Nanoengineered chiral Pt-Ir alloys for high-performance enantioselective electrosynthesis

Wireless asymmetric umpolung electrosynthesis

Electroorganic synthesis has become an exciting tool for the asymmetric conversion of pro-chiral compounds. Herein, we introduced a wireless methodology based on bipolar electrochemistry in synergy with the enantioselective capabilities of inherently chiral oligomers to induce an umpolung chirality transfer. This was exemplified by the electro-conversion of a racemic mixture of lansoprazole to an enantio-enriched solution of a single antipode.

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.

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.

Enantioselective recognition, synthesis, and separation of pharmaceutical compounds at chiral metallic surfaces

The development of new pharmaceutical compounds is challenging because most of them are based on enantiopure chiral molecules, which exhibit unique properties for therapy. However, the synthesis of pharmaceutical compounds in the absence of a chiral environment naturally leads to a racemic mixture. Thus, to control their synthesis, an asymmetric environment is required, and chiral homogeneous catalysts are typically used to synthesize enantiopure pharmaceutical compounds (EPC). Nevertheless, homogeneous catalysts are difficult to recover after the reaction, generating additional problems and costs in practical processes. Thus, the development of chiral heterogeneous catalysts is a timely topic. In a more general context, such chiral materials cannot only be used for synthesis, but also to recognize and separate enantiomers. In the frame of these different challenges, we give in this review a short introduction to strategies to extrinsically and intrinsically modify heterogeneous metal matrixes for the enantioselective synthesis, recognition, and separation of chiral pharmaceutical compounds.

Mesoporous alloy chiral nanoparticles with high production yield and strong optical activities

Applying galvanic replacement reactions (GRRs) to the host chiral nanoparticles (CNPs) is an exclusive method to generate alloy CNPs with mesoporous structures through chirality transfer. However, the GRR-mediated chirality transfer is too inefficient to impose strong optical activities on the alloy mesoporous CNPs (or m-CNPs). Here we dope the host with gold (Au) to significantly enhance the chirality transfer, and additionally employ the Au adhesion layer to increase the production yield (PY) of binary m-CNPs.

A tutorial on asymmetric electrocatalysis

Electrochemistry has emerged as a powerful means to enable redox transformations in modern chemical synthesis. This tutorial review delves into the unique advantages of electrochemistry in the context of asymmetric catalysis. While electrochemistry has historically been used as a green and mild alternative for established enantioselective transformations, in recent years asymmetric electrocatalysis has been increasingly employed in the discovery of novel asymmetric methodologies based on reaction mechanisms unique to electrochemistry. This tutorial review first provides a brief tutorial introduction to electrosynthesis, then explores case studies on homogenous small molecule asymmetric electrocatalysis. Each case study serves to highlight a key advance in the field, starting with the historic electrification of known asymmetric transformations and culminating with modern methods relying on unique electrochemical mechanistic sequences. Finally, we highlight case studies in the emerging reasearch areas at the interface of asymmetric electrocatalysis with biocatalysis and heterogeneous catalysis.

Highly Enantioselective Synthesis of Pharmaceuticals at Chiral-Encoded Metal Surfaces

Enantioselective catalysis is of crucial importance in modern chemistry and pharmaceutical science. Although various concepts have been used for the development of enantioselective catalysts to obtain highly pure chiral compounds, most of them are based on homogeneous catalytic systems. Recently, we successfully developed nanostructured metal layers imprinted with chiral information, which were applied as electrocatalysts for the enantioselective synthesis of chiral model compounds. However, so far such materials have not been employed as heterogeneous catalysts for the enantioselective synthesis of real pharmaceutical products. In this contribution, we report the asymmetric synthesis of chiral pharmaceuticals (CPs) with chiral imprinted Pt-Ir surfaces as a simple hydrogenation catalyst. By fine-tuning the experimental parameters, a very high enantioselectivity (up to 95 % enantiomeric excess) with good catalyst stability can be achieved. The designed materials were also successfully used as catalytically active stationary phases for the continuous asymmetric flow synthesis of pharmaceutical compounds. This illustrates the possibility of producing real chiral pharmaceuticals at such nanostructured metal surfaces for the first time.

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.

