Broad Chiroptical Activity from Ultraviolet to Short-Wave Infrared by Chirality Transfer from Molecular to Micrometer Scale

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.

Achiral and chiral ligands synergistically harness chiral self-assembly of inorganics

Chiral structures and functions are essential natural components in biominerals and biological crystals. Chiral molecules direct inorganics through chiral growth of facets or screw dislocation of crystal clusters. As chirality promoters, they initiate an asymmetric hierarchical self-assembly in a quasi-thermodynamic steady state. However, achieving chiral assembly requires a delicate balance between intricate interactions. This complexity causes the roles of achiral-chiral and inorganic components in crystallization to remain ambiguous. Here, we elucidate a definitive mechanism using an achiral-chiral ligand strategy to assemble inorganics into hierarchical, self-organized superstructures. Achiral ligands cluster inorganic building blocks, while chiral ligands impart chiral rotation. Achiral and chiral ligands can flexibly modulate the chirality of superstructures by fully using their competition in coordination chemistry. This dual-ligand strategy offers a versatile framework for engineering chiroptical nanomaterials tailored to optical devices and metamaterials with optical activities across a broad wavelength range, with applications in imaging, detection, catalysis, and sensing.

Glutathione-mediated copper sulfide nanoplatforms with morphological and vacancy-dependent photothermal catalytic activity for multi-model tannic acid assays

Interface engineering and vacancy engineering play an important role in the surface and electronic structure of nanomaterials. The combination of the two provides a feasible way for the development of efficient photocatalytic materials. Here, we use glutathione (GSH) as a coordination molecule to design a series of CuxS nanomaterials (CuxS-GSH) rich in sulfur vacancies using a simple ultrasonic-assisted method. Interface engineering can induce amorphous structure in the crystal while controlling the formation of porous surfaces of nanomaterials, and the formation of a large number of random orientation bonds further increases the concentration of sulfur vacancies in the crystal structure. This study shows that interface engineering and vacancy engineering can enhance the light absorption ability of CuxS-GSH nanomaterials from the visible to the near-infrared region, improve the efficiency of charge transfer between CuxS groups, and promote the separation and transfer of optoelectronic electron-hole pairs. In addition, a higher specific surface area can produce a large number of active sites, and the synergistic and efficient photothermal conversion efficiency (58.01%) can jointly promote the better photocatalytic performance of CuxS-GSH nanomaterials. Based on the excellent hot carrier generation and photothermal conversion performance of CuxS-GSH under illumination, it exhibits an excellent ability to mediate the production of reactive oxygen species (ROS) through peroxide cleavage and has excellent peroxidase activity. Therefore, CuxS-GSH has been successfully developed as a nanoenzyme platform for detecting tannic acid (TA) content in tea, and convenient and rapid detection of tannic acid is achieved through the construction of a multi-model strategy. This work not only provides a new way to enhance the enzyme-like activity of nanomaterials but also provides a new prospect for the application of interface engineering and vacancy engineering in the field of photochemistry.

Emerging trends in chiral inorganic nanomaterials for enantioselective catalysis

Asymmetric transformations and synthesis have garnered considerable interest in recent decades due to the extensive need for chiral organic compounds in biomedical, agrochemical, chemical, and food industries. The field of chiral inorganic catalysts, garnering considerable interest for its contributions to asymmetric organic transformations, has witnessed remarkable advancements and emerged as a highly innovative research area. Here, we review the latest developments in this dynamic and emerging field to comprehensively understand the advances in chiral inorganic nanocatalysts and stimulate further progress in asymmetric catalysis.

