Nonresonant and Local Field Effects in Peptidic Nanostructures Bearing Oligo(p-phenylenevinylene) Units

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

Supramolecular materials derived from the self-assembly of engineered molecules continue to garner tremendous scientific and technological interest. Recent innovations include the realization of nano- and mesoscale particles (0D), rods and fibrils (1D), sheets (2D), and even extended lattices (3D). Our research groups have focused attention over the past 15 years on one particular class of supramolecular materials derived from oligopeptides with embedded π-electron units, where the oligopeptides can be viewed as substituents or side chains to direct the assembly of the central π-electron cores. Upon assembly, the π-systems are driven into close cofacial architectures that facilitate a variety of energy migration processes within the nanomaterial volume, including exciton transport, voltage transmission, and photoinduced electron transfer. Like many practitioners of supramolecular materials science, many of our initial molecular designs were designed with substantial inspiration from biologically occurring self-assembly coupled with input from chemical intuition and molecular modeling and simulation. In this feature article, we summarize our current understanding of the π-peptide self-assembly process as documented through our body of publications in this area. We address fundamental spectroscopic and computational tools used to extract information regarding the internal structures and energetics of the π-peptide assemblies, and we address the current state of the art in terms of recent applications of data science tools in conjunction with high-throughput computational screening and experimental assays to guide the efficient traversal of the π-peptide molecular design space. The abstract image details our integrated program of chemical synthesis, spectroscopic and functional characterization, multiscale simulation, and machine learning which has advanced the understanding and control of the assembly of synthetic π-conjugated peptides into supramolecular nanostructures with energy and biomedical applications.

100th Anniversary of Macromolecular Science Viewpoint: User's Guide to Supramolecular Peptide-Polymer Conjugates

This Viewpoint highlights the design principles and development of peptide-based supramolecular polymers. Here we delve deep into the practicalities of synthesizing and characterizing these macromolecular structures and provide a thorough overview of the benefits and challenges that come with these systems. This Viewpoint emphasizes to beginners and experts alike the importance of understanding the fundamental behavior and self-assembly processes when designing these complex and dynamic functional materials.

Torsional Impacts on Quaterthiophene Segments Confined within Peptidic Nanostructures

The co-assembly behavior of peptide-π-peptide and peptide-alkyl-peptide triblock molecules that form one-dimensional (1D) nanostructures under acidic, aqueous environments is dependent on the peptide sequence and the torsional constraints imposed within the nanomaterial volume. Although a hydrophilic tripeptide sequence (Asp-Asp-Asp, DDD-) previously promoted isolation/dilution of minority π-electron components in the matrix of aliphatic peptides, a β-sheet promoting sequence (Asp-Val-Val, DVV-) led to blocks of the two components distributed within larger 1D self-assembled nanostructures. Furthermore, torsional restrictions exerted on the oligoaromatic π-electron unit by the self-assembly process can lead to changes in its conformation (for example, planarity), which has ramifications on its functionality within the peptide matrix. Here, we study this impact on thiophene-based π-electron units with inherently different geometries, viz., relatively planar 2,2':5',2″:5″,2‴-quaterthiophene and 3″,4'-dimethyl-2,2':5',2″:5″,2‴-quaterthiophene, which is twisted at the core bithiophene unit due to the presence of two methyl groups. These peptides were co-assembled at 5 and 20 mol % with peptide- n-decyl-peptide triblock molecules, and the resultant assemblies were studied using UV-vis absorption, photoluminescence, and circular dichroism spectroscopies. We found that torsional restriction in dimethylated quaterthiophene units can impact the stacking behavior of these 1D peptide nanoassemblies and have consequences on their photophysical properties. Additionally, these insights help in the understanding of the dependence of the optoelectronic properties of these materials on both the intrinsic conformation of π-units and the geometric constraints imposed by their immediate local environment under aqueous conditions.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Transforming a C 3-Symmetrical Liquid Crystal to a π-Gelator by Alkoxy Chain Variation

Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three C ₃-symmetrical molecules based on oligo(p-phenylenevinylene), C ₃ OPV1-3. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, C ₃ OPV1 having nine alkoxy chains (-OC₁₂H₂₅) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the -OC₁₂H₂₅ groups from each of the end benzene rings is knocked out, the resultant molecule, C ₃ OPV2 lost the LC property, however, transformed as a gelator in toluene and n-decane. Surprisingly, when the -OC₁₂H₂₅ group from the middle position is removed, the resultant molecule C ₃ OPV3 failed to form either the LC or the gel phases.

Photon management in supramolecular peptide nanomaterials

Self-assembling peptides with covalent pi-electron functionality offer new ways to create delocalized conduits within protein-based nanomaterials. My group's recent research is summarized in this regard, detailing foundational self-assembly and photophysical characterizations that validate the electronic couplings existing within the resulting peptidic nanomaterials. Using these initial studies as a benchmark, ongoing studies to create even more complex photonic energy delocalization schemes are presented, spanning excitonic and Förster energy transfer to low-bandgap dopant sites (whereby 46% of the observed photoluminescence could be quenched by the addition of 1 mol% of an energy acceptor), the creation of charge separated states following photoinduced electron transfer that persisted for over a nanosecond, and use of kinetic control to dictate self-sorting (at long time scales, ca. several hours) or intimate coassembly (at short time scales, ca. several seconds) of multiple peptide components. Peptide coassemblies are described that exhibit both directed exciton migration to low-energy sites and follow-up charge separation events, very much in mimicry with relevant photosynthetic processes.