Mesoporous multimetallic nanospheres with exposed highly entropic alloy sites

Multimetallic alloys (MMAs) with various compositions enrich the materials library with increasing diversity and have received much attention in catalysis applications. However, precisely shaping MMAs in mesoporous nanostructures and mapping the distributions of multiple elements remain big challenge due to the different reduction kinetics of various metal precursors and the complexity of crystal growth. Here we design a one-pot wet-chemical reduction approach to synthesize core-shell motif PtPdRhRuCu mesoporous nanospheres (PtPdRhRuCu MMNs) using a diblock copolymer as the soft template. The PtPdRhRuCu MMNs feature adjustable compositions and exposed porous structures rich in highly entropic alloy sites. The formation processes of the mesoporous structures and the reduction and growth kinetics of different metal precursors of PtPdRhRuCu MMNs are revealed. The PtPdRhRuCu MMNs exhibit robust electrocatalytic hydrogen evolution reaction (HER) activities and low overpotentials of 10, 13, and 28 mV at a current density of 10 mA cm-2 in alkaline (1.0 M KOH), acidic (0.5 M H2SO4), and neutral (1.0 M phosphate buffer solution (PBS)) electrolytes, respectively. The accelerated kinetics of the HER in PtPdRhRuCu MMNs are derived from multiple compositions with synergistic interactions among various metal sites and mesoporous structures with excellent mass/electron transportation characteristics.

New Conceptual Catalyst on Spatial High-Entropy Alloy Heterostructures for High-Performance Li-O2 Batteries

High-entropy alloys (HEAs) are attracting increased attention as an alternative to noble metals for various catalytic reactions. However, it is of great challenge and fundamental importance to develop spatial HEA heterostructures to manipulate d-band center of interfacial metal atoms and modulate electron-distribution to enhance electrocatalytic activity of HEA catalysts. Herein, an efficient strategy is demonstrated to construct unique well-designed HEAs spatial heterostructure electrocatalyst (HEA@Pt) as bifunctional cathode to accelerate oxygen reduction and evolution reaction (ORR/OER) kinetics for Li-O₂ batteries, where uniform Pt dendrites grow on PtRuFeCoNi HEA at a low angle boundary. Such atomically connected HEA spatial interfaces engender efficient electrons from HEA to Pt due to discrepancy of work functions, modulating electron distribution for fast interfacial electron transfer, and abundant active sites. Theoretical calculations reveal that electron redistribution manipulates d-band center of interfacial metal atoms, allowing appropriate adsorption energy of oxygen species to lower ORR/OER reaction barriers. Hence, Li-O₂ battery based on HEA@Pt electrocatalyst delivers a minimal polarization potential (0.37 V) and long-term cyclability (210 cycles) under a cut-off capacity of 1000 mAh g^-1 , surpassing most previously reported noble metal-based catalysts. This work provides significant insights on electron-modulation and d-band center optimization for advanced electrocatalysts.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Greenificated Molecularly Imprinted Materials for Advanced Applications

Molecular imprinting technology (MIT) produces artificial binding sites with precise complementarity to substrates and thereby is capable of exquisite molecular recognition. Over five decades of evolution, it is predicted that the resulting host imprinted materials will overtake natural receptors for research and application purposes, but in practice, this has not yet been realized due to the unsustainability of their life cycles (i.e., precursors, creation, use, recycling, and end-of-life). To address this issue, greenificated molecularly imprinted polymers (GMIPs) are a new class of plastic antibodies that have approached sustainability by following one or more of the greenification principles, while also demonstrating more far-reaching applications compared to their natural counterparts. In this review, the most recent developments in the delicate design and advanced application of GMIPs in six fast-growing and emerging fields are surveyed, namely biomedicine/therapy, catalysis, energy harvesting/storage, nanoparticle detection, gas sensing/adsorption, and environmental remediation. In addition, their distinct features are highlighted, and the optimal means to utilize these features for attaining incredibly far-reaching applications are discussed. Importantly, the obscure technical challenges of the greenificated MIT are revealed, and conceivable solutions are offered. Lastly, several perspectives on future research directions are proposed.

Chiral molecular imprinting-based SERS detection strategy for absolute enantiomeric discrimination

Chiral discrimination is critical in environmental and life sciences. However, an ideal chiral discrimination strategy has not yet been developed because of the inevitable nonspecific binding entity of wrong enantiomers or insufficient intrinsic optical activities of chiral molecules. Here, we propose an "inspector" recognition mechanism (IRM), which is implemented on a chiral imprinted polydopamine (PDA) layer coated on surface-enhanced Raman scattering (SERS) tag layer. The IRM works based on the permeability change of the imprinted PDA after the chiral recognition and scrutiny of the permeability by an inspector molecule. Good enantiomer can specifically recognize and fully fill the chiral imprinted cavities, whereas the wrong cannot. Then a linear shape aminothiol molecule, as an inspector of the recognition status is introduced, which can only percolate through the vacant and nonspecifically occupied cavities, inducing the SERS signal to decrease. Accordingly, chirality information exclusively stems from good enantiomer specific binding, while nonspecific recognition of wrong enantiomer is curbed. The IRM benefits from sensitivity and versatility, enabling absolute discrimination of a wide variety of chiral molecules regardless of size, functional groups, polarities, optical activities, Raman scattering, and the number of chiral centers.

