Oligo(p-phenylenevinylene)−Peptide Conjugates: Synthesis and Self-Assembly in Solution and at the Solid−Liquid Interface

Abstract

Two oligo(p-phenylenevinylene)-peptide hybrid amphiphiles have been synthesized using solid- and liquid-phase strategies. The amphiliphiles are composed of a pi-conjugated oligo(p-phenylenevinylene) trimer (OPV) which is coupled at either a glycinyl-alanyl-glycinyl-alanyl-glycine (GAGAG) silk-inspired beta-sheet or a glycinyl-alanyl-asparagyl-prolyl-asparagy-alanyl-alanyl-glycine (GANPNAAG) beta-turn forming oligopeptide sequence. The solid-phase strategy enables one to use longer peptides if strong acidic conditions are avoided, whereas the solution-phase coupling gives better yields. The study of the two-dimensional (2D) self-assembly of OPV-GAGAG by scanning tunneling microscopy (STM) at the submolecular level demonstrated the formation of bilayers in which the molecules are lying antiparallel in a beta-sheet conformation. In the case of OPV-GANPNAAG self-assembled monolayers could not be observed. Absorption, fluorescence, and circular dichroism studies showed that OPV-GAGAG and OPV-GANPNAAG are aggregated in a variety of organic solvents. In water cryogenic temperature transmission electron microscopy (cryo-TEM), atomic force microscopy (AFM), light scattering, and optical studies reveal that self-assembled nanofibers are formed in which the helical organization of the OPV segments is dictated by the peptide sequence.

Fluidic‐Directed Assembly of Aligned Oligopeptides with π‐Conjugated Cores

“…[ 18,19 ] A limited number of investigations have utilized peptide oligomers with π -conjugated cores for supramolecular assembly. [ 17,[20][21][22][23][24] In general, the electronic properties of these assemblies (e.g., n -or p -channel activity, fl uorescence, excited state transport) are determined by the π -delocalized structures that form through interactions within the molecular core, whereas peptide sequences are chosen to bias their assembly into one-dimensional stacked architectures.…”

“…The absorption and emission spectral signatures observed during assembly of DFAA and DFAG are consistent with classic H-aggregate formation. [ 18,21,25 ] DFAA gels show a distinct vibronic structure in their fl uorescence emission, which arises due to the OPVs twist alignment within the H stack. [ 19,26 ] However, DFAG gels show a bathochromic-shifted fl uorescence emission, indicative of a chargetransfer emissive state.…”

A clickable, highly soluble oligopeptide that easily forms organogels

“…For instance, GAGA sequence, presented in silk protein as the repeating unit, forms antiparallel b-sheet structures by self-assembly (4 -6). It was used to adjust the nanostructure of conventional synthetic polymers (7)(8)(9) and p-conjugated oligomers (10)(11)(12)(13)(14). These reports strongly supported the use of oligopeptides as versatile building blocks for facilitating self-assembled supramolecular structures with definite properties.…”

Peptide π-Electron Conjugates: Organic Electronics for Biology?

“…[42][43][44] Other examples of peptide-pi hybrids were synthesized using solution-based reactions that couple the pi-system within or at the end of the main peptide chain (or the side chains). 39,45,46 Although solutionphase synthesis gives better yields, solid-phase synthesis enables the construction of longer peptides and coupling with longer, insoluble pi-electron systems. 45,47 Tovar and co-workers developed solid-phase synthetic approaches that are generally applicable to a wide variety of pi-electron units ("plug-andplay").…”