Porphyrin Aggregation Regulated By Aromatic Short Peptides And The Photoelectric Properties

The national economy is developing rapidly in the past decades.However,the problem of energy shortage and environmental pollution is becoming more and more serious owing to excessive reliance of traditional fossil fuels.It is necessary to look for an environmental benign energy to replace oil and coal.Great attention has been paid to solar energy utilization including the conversion of solar energy to electrical energy or chemical fuels.In nature,photosynthesis occurred in green plants and certain bacteria is a perfect model for the transformation of solar energy to chemical energy,where CO₂is absorbed and O₂is released through the photosynthesis process to maintain the balance of carbon and oxygen on the earth.This inspires people to explore the intrinsic mechanism and the internal composition,structure and function of the photosynthesis system.Porphyrin possesses similar structure with chlorophyll?existed in natural photosystem and exhibits excellent light capturing ability.Porphyrin has a large planar conjugating structure,which allows them to undergo intramolecular and intermolecular electron transfer under light irradiation,and thus porphyrin and their derivatives are suitable for using in the photochemical conversion materials,molecular devices,solar cells and so on.Therefore,in the present work,integrated nanostructures were constructed to investigate the electron transfer and generation of NADH from NAD⁺during the light irradiation.Porphyrin was used as light capturing molecules,expensive metal nanoclusters were used to help the separation and transition of photo-generated electrons,and short cationic peptides were used to regulate their aggregation.The interaction between short peptides and porphyrins,and the relationship between the structures and properties of the peptide-porphyrin aggregates were studied systematically.Ordered aggregation structures of TPPS were formed under relatively mild conditions,and their light capturing and photoelectric conversion performance were improved remarkably.This provides valuable references for the construction of advanced artificial photosynthesis cooperation systems,and also helps to promote the development of new photoelectric conversion materials and molecular devices.(1)Two cationic short peptides including Ac-FFGK-NH₂(Ac-FFGK),Ac-Cha Cha GK-NH₂(Ac-Cha Cha GK)were designed and synthesized.They possessed similar amino acid sequences but different side chain groups.The peptides were self-assemble into regular nanostructures in aqueous solution driven by the hydrophobic interaction,hydrogen bonding,and?-?stacking.And then the preassembled peptides were used as templates to regulate tetraphenyl sulfonyl porphyrin(TPPS)aggregation and peptide/porphyrin aggregates were obtained at a relatively mild condition.The effects of the structure of short peptides,the concentration of the peptides and porphyrins,and the molar ratio of the two components on the aggregation behavior and photo-physical properties of the aggregates were systematically studied.The results showed that the peptide-porphyrin aggregates regulated by Ac-Cha Cha GK possessed higher content of J-aggregates.Furthermore,peptide/porphyrin/Pt hybrids were obtained via in-situ metal reduction under light irradiation in the presence of the peptide/porphyrin aggregates.The hybrids exhibited higher catalytic activity during the photo-catalytic conversion of NAD⁺to NADH.(2)On the basis of the above research,larger Fmoc units as the terminal groups were introduced into short peptides,and cationic short peptides Fmoc-FFGK-NH2(Fmoc-FFGK)and Fmoc-Cha Cha GK-NH₂(Fmoc-Cha Cha GK)were designed and self-assembled in aqueous solution.Peptide/porphyrin aggregates were formed templated by the preassembled peptides.Effects of the concentration of peptide and porphyrin,the molar ration of the two components were on the aggregation behavior and photo-physical properties of the aggregates were systematically investigated.By comparison,the aggregates templated by Fmoc-Cha Cha GK possessed higher J-aggregates content,photocurrent response and conversion of NAD+to NADH,although the content of J-aggregates in the Fmoc-FFGK/TPPS aggregates increased remarkably than that of the Ac-FFGK/TPPS aggregates.Results in this work would provide valuable reference for the research of the solar energy utilization including the construction of the artificial photosynthesis systems or devices.