Biomimetic Chiral Nanomaterials with Selective Catalysis Activity

Chiral nanomaterials with unique chiral configurations and biocompatible ligands have been booming over the past decade for their interesting chiroptical effect, unique catalytical activity, and related bioapplications. The catalytic activity and selectivity of chiral nanomaterials have emerged as important topics, that can be potentially controlled and optimized by the rational biochemical design of nanomaterials. In this review, chiral nanomaterials synthesis, composition, and catalytic performances of different biohybrid chiral nanomaterials are discussed. The construction of chiral nanomaterials with multiscale chiral geometries along with the underlying principles for enhancing chiroptical responses are highlighted. Various biochemical approaches to regulate the selectivity and catalytic activity of chiral nanomaterials for biocatalysis are also summarized. Furthermore, attention is paid to specific chiral ligands, materials compositions, structure characteristics, and so on for introducing selective catalytic activities of representative chiral nanomaterials, with emphasis on substrates including small molecules, biological macromolecule, and in-site catalysis in living systems. Promising progress has also been emphasized in chiral nanomaterials featuring structural versatility and improved chiral responses that gave rise to unprecedented chances to utilize light for biocatalytic applications. In summary, the challenges, future trends, and prospects associated with chiral nanomaterials for catalysis are comprehensively proposed.

Surfactant Directed Synthesis of Intrinsically Chiral Plasmonic Nanostructures and Precise Tuning of their Optical Activity through Controlled Self-Assembly

Fabrication and transmission of plasmonic chirality is a rapidly developing area of research. While nanoscale chirality is reasonably well explored, research on intrinsically chiral nanostructures, that has ramifications to origin of homochirality, is still in its infancy. Herein, we report the synthesis of dog-bone shaped chiral gold nanostructures using a chiral cationic surfactant with excess ascorbic acid. Chiral growth is attributed to the specific binding and structure breaking ability of chiral surfactant and ascorbic acid. The controlled assembly of particles facilitated tuning and enhancement of chiral signals. Experimental observations were validated with theoretical simulations modelled in frequency domain with a surface integral-equation parameterization. Work highlighting the generation and tuning of plasmonic chirality provides new insights into the understanding of intrinsic chirality and paves way for their application in enantioselective catalysis and biosensing.

Phosphonated Polyethylenimine Maghemite Nanoparticles: A Convenient Support of Palladium for Cross-Coupling Reactions

Phosphonated polyethylenimine grafted on iron oxide nanoparticles was used as a magnetic support for loading palladium. This cheap and accessible heterogeneous catalyst demonstrated good efficiency in Suzuki-Miyaura, Mizoroki-Heck, and Tsuji-Trost couplings. The nanocomposite is resistant to harsh conditions and can therefore be recycled up to 10 cycles with high catalyst efficiency.

Recent advances in chiral nanomaterials with unique electric and magnetic properties

Research on chiral nanomaterials (NMs) has grown radically with a rapid increase in the number of publications over the past decade. It has attracted a large number of scientists in various fields predominantly because of the emergence of unprecedented electric, optical, and magnetic properties when chirality arises in NMs. For applications, it is particularly informative and fascinating to investigate how chiral NMs interact with electromagnetic waves and magnetic fields, depending on their intrinsic composition properties, atomic distortions, and assembled structures. This review provides an overview of recent advances in chiral NMs, such as semiconducting, metallic, and magnetic nanostructures.

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.

Reconfigurable Chirality of DNA-Bridged Nanorod Dimers

Gold nanorods assembled in a side-by-side chiral configuration have potential applications in sensing due to their strong chiroptical surface plasmon resonances. Recent experiments have shown that dimers of gold nanorods bridged by double-stranded DNA exhibit variable chiral configurations depending on the chemical and ionic properties of the solvent medium. Here, we uncover the underlying physics governing this intriguing chiral behavior of such DNA-bridged nanorods by theoretically evaluating their configurational free energy landscape. Our results reveal how chiral configurations emerge from an interplay between the twist-stretch coupling of the intervening DNA and the intermolecular interactions between the nanorods, with dimers exhibiting left-handed chirality when the interparticle interactions are dominated by attractive depletion or van der Waals forces and right-handed chirality when dominated by repulsive electrostatic or steric forces. We demonstrate how changes in the depletant or ion concentration of the solvent medium lead to different classes of configurational responses by the dimers, including chirality-switching behavior, in good agreement with experimental observations. Based on extensive analyses of how material properties like nanorod aspect ratio, DNA length, and graft height modulate the free energy landscape, we propose strategies for tuning the environmentally responsive reconfigurability of the nanorod dimers. Overall, this work should help control the chirality and related optical activity of nanoparticle dimers and higher-order assemblies for various applications.

