Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Structural chirality and related properties in periodic inorganic solids: review and perspectives

Chirality refers to the asymmetry of objects that cannot be superimposed on their mirror image. It is a concept that exists in various scientific fields and has profound consequences. Although these are perhaps most widely recognized within biology, chemistry, and pharmacology, recent advances in chiral phonons, topological systems, crystal enantiomorphic materials, and magneto-chiral materials have brought this topic to the forefront of condensed matter physics research. Our review discusses the symmetry requirements and the features associated with structural chirality in inorganic materials. This allows us to explore the nature of phase transitions in these systems, the coupling between order parameters, and their impact on the material's physical properties. We highlight essential contributions to the field, particularly recent progress in the study of chiral phonons, altermagnetism, magnetochirality between others. Despite the rarity of naturally occurring inorganic chiral crystals, this review also highlights a significant knowledge gap, presenting challenges and opportunities for structural chirality mostly at the fundamental level, e.g. chiral displacive phase transitions, possibilities of tuning and switching structural chirality by external means (electric, magnetic, or strain fields), whether chirality could be an independent order parameter, and whether structural chirality could be quantified, etc. Beyond simply summarizing this field of research, this review aims to inspire further research in materials science by addressing future challenges, encouraging the exploration of chirality beyond traditional boundaries, and seeking the development of innovative materials with superior or new properties.

Universal Chiral Nanopaint for Metal Oxide Biomaterials

Chirality is widespread in nature and governs the properties of various materials including inorganic nanomaterials. However, previously reported chiral inorganic materials have been limited to a handful of compositions owing to the physicochemical restrictions that impart chirality. Herein, chiral nanopaint applicable to diverse inorganic materials is presented. Various metal oxide nanoparticles (NPs) show chiroptical properties after coating with our chiral nanopaint, while maintaining their properties, such as magnetic properties. The combination of magnetism and chirality brings biomedical functionalities to chiral NPs, such as anticancer hyperthermia treatment. In vitro, d-nanopainted iron oxide NPs showed more than 50% higher cellular uptake compared to l-nanopainted iron oxide NPs, and this was due to the enantiospecific interaction between the cellular receptors on the cell surface and the chiral NPs. In vivo, d-nanopainted iron oxide NPs showed 4-fold superior anticancer efficiency by magnetic hyperthermia compared to l-nanopainted iron oxide NPs owing to improved adsorption to tumors. These chiral nanoparticles may provide potential synthesis strategies for chiral inorganic biomaterials, which exhibit elaborate combinations of intrinsic physical properties and extrinsic enantioselective properties for a variety of applications.

Recent developments and applications of solid membrane in chiral separation

Chirality is a fundamental property in nature, and chiral molecules are closely related to human health and the origin of life. Therefore, the exploration and preparation of optically active compounds of paramount importance. Membrane separation is a large-scale and continuous separation technique that has been developing quickly in recent years. It has many potential applications, particularly in chiral membrane separation technology, which is currently a hotspot for study. Depending on the types of membranes, chiral membranes can be divided into two categories: chiral solid membranes and chiral liquid membranes. Solid membranes outperform the others in terms of better mechanical performance and separation efficiency. This review presents in-depth summaries of chiral solid membranes made of different materials, and their applications in drug separation. It also providing insights into the potential for the future development of chiral solid membranes.

Development of Nanomaterials-Based Agents for Selective Antibacterial Activity

Bacterial infections continue to threaten public health due to limitations in rapid and accurate diagnostic techniques. While broad-spectrum antibiotics offer empirical treatment, their overuse has fuelled the emergence of antimicrobial resistance (AMR) pathogens, posing a critical global public health challenge. In this critical scenario, nanomaterial-based antibacterial agents emerge as a promising solution to combat bacteria and inhibit their proliferation. However, selective elimination of pathogenic bacteria is paramount. This review highlights recent advancements in developing nanomaterials for selective antibacterial activity. We categorize these agents based on their mode of action, exploring how they selectively interact with bacteria and their potential antibacterial mechanisms. This review offers crucial insights for researchers exploring the potential of nanotechnology to address the growing threat of AMR.

