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Directed self-assembly of peptide–diketopyrrolopyrrole conjugates – a platform for bio-organic thin film preparation

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Abstract

Increased water solubility and long-range intermolecular ordering have been introduced into the fluorescent organic molecule thiophene-diketopyrrolopyrrole (TDPP) via its conjugation to the octapeptide HEFISTAH, which is derived from the protein–protein β-interface of the homo-tetramer protein diaminopimelate decarboxylase. The octapeptide, and its TDPP mono- and cross-linked conjugates were synthesised using 9-fluorenylmethoxycarbonyl (Fmoc) based solid-phase peptide synthesis (SPPS). Unlike the unmodified peptide, the resulting mono-linked and cross-linked peptides showed a fibrous morphology and formed hydrogels at 4 wt% in water at neutral pH, but failed to assemble at pH 2 and pH 9. Further peptide characterization showed that the TDPP organic core enhances peptide self-assembly and that both peptides assembled into fibers with a parallel β-sheet structure. Furthermore, UV-vis spectroscopic analysis suggests that the TDPP molecules form H-type aggregates where the chromophores are likely to be co-facially packed, but rotationally and/or laterally offset from one another. This intermolecular coupling indicates that π–π stacking interactions are highly likely – a favourable sign for charge transport. The enhanced aqueous solubility and self-assembling properties of the TDPP–peptide conjugates allowed the successful preparation of thin films. Atomic force microscopy, X-ray diffraction and UV-vis spectroscopic analysis of these thin films revealed that the hybrid materials retained a fibrous morphology, β-sheet structures and strong intermolecular coupling between neighbouring TDPP molecules. These results open an exciting avenue for bio-organic materials development, through structural and electronic tuning of the TDPP core.

Graphical abstract: Directed self-assembly of peptide–diketopyrrolopyrrole conjugates – a platform for bio-organic thin film preparation

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Article information


Submitted
10 Jun 2020
Accepted
22 Jun 2020
First published
22 Jun 2020

Soft Matter, 2020, Advance Article
Article type
Paper

Directed self-assembly of peptide–diketopyrrolopyrrole conjugates – a platform for bio-organic thin film preparation

A. Rani, I. Kavianinia, P. Hume, L. M. De Leon-Rodriguez, S. Kihara, D. E. Williams, D. J. McGillivray, N. O. V. Plank, J. Gerrard, J. M. Hodgkiss and M. A. Brimble, Soft Matter, 2020, Advance Article , DOI: 10.1039/D0SM01071E

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