Iron-Palladium magnetic nanoparticles for decolorizing rhodamine B and scavenging reactive oxygen species

HYPOTHESIS

Here, FePd magnetic nanoparticles (MNPs) are developed as artificial enzymes with high biocompatibility and reusability.

EXPERIMENT

The nanoparticles (NPs) are synthesized in an aqueous solvent by one-pot synthesis utilizing glutathione (GSH) and cysteine (Cys) as surfactants.

FINDINGS

The prepared hydrophilic FePd NPs are redispersible in water. Further, they exhibit catalytic activity for the degradation of rhodamine B (RhB), as well as for the inhibition of reactive oxygen species (ROS) production induced by H₂O₂, which are two- and seven-fold enhancements of their catalytic performances, respectively, compared with that of horseradish peroxidase. The computational simulation and electrochemical analysis indicate that the enhancement of the catalytic effect is due to the protection of the MNP surface by GSH and Cys. In vitro experiments reveal that FePd MNPs behave like a peroxidase and decrease the ROS in mammalian cells. The cytotoxicity assessment of FePd MNPs via exposures to different cell lines for over seven days indicates that they can maintain the cell viability of >90% for up to 20 μgmL^-1 concentration. FePd MNPs with high saturation magnetization and biocompatibility can be utilized as recyclable peroxidase-mimicking nanozymes and biosensors in a variety of catalytic and biological applications.

Chiral Rhodium Nanoparticle-Catalyzed Asymmetric Arylation Reactions

The development of heterogeneous catalyst systems for enantioselective reactions is an important subject in modern chemistry as they can be easily separated from products and potentially reused; this is particularly favorable in achieving a more sustainable society. Whereas numerous homogeneous chiral small molecule catalysts have been developed to date, there are only limited examples of heterogeneous ones that maintain high activity and have a long lifetime. On the other hand, metal nanoparticle catalysts have attracted much attention in organic chemistry due to their robustness and ease of deposition on solid supports. Given these advantages, metal nanoparticles modified with chiral ligands, defined as "chiral metal nanoparticles", would work efficiently in asymmetric catalysis. Although asymmetric hydrogenation catalyzed by chiral metal nanoparticles was pioneered in the late twentieth century, the application of chiral metal nanoparticle catalysis for asymmetric C-C bond-forming reactions that give a high level of enantioselectivity with wide substrate scope was very limited.This Account summarizes recent investigations that we have carried out in the field of chiral rhodium (Rh) nanoparticle catalysis for asymmetric arylation reactions. We initially utilized composites of polystyrene-based copolymers with cross-linking moieties and carbon black incarcerated Rh nanoparticle catalysts for the asymmetric 1,4-addition of arylboronic acids to enones. We found that chiral diene-modified heterogeneous Rh nanoparticles were effective in these reactions, with excellent enantioselectivities and without causing metal leaching, and that bimetallic Rh/Ag nanoparticle catalysts enhanced activity. The catalyst could be easily recovered and reused more than ten times, thus demonstrating the robustness of metal nanoparticle catalysts.We then developed a secondary amide-substituted chiral diene modifier designed as a bifunctional ligand that possesses a metal biding site and a NH group to activate a substrate through hydrogen bonding. This chiral diene was very effective for the Rh/Ag nanoparticle-catalyzed asymmetric arylation of various electron-deficient olefins, including enones, unsaturated esters, unsaturated amides and nitroolefins, and imines to afford the corresponding products in excellent yields and with outstanding enantioselectivities. The system was also applicable for the synthesis of intermediates of various useful compounds. Furthermore, the compatibility of chiral Rh nanoparticles with other catalysts was confirmed, enabling the development of tandem reaction systems and cooperative catalyst systems.The nature of the active species was investigated. Several characteristic features of the heterogeneous nanoparticle systems that were completely different from those of the corresponding homogeneous metal complex systems were found.