Mechanisms for translating chiral enantiomers separation research into macroscopic visualization

Chirality is a common phenomenon in nature, including the dominance preference of small biomolecules, the special spatial conformation of biomolecules, and the biological and physiological processes triggered by chirality. The selective chiral recognition of molecules in nature from up-bottom or bottom-up is of great significance for living organisms. Such as the transcription of DNA, the recognition of membrane proteins, and the catalysis of enzymes all involve chiral recognition processes. The selective recognition between these macromolecules is mainly achieved through non covalent interactions such as hydrophobic interactions, ammonia bonding, electrostatic interactions, metal coordination, van der Waals forces, and π-π stacking. Researchers have been committed to studying how to convert this weak non covalent interaction into macroscopic visualization, which has further understood of the interactions between chiral molecules and is of great significance for simulating the interactions between molecules in living organisms. This article reviews several models of chiral recognition mechanisms, the interaction forces involved in the chiral recognition process, and the research progress of chiral recognition mechanisms. The outlook in this review points out that studying chiral recognition interactions provides an important bridge between chiral materials and the life sciences, providing an ideal platform for studying chiral phenomena in biological systems.

Chiral Inorganic Nanomaterials Characterized by Advanced TEM: A Qualitative and Quantitative Study

Chiral inorganic nanomaterials (CINMs) have garnered significant interest due to their exceptional optical, electronic, and catalytic properties, offering promising advancements in energy conversion, data storage, catalysis, and biomedicine. While traditional optical spectrophotometers reveal the chiroptical performance of CINMs on an ensemble level, the direct structural visualization for the qualitative and quantitative discernment of their chiral features has become increasingly distinct with the advancements of transmission electron microscopy (TEM) techniques. The need for reasonable and high-standard discrimination requirements of CINMs has driven the progress of chirality-based TEM technologies. Therefore, this review in the good season takes the initiative to summarize the current advancements in TEM technologies for CINMs characterization, emphasizing a qualitative analysis of chiral atomic-level features, 0D, 1D, and 2D nanocrystals, and assembled nanomaterials. Then, the quantitative methods for determining chirality is also highlighted, such as 3D electron tomography, and further address the evolution of chiral structures monitored by the Ex-situ and In-situ TEM technologies. By providing a roadmap for the current challenges and proposing future advancements in TEM technologies for the qualitative, quantitative, and real-time analysis of CINMs, it can drive innovations in the field of chiral nanomaterials as well as the development of TEM technologies.

Stimulating Chiral Selective Expression of Room Temperature Phosphorescence for Chirality Recognition

Chiral recognition is crucial for applications in chiral purity assessment and biomedical fields. However, achieving chiral recognition through visible room temperature phosphorescence remains challenging. Here, two chiral molecules, designated as host and guest are synthesized, which possess similar structural configurations. A viable strategy involving a chiral configuration-dependent energy transfer process to enable selective phosphorescence expression is proposed, thereby enabling chiral recognition in a host-guest doping system. The chiral and structural similarity between host and guest facilitates efficient Dexter energy transfer due to the reduced spatial distance between the molecules. This mechanism significantly enhances the intensity of red phosphorescence from the guest molecule, characterized by an emission peak at 612 nm and a prolonged lifetime of 32.7 ms. This work elucidates the mechanism of chiral-dependent energy transfer, demonstrating its potential for selectively expressing phosphorescence in chiral recognition.

Regulating Catalytic Oxidation Enantiomers Behavior by Imparting Chiral Microenvironment in Zr-Based Metal-Organic Frameworks

Chiral inversions of enantiomers have significantly different biological activities, so it is important to develop simple and effective methods to efficiently identify optically pure compounds. Inspired by enzyme catalysis, the construction of chiral microenvironments resembling enzyme pockets in the pore space structure of metal-organic frameworks (MOFs) to achieve asymmetric enantioselective recognition and catalysis has become a new research hotspot. Here, a super-stable porphyrin-containing material PCN-224 is constructed by solvothermal method and a chiral microenvironment around the existing catalytic site of the material is created by post-synthesis modifications of the histidine (His) enantiomers. Experimental and theoretical calculations results show that the modulation of chiral ligands around Zr oxide clusters produces different spatial site resistances, which can greatly affect the adsorption and catalytic level of the enantiomeric molecules of tryptophan guests, resulting in a good enantioselective property of the material. It provides new ideas and possibilities for future chiral recognition and asymmetric catalysis.