Applications of Alternating Current/Alternating Potential Electro­lysis in Organic Synthesis

This review summarises the rarely used method of alternating current electrolysis for the synthesis of organic products. Different waveforms have been investigated which opens the possibility for further influence the outcome of the electrolysis by variation of the frequency as well as the highest peak current. In recent years alternating current electrolysis has been applied in increasingly more complex transformations. Especially the functionalisation of (hetero)arenes, functional group manipulation, metathesis reactions, and transition-metal-catalysed cross-coupling reactions were reported in recent years and the results of these and some other investigations are summarized in this review article.

1 Introduction

1.1 Waveforms

1.2 Objectives

1.3 Early Examples of the Optimisation of Alternating Current Electrolysis

2 Recent Applications of Alternating Current Electrolysis for Organic Synthesis

2.1 Substitution Reaction on Arenes

2.2 Nitrogen–Sulfur Bond Formation and Sulfur–Sulfur Bond Metathesis

2.3 Oxidation and Reduction

2.4 Cross-Coupling Reactions

2.5 Frequency Optimisation

3 Conclusion

Tuning the Selective Ethanol Oxidation on Tensile-Trained Pt(110) Surface by Ir Single Atoms

Development of efficient and robust electrocatalysts for complete oxidation of ethanol is critical for the commercialization of direct ethanol fuel cells. However, the complete oxidation of ethanol suffers from poor efficiency due to the low C1 pathway selectivity. Herein, single-atomic Ir (Ir₁ ) on hcp-PtPb/fcc-Pt core-shell hexagonal nanoplates (PtPb@PtIr₁ HNPs) enclosed by Pt(110) surface with a 7.2% tensile strain is constructed to drive complete electro-oxidation of ethanol. Benefiting from the construction of Ir₁ sites, the PtPb@PtIr₁ HNPs exhibit a Faraday efficiency of 57.93% for the C1 pathway, which is ≈8.3 times higher than that of the commercial Pt/C-JM. Furthermore, the PtPb@PtIr₁ HNPs show a top-ranked electro-activity achieving 45.1-fold and 56.3-fold higher than the specific and mass activities of Pt/C-JM, respectively. Meanwhile, the durability can be significantly enhanced by the construction of Ir₁ sites. Density functional theory calculations indicate that the strong synergy on the PtPb@PtIr₁ HNPs surface significantly promotes the breaking of CC bond of CH₂ CO* and facilitates CO oxidation and suppresses the deactivation of the catalyst. This work offers a unique single-atom approach using low-coordination active sites on shape-controlled nanocrystals to tune the selectivity and activity toward complicated catalytic reactions.

An amorphous ultrathin iridium/carbon catalyst realizing efficient electrochemical hydrogen evolution

An amorphous 1.1 nm Ir/C catalyst exhibits ultralow overpotentials of 10 and 64 mV for the hydrogen evolution reaction at current densities of 10 and 100 mA cm^-2, together with 117 A mg^-1 mass activity and outstanding long-term durability, superior to those of the commercial Pt/C catalyst.

Synthesis of Chiral Au Nanocrystals with Precise Homochiral Facets for Enantioselective Surface Chemistry

Metal surfaces with intrinsic chirality play an irreplaceable role in many significant enantioselective chemical processes such as enantioselective catalysis, sensing, and separation. Nonetheless, current methods for the precise preparation of such chiral surfaces suffer with issues of unscalable production and low surface areas. Herein, we report the synthesis of chiral Au nanoparticles with precisely determined homochiral facets. Though a scalable wet chemical method, {125̅8}^R and {85̅12}^S high-Miller-index facets are obtained with the l- and d-chiral Au nanocrystals, respectively. The growth process of these homochiral facets is investigated, and a new nanocrystal growth pathway is revealed. More importantly, the remarkable enantioselective recognition properties of these homochiral surfaces are demonstrated and enable an efficient electrochemical method for chiral discrimination of l-/d-tryptophan. These results provide a foundation of fundamental studies of heterogeneous enantioselective processes and may pave way for the development of nanocatalysts for enantioselective chemistry.