Perovskite-Supramolecular Co-Assembly for Chiral Optoelectronics

Hybrid inorganic-organic perovskites with chiral response and outstanding optoelectronic characteristics are promising materials for next-generation spin-optoelectronics. In particular, two-dimensional (2D) perovskites are promising chiroptical candidates due to their unique ability to incorporate chiral organic cations into their crystal structure, which imparts chirality. To enable their practical applications in chiral optoelectronic devices, it is essential to achieve an anisotropy factor (gCD ∼ 2) in chiral 2D perovskites. Currently, chiral 2D perovskites exhibit a relatively low gCD of 3.1 × 10-3. Several approaches have been explored to improve the chiral response of chiral 2D perovskites, including tailoring the molecular structure of chiral cations and increasing the degree of octahedral tilting in the perovskite lattice. However, current methods for chiral amplification have only achieved a moderate enhancement of gCD by 2-fold and are often accompanied by undesirable shifts or inversion in the circular dichroism spectra. There is a need for a more efficient approach to enhancing the chirality in 2D perovskites. Here, we report an innovative coassembly process that allows us to seamlessly grow chiral 2D perovskites on supramolecular helical structures. We discover that the interactions between perovskites and chiral supramolecular structures promote crystal lattice distortion in perovskites, which improves the chirality of 2D perovskites. Additionally, the obtained hierarchical coassembly can effectively harness the structural chirality of the supramolecular helices. The multilevel chiral enhancement leads to an enhancement in gCD by 2.7-fold without compromising the circular dichroism spectra of 2D perovskites.

Amino acid-mediated amorphous copper sulphide with enhanced photothermal conversion efficiency for antibacterial application

Pathogenic bacteria in daily life, such as Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), often seriously affect human life and health. The extensive use of antibiotics has led to the emergence of drug-resistant bacteria, so it is urgent to develop efficient and non-drug-resistant sterilization methods. Here, we use small-molecule cysteine (Cys) as an auxiliary agent to synthesize spherical porous amorphous CuS-Cysteine (CuS-C) nanoparticles, which have good dispersion in aqueous solutions, and explore the reaction mechanism of Cys-induced CuS synthesis. The synthesized composite nanomaterials have strong near-infrared light absorption ability and efficient photothermal conversion ability and can effectively ablate pathogenic bacteria under the irradiation of an 808 nm laser. In addition, antibacterial experiments showed that CuS-C composites had no bactericidal effect without near-infrared light, but they had a good photothermal bactericidal effect on S. aureus and E. coli under radiation conditions. Considering the simple synthesis process, strong photothermal conversion ability, low cost, and suitability for large-scale production, CuS-C nanocomposites, as a promising antibacterial material, will provide a feasible scheme for the treatment of drug-resistant pathogens.

Near-Infrared Chiroptical Activity Titanium Dioxide Supraparticles with Circularly Polarized Light Induced Antibacterial Activity

Titanium dioxide (TiO2) has attracted significant attention in the fields of antibacterial activity and pollutant degradation due to its well-known photocatalytic properties. However, the application of TiO2 is significantly limited by its large band gap width, which only allows excitation by ultraviolet light below 400 nm. Here, we propose the use of surface chiral functionalization of TiO2 to tune its band gap width, thus enabling it to be excited by near-infrared-region light (NIR), resulting in the effective separation of electron-hole pairs. By controlling the solvent polarity and forming numerous weak interactions (such as hydrogen bonding) between chiral ligands and TiO2, we successfully prepared chiral TiO2 superparticles (SPs) that exhibited a broad circular dichroism (CD) absorption at 792 nm. Under circularly polarized light (CPL) at 808 nm, the chiral SPs induced the separation of electron-hole pairs in TiO2, thus generating hydroxyl and singlet oxygen radicals. Antibacterial tests under CPL in NIR showed that the chiral TiO2 SPs exhibited excellent antibacterial performance, with inhibition rates of 99.4% and 100% against Gram-positive and Gram-negative bacteria, respectively. Recycling-reuse experiments and biocompatibility evaluation of the material demonstrated that the chiral TiO2 SPs are stable and safe antibacterial materials, thus indicating the potential application of chiral TiO2 SPs in antibacterial aspects of medical implants.