Synthesis of chiral graphene structures and their comprehensive applications: a critical review

From a molecular viewpoint, chirality is a crucial factor in biological processes. Enantiomers of a molecule have identical chemical and physical properties, but chiral molecules found in species exist in one enantiomer form throughout life, growth, and evolution. Chiral graphene materials have considerable potential for application in various domains because of their unique structural framework, properties, and controlled synthesis, including chiral creation, segregation, and transmission. This review article provides an in-depth analysis of the synthesis of chiral graphene materials reported over the past decade, including chiral nanoribbons, chiral tunneling, chiral dichroism, chiral recognition, and chiral transfer. The second segment focuses on the diverse applications of chiral graphene in biological engineering, electrochemical sensors, and photodetectors. Finally, we discuss research challenges and potential future uses, along with probable outcomes.

Iridium-Catalyzed Asymmetric Hydroarylation of Unactivated Alkenes with Heterobiaryls: Simultaneous Construction of Axial and Central Chirality

There are only a few examples being reported for the simultaneous control of central chirality and axial chirality because it is more challenging. Herein, we report an iridium-catalyzed asymmetric hydroarylation of unactivated alkenes with heterobiaryls to simultaneously construct axial and central chirality. The reaction showed a broad substrate scope and delivered the products with satisfactory results. The results of the control experiments demonstrated that the FerroLANE ligand promotes the reaction to proceed along a specific modified Chalk-Harrod mechanism.

Potential Application Prospects of Biomolecule-Modified Two-Dimensional Chiral Nanomaterials in Biomedicine

Chirality, one of the most fundamental properties of natural molecules, plays a significant role in biochemical reactions. Nanomaterials with chiral characteristics have superior properties, such as catalytic properties, optoelectronic properties, and photothermal properties, which have significant potential for specific applications in nanomedicine. Biomolecular modifications such as nucleic acids, peptides, proteins, and polysaccharides are sources of chirality for nanomaterials with great potential for application in addition to intrinsic chirality, artificial macromolecules, and metals. Two-dimensional (2D) nanomaterials, as opposed to other dimensions, due to proper surface area, extensive modification sites, drug loading potential, and simplicity of preparation, are prepared and utilized in diagnostic applications, drug delivery research, and tumor therapy. Current advanced studies on 2D chiral nanomaterials for biomedicine are focused on novel chiral development, structural control, and materials sustainability applications. However, despite the advances in biomedical research, chiral 2D nanomaterials still confront challenges such as the difficulty of synthesis, quality control, batch preparation, chiral stability, and chiral recognition and selectivity. This review aims to provide a comprehensive overview of the origins, synthesis, applications, and challenges of 2D chiral nanomaterials with biomolecules as cargo and chiral modifications and highlight their potential roles in biomedicine.

One-step simultaneous liquid phase exfoliation-induced chirality in graphene and their chirality-mediated microRNA delivery

Graphene (G) has established itself as an exciting prospect for a broad range of applications owing to its remarkable properties. Recent innovations in chiral nanosystems have led to sensors, drug delivery, catalysis, etc. owing to the stereospecific interactions between various nanosystems and enantiomers. As the molecular structure of G itself is achiral introducing chirality in G by simple attachment of a functional group (a chiral ligand) on the G nanosheet may result in more diverse applications. Herein, we demonstrate direct liquid phase exfoliation and chiral induction in G nanosheets abbreviated as l-graphene and d-graphene in the presence of chiral l-tyrosine and d-tyrosine and by applying high-temperature sonication. The obtained exfoliated nanosheets demonstrated stable chirality confirmed by circular dichroism. Fourier transform infrared (FTIR) spectra, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC) showed functional, structural, morphological, surface, and thermal characteristics of l-graphene and d-graphene. The hemo-compatibility of these chiral graphenes was evaluated for the very first time utilizing human red blood cells. Lastly, for the very first time, an attempt was made to explore enantiomeric binding between chiral l-graphene and d-graphene with microRNA (miR-205) and their possibility towards chirality-mediated gene delivery in prostate cancerous cells.

