Self-Assembled Bio-Organometallic Nanocatalysts for Highly Enantioselective Direct Aldol Reactions.

Supramolecular nanocatalysts were designed for asymmetric reactions through the self-assembly process of a bio-organometallic molecule, ferrocene-l-prolinamide (Fc-CO-NH-P). Fc-CO-NH-P could self-assemble into versatile nanostructures in water, including nanospheres, nanosheets, nanoflowers, and pieces. In particular, the self-assembled nanoflowers exhibited a superior specific surface area, high stability, and delicate three-dimensional (3D) chiral catalytic active sites. The nanoflowers could serve as heterogeneous catalysts with an excellent catalytic performance toward direct aldol reactions in aqueous solution, achieving both high yield (>99%) and stereoselectivity (anti/syn = 97:3, ee% >99%). This study proposed a significant strategy to fabricate supramolecular chiral catalysts, serving as a favorable template for designing new asymmetric catalysts.

Self-Assembly of Peptide Chiral Nanostructures with Sequence-Encoded Enantioseparation Capability.

Biopolymers such as polysaccharides and proteins have been widely used for the chiral separation of various components due to the intrinsic chirality of the polymers. Amyloid-like short peptides can also self-assemble into diverse chiral supramolecular nanostructures or polymers with precisely tailored architectures driving by noncovalent interactions. However, the use of such supramolecular nanostructures for the resolution and separation of chiral components remains largely unexplored. Here, we report that the self-assembled peptide supramolecular nanostructures can be used for the highly efficient chiral separation of various enantiomers. By rationally designing the constituent amino acid sequence of the peptides and the self-assembling environment, we can fabricate supramolecular polymers with distinct surface charges and architectures, including nanohelices, nanoribbons, nanosheets, nanofibrils, and nanospheres. The various supramolecular nanostructures were then used to resolve the racemic mixtures of α-methylbenzylamine, 2-phenylpropionic acid, and 1-phenylethanol. The results indicated that the self-assembled peptide polymers showed excellent enantioselective separation efficiency for different chiral molecules. The enantioselective separation efficiency of the peptide nanostructures can be tailored by changing their surface charges, morphology, and the constituent amino acid sequences of the peptides.

Protamine-induced condensation of peptide nanofilaments into twisted bundles with controlled helical geometry.

Chiral self-assembly of peptides is of fundamental interest in the field of biology and material science. Protamine, an alkaline biomacromolecule which is ubiquitous in fish and mammalian, plays crucial roles in directing the helical twisting of DNA. Inspired by this, we reported a bioinspired pathway to direct the hierarchical chiral self-assembly of a short synthetic dipeptide. The peptide could self-assemble into negatively charged chiral micelles in water that spontaneously formed a nematic liquid crystalline phase. By incorporation with protamine, the micelles condensed with the protamine into large helical bundles with precisely controlled diameter. Furthermore, to simulate the intracellular environments, we investigated macromolecular crowding on the coassembly of peptide and protamine, which leads to the formation of much thinner helical structures. The results highlight the roles of highly charged biomacromolecules and macromolecular crowding on peptide self-assembly, which are beneficial for the practical applications of self-assembling peptides in biomedicine and sensing.

Polyamine-induced, chiral expression from liquid crystalline peptide nanofilaments to long-range ordered nanohelices.

We reported the condensation and transformation of peptide micelles into well-defined nanohelices through the incorporation of natural polyamines. The liquid-crystalline peptide micelles are assembled by a short dipeptide amphiphile driven by strong electrostatic repulsions and aromatic stacking attractions. By incorporating polyamines into the peptide solutions, like-charge attractions were achieved to induce the condensation of the like-charged nanofilaments into giant bundles. Intriguingly, by increasing the temperature or electrostatic screening effects, the nanofilaments within the bundles fuse with each other into well-defined flat ribbons which then spontaneously twisted into macroscopically aligned nanohelices. Moreover, the chiral interactions between the aromatic groups of adjacent peptides are inverted from right-handedness to left-handedness during the formation of nanohelices. The results provide new insights into the chiral evolution during peptide self-assembly and offer opportunities for the design of peptide materials with new properties, such as anisotropic hydrogels and long-range ordered chiral nanostructures.

In situ fabrication of multifunctional gold-amino acid superstructures based on self-assembly.

A facial strategy to construct multifunctional gold-amino acid superstructures is reported. The ferrocene-tryptophan conjugate could self-assemble into three-dimensional microflowers. What's more, gold nanoparticles could be biomineralized on the surface of the microflowers, achieving gold-amino acid superstructures. The formed superstructures exhibited significant photothermal effects and catalytic activity.

Highly efficient and selective production of FFCA from CotA-TJ102 laccase-catalyzed oxidation of 5-HMF.

5-Formyl-2-furancarboxylic acid (FFCA) is increasingly important building blocks, which has promising applications in fuels, chemical intermediates, drugs, etc. However, highly selective oxidation of 5-hydroxymethylfurfural (5-HMF) to FFCA by enzyme catalysis is a new challenging problem due to the absence of specific enzymes. Recently we identified a kind of laccase (CotA-TJ102) from Bacillus subtilis TJ-102 could convert selectively 5-HMF to FFCA, and no further oxidation production (such as FDCA). The initial conditions resulted in low 5-HMF conversion ratio at 23.5% and low FFCA yield at 19.3% after 96 h, but high FFCA selectivity at 82.4%. Then the proposed mechanism in detail for the selective oxidation of HMF to FFCA by CotA-TJ102 was deduced and discussed. After optimization of reaction parameters such as pH, TEMPO concentration and temperature, FFCA could be obtained in a high yield of 98.55% with a 5-HMF conversion ratio of nearly 100% after a short reaction time of 12 h. Finally, after immobilization of CotA-TJ102 on magnetic nanoparticles, the FFCA yield remained 83.28% for 10 of recycling times based on the high FFCA selectivity (>96%), which reflected high stability and good reusability. Therefore, this enzymatic approach constitutes a promising method for the green production of FFCA.

Aromatic Motifs Dictate Nanohelix Handedness of Tripeptides.

Self-assembly of peptides and amyloid fibrils offers an appealing approach for creating chiral nanostructures, which has promising applications in the fields of biology and materials science. Although numerous self-assembled chiral materials have been designed, the precise control of their twisting tendency and their handedness is still a challenge. Herein, we report the self-assembly of chiral nanostructures with precisely tailored architectures by changing the amino acid sequences of the peptides. We designed a series of self-assembling tripeptides bearing different l-amino acid sequences. The peptide with l-Phe-l-Phe sequence preferred to self-assemble into left-handed nanohelices, while with l-Phe-l-Trp right-handed nanohelices would be formed. Moreover, the diameter of the self-assembled nanohelices could be tailored by changing the terminal amino acids (His, Arg, Ser, Glu, and Asp). Circular dichroism (CD) and molecular dynamics simulations (MDSs) revealed that both of the right- and left-handed nanohelices formed by the tripeptides showed negative Cotton effects in the peptide adsorption region but exhibited nearly opposite CD Cotton effects in the aromatic regions. These results indicated that the handedness of the self-assembled helical nanofibers was not only determined by the chirality of the peptide backbone but also closely related to the aromatic stacking, hydrogen bonding and steric interactions induced by the side chains. The findings deepen our understanding on the chiral self-assembly of peptide and offer opportunities for the creation of highly functional chiral nanomaterials.