Lanthanide–EDTA complexes covalently bonded on Fe3O4@SiO2 magnetic nanoparticles promote the green, stereoselective synthesis of N-acylhydrazones

Highly efficient stereoselective synthesis of E–N-acylhydrazones using magnetic nanoparticles-Ln³⁺ as heterogeneous catalysts.

Cl-assisted highly efficient synthesis of FePd3 alloys encapsulated in graphite papers: a two stage CVD approach

We propose an advanced two-stage CVD method which allows the synthesis of very thick deposits of planar rolled-like graphite structures filled with FePd₃ alloys as dominant product in the entire reactor.

Indirect conversion of ambient pressure CO2 into oxazolidin-2-ones by a copper-based magnetic nanocatalyst

A magnetically recyclable Cu-based catalytic system was developed for the indirect conversion of ambient pressure of CO₂ into oxazolidin-2-ones.

Activated nanostructured bimetallic catalysts for C–C coupling reactions: recent progress

This minireview highlights the recent progress made in the last decade towards the development of activated bimetallic alloy nanoparticle catalysts for C–C coupling reactions, including asymmetric C–C bond coupling reactions.

Combining hard and soft magnetism into a single core-shell nanoparticle to achieve both hyperthermia and image contrast

BACKGROUND

A biocompatible core/shell structured magnetic nanoparticles (MNPs) was developed to mediate simultaneous cancer therapy and imaging.

METHODS & RESULTS

A 22-nm MNP was first synthesized via magnetically coupling hard (FePt) and soft (Fe3O4) materials to produce high relative energy transfer. Colloidal stability of the FePt@Fe3O4 MNPs was achieved through surface modification with silane-polyethylene glycol (PEG). Intravenous administration of PEG-MNPs into tumor-bearing mice resulted in a sustained particle accumulation in the tumor region, and the tumor burden of treated mice was a third that of the mice in control groups 2 weeks after a local hyperthermia treatment. In vivo magnetic resonance imaging exhibited enhanced T2 contrast in the tumor region.

CONCLUSION

This work has demonstrated the feasibility of cancer theranostics with PEG-MNPs.

Synthesis of benzil derivatives via oxidation of alkynes catalyzed by Pd–Fe3O4 heterodimer nanocrystals

An efficient, iterative, catalytic, Wacker-type oxidation of alkynes to 1,2-diketones using a Pd–Fe₃O₄ heterodimer nanocrystalline catalyst has been developed.

Chiral metal nanoparticle-catalyzed asymmetric C-C bond formation reactions

Chiral ligand-modified metal nanoparticles possess an attractive potential for application in asymmetric synthesis. This article focuses on chiral-nanoparticle-catalyzed asymmetric C-C bond formation reactions and discusses the nature of the active species.