Chirality-Induced Spin Selectivity in Supramolecular Chirally Functionalized Graphene

Chiral graphene hybrid materials have attracted significant attention in recent years due to their various applications in the areas of chiral catalysis, chiral separation and recognition, enantioselective sensing, etc. On the other hand, chiral materials are also known to exhibit chirality-dependent spin transmission, commonly dubbed "chirality induced spin selectivity" or CISS. However, CISS properties of chiral graphene materials are largely unexplored. As such, it is not clear whether graphene is even a promising material for the CISS effect given its weak spin-orbit interaction. Here, we report the CISS effect in chiral graphene sheets, in which a graphene derivative (reduced graphene oxide or rGO) is noncovalently functionalized with chiral Fmoc-FF (Fmoc-diphenylalanine) supramolecular fibers. The graphene flakes acquire a "conformational chirality" postfunctionalization, which, combined with other factors, is presumably responsible for the CISS signal. The CISS signal correlates with the supramolecular chirality of the medium, which depends on the thickness of graphene used. Quite interestingly, the noncovalent supramolecular chiral functionalization of conductive materials offers a simple and straightforward methodology to induce chirality and CISS properties in a multitude of easily accessible advanced conductive materials.

Chirality-enhanced transport and drug delivery of graphene nanocarriers to tumor-like cellular spheroid

Chirality, defined as "a mirror image," is a universal geometry of biological and nonbiological forms of matter. This geometry of molecules determines how they interact during their assembly and transport. With the development of nanotechnology, many nanoparticles with chiral geometry or chiroptical activity have emerged for biomedical research. The mechanisms by which chirality originates and the corresponding synthesis methods have been discussed and developed in the past decade. Inspired by the chiral selectivity in life, a comprehensive and in-depth study of interactions between chiral nanomaterials and biological systems has far-reaching significance in biomedicine. Here, we investigated the effect of the chirality of nanoscale drug carriers, graphene quantum dots (GQDs), on their transport in tumor-like cellular spheroids. Chirality of GQDs (L/D-GQDs) was achieved by the surface modification of GQDs with L/D-cysteines. As an in-vitro tissue model for drug testing, cellular spheroids were derived from a human hepatoma cell line (i.e., HepG2 cells) using the Hanging-drop method. Our results reveal that the L-GQDs had a 1.7-fold higher apparent diffusion coefficient than the D-GQDs, indicating that the L-GQDs can enhance their transport into tumor-like cellular spheroids. Moreover, when loaded with a common chemotherapy drug, Doxorubicin (DOX), via π-π stacking, L-GQDs are more effective as nanocarriers for drug delivery into solid tumor-like tissue, resulting in 25% higher efficacy for cancerous cellular spheroids than free DOX. Overall, our studies indicated that the chirality of nanocarriers is essential for the design of drug delivery vehicles to enhance the transport of drugs in a cancerous tumor.

Synthesis and Characterization of Gold Chiral Nanoparticles Functionalized by a Chiral Drug

Inorganic chiral nanoparticles are attracting more and more attention due to their peculiar optical properties and potential biological applications, such as bioimaging, therapeutics, and diagnostics. Among inorganic chiral nanoparticles, gold chiral nanostructures were demonstrated to be very interesting in this context, with good physical chemical stability and also the possibility to decorate the surface, improving biomedical application as the interaction with the bio-systems. Gold (Au) nanostructures were synthesized according to a seed-mediated procedure which envisages the use of cetyltrimethylammonium bromide (CTAB) as the capping agent and L- and D-cysteine to promote chirality. Au nanostructures have been demonstrated to have opposite circular dichroism signals depending on the amino acid enantiomer used during the synthesis. Then, a procedure to decorate the Au surface with penicillamine, a drug used for the treatment of Wilson's disease, was developed. The composite material of gold nanoparticles/penicillamine was characterized using electron microscopy, and the penicillamine functionalization was monitored by means of UV-Visible, Raman, and infrared spectroscopy, highlighting the formation of the Au-S bond. Furthermore, electron circular dichroism was used to monitor the chirality of the synthesized nanostructures and it was demonstrated that both penicillamine enantiomers can be successfully bonded with both the enantiomers of the gold nanostructures without affecting gold nanoparticles' chirality. The effective modification of nanostructures' surfaces via penicillamine introduction allowed us to address the important issue of controlling chirality and surface properties in the chiral nano-system.

