Chiral Materials: Progress, Applications, and Prospects.

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Chiral MOFs encapsulated by polymers with poly-metallic coordination as chiral biosensors.

Chiral materials have drawn the widespread attention for their its chiral recognition ability. The design and synthesis of chiral material are of importance owing to the unpredictability in controlling chirality during the synthesis process. To circumvent problems, a chiral MOF (D-His-ZIF-8) was synthesized by ligand exchange of 2-methylimidazole (Hmim) on ZIF-8 by D-histidine (D-His), which can be treated as chiral host to distinguish amino acid enantiomers. The obtained D-His-ZIF-8 can provide chiral nanochannels for amino acid guests. Meanwhile, polynary transition-metal ion (Co2+ and Fe3+) coordinating with polydopamine (PDA) wrapped on the surface of D-His-ZIF-8 can increase the active sites. The electrochemical chiral recognition behavior showed that D-His-ZIF-8@CoFe-PDA exhibited good recognition of the tryptophan enantiomer (L/D-Trp) (working potential of -0.2 V vs. Hg/HgCl2). The LOD and LOQ of L-Trp were 0.066 mM and 0.22 mM, respectively, while the LOD and LOQ of D-Trp were 0.15 mM and 0.50 mM, respectively. Finally, the usefulness of D-His-ZIF-8@CoFe-PDA/GCE was evaluated with a recovery of 94.4-103%. The analysis of real  samples shows that D-His-ZIF-8@CoFe-PDA/GCE is a feasible sensing platform for the detection of L-Trp and D-Trp.

Chiral template-induced porphyrin-based self-assembled materials for electrochemical chiral sensing.

Chirality plays a key role in many fields of natural sciences as well as life sciences. Chiral materials are widely developed and used for electrochemical chiral recognition. In recent years, carbon quantum dots (CQDs) have been widely used as a novel carbon nanomaterial due to their excellent charge transfer properties, good biocompatibility, and low cost. The special structure of π-conjugated porphyrin attracts attention. Supramolecular self-assembly shows a way to construct chiral materials by self-assembling simple molecules into chiral composites. Herein, we demonstrate the self-assembly of achiral porphyrins induced by chiral carbon quantum dots assembled from L- and or D-tryptophan (L- and or D-Trp) with carbon quantum dots, resulting in 5,10,15,20-tetrakis (4-carboxyPheyl) (TCPP) self-assembled structure. The electrochemical chiral recognition of chiral self-assembled materials was studied using Phenylalanine (Phe) enantiomer as a chiral analyte. Electrochemical chiral recognition results showed that the chiral self-assembled materials induced by chiral templates have a good ability to discriminate Phe enantiomers. Therefore, this research provides a new idea for the synthesis of chiral composites and further expands applications to electrochemical chiral recognition.

Involvement of gut microbiota recovery and autophagy induction in Youhua Kuijie Formula's protection against experimental ulcerative colitis.

Ulcerative colitis (UC) is characterized by overactive inflammatory response, impaired intestinal mucosal barrier and disrupted gut microbiota. Youhua Kuijie formula is a classic empirical prescription based on the pathogenesis of UC. The present study was designed to verify the protective effect of Youhua Kuijie Formula on DSS-induced UC in mice and uncover the related mechanism. Youhua Kuijie Formula were orally administrated to UC mice induced by DSS dissolved in drinking water for ten days. The protective effect of Youhua Kuijie Formula was evidenced by reduced pathological symptoms accompanied by palliative inflammatory response and relatively intact intestinal barrier. The data from 16S rRNA gene sequencing and GC-MS untargeted metabolomics indicated that the supplement of Youhua Kuijie Formula restructured gut microbiota community structure, and thereby modulated the metabolic profiles in UC mice. The analysis of pathway enrichment analysis suggested the major alterations in metabolic pathway were related to protein digestion and absorption. Besides, the results of the following experiments suggested that Youhua Kuijie Formula treatment increased adenosine monophosphate-activated protein kinase (AMPK) activation, decreased mechanistic target of rapamycin (mTOR) phosphorylation, and thereby reversing autophagy deficiency in the intestinal tract of UC mice. Collectively, our results demonstrated that the regulation of AMPK/mTOR was involved in Youhua Kuijie Formula administration mediated protective effect on UC.

