Peptide Amphiphile Nanofibers with Conjugated Polydiacetylene Backbones in Their Core

Abstract

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the β-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the β-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in β-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.

Induction and control of supramolecular chirality by light in self-assembled helical nanostructures

“…The handedness of the aggregates is exclusively dictated by the rotational direction of the CPL and can even be switched in a totally reversible manner. Furthermore, by incorporating a diacetylene (DA) moiety that undergoes topochemical photopolymerization by ultraviolet (254 nm) 24, 25 , we demonstrate that the desired handedness can be permanently locked by circularly polarized ultraviolet light (CPUL) irradiation, which knits the self-assembled structure with covalent bonds [26][27][28] . We believe this to be the first example of light-induced self-assembling systems where the entire process of induction, control and locking of supramolecular chirality can be solely manipulated by CPL.…”

β-Sheet peptide-assisted polymerization of diacetylene at the air–water interface and thermochromic property

“…12 Recently, numerous research groups have demonstrated that amphiphilic peptides self-assemble into b-sheet nanofiber architectures, [13][14][15][16][17][18][19][20] the surface of which has potential as a novel nanotemplate. [21][22][23] Several groups [24][25][26][27] have separately used b-sheet peptide nanofibers as templates to organize diacetylenes or dienes and promote their topochemical polymerization. In this study, we used Langmuir monolayers at the air-water interface and b-sheetforming oligopeptides to align diacetylene groups one-dimensionally, promoting facile topochemical polymerization and stabilizing the resultant well-conjugated polydiacetylenes.…”

Synthesis of Diacetylene‐Containing Peptide Building Blocks and Amphiphiles, Their Self‐Assembly and Topochemical Polymerization in Organic Solvents

“…The UV-induced topochemical polymerization within the b-sheet aggregates was successful, proving parallel bstrand orientation and highlighting the effect of the number and pattern of N-H···O=C hydrogen-bonding sites as well as the hydrophobic residue in the molecular structure on the formation of higher structures and reactivity. Keywords: acetylenes · oligopeptides · organogels · self-assembly · supramolecular chemistry Thus, a variety of diacetylenecontaining lipid amphiphiles with chiral polar head groups, such as phosphatidyl cholines, [41][42][43][44] aldonamides, [45,46] amino acids, [47,48] and oligopeptides [49] was found to furnish one-dimensional supramolecular aggregates with helical superstructures that could be covalently cross-linked by UV irradiation. While, in all of these examples, hydrogen bonding between the head groups plays an important role to translate the molecular chirality into a helical superstructure, the phase segregation and crystallization of the long-chain hydrophobic tails (or spacers) was the decisive factor for the formation of supramolecular aggregates.…”

“…It is very important to acknowledge that these observed gelation properties are distinctly different from the behavior of the macromonomers 1 and more in line with the properties of typical diacetylene-containing amphiphiles. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] Despite their significantly larger number of NÀH···O=C hydrogen bonds and resulting tendency to aggregate at even micromolar concentrations, the macromonomers 1 had not shown any tendency to form macroscopic gels in organic solvents at all even at high concentrations, presumably due to the presence of more soluble [61] and uniform supramolecular polymers without branching points with extreme persistence lengths, and, accordingly, little tendency to form entanglement networks.…”