The photoelectronic properties of porphyrins have been harnessed by nature to power such widely known processes as photosynthesis. When excited by light, many porphyrins release electrons; however, without an efficient or directed method to transport them, this energy is typically limited to facilitating local enzymatic reactions. We investigated a series of peptides containing partial and complete porphyrin binding regions (PBRs) for their ability to promote meso-tetra(4-sulfonatophenyl)porphine (TPPS42-) to form electrically conductive structures known as J-aggregates. While aggregation has previously been shown to occur in the absence of peptide, this requires very acidic conditions (pH &lt; 1) and the resultant aggregates are too small and irregular to effectively conduct electrons. Our approach uses amphiphilic peptides containing complete PBRs (Lys3) as well as partial (Lys1 or Lys2) regions located at the peptide termini. Our goal is to induce the concurrent binding of TPPS to the incomplete domains of two peptides, forming a bridge between them. Binding was assessed in aqueous solution by monitoring the soret and Q-bands of TPPS42-) across various peptide concentrations and pH levels. The absorbance transitions are sensitive to the formation of the electronically conductive J-aggregate, allowing for rapid spectroscopic identification. Fluorescence spectroscopy, circular dichroism, and dynamic light scattering were also used to assess J-aggregate formation. The peptides were shown to induce the formation of J-aggregates up to solution pH 3.0, but maintains the ability to bind porphyrin at neutral pH. Time-based precipitation assays corroborate these studies. Notably, the peptides were shown to adopt an unstructured conformation at low pH but become somewhat helical at neutral pH. Studies of mixed peptide binding stoichiometry indicate formation of complementary heterooligomers that retain their porphyrin-binding capabilities and produce an additional binding site at their junction. These results have implications for the design of photoelectronically active biomaterials.

Peptide-assisted supramolecular polymerization of the anionic porphyrin meso-tetra(4-sulfonatophenyl)porphine

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.