Nanostructured catalysts for organic transformations

The development of green, sustainable and economical chemical processes is one of the major challenges in chemistry. Besides the traditional need for efficient and selective catalytic reactions that will transform raw materials into valuable chemicals, pharmaceuticals and fuels, green chemistry also strives for waste reduction, atomic efficiency and high rates of catalyst recovery. Nanostructured materials are attractive candidates as heterogeneous catalysts for various organic transformations, especially because they meet the goals of green chemistry. Researchers have made significant advances in the synthesis of well-defined nanostructured materials in recent years. Among these are novel approaches that have permitted the rational design and synthesis of highly active and selective nanostructured catalysts by controlling the structure and composition of the active nanoparticles (NPs) and by manipulating the interaction between the catalytically active NP species and their support. The ease of isolation and separation of the heterogeneous catalysts from the desired organic product and the recovery and reuse of these NPs further enhance their attractiveness as green and sustainable catalysts. This Account reviews recent advances in the use of nanostructured materials for catalytic organic transformations. We present a broad overview of nanostructured catalysts used in different types of organic transformations including chemoselective oxidations and reductions, asymmetric hydrogenations, coupling reactions, C-H activations, oxidative aminations, domino and tandem reactions, and more. We focus on recent research efforts towards the development of the following nanostructured materials: (i) nanostructured catalysts with controlled morphologies, (ii) magnetic nanocomposites, (iii) semiconductor-metal nanocomposites, and (iv) hybrid nanostructured catalysts. Selected examples showcase principles of nanoparticle design such as the enhancement of reactivity, selectivity and/or recyclability of the nanostructured catalysts via control of the structure, composition of the catalytically active NPs, and/or nature of the support. These principles will aid researchers in the rational design and engineering of new types of multifunctional nanocatalysts for the achievement of green and sustainable chemical processes. Although the past decade has brought many advances, there are still challenges in the area of nanocatalysis that need to be addressed. These include loss of catalytic activity during operation due to sintering, leaching of soluble species from the nanocatalysts under harsh reaction conditions, loss of control over well-defined morphologies during the scale-up synthesis of the nanocomposites, and limited examples of enantioselective nanocatalytic systems. The future of nanocatalyst research lies in the judicious design and development of nanocomposite catalysts that are stable and resistant to sintering and leaching, and yet are highly active and enantioselective for the desired catalytic organic transformations, even after multiple runs. The successful generation of such multifunctional nanocatalysts especially in tandem, domino, or cascade reactions would provide a powerful tool for the establishment of green and sustainable technologies.

PEGylated FePt@Fe2O3 core-shell magnetic nanoparticles: potential theranostic applications and in vivo toxicity studies

Herein, we develop FePt@Fe2O3 core-shell magnetic nanoparticles as a T2 magnetic resonance (MR) imaging contrast agent as well as a drug carrier for potential cancer theranostic applications. The FePt@Fe2O3 core-shell nanoparticles are synthesized and then functionalized with polyethylene glycol (PEG). Folic acid (FA) is conjugated on the surface of FePt@Fe2O3-PEG nanoparticles for effective targeting of folate receptor (FR)-positive tumor cells. A chemotherapy drug, doxorubicin (DOX), is then loaded onto those nanoparticles via hydrophobic physical adsorption, for targeted intracellular drug delivery and selective cancer cell killing. We then use those FePt@Fe2O3-PEG nanoparticles for in vivo MR imaging, observing obvious tumor MR contrasts, which resulted from both passive tumor accumulation and active tumor targeting of nanoparticles. Moreover, both in vitro and in vivo studies uncover no obvious toxicity for FePt@Fe2O3-PEG nanoparticles. Therefore, our PEGylated FePt@Fe2O3 core-shell nanoparticles could serve as a promising multifunctional theranostic nano-platform in imaging guided cancer therapy.

FROM THE CLINICAL EDITOR

In this study of PEGylated FePt@Fe2O3 core-shell magnetic nanoparticles, both therapeutic and diagnostic applications are demonstrated. Folic acid surface-conjugation resulted in uptake by folate receptor positive cancer cells, the iron oxide particles enabled MRI imaging using T2* weighted sequences, and the absorbed doxorubicin provided treatment effects in this model. Similar multi-modality approaches will hopefully find their way to clinical applications in the near future.

Optical activity of achiral ligand SCH3 adsorbed on achiral Ag55 clusters: relationship between adsorption site and circular dichroism

The electronic circular dichroism (CD) spectra of a methyl-thiol adsorbed at different sites on an icosahedral silver nanoparticle is studied by using time-perturbed density functional theory. Despite that separately molecule and nanoparticle are achiral and consequently optically inactive, the Ag(55)-SCH(3) compound emerges with a new symmetry, which may be chiral or not depending on the adsorption site and orientation of the molecule. It is found that chirality is favored when the thiol is adsorbed between two atoms of different coordination number. Chiral compounds have characteristic CD spectra in the UV-visible region, where Ag(55) shows optical absorption but SCH(3) does not; revealing that highly degenerated molecular-like electronic states of Ag(55) are modified by the presence of the molecule inducing optical activity. It is concluded that CD line-shapes and magnitude strongly depend on the site where the adsorption takes place, while its intensity is modulated by the molecule orientation.