Stereospecific Self-Assembly Processes of Porphyrin-Proline Conjugates: From the Effect of Structural Features and Bulk Solvent Properties to the Application in Stereoselective Sensor Systems

Conjugating the porphyrin ring with an amino acid via amide linkage represents a straightforward way for conferring both amphiphilicity and chirality to the macrocycle. Proline residue is a good choice in this context since its conformational rigidity allows for porphyrin assembling where molecular chirality is efficiently transferred and amplified using properly honed aqueous environments. Herein, we describe the evolution of the studies carried out by our group to achieve chiral systems from some porphyrin-proline derivatives, both in solution and in the solid state. The discussion focuses on some fundamental aspects reflecting on the final molecular architectures obtained, which are related to the nature of the appended group (stereochemistry and charge), the presence of a metal ion coordinated to the porphyrin core and the bulk solvent properties. Indeed, fine-tuning the mentioned parameters enables the achievement of stereospecific structures with distinctive chiroptical and morphological features. Solid films based on these chiral systems were also obtained and their recognition abilities in gaseous and liquid phase are here described.

A visual chiroptical system with chiral assembly graphene quantum dots for D-phenylalanine detection

Chirality is a fundamental phenomenon of nature, and the enantioselective recognition of amino acids isomers is especially important for life science. In this study, chiroptical system based on chiral assembly graphene quantum dots (GQDs) was developed for visual testing of D-phenylalanine (D-Phe). Here, GQDs were used as the fluorescent element, and chiral functional moieties of 1,3,5-triformylphloroglucinol-functionalized chiral ( +)-diacetyl-L-tartaric anhydride (TPTA) were used as the chiral recognition elements. Based on the formed chiral microenvironment, the fluorescence intensity of TPTA-assembled GQDs had a good linear relationship with D-Phe in the concentration range of 0.1-5 μM, and the detection limit was 0.023 μM. According to the variation in luminance of TPTA-assembled GQDs, visual testing to D-Phe was realized using a smartphone-assisted chiroptical system with a detection limit of 0.050 μM. The spiked recoveries of both chiroptical sensing methods based on TPTA-assembled GQDs from the food matrix ranged from 86.20 to 110.0%. Furthermore, TPTA-assembled GQDs were successfully applied to intracellular chiroptical imaging in response to D-Phe in vitro. The developed chiral nanomaterial TPTA-assembled GQDs with excellent photochemical stability, optical properties, and bioimaging capabilities provide a promising technique for the visual detection of amino acid isomers in the field of smart devices.

Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review

Graphene-based nanomaterials have shown wide applications in antimicrobial fields due to their accelerated rate of pathogen resistance and good antimicrobial properties. To apply graphene materials in the antimicrobial test, the graphene materials are usually fabricated as two-dimensional (2D) membranes. In addition, to improve the antimicrobial efficiency, graphene membranes are modified with various functional nanomaterials, such as nanoparticles, biomolecules, polymers, etc. In this review, we present recent advances in the fabrication, functional tailoring, and antimicrobial applications of graphene-based membranes. To implement this goal, we first introduce the synthesis of graphene materials and then the fabrication of 2D graphene-based membranes with potential techniques such as chemical vapor deposition, vacuum filtration, spin-coating, casting, and layer-by-layer self-assembly. Then, we present the functional tailoring of graphene membranes by adding metal and metal oxide nanoparticles, polymers, biopolymers, metal–organic frameworks, etc., with graphene. Finally, we focus on the antimicrobial mechanisms of graphene membranes, and demonstrate typical studies on the use of graphene membranes for antibacterial, antiviral, and antifungal applications. It is expected that this work will help readers to understand the antimicrobial mechanism of various graphene-based membranes and, further, to inspire the design and fabrication of functional graphene membranes/films for biomedical applications.

Insight into the Effects of Chiral Diphosphine Ligands on the Structure and Optical Properties of the Au24Cd2 Nanocluster

Introduction of chiral ligands has been regarded as an effective strategy to obtain nanoclusters with optical purity. However, how the chiral ligands work is still unclear due to the lack of structural comparison between racemic nanoclusters and the corresponding optically active ones. In this work, three structurally related Au₂₄Cd₂ nanoclusters, including one racemic and two homochiral nanoclusters, were synthesized, and their crystal structures were characterized using single-crystal X-ray crystallography (SC-XRD). Based on their crystal structures, the origin of the chirality in Au₂₄Cd₂ was found to be the twist of the kernel and the chiral arrangement of the metal-ligand surface. Au₂₄Cd₂ protected with chiral ligands exhibits a more twisted kernel than the racemic one. Therefore, the chirality of chiral diphosphine was found to transfer from the ligands to the metal-ligand interface and then to the metal core, inducing its distortion to produce enhanced chirality. In addition, the optical properties including optical absorption and circular dichroism of these structurally related Au₂₄Cd₂ nanoclusters were compared.

