Aqueous Self-Assembly of Peptide–Diketopyrrolopyrrole Conjugates with Variation of N-Alkyl Side Chain and π-Core Lengths

Abstract

Peptidic sequences when conjugated to π-electronic groups form self-assembled networks of π-electron pathways. These materials hold promise for bio-interfacing charge transporting applications because of their aqueous processability and compatibility. In this work, we incorporated diketopyrrolopyrrole (DPP), a well-established π-core for organic electronic applications, within the peptidic sequence. We embedded different numbers of thiophene rings (2 and 3) on both sides of the DPP to alter the length of the π-cores. We also varied the length of the N-alkyl side chains (methyl, butyl, hexyl) attached to the DPP core. These variations allowed us to explicitly study the effect of π-core and N-alkyl side-chain length on photophysical properties and morphology of the resulting nanomaterials. All of these molecules formed H-type aggregates in the assembled state. Longer π-cores have relatively red-shifted absorption maxima whereas the N-alkyl variation did not present significant photophysical changes.

Hybrid computational–experimental data-driven design of self-assembling π-conjugated peptides

“…In our prior work on p-conjugated oligopeptides, we typically synthesized the peptide wings with the ionizable residue responsible for actuating pH-triggered assembly located at the C-terminus to locate it as far away as possible from the p-core: our motivation for this design choice was that the hydrophilic and polar nature of these residues which, together with their steric bulk, was anticipated to disrupt good supramolecular assembly of the p-cores. 14,15,70,[88][89][90][91] Interestingly, our active learning screen appears to have also learned this design rule without any explicit human instruction and thus furnished post hoc support for this intuitive choice. Similarly, our recent computational and experimental work 30,31,92 is consistent with prior chemical intuition 88 that the placement of small non-polar residues adjacent to the p-core should promote good co-facial stacking of the cores.…”