Optical Asymmetry and Structural Complexity in Hierarchically Organized Chiral CuO Nanostructures: Insight into the Geometric and Crystallographic Effects on Cooperative Chirality

Optical asymmetry and structural complexity across different length scales were realized in flower-shaped CuO nanostructures, prepared through refluxing an aqueous solution of copper acetate, sodium hydroxide, and D-tartaric acid, as well as in their toroid-like forms obtained on calcination at 600 °C. Atomic scale chirality in the flower morphology could be visualized as putative Boerdijk-Coexter-Bernal like tetrahelical fragments, while that in the toroid form could be identified as screw dislocation-driven helicity. The fraction of asymmetry in the nanostructures has been evaluated from their chiroptical responses based on Kuhn asymmetry factor (g) from circular dichroism (CD) spectroscopy in the entire UV-vis range. The origin of chirality in the two CuO nanostructures has been assigned to the helical arrangement of the Cu-O-Cu network in accordance with their microscopic and spectroscopic observations. Attempts have been made to interpret the crystallographic and geometric chiralities in the two CuO nanostructures based on the redshift and augmented intensity of the CD signal along with an increase in their corresponding anisotropic factor on calcination. Further, the diverse interaction of the toroid-shaped CuO nanostructures with enantiomeric tryptophan moieties has been illustrated from the measurement of their corresponding thermodynamic parameters.

Chiral Spectroscopy of Nanostructures

ConspectusChirality is ubiquitous in the universe and in living creatures over detectable length scales from the subatomic to the galactic, as exemplified in the two extremes by subatomic particles (neutrinos) and spiral galaxies. Between them are living creatures that display multiple levels of chirality emerging from hierarchically assembled asymmetric building blocks. Not too far from the bottom of this pyramid are the foundational building blocks with chiral atomic centers on sp³ carbon atoms exemplified by l-amino acids and d-sugars that are self-assembled into higher-order structures with increasing dimensions forming highly complex, amazingly functional, and energy-efficient living systems. The organization and materials employed in their construction inspired scientists to replicate complex living systems via the self-assembly of chiral components. Multiple studies pointed to unexpected and unique electromagnetic properties of chiral structures with nanoscale and microscale dimensions, including giant circular dichroism and collective circularly polarized scattering that their constituent units did not possess.To address the wide variety of chiral geometries observed in continuous materials, singular particles, and their complex systems, multiple analytic techniques are needed. Simultaneously, their spectroscopic properties create a pathway to multiple applications. For example, mirror-asymmetric vibrations at chiral centers formed by sp³ carbon atoms lead to optical activity for the infrared (IR) wavelength regions. At the same time, understanding the optical activity in, for example, the IR region enables biomedical applications because multiple modalities of biomedical imaging and vibrational optical activity (VOA) of biomolecules are known for IR range. In turn, VOA can be realized in both absorption and emission modalities due to large magnetic transition moments, as vibrational circular dichroism (VCD) or Raman optical activity (ROA) spectroscopy. In addition to the VOA, in the range of longer wavelengths, lattice vibrational mode or phononic behavior occurs in chiral crystals and nanoassemblies, which can be readily detected by terahertz circular dichroism (TCD) spectroscopy. Meanwhile, chiral self-assembly can induce circularly polarized light emission (CPLE) regardless of the existence of chirality in coassembled fluorophores. The CPLE from self-assembled chiral materials is particularly interesting because the CPLE can originate from both circularly polarized luminescence and circularly polarized scattering (CPS). Furthermore, because self-assembled nanostructures often exhibit stronger optical activity than their building blocks owing to dimension and resonance effects, the optical activity of single assembled nanostructures can be investigated by using microscopic technology combined with chiral optics. Here, we describe the state of the art for spectroscopic methods for the comprehensive analysis of chiral nanomaterials at various photon wavelengths, addressed with special attention given to new tools emerging both for materials with self-organized hierarchical chirality and single-particle spectroscopy.

Chirality Analysis of Complex Microparticles using Deep Learning on Realistic Sets of Microscopy Images