Site-Specific Reduction-Induced Hydrogenation of a Helical Bilayer Nanographene with K and Rb Metals: Electron Multiaddition and Selective Rb+ Complexation

The chemical reduction of π-conjugated bilayer nanographene 1 (C138 H120 ) with K and Rb in the presence of 18-crown-6 affords [K+ (18-crown-6)(THF)2 ][{K+ (18-crown-6)}2 (THF)0.5 ][C138 H122 3- ] (2) and [Rb+ (18-crown-6)2 ][{Rb+ (18-crown-6)}2 (C138 H122 3- )] (3). Whereas K+ cations are fully solvent-separated from the trianionic core thus affording a "naked" 1.3 - anion, Rb+ cations are coordinated to the negatively charged layers of 1.3 - . According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site-specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction-induced site-specific hydrogenation provokes dramatic changes in the (electronic) structure of 1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.

Biological applications of chiral inorganic nanomaterials

Chirality is common in nature and plays the essential role in maintaining physiological process. Chiral inorganic nanomaterials with intense optical activity have attracted more attention due to amazing properties in recent years. Over the past decades, many efforts have been paid to the preparation and chirality origin of chiral nanomaterials; furthermore, emerging biological applications have been investigated widely. This review mainly summarizes recent advances in chiral nanomaterials. The top-down and bottom-up preparation methods and chirality origin of chiral nanomaterials are introduced; besides, the biological applications, such as sensing, therapy, and catalysis, will be introduced comprehensively. Finally, we also provide a perspective on the biomedical applications of chiral nanomaterials.

Chirally modified cobalt-vanadate grafted on battery waste derived layered reduced graphene oxide for enantioselective photooxidation of 2-naphthol: Asymmetric induction through non-covalent interaction

The cobalt oxide-vanadium oxide (Co₃O₄-V₂O₅) combined with reduced graphene oxide (rGO) having band gap of ∼ 3.3 eV appeared as a suitable photocatalyst for selective oxidation of 2-naphthol to BINOL. C2-symmetric BINOL was achieved with good yield using hydrogen peroxide as the oxidant under UV-light irradiation. The same catalyst was chirally modified with cinchonidine and a newly synthesized chiral Schiff base ligand having a sigma-hole center. The strong interaction of the chiral modifiers with the cobalt-vanadium oxide was truly evident from various spectroscopic studies and DFT calculations. The chirally modified mixed metal oxide transformed the oxidative CC coupling reaction with high enantioselectivity. High enantiomeric excess upto 92 % of R-BINOL was obtained in acetonitrile solvent and hydrogen peroxide as the oxidant. A significant achievement was the formation of S-BINOL in the case of the cinchonidine modified catalyst and R-BINOL with the Schiff base ligand anchored chiral catalyst. The UV-light induced catalytic reaction was found to involve hydroxyl radical as the active reactive species. The spin trapping ESR and fluorescence experiment provided relevant evidence for the formation of such species through photodecomposition of hydrogen peroxide on the catalyst surface. The chiral induction to the resultant product was found to induce through supramolecular interaction like OH…π, H…Br interaction. The presence of sigma hole center was believed to play significant role in naphtholate ion recognition during the catalytic cycle.

Anisotropic nanomaterials for asymmetric synthesis

The production of enantiopure chemicals is an essential part of modern chemical industry. Hence, the emergence of asymmetric catalysis led to dramatic changes in the procedures of chemical synthesis, and now it provides the most advantageous and economically executable solution for large-scale production of chiral chemicals. In recent years, nanostructures have emerged as potential materials for asymmetric synthesis. Indeed, on the one hand, nanomaterials offer great opportunities as catalysts in asymmetric catalysis, due to their tunable absorption, chirality, and unique energy transfer properties; on the other hand, the advantages of the larger surface area, increased number of unsaturated coordination centres, and more accessible active sites open prospects for catalyst encapsulation, partial or complete, in a nanoscale cavity, pore, pocket, or channel leading to alteration of the chemical reactivity through spatial confinement. This review focuses on anisotropic nanomaterials and considers the state-of-the-art progress in asymmetric synthesis catalysed by 1D, 2D and 3D nanostructures. The discussion comprises three main sections according to the nanostructure dimensionality. We analyze recent advances in materials and structure development, discuss the functional role of the nanomaterials in asymmetric synthesis, chirality, confinement effects, and reported enantioselectivity. Finally, the new opportunities and challenges of anisotropic 1D, 2D, and 3D nanomaterials in asymmetric synthesis, as well as the future prospects and current trends of the design and applications of these materials are analyzed in the Conclusions and outlook section.

