Supramolecular chirality in self-assembled peptide amphiphile nanostructures

Abstract

Induced supramolecular chirality was investigated in the self-assembled peptide amphiphile (PA) nanosystems. Having shown that peptide chirality can be transferred to the covalently-attached achiral pyrene moiety upon PA self-assembly, the chiral information is transferred to molecular pyrene via weak noncovalent interactions. In the first design of a supramolecular chiral system, the chromophore was covalently attached to a peptide sequence (VVAGH) via an e-aminohexanoic acid spacer. Covalent attachment yielded a PA molecule self-assembling into nanofibers. In the second design, the chromophore was encapsulated within the hydrophobic core of self-assembled nanofibers of another PA consisting of the same peptide sequence attached to lauric acid. We observed that supramolecular chirality was induced in the chromophore by PA assembly into chiral nanostructures, whether it was covalently attached, or noncovalently bound. and Stupp 8 groups have shown that a chiral center in an alkyl group of a molecule can affect the overall helicity of a supramolecular polymer. It was also observed that chiral molecules could induce chiral organization of achiral molecules by strong noncovalent interactions, such as electrostatic and coordination interactions; thus representing an interesting tool for control of materials' properties. 9-11Chiral molecules such as peptides are interesting model structures for studying induced chirality. All of the natural amino acids, except glycine, used in mRNA translation are chiral; therefore polypeptides are intrinsically chiral. Molecular chirality of peptides can be used to induce supramolecular chirality upon assembly of individual molecules into one-dimensional nanostructures. 12-14Effective assembly of this type can be achieved when a certain peptide sequence is attached to a hydrophobic fatty acid. Aliphatic peptide amphiphiles (PAs) possess this type of design and exhibit self-assembly properties. Aliphatic PAs comprise an oligopeptide sequence and a covalently attached aliphatic tail, which is typically 12-16 carbon atoms long.15 PAs can self-assemble into various nanostructures such as nanoribbons, nanofibers and micelles 16 depending on their amino acid sequence and aliphatic tail.Here we exploited nanofiber forming PAs, because nanofiber formation leads to helical arrangement of individual PA molecules along the nanofiber axis.17 Helical arrangement stems from the twisted geometry of b-sheets forming the PA nanofibers; nevertheless, helicity is not translated into fiber morphology and lateral stacking of b-sheets interdigitated along hydrophobic tails leads to almost flat nanofibers with helical interior. Nanofibers formed from all-L and all-D peptide isomers are expected to possess leftand right-handed interior, respectively. However, there are some reports on handedness inversion in peptide and protein based nanofibers. 18,19 As shown here, this type of arrangement forces covalently attached or noncovalently encapsulated chromophore molecules to exhibit induced chirality. The lett...

Effects of temperature, pH and counterions on the stability of peptide amphiphile nanofiber structures

“…24 Valine and alanine residues in particular are b-sheet promoting amino acids, and the VVAG motif in the lauryl-VVAGERGD peptide is capable of mediating its self-assembly through b-sheet formation. 47 Minimal changes were observed between Na + and Cl À -mediated assembly; however, the Cl Àmediated assembly (the PA3 nanober) also had more b-sheet formation compared to the Na + -mediated (the PA1 nanober) Fig. 8 Snapshots of the gradually heated PA1 nanofiber from 300 K to 358 K (simulation-2).…”

Solvent‐Tuned Supramolecular Assembly of Fluorescent Catechol/Pyrene Amphiphilic Molecules

“…On the other hand, it is well known that pyrene moieties are able to self‐aggregate, thus establishing weak intermolecular interactions (i.e., π–π interactions) to form ordered mesophases or even induce supramolecular chirality . Moreover, pyrene optical properties (absorption and luminescence) are highly sensitive to the medium polarity and to the molecular packing processes and supramolecular associations in the microenvironment that surround the probe, which makes it a good sensor for self‐assembly processes and micelle/vesicle formation …”

“…[14] On the other hand, it is well knownt hat pyrene moieties are able to self-aggregate, thus establishing weaki ntermolecular interactions (i.e., p-p interactions) to form ordered mesophases [15] or even induce supramolecular chirality. [16] Moreover, pyrene optical properties (absorption andl uminescence) are highly sensitive to the mediump olarity andt ot he molecular packing processes and supramolecular associations in the microenvironment that surround the probe, which makes it a good sensorf or self-assembly processes and micelle/vesicle formation. [17,18] This study is primarily aimed at the control and tuning of the supramolecular self-assembly process between catecholcontaining amphiphilic molecules with two differentm oieties able to establish intermolecular interactions.…”

Tuning Optoelectronic and Chiroptic Properties of Peptide‐Based Materials by Controlling the Pathway Complexity

“…[3] Among other sophisticated and efficient molecular building blocks, the use of synthetic peptides able to favor p-p interac-tions betweenp hoto-and electroactivea romatic systemsh as been recognized as an effective strategy to achieve supramolecular polymeric materialsw ith applicationsin organic electronics. Recent investigations have been focused in this direction, for which amino acid mutation, [6] enhancement of the intermolecular p-p interactions betweena romatic units, [7] or solvent-controlled assembly [8] have been used to modify the properties of the functional supramolecular materials. [5] Furthermore, their final function and applications are dramatically affected by these parameters.…”