Nanostructure Control of a Regioregular Poly(3-alkylthiophene) Using an Oligopeptide Side Chain

Abstract

With the aim of probing the competitive roles of π–π stacking and hydrogen bonding in modulating the aggregation state of conjugated polymers, a functionalized thiophene monomer containing a clickable azide group was copolymerized with 2,5-dibromo-3-hexylthiophene via Grignard metathesis (GRIM) to form either a block or a random copolymer, which was then covalently linked via click chemistry to a tetrapeptide (Gly-Val-Gly-Val) that is prone to forming β-sheets. A series of polythiophene–peptide hybrids with similar backbone lengths but different oligopeptide side-chain contents were obtained by adjusting the ratio of the clickable monomer during the polymerization process. The self-assembly behavior of the oligopeptide–polythiophene hybrids was studied in detail. Very interestingly, it is found that the self-assembly behavior strongly depends on the amount of the tetrapeptide side chain in the hybrids, while the influence of the regioregularity (random or block copolymer) is less profound. Specifically, both the random and block copolymers with low oligopeptide contents (33 mol % and lower) self-assemble into nanofibers. On the other hand, the block and random copolymers with high oligopeptide contents (higher than 40 mol %) and the homopolymer with a 100 mol % oligopeptide side chain form spheres with a diameter of around 0.05–1.0 μm. Fourier-transformed infrared spectroscopy (FTIR) analysis demonstrates that more β-sheets are formed in the copolymers containing fewer oligopeptide side chains, more random coils are formed in the copolymers with higher oligopeptide side-chain contents, and only random coils are formed in the homopolymer. Ultraviolet-visible light spectroscopy analysis shows that only when the oligopeptide side-chain content is low could a strong intermolecular π–π stacking be observed; when the oligopeptide side-chain content increased, such an intermolecular electronic communication disappeared. This study offers new insights on how the complex roles of the hydrogen bonding and π–π stacking control the self-assembly evolution of polythiophenes decorated with oligopeptide side chains.

Development of Polythiophene–Tripeptide Covalent Conjugates Showing Excellent Structure-Dependent Photophysical and Photocurrent Properties

“…The oligothiophene conjugated peptide was first developed by Bäuerle and coworkers in 2004, and since then, different oligothiophene-peptide and polythiophene-peptide conjugated systems have been developed to improve solubility and physicochemical properties. , Wan and coworkers have developed a series of polythiophene conjugated peptide hybrid systems exhibiting tunable self-assembly behavior . Lin et al .…”

“…40,44 Wan and coworkers have developed a series of polythiophene conjugated peptide hybrid systems exhibiting tunable self-assembly behavior. 45 Lin et al 46 have reported an electrochemical biosensor consisting of a Gly-Gly-His tripeptide covalently attached to poly(3-thiopheneacetic acid) (PTAA). Here, the authors have shown that the Gly-Gly-His-modified PTAA electrode exhibited a greater affinity toward Cu 2+ ions compared to the other ions and the electrode was found to be highly selective for Cu 2+ ions in the range of 0.02−20 μM.…”

A Review on Self-Assembly Driven Optoelectronic Properties of Polythiophene-Peptide and Polythiophene-Polymer Conjugates

“…Thereafter, many oligo/poly thiophene peptide conjugates have been developed ,, to improve the physicochemical properties. Wan and co-workers covalently linked a series of PT-tetrapeptide (Gly-Val-Gly-Val) conjugates via click chemistry and observed that the self-assembly strongly depends on the quantity of the tetrapeptide side chain; however, the effect of PT-regioregularity was found to be less important. Both block and random copolymers of PT self-assemble into nanofibers with low oligopeptide contents (<33 mol %), while high oligopeptide contents (>40 mol %) form spheres of 0.05–1.0 μm diameter.…”

Evolution of π-Peptide Self-Assembly: From Understanding to Prediction and Control

“…This attention could be conceived to have originated from the early compositional introductions of Chmielewski, Bäuerle, and Nowick, who joined peptide sequences with π-electron cores. This attention is currently manifest in the many modern day examples showcasing the structures, morphologies, and properties of these hybrid bioelectronic materials. − In general, π-peptide conjugates can self-assemble into hierarchical nanostructures such as tapes and fibrils in line with many standard oligopeptides that are capable of forming amyloid-like nanomaterials. Importantly, they offer the additional ability to foster intermolecular π-stacking of the electronic cores which is required for energy migration in a broad sense.…”