Preparation of a novel bridged bis(β-cyclodextrin) chiral stationary phase by thiol-ene click chemistry for enhanced enantioseparation in HPLC

A bridged bis(β-cyclodextrin) ligand was firstly synthesized via a thiol–ene click chemistry reaction between allyl-ureido-β-cyclodextrin and 4-4′-thiobisthiophenol, which was then bonded onto a 5 μm spherical silica gel to obtain a novel bridged bis(β-cyclodextrin) chiral stationary phase (HTCDP). The structures of HTCDP and the bridged bis(β-cyclodextrin) ligand were characterized by the ¹H nuclear magnetic resonance (¹H NMR), solid state ¹³C nuclear magnetic resonance (¹³C NMR) spectra spectrum, scanning electron microscope, elemental analysis, mass spectrometry, infrared spectrometry and thermogravimetric analysis. The performance of HTCDP in enantioseparation was systematically examined by separating 21 chiral compounds, including 8 flavanones, 8 triazole pesticides and 5 other common chiral drugs (benzoin, praziquantel, 1-1′-bi-2-naphthol, Tröger's base and bicalutamide) in the reversed-phase chromatographic mode. By optimizing the chromatographic conditions such as formic acid content, mobile phase composition, pH values and column temperature, 19 analytes were completely separated with high resolution (1.50–4.48), in which the enantiomeric resolution of silymarin, 4-hydroxyflavanone, 2-hydroxyflavanone and flavanone were up to 4.34, 4.48, 3.89 and 3.06 within 35 min, respectively. Compared to the native β-CD chiral stationary phase (CDCSP), HTCDP had superior enantiomer separation and chiral recognition abilities. For example, HTCDP completely separated 5 other common chiral drugs, 2 flavanones and 3 triazole pesticides that CDCSP failed to separate. Unlike CDCSP, which has a small cavity (0.65 nm), the two cavities in HTCDP joined by the aryl connector could synergistically accommodate relatively bulky chiral analytes. Thus, HTCDP may have a broader prospect in enantiomeric separation, analysis and detection.

Separation of chiral compounds on HTCDP.

l-Cysteine-Modified Graphene Oxide-Based Membrane for Chiral Selective Separation

A novel chiral separation membrane was fabricated by assembling l-cysteine (l-Cys)-modified graphene oxide sheets. l-Cys modification leads to an enantiomer separation membrane with an accessible interlayer spacing of 8 Å, which allows high solvent permeability. In the racemate separation experiments under isobaric conditions, the enantiomeric excess (ee) values of alanine (Ala), threonine (Thr), tyrosine (Tyr), and penicillamine (Pen) racemates in the permeation solution were 43.60, 44.11, 27.43, and 46.44%, respectively. In the racemate separation experiments under negative pressure, the separation performances of Ala, Thr, and Tyr were still maintained, and the enantiomeric excess (ee) values of the filtrate after separation were 56.80, 54.57, and 32.34%, respectively. These results indicate that the as-prepared GO-Cys membrane has a great practical value in the field of enantiomer separation.

Preparation and Chiral Applications of Optically Active Polyamides

Chirality is omnipresent in nature and plays vital roles in living organism, and has become a hot research topic across multidisciplinary fields including chemistry, biology, physics, and material science. Meanwhile, polyamides constitute an important class of polymers and have received significant attention owing to their outstanding properties and wide-ranging applications in many areas. Judiciously introducing chirality into polyamides will undoubtedly obtain attractive chiral polymers, namely, optically active polyamides. This review describes the preparation methods of chiral polyamides, including solution polycondensation, interfacial polycondensation, ring-open polymerization, and others; the newly emerging categories of chiral polyamides, i.e., helical polyamides, chiral polyamide-imides, are also presented. The applications of optically active polyamides in chiral research fields including asymmetric catalysis, membrane separation, and enantioselective crystallization are also summarized. In addition, current challenges in chiral polyamides are further presented and future perspectives in the field are proposed.

