Toward cheaper light harvesting systems: Using earth-abundant metal oxide nanoparticles in self-assembled peptide-porphyrin nanofibers.

Cheap artificial light harvesting systems, which competently harvest solar energy and promote efficient energy transfer, are highly sought after in the renewable sector. We report the synthesis of self-assembled peptide-porphyrin fibers (SJ 6) fabricated with iron(III) oxide (Fe3 O4 ) nanoparticles as feasible electron acceptors. Charge-complementarity between the negatively charged peptide (20E) and the protonated Zn-tetraphenyl porphyrin (ZnTPyP) led to an ordered assembly of the ZnTPyP molecules, enabling efficient light harvesting. X-ray diffraction data indicates a more ordered structure in SJ 6 compared to 20E and ZnTPyP. The incorporation of Fe3 O4 nanoparticles into SJ 6 showed significant fluorescence quenching, indicating efficient electron flow from the donor to the acceptor. The SJ 6-nFe3 O4 system performed the light reaction of photosynthesis as confirmed by the reduction of 1 mM NAD+ to 0.180 mM NADH upon exposure to visible light (Xe lamp λ > 420 nm) for 1 h. The photochemical regeneration of NADH using the SJ 6-nFe3 O4 system was coupled to glutamate dehydrogenase-catalyzed conversion of α-ketoglutarate to L-glutamate. These results confirm the successful synthesis of an artificial light harvesting peptide-porphyrin system with Fe3 O4 nanoparticles as promising low-cost electron separators.