Chirality in peptide-based materials: From chirality effects to potential applications

Multichiral Mesoporous Silica Screws with Chiral Differential Mucus Penetration and Mucosal Adhesion for Oral Drug Delivery

In the harsh gastrointestinal tract, helical bacteria with hierarchical chiral architectures possess strong abilities. Taking inspirations from nature, we developed a multichiral mesoporous silica nanoscrew (L/D-MCNS) as an efficient oral drug delivery platform by modifying the structural chiral silica nanoscrew (CNS) with L/D-alanine (L/D-Ala) enantiomers via the sequential application of a chiral template and postmodification strategies. We demonstrated that L-MCNS showed differential biological behaviors and superior advantages in oral adsorption compared to those of CNS, D-MCNS, and DL-MCNS. During the delivery, helical L/D-MCNS presenting distinctive topological structures, including small section area, large rough external surface, and a screw-like body, displayed multiple superiorities in mucus diffusion and mucosal adhesion. Meanwhile, the grafted chiral enantiomers enabled positive or negative chiral recognition with the biosystems. Once racemic flurbiprofen (FP) was encapsulated into the nanopores of L/D-MCNS (FP@L/D-MCNS), L/D-MCNS providing highly cross-linked and mesoscopic chiral nanochannels was beneficial for controlling the drug loading/release kinetics with chiral microenvironment sensitivity. Particularly, we noticed enantioselective absorption of FP in vivo, which could be attributed to the differential biological behaviors of L/D-MCNS. By simple design and regulation of the multilevel chirality of nanocarriers, L/D-MCNS can be employed for efficient oral drug delivery from the perspectives of material science, pharmacy, and bionics.

Stereoselective transport of 2-aryl propionic acid enantiomers in porous media subjected to chiral organic acids

The study examined the transport behavior of the 2-aryl propionic acid (2-APA) chiral pharmaceutical enantiomers by means of a laboratory-scale saturated quartz sand column experiment. Four typical of 2-APA and their enantiomers were selected for the study under different types of chiral organic acids (COAs)-mediated effects. Differences in the transport of the 2-APA enantiomeric pairs have been identified in response to various pH, types of COAs, and enantiomeric structures of COAs. Redundancy analysis identified the factors responsible for the largest differences in transport of 2-APA enantiomeric pairs, while spectroscopic characterization and density function theory (DFT) studies elucidated the underlying mechanisms contributing to the differences in transport of enantiomeric pairs. Obvious correlations among homochirality or heterochirality between COAs and 2-APA enantiomeric pairs were observed for changes in the mobility of 2-APA. The results indicate widespread COAs significantly affect the transport behavior of chiral man-made chemicals, suggesting more attention is needed to fill the gap in the perception of the transport behavior of chiral compounds.

Chirality-controlled polymerization-induced self-assembly

Recent studies have shown that biodegradable nanoparticles can be efficiently prepared with polymerization of N-carboxyanhydrides-induced self-assembly (NCA-PISA). However, thus far, the effect of chiral monomer ratio on such NCA-PISA formulations and the resulting nanoparticles has not yet been fully explored. Herein, we show, for the first time, that the morphology, secondary structure, and biodegradation rate of PISA nanoparticles can be controlled by altering the chiral ratio of the core-forming monomers. This chirality-controlled PISA (CC-PISA) method allowed the preparation of nanoparticles that are more adjustable and applicable for future biomedical applications. Additionally, the complex secondary peptide structure (ratio of α-helix to β-sheet) and π-π stacking affect the polymer self-assembly process. More specifically, a PEG45 macro-initiator was chain-extended with l- and d-phenylalanine (l- and d-Phe-NCA) in various molar ratios in dry THF at 15 wt%. This ring-opening polymerization (ROP) allowed the preparation of homo- and hetero-chiral Phe-peptide block copolymers that self-assembled in situ into nanoparticles. For homo-chiral formulations, polymers self-assembled into vesicles once a sufficiently high phenylalanine degree of polymerization (DP) was obtained. Hetero-chiral formulations formed larger nanoparticles with various morphologies and, much to our surprise, using an equal enantiomer ratio inhibited PISA and led to a polymer solution instead. Finally, it was shown that the enzymatic biodegradation rate of such PISA particles is greatly affected by the polymer chirality. This PISA approach could be of great value to fabricate nanoparticles that exploit chirality in disease treatment.

Supramolecular Hydrogels: Design Strategies and Contemporary Biomedical Applications

Self-assembly of supramolecular hydrogels is driven by dynamic, non-covalent interactions between molecules. Considerable research effort has been exerted to fabricate and optimise supramolecular hydrogels that display shear-thinning, self-healing, and reversibility, in order to develop materials for biomedical applications. This review provides a detailed overview of the chemistry behind the dynamic physicochemical interactions that sustain hydrogel formation (hydrogen bonding, hydrophobic interactions, ionic interactions, metal-ligand coordination, and host-guest interactions). Novel design strategies and methodologies to create supramolecular hydrogels are highlighted, which offer promise for a wide range of applications, specifically drug delivery, wound healing, tissue engineering and 3D bioprinting. To conclude, future prospects are briefly discussed, and consideration given to the steps required to ultimately bring these biomaterials into clinical settings.

Self-assembly driven chiral transfer from a dipeptide to the twist and stacking handedness of cyanobiphenylyl groups

The chiral transfer phenomenon was studied on four Ala–Ala lipodipeptides with a cyanobiphenylyl group at the terminal alkyl chain.

Recognition of Chiral Carboxylates by Synthetic Receptors

Recognition of anionic species plays a fundamental role in many essential chemical, biological, and environmental processes. Numerous monographs and review papers on molecular recognition of anions by synthetic receptors reflect the continuing and growing interest in this area of supramolecular chemistry. However, despite the enormous progress made over the last 20 years in the design of these molecules, the design of receptors for chiral anions is much less developed. Chiral recognition is one of the most subtle types of selectivity, and it requires very precise spatial organization of the receptor framework. At the same time, this phenomenon commonly occurs in many processes present in nature, often being their fundamental step. For these reasons, research directed toward understanding the chiral anion recognition phenomenon may lead to the identification of structural patterns that enable increasingly efficient receptor design. In this review, we present the recent progress made in the area of synthetic receptors for biologically relevant chiral carboxylates.

pH-influenced handedness inversion of circularly polarized luminescence

Supramolecular co-assemblies between tolane-derived Phe–Phe dipeptides and 1,2-diaminoethane were fabricated, and CPL handedness inversion was achieved by regulating the pH value.