A Study of Molecular Dynamic Simulation and Experimental Performance of the Eucommia Ulmoides Gum-Modified Asphalt.

In recent years, eucommia ulmoides gum (EUG), also known as gutta-percha, has been extensively researched. Molecular dynamic simulations and experiments were used together to look at how well gutta-percha and asphalt work together and how gutta-percha-modified asphalt works. To investigate the gutta-percha and asphalt blending systems, the molecular models of asphalt and various dosages of gutta-percha-modified asphalt were set up using Materials Studio (MS), and the solubility parameters, intermolecular interaction energy, diffusion coefficient, and mechanical properties (including elastic modulus, bulk modulus, and shear modulus) of each system were calculated using molecular dynamic simulations at various temperatures. The findings indicate that EUG and asphalt are compatible, and sulfurized eucommia ulmoides gum (SEUG) and asphalt are more compatible than EUG. However, SEUG-modified asphalt has better mechanical properties than EUG, and the best preparation conditions are 10 wt% doping and 1 h of 180 °C shearing. Primarily, physical modifications are required for gutta-percha-modified asphalt.

Design and Electrochemical Chiral Sensing of the Robust Sandwich Chiral Composite d-His-ZIF-8@Au@ZIF-8.

In the pursuit of chiral materials with significant chiral recognition effects and stability, various strategies have been explored, among which the integration of metal nanoparticles and chiral metal-organic frameworks (CMOFs) is highly promising. However, metal nanoparticles (MNPs)/CMOFs show high chiral properties but inferior stabilities due to the MNPs being easily detached from the outside layer under certain conditions. Sandwich MOFs@MNPs@CMOF chiral materials can overcome this dilemma because the sandwich structure can maximize the regulation of the chiral interface activity, while the controlled outer layer can stop the MNPs from falling off in the procedure of chiral recognition. Here, a novel sandwich chiral material (d-His-ZIF-8@Au@ZIF-8) was synthesized by a ligand-assisted strategy with a well-defined sandwich morphology and chiral recognition capabilities. The electrochemical chiral recognition showed that d-His-ZIF-8@Au@ZIF-8 was the most efficient for the enantiomer of phenylalanine (Phe). This experiment presents a novel perspective for the fabrication of a chiral electrochemical sensing platform based on a solid sandwich chiral nanocomposite.

Induction of chiral polymers from metal-organic framework for stereoselective recognition.

So far, the fabrication of chiral metal-organic framework (CMOF) is difficult to predict and the chiral functionality mainly comes from the building blocks that is a part of the frameworks. The induction effect in the chiral nanochannels of the metal-organic framework (MOF) makes achiral polymers have chiral properties, which has not been well explored. Therefore, CMOFs with chiral nanochannels or chiral pores appear to have special functions. Herein, CMOFs (D-his-ZIF-8) with chiral micropores or chiral nanochannels are prepared through a simple 2-methyl imidazolate in-situ substitution by d-histidine. The unmodified polyaniline with chirality (c-PANI) was synthesized in chiral nanochannels and pores of CMOF, which brought about chiral induction from the chiral nanochannels and pores of CMOF to c-PANI chains. The circular dichroism shows that the c-PANI chains released from the chiral nanochannel still maintains the chiral properties even leaves the chiral nanochannel. It can be seen from the electrochemical results that c-PANI has excellent conductivity, and the conductivity of CMOF is very poor. Electrochemical recognition showed that both CMOF and c-PANI have certain chiral recognition effects for L-Trp and D-Trp, from which the optimal recognition effect was obtained from c-PANI chains. This shows that the excellent conductivity of c-PANI not only expands the electrochemical signal, but also the helical structure of the c-PANI chains accelerates the distinction of chiral molecules. This study provides a novel perspective to induce chiral polymer chains with better conductivity in the nanochannels of CMOF.

Spin-liquid ground state of the S = 1/2 kagome Heisenberg antiferromagnet.

We use the density matrix renormalization group to perform accurate calculations of the ground state of the nearest-neighbor quantum spin S = 1/2 Heisenberg antiferromagnet on the kagome lattice. We study this model on numerous long cylinders with circumferences up to 12 lattice spacings. Through a combination of very-low-energy and small finite-size effects, our results provide strong evidence that, for the infinite two-dimensional system, the ground state of this model is a fully gapped spin liquid.