Fmoc-Dipeptide/Porphyrin Molar Ratio Dictates Energy Transfer Efficiency in Nanostructures Produced by Biocatalytic Co-Assembly.

The controlled self-assembly of porphyrin derivatives (TCPP, tetrakis(4-carboxyphenyl)porphyrin) within Fmoc-protected (Fmoc=9-Fluorenylmethyloxycarbonyl) dipeptide (Fmoc-TL-NH2 ) nanofibers is demonstrated. The biocatalytic co-assembly in aqueous medium generated an energy transfer hydrogel. Depending on the concentrations of porphyrin used, the resulting nanofibrous gels show two distinct regions of self-assembly behavior that is, integration of TCPP into nanostructures to produce two-component co-assembly fibers, or heterogeneous self-aggregation of TCPP within the self-assembled matrix observed at higher concentrations. The mode of assembly directly impacts on the energy transfer efficiency of these nanostructures. These results show that reversible biocatalytic co-assembly of structural and functional components enables fine-tuning of peptide/porphyrin energy transfer nanostructures.

Amino-acid-encoded biocatalytic self-assembly enables the formation of transient conducting nanostructures.

Aqueous compatible supramolecular materials hold promise for applications in environmental remediation, energy harvesting and biomedicine. One remaining challenge is to actively select a target structure from a multitude of possible options, in response to chemical signals, while maintaining constant, physiological conditions. Here, we demonstrate the use of amino acids to actively decorate a self-assembling core molecule in situ, thereby controlling its amphiphilicity and consequent mode of assembly. The core molecule is the organic semiconductor naphthalene diimide, functionalized with D- and L- tyrosine methyl esters as competing reactive sites. In the presence of α-chymotrypsin and a selected encoding amino acid, kinetic competition between ester hydrolysis and amidation results in covalent or non-covalent amino acid incorporation, and variable supramolecular self-assembly pathways. Taking advantage of the semiconducting nature of the naphthalene diimide core, electronic wires could be formed and subsequently degraded, giving rise to temporally regulated electro-conductivity.

Dynamic peptide libraries for the discovery of supramolecular nanomaterials.

Sequence-specific polymers, such as oligonucleotides and peptides, can be used as building blocks for functional supramolecular nanomaterials. The design and selection of suitable self-assembling sequences is, however, challenging because of the vast combinatorial space available. Here we report a methodology that allows the peptide sequence space to be searched for self-assembling structures. In this approach, unprotected homo- and heterodipeptides (including aromatic, aliphatic, polar and charged amino acids) are subjected to continuous enzymatic condensation, hydrolysis and sequence exchange to create a dynamic combinatorial peptide library. The free-energy change associated with the assembly process itself gives rise to selective amplification of self-assembling candidates. By changing the environmental conditions during the selection process, different sequences and consequent nanoscale morphologies are selected.