Nanoscale chirality is an actively growing research field spurred by the giant chiroptical activity, enantioselective biological activity, and asymmetric catalytic activity of chiral nanostructures. Compared to chiral molecules, the handedness of chiral nano- and microstructures can be directly established via electron microscopy, which can be utilized for the automatic analysis of chiral nanostructures and prediction of their properties. However, chirality in complex materials may have multiple geometric forms and scales. Computational identification of chirality from electron microscopy images rather than optical measurements is convenient but is fundamentally challenging, too, because (1) image features differentiating left- and right-handed particles can be ambiguous and (2) three-dimensional structure essential for chirality is 'flattened' into two-dimensional projections. Here, we show that deep learning algorithms can identify twisted bowtie-shaped microparticles with nearly 100% accuracy and classify them as left- and right-handed with as high as 99% accuracy. Importantly, such accuracy was achieved with as few as 30 original electron microscopy images of bowties. Furthermore, after training on bowtie particles with complex nanostructured features, the model can recognize other chiral shapes with different geometries without retraining for their specific chiral geometry with 93% accuracy, indicating the true learning abilities of the employed neural networks. These findings indicate that our algorithm trained on a practically feasible set of experimental data enables automated analysis of microscopy data for the accelerated discovery of chiral particles and their complex systems for multiple applications.

Full-Color and Switchable Circularly Polarized Light from a Macroscopic Chiral Dendritic Film through a Solid-State Supramolecular Assembly

Chiral materials displaying chirality across multiple length scales have attracted increasing interest due to their potential applications in diverse fields. Herein, we report an efficient approach for the construction of macroscopic crystal dendrites with hierarchical chirality based on an in situ solid assembly in a block copolymer film. Chiral fluorescent crystals are formed by enantiopure d-/l-dibenzoyl tartaric acid and pyrenecarboxylic acid in a poly(1,4-butadiene)-b-poly(ethylene oxide) film. The chiro-optical activity of the crystalline dendrites can be greatly amplified in the absorption and scattering regions and goes along with the dimension of dendrites. Notably, the chiral dendrites exhibited strong circularly polarized luminescence emission with a high dissymmetric factor (0.03). The enhancement of the quantum yield of the chiral film was up to 28%, which was 14 times higher that of the corresponding fluorescent molecules. The circularly polarized emission bands of the films can be fine-tuned by contriving the emissive bands of fluorescent molecules. More importantly, the chiral signals are able to be wiped when the fluorescent group photodimerizes under UV irradiation. This work provides an efficient way to develop functional materials through solid self-assembly.

Chiral Biomaterials for Nanomedicines: From Molecules to Supraparticles

Chirality, the property whereby an object or a system cannot be superimposed on its mirror image, prevails amongst nature over various scales. Especially in biology, numerous chiral building blocks and chiral-specific interactions are involved in many essential biological activities. Despite the prevalence of chirality in nature, it has been no longer than 70 years since the mechanisms of chiral-specific interactions drew scientific attention and began to be studied. Owing to the advent of chiral-sensitive equipment such as circular dichroism spectrometers or chiral liquid columns for chromatography, it has recently been possible to achieve a deeper understanding of the chiral-specific interactions and consequential impacts on the functionality and efficiency of nanomedicine. From this point of view, it is worthwhile to examine previously reported chiral biomaterials with their compositions and possible applications to achieve new paradigms of biomaterials. This review discusses chiral materials on various scales and their biological applications.

Field-Free Magnetoplasmon-Induced Ultraviolet Circular Dichroism Switching in Premagnetized Magnetic Nanowires

Broadband modulation of magnetic circular dichroism (MCD) using a relatively low magnetic field or by producing a field-free magnetoplasmonic effect in the remnant magnetic state was achieved by the integration of the noble metals (NMs) Au and Ag and the perpendicular magnetic anisotropy of Co with ZnO nanowires (NWs) used as the template. The samples containing NMs revealed MCD sign reversals and enhancements when compared with the original Co/ZnO NWs. The magnetoplasmonic effect of Au close to the visible light spectrum could induce the CD change in the visible region. Notably, the ultraviolet (UV) CD in Ag/Co/ZnO NWs is 12.5 times larger under a magnetic field (∼0.2 T) and 10 times greater in the remnant state (field-free) than those of the original Co/ZnO NWs because of the magnetoplasmonic effect of Ag in the UV spectrum. These results are attributable to the coupling of the remnant magnetic state of Co magnetization, the magnetoplasmons of the NMs, and the excitons of the ZnO NWs. The findings are potentially applicable in magneto-optical recording, biosensing, and energy contexts involving magnetoplasmonic functionalization.