Chiral Nanoparticles with Enhanced Thermal Stability of Chiral Structures through Alloying

Metallic chiral nanoparticles (CNPs) promisingly function as asymmetric catalysts but lack an important study in thermal stability of optical activity that stems from metastable chiral lattices. In this work, annealing is applied to silver (Ag) CNPs, fabricated by glancing angle deposition (GLAD), and causes elimination of optical activity at 200 °C, mainly ascribed to chiral-to-achiral lattice transformation. The Ag CNPs are remarkedly enhanced in thermal stability through an alloying with aluminum (Al) via layer-by-layer GLAD to generate binary Ag_0.5 Al_0.5 CNPs composed of solid-state liquids, whose optical activity vanishes at 700 °C. Ease in the diffusion of Al atoms in the host Ag CNPs and thermal insulation from the Al₂ O₃ layers partially covering the binary CNPs effectively prohibit structural relaxation of the metastable chiral lattices, accounting for the significant enhancement in thermal stability of chiral lattices. This is a pioneering work to investigate the fundamental principles determining the thermal stability of metallic CNPs in terms of chiral structures and optical activity. It paves the way toward applying metallic CNPs to asymmetric catalysis at high temperature to accelerate an asymmetric synthesis of enantiomers with designable chirality, which is one of the most important topics in modern chemistry.

Helically aligned fused carbon hollow nanospheres with chiral discrimination ability

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe₃O₄ nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Self-assembled monolayer protection of chiral-imprinted mesoporous platinum electrodes for highly enantioselective synthesis

In modern chemistry, chiral (electro)catalysis is a powerful strategy to produce enantiomerically pure compounds (EPC). However, it still struggles with uncontrollable stereochemistry due to side reactions, eventually producing a racemic mixture. To overcome this important challenge, a well-controlled design of chiral catalyst materials is mandatory to produce enantiomers with acceptable purity. In this context, we propose the synergetic combination of two strategies, namely the elaboration of mesoporous Pt films, imprinted with chiral recognition sites, together with the spatially controlled formation of a self-assembled monolayer. Chiral imprinted metals have been previously suggested as electrode materials for enantioselective recognition, separation and synthesis. However, the outermost surface of such electrodes is lacking chiral information and thus leads to unspecific reactions. Functionalising selectively this part of the electrode with a monolayer of organosulfur ligands allows an almost total suppression of undesired side reactions and thus leads to a boost of enantiomeric excess to values of over 90% when using these surfaces in the frame of enantioselective electrosynthesis. In addition, this strategy also decreases the total reaction time by one order of magnitude. The study therefore opens up promising perspectives for the development of heterogeneous enantioselective electrocatalysis strategies.

Environmental Modulation of Chiral Prolinamide Catalysts for Stereodivergent Conjugate Addition

Synthetic chiral catalysts generally rely on proximal functional groups or ligands for chiral induction. Enzymes often employ environmental chirality to achieve stereoselectivity. Environmentally controlled catalysis has benefits such as size and shape selectivity but is underexplored by chemists. We here report molecularly imprinted nanoparticles (MINPs) that utilized their environmental chirality to either augment or reverse the intrinsic selectivity of a chiral prolinamide cofactor. The latter ability allowed the catalyst to produce products otherwise disfavored in the conjugate addition of aldehyde to nitroalkene. The catalysis occurred in water at room temperature and afforded γ-nitroaldehydes with excellent yields (up to 94%) and ee (>90% in most cases). Up to 25:1 syn/anti and 1:6 syn/anti ratios were achieved through a combination of catalyst-derived and environmentally enabled selectivity. The high enantioselectivity of the MINP also made it possible for racemic catalysts to perform asymmetric catalysis, with up to 80% ee for the conjugate addition.

Electrochemiluminescent enantioselective detection with chiral-imprinted mesoporous metal surfaces

Chiral-imprinted mesoporous Pt-Ir alloy surfaces were combined in a synergetic way with electrochemiluminescence (ECL) to detect the two enantiomers of phenylalanine (PA) as a model compound, acting simultaneously as a...

Heterogeneous Enantioselective Catalysis with Chiral Encoded Mesoporous Pt-Ir Films Supported on Ni Foam

The development of heterogeneous catalysts for asymmetric synthesis is one of the most challenging topics in chemistry, as it allows obtaining enantiomerically pure compounds. Recently, metal layers incorporating molecular chiral cavities, obtained by electroreduction of a metal source in the simultaneous presence of a non-ionic surfactant and asymmetric molecules, have been proposed for a wide range of applications, including enantioselective electroanalysis and electrosynthesis, as well as chiral separation. In contrast to this previous work, solely based on electrochemical phenomena, herein we designed and employed nanostructured chiral encoded Pt-Ir alloys, supported on high surface area nickel foams, as heterogeneous catalysts for the asymmetric hydrogenation of aromatic ketones. Fine-tuning the experimental conditions allows achieving very high enantioselectivity (>80%), combined with improved catalyst stability.