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

Abstract

Increased water solubility and long-range intermolecular ordering have been introduced into the fluorescent organic molecule thiophene-diketopyrrolopyrrole via its conjugation to the octapeptide HEFISTAH, derived from a protein–protein β-interface.

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

“…46 Previously, Draper et al also reported broadening of the ICT transition in H-type DPP-peptide conjugates, 37 whereas Rani et al characterized the H-type aggregates by diminished intensity of the 0-0 transition relative to the 0-1 transition in DPP-octapeptide conjugates. 38 To the best of our knowledge, this is the first example of unique blue-shifts observed in DPP-peptide conjugates upon moving to the aggregated state. The prominent shoulder around 660 nm red-shifted to 690 nm possibly due to the restricted rotational motion of the chromophore with aggregation.…”

“…Due to the complexity of the core, we expect this to engage in non-ideal H-type aggregation (rotationally and translationally shifted). 38 The lower intensity of π-π* transition may be due to the better H-type (parallel) aggregation of the thiophene groups in presence of the methyl group side chain as compared to longer side chains. Overall, we observed minute change in optical absorption with variation of side chain, in line with previous reports.…”

“…The ICT transition has a relatively low quantum yield, as observed by the lower intensity of the emission spectra in basic medium (monomeric state), which is in contrast to the previous DPP-peptide conjugates studied in aqueous medium. 38 The low intensity could be attributed to the non-radiative relaxation of the ICT transition. However, we cannot rule out the possibility of assembled structures pre-existing to some extent in basic medium considering the high stacking propensity of the DPP core.…”

“…33 Examples of DPP conjugates that are processable in aqueous condition are much rarer, [37][38][39][40][41][42][43] and out of those, DPP-peptide conjugates have not been extensively explored. [37][38][39] Draper et al prepared conductive hydrogels by conjugating phenylalanine to the amide functionalities of a thiophene-conjugated DPP core. 37 Rani et al also targeted the DPP amide functionality by conjugating an octapeptide to the DPP core, which resulted in H-type aggregates in aqueous solution.…”

“…37 Rani et al also targeted the DPP amide functionality by conjugating an octapeptide to the DPP-core, which resulted in H-type aggregates in aqueous solution. 38 In this work, we describe the effect of incorporating different πconjugated core lengths in the peptide backbone as well as different N-alkyl side chain lengths oblique to the peptide backbone. This work diverges from other DPP-peptide conjugates studied previously in that the long pi-conjugation axes of the DPP oligomers are coincident with the peptide backbone directionality, while the N-atoms of the DPP cores are engaged for alkyl group substitution rather than for peptide amidation (Scheme 1).…”