Peptoid Helix Displaying Flavone and Porphyrin: Synthesis and Intramolecular Energy Transfer

Abstract

Natural light-harvesting complexes (LHCs) absorb a broad spectrum of sunlight using a collection of photosynthetic pigments whose spatial arrangement is controlled by a protein matrix and exhibit efficient energy transfer. We constructed a novel light-harvesting protein mimic, which absorbs light in the UV to visible region (280–700 nm) by displaying flavone and porphyrin on a peptoid helix. First, an efficient synthesis of 4′-derivatized 7-methoxyflavone (7-MF, 3 and 4) was developed. The flavone–porphyrin–peptoid conjugate (FPPC) was then prepared via Miyaura borylation on a resin-bound peptoid followed by Suzuki coupling between the peptoid and pigment. Circular dichroism spectroscopy indicated that the FPPC underwent helix-to-loop conversion of the peptoid scaffold upon changing the solvent conditions. A distinct intramolecular energy transfer was observed from 7-MF to porphyrin with greater efficiency in the helix than that in the loop conformation of the peptoid, whereas no clear evidence of energy transfer was obtained for unstructured FPPC. We thus demonstrate the value of the helical peptoid, which provided a controlled orientation for 7-MF and porphyrin and modulated the energy transfer efficiency via conformational switching. Our work provides a way to construct a sophisticated LHC mimic with enhanced coverage of the solar spectrum and controllable energy transfer efficiency.

Using Fluorescence to Enable Innovative Functions of Foldamers

“…In acetonitrile, a significant population of non‐helical conformations of 13 were observed, and these conformations position the chromophores ∼14 Å from one another. By contrast, the conformation of 13 in methanol was expected to position the dyes at a distance of ∼6 Å; this shorter distance enabled the increased energy transfer efficiency [45] …”

“…To emulate natural energy‐transport scaffolds wherein chlorophyll or other pigments are arranged on helical scaffolds within larger protein light‐harvesting complexes, porphyrin and/or flavone chromophores have been appended to helical peptoids, 12 and 13 [43–45] . Fluorescence experiments measured the energy transfer between the pigments in these artificial light‐harvesting complexes in organic solvents.…”

Recent advances in the synthesis of 4H-chromen-4-ones (2012 − 2021)

“…167 Yang et al synthesized 4 0 -bromo-7-methoxy-4H-chromen-4-one via Claisen condensation reaction of 2 0 ,4 0 -dimethoxyacetophenone with methyl 4-bromobenzoate using sodium bis(trimethylsilyl)amide to produce the corresponding 1,3-diketone followed by demethylative cyclization reaction upon treatment with hydrobromic acid and sodium iodide in acetic acid. 168 Polymethoxy-4H-chromen-4-ones have been prepared by condensation of 2 0 -hydroxyacetophenone derivatives and acylbenzotriazoles in the presence of lithium bis(trimethylsilyl)amide (LiHMDS) in dry THF at À78 to 0 °C, followed by cyclodehydration promoted by p-PTSA in toluene at 80 °C. 169 Scheme 18…”

Peptoid-phthalocyanine architectures with different grafting positions: Synthetic strategy and photoproperties

“…32b So far, the insertion of one or several porphyrins on peptoid scaffolds has been performed to optimize the cellular uptake efficiency of photosensitising porphyrins 36 , 37 or mimic the protein-chlorophyll ensemble found in photosynthetic antenna. 38 Jiwon Seo and his team beautifully used peptoid scaffolds to control porphyrin interactions, in the case of pure 19,39 or mixed 40,41,42 porphyrinic arrays.…”