 40 layers of partially oriented photosystem I (PSI) complexes isolated from the red alga Cyanidioschyzon merolae formed on the conducting glass through electrodeposition was investigated by time-resolved absorption spectroscopy and chronoamperometry. The experiments were performed at a range of electric potentials applied to the film and at different compositions of electrolyte solution being in contact with the film. The amount of immobilized proteins supporting light-induced charge separation (active PSI) ranged from similar to 10%, in the absence of any reducing agents (redox compounds or low potential), to similar to 20% when ascorbate and 2,6-dichlorophenolindophenol were added, and to similar to 35% when the high negative potential was additionally applied. The origin of the large fraction of permanently inactive PSI (65-90%) was unclear. Both reducing agents increased the subpopulation of active PSI complexes, with the neutral P700 primary electron donor, by reducing significant fractions of the photo-oxidized P700 species. The efficiencies of light-induced charge separation in the PSI film (10-35%) did not translate into an equally effective generation of photocurrent, whose internal quantum efficiency reached the maximal value of 0.47% at the lowest potentials. This mismatch indicates that the vast majority of the charge-separated states in multilayered PSI complexes underwent charge recombination.

Automated summary

This study investigates PSI complexes in the red alga and finds that the addition of reducing agents increases the proportion of active PSI complexes, but the efficiency of light-induced charge separation does not directly translate into photocurrent generation.