Kinetically controlled coassembly of multichromophoric peptide hydrogelators and the impacts on energy transport

We report a peptide-based multichromophoric hydrogelator system, wherein π-electron units with different inherent spectral energies are spatially controlled within peptidic 1-D nanostructures to create localized energy gradients in aqueous environments. This is accomplished by mixing different π-conjugated peptides prior to initiating self-assembly through solution acidification. We can vary the kinetics of the assembly and the degree of self-sorting through the choice of the assembly trigger, which changes the kinetics of acidification. The hydrolysis of glucono-δ-lactone (GdL) provides a slow pH drop that allows for stepwise triggering of peptide components into essentially self-sorted nanostructures based on subtle pKa differences, whereas HCl addition leads to a rapid formation of mixed components within a nanostructure. Using 1H NMR spectroscopy and fiber X-ray diffraction, we determine the conditions and peptide mixtures that favor self-sorting or intimate comixing. Photophysical investigations in the solution phase provide insight into the correlation of energy-transport processes occurring within the assemblies to the structural organization of the π-systems

Concentration-Driven Assembly and Sol–Gel Transition of π-Conjugated Oligopeptides

Advances in supramolecular assembly have enabled the design and synthesis of functional materials with well-defined structures across multiple length scales. Biopolymer-synthetic hybrid materials can assemble into supramolecular structures with a broad range of structural and functional diversity through precisely controlled noncovalent interactions between subunits. Despite recent progress, there is a need to understand the mechanisms underlying the assembly of biohybrid/synthetic molecular building blocks, which ultimately control the emergent properties of hierarchical assemblies. In this work, we study the concentration-driven self-assembly and gelation of π-conjugated synthetic oligopeptides containing different π-conjugated cores (quaterthiophene and perylene diimide) using a combination of particle tracking microrheology, confocal fluorescence microscopy, optical spectroscopy, and electron microscopy. Our results show that π-conjugated oligopeptides self-assemble into β-sheet-rich fiber-like structures at neutral pH, even in the absence of electrostatic screening of charged residues. A critical fiber formation concentration cfiber and a critical gel concentration cgel are determined for fiber-forming π-conjugated oligopeptides, and the linear viscoelastic moduli (storage modulus G′ and loss modulus G″) are determined across a wide range of peptide concentrations. These results suggest that the underlying chemical structure of the synthetic π-conjugated cores greatly influences the self-assembly process, such that oligopeptides appended to π-conjugated cores with greater torsional flexibility tend to form more robust fibers upon increasing peptide concentration compared to oligopeptides with sterically constrained cores. Overall, our work focuses on the molecular assembly of π-conjugated oligopeptides driven by concentration, which is controlled by a combination of enthalpic and entropic interactions between oligopeptide subunits