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

Chirality is ubiquitous in nature with primary cellular functions that include construction of right-/left-handed helix and selective communications among diverse biomolecules. Of particularly intriguing are the chiral peptide-based materials that can be deliberately designed to change physicochemistry properties via tuning peptide sequences. Critically, understanding their chiral effects are fundamental for the development of novel materials in chemistry and biomedicine fields. Here, we review recent researches on chirality in peptide-based materials, summarizing relevant typical chiral effects towards recognition, amplification, and induction. Driven forces for the chiral discrimination in affinity interaction as well as the handedness preferences in supramolecular structure formation at both the macroscale and microscale are illustrated. The implementation of such chirality effects of artificial copolymers, assembled aggregates and their composites in the fields of bioseparation and bioenrichment, cell incubation, protein aggregation inhibitors, chiral smart gels, and bionic electro devices are also presented. At last, the challenges in these areas and possible directions are pointed out. The diversity of chiral roles in the origin of life and chirality design in different organic or composite systems as well as their applications in drug development and chirality detection in environmental protection are discussed.

Macroscopic Supramolecular Assembly Strategy to Construct 3D Biocompatible Microenvironments with Site-Selective Cell Adhesion

Three-dimensional (3D) scaffolds with chemical diversity are significant to direct cell adhesion onto targeted surfaces, which provides solutions to further control over cell fates and even tissue formation. However, the site-specific modification of specific biomolecules to realize selective cell adhesion has been a challenge with the current methods when building 3D scaffolds. Conventional methods of immersing as-prepared structures in solutions of biomolecules lead to nonselective adsorption; recent printing methods have to address the problem of switching multiple nozzles containing different biomolecules. The recently developed concept of macroscopic supramolecular assembly (MSA) based on the idea of "modular assembly" is promising to fabricate such 3D scaffolds with advantages of flexible design and combination of diverse modules with different surface chemistry. Herein we report an MSA method to fabricate 3D ordered structures with internal chemical diversity for site-selective cell adhesion. The 3D structure is prepared via 3D alignment of polydimethylsiloxane (PDMS) building blocks with magnetic pick-and-place operation and subsequent interfacial bindings between PDMS based on host/guest molecular recognition. The site-specific cell affinity is realized by distributing targeted building blocks that are modified with polylysine molecules of opposite chiralities: PDMS modified with films containing poly-l-lysine (PLL) show higher cell density than those with poly-d-lysine (PDL). This principle of selective cell adhesion directed simply by spatial distribution of chiral molecules has been proven effective for five different cell lines. This facile MSA strategy holds promise to build complex 3D microenvironment with on-demand chemical/biological diversities, which is meaningful to study cell/material interactions and even tissue formation.

V2C Nanosheets as Dual-Functional Antibacterial Agents

Antibiotic-resistant bacterial strains have been continuously increasing and becoming a supreme threat to public health globally. The nanoparticle-based photothermal treatment has emerged as a powerful tool to combat toxic bacteria. Photothermal agents (PTAs) with cost-effective and high photothermal conversion efficiency are highly desirable. Herein, we unite the green process for delamination of V2AlC to produce a high yield mass of two-dimensional (2D) V2C nanosheets (NSs) by using algae extracts and demonstrate their high antibacterial efficiency. The resultant V2C NSs present decent structural reliability and intrinsic antibacterial ability. Powerful near-infrared (NIR) absorption and extraordinary photothermal conversion proficiency make it a good PTA for the photothermal treatment of bacteria. The antibacterial efficiency evaluation indicated that V2C NSs could effectively kill both Gram-positive S. aureus and Gram-negative E. coli. About 99.5% of both types of bacteria could be killed with low-dose of V2C NSs suspension (40 μg/mL) with 5 min NIR irradiation due to the intrinsic antibacterial ability and photothermal effect of V2C NSs, which is much higher than previous reports on Ta4C3, Ti3C2, MoSe2, and Nb2C. This work expands the application of MXene V2C NSs for rapid bacteria-killing and would gain promising attention for applications in the sterilization industry.