Self-assembly Of Small Biomolecules Towards Biomimetic Photosynthesis And Antitumor Photodynamic Therapy

Small biomolecules build up biological functional systems with complexed structures via hierarchical self-organization.Inspired by biological assemblies,hierarchical self-assembly of small biomolecules provides a novel strategy to fabricate functional materials,and a new perspective to under biological phenomena.Natural photosynthetic system can efficiently convert solar energy into chemical energy,which provides a blueprint for artificial solar energy utilization.How to mimic the elaborate organization of proteins,pigments and cofactors to improve light harvesting,charge separation and sustainability of catalysis become the key scientific issues in fabrication of biomimetic photosystems.Small biomolecules,such as amino acids,oligopeptides,and porphyrins,were chosen as building blocks to fabricate artificial photosystems via molecular self-assembly,mimicking the architectural principles and functional mechanisms of photosynthetic system.Two basic strategies were used to fabricate porphyrin-based biomimetic photosystems:One is synergetic co-assembly of oligopeptides and porphyrins;The other is to tune the organization of porphyrins by templates assembled from oligopeptides or amino acids and metal ions.In the fabrication of primitive photosystem,heat energy is used to drive the transformation of non-photosynthetic amino acid-metal ion assembly to prebiotic pigment(primitive light harvesting system).The concrete research content is mainly divided into the following four parts:(1)Hydrophilic dipeptide tunes the hierarchical self-assembly of porphyrin to form long-range ordered fiber bundles.Porphyrins are organized in J-aggregation and the J-aggregated nanorods are aligned,which mimics the organization model of bacteriochlorin in chlorosomes,leading to enhanced light capture and energy transfer.After integration of reaction center via in situ self-mineralization,the hybrid fiber bundles can produce hydrogen under visible light illumination.(2)Self-assembled amphiphilic amino acid nanofiber is modified by levodopa,which is functional moiety in adhesive protein,to form adhering nanofiber template,containing phenol and quinone groups.The template can be used to tune the organization of metalloporphyrin and metallic oxide(catalyst for oxygen evolution)via coordination and electrostatic interactions.Metalloporphyrins are organized in circle on the surface of the nanofiber,and quinone acts as electron acceptor,which mimics the light harvesting complex in purple bacteria and quinone-type reaction center in oxygenic photosynthesis,respectively,resulting in enhanced charge separation.The hybrid nanofibers can produce oxygen under visible light illumination.(3)Inspired by pathological processes of cystine stone,metal ion is used to tune the crystallization of cystine via coordination and hydrogen bonds,and hierarchical ordered microspheres arising from splitting growth of nanorods are obtained.The microspheres can encapsulate porphyrin and enzyme during the crystal growth via electrostatic interaction.The resulting microspheres simultaneously mimic the structure of grana and the light-dark coupled reactions in chloroplast,resulting in enhanced sustainability in photocatalytic fuel production.(4)Amino acids and metal ions are used as prebiotic model molecules,and their self-evolution behaviors are studied in hydrothermal environment.Driven by heat energy,cystine-zinc assemblies are transformed into carbon doped hierarchical zinc sulfide microspheres.The microspheres can capture both ultraviolet and visible light,and then utilize them in primitive photocatalytic reactions.It provides an evolution model for primitive photosystem,as well as experimentally proves the self-evolution process of prebiotic molecules under the flow heat and light.Self-assembly of small biomolecules can also be used in biomedical field.Aiming at the question of low bioavailability for photosensitive drugs in photodynamic therapy,a novel photosensitizer delivery system has been fabricated by oligopeptides-tuned self-assembly of photosensitizers.Amphiphilic oligopeptides are used to regulate intermolecular electrostatic,hydrophobic,and ?-? interactions,which controls the self-assembly of photosensitizers to the nanoscale to form nanospheres.Assembled photosensitive nanospheres exhibit multiple favorable therapeutic features,including high loading efficiency,responsive release as well as tumor targeting,which improves the bioavailability of photosensitizers,achieving good therapeutic effect in anticancer photodynamic therapy.In summary,functional systems with complex structures are fabricated via hierarchical self-assembly of small biomolecules,which can be applied in biomimetic photosynthesis and anticancer photodynamic therapy.The key point to assembly-induced functional enhancement is to design molecular structure of building blocks,to tune the self-assembly process in molecular,nano and micro scale based on the synergy of weak intermolecular interactions,and to control the dimension and structure of the assemblies.