Search Results (69)

Hydrogen peroxide (H₂O₂) plays a vital role as an eco-friendly oxidizer, extensively used in environmental cleanup, energy transformation, and organic production. Nonetheless, the conventional method of creating anthraquinones is intricate, resulting in significant energy and ecological costs, which calls for the development of more eco-friendly and efficient substitute technologies. The article methodically examines the reaction processes and methods for improving efficiency in photocatalytic H₂O₂ generation in the past few years. This review summarizes the design principles and key structural features of various novel catalytic materials, focusing on light absorption, charge separation and migration, surface redox reactions, and enhanced mass transfer. Approaches such as expanding the range of bandgap absorption, building conjugated structures, and incorporating metal nanoclusters can significantly enhance the efficiency of light absorption. In the charge separation process, constructing built-in electric fields at the interfaces of heterojunctions, homojunctions, and Schottky junctions is crucial for improving reaction efficiency. Additionally, defect engineering may encourage targeted carrier movement and minimize recombination. The review highlights the latest advancements in enhancing selectivity and reducing H₂O₂ breakdown in surface redox reactions, achieved by regulating active sites, introducing new functional groups, and developing dual-channel reaction pathways. Furthermore, constructing three-phase interfaces, regulating asymmetric wettability, and designing cyclic/flow reactors provide innovative engineering solutions to address the challenges of insufficient oxygen supply and large-scale continuous production. Ultimately, the potential for producing H₂O₂ in photocatalytic systems is detailed. Full article

For those who did not follow the invention and development of enantioselective catalysis, this review introduces pertinent historical aspects of the field and presents the scientific concepts of asymmetric bio- and organocatalysis. They are powerful technologies applied in organic laboratories and industry. They realize chiral amplification by converting inexpensive achiral substrates and reagents into enantiomerically enriched products using readily recoverable solvents, if any are used. Racemic substrates can also be deracemized catalytically. More sustainable fabrications are now available that require neither toxic metallic species nor costly reaction conditions in terms of energy, atmosphere control, product purification, and safety. Nature has been the source of the first asymmetric catalysts (microorganisms, enzymes, alkaloids, amino acids, peptides, terpenoids, sugars, and their derivatives). They act as temporary chiral auxiliaries and lower the activation free energy of the reaction by altering the reaction mechanism. Reductions, oxidations, carbon-carbon and carbon-heteroatom bond-forming reactions are part of the process panoply. Asymmetric catalyzed multicomponent and domino reactions are becoming common. Typical modes of activation are proton transfers, hydrogen bonded complex formation, charged or uncharged acid/base pairing (e.g., σ-hole catalysts), formation of equilibria between achiral aldehydes and ketones with their chiral iminium salt or/and enamine intermediates, umpolung of aldehydes and ketones by reaction with N-heterocyclic carbenes (NHCs), phase transfer catalysis (PTC), etc. Often, the best enantioselectivities are observed with polyfunctional catalysts derived from natural compounds, but not always. They may combine to form chiral structures containing nitrogen, phosphorus, sulfur, selenium, and iodine functional moieties. Today, man-made enantiomerically enriched catalysts, if not enantiomerically pure, are available in both enantiomeric forms. Being robust, they are recovered and reused readily. Full article

A computational study of the mechanism of asymmetric hydrogenation of γ-keto acids with the Ni(S,S)-QuinoxP* system was conducted. The main steps of the reaction mechanism were determined, including the formation of the NiH(S,S-QuinoxP*)⁺ complex starting from a γ-keto acid molecule and the involvement of the hydrogen “metathesis” step. The rate-limiting and stereo-determining step of the reaction was identified as the transfer of a hydrogen atom from the catalytic particle to the carbonyl group of the substrate molecule. The stereochemical outcome of the process was calculated. The influence of weak interactions on the stereoselectivity of the process was demonstrated using NCI and sobEDAw analyses. Full article

Catalytic transfer hydrogenation (CTH) provides a practical and sustainable approach for reducing unsaturated compounds, serving as an alternative to high-pressure H₂ in laboratory and fine chemical contexts. This broad reaction class includes asymmetric transfer hydrogenation (ATH), a key strategy in enantioselective synthesis due to its operational simplicity, high stereocontrol, and compatibility with sensitive functional groups. A central variable governing CTH efficiency is the role of bases, which may function as essential activators, co-hydrogen donors, or be entirely absent depending on the catalytic system. This review provides a comparison of base-assisted, base-free, and base-as-co-hydrogen-donor CTH methodologies across diverse metal catalysts and substrates. We highlight how bases such as triethylamine, K₂CO₃, and NaOH facilitate catalyst activation, modulate hydride formation, and tune reactivity and selectivity. The dual function of bases in formic-acid-driven systems is examined alongside synergistic effects observed with mixed-base additives. In contrast, base-free CTH platforms demonstrate how tailored ligand frameworks, metal-ligand cooperativity, and engineered surface basicity can eliminate the need for external additives while maintaining high activity. Through mechanistic analysis and cross-system comparison, this review identifies the key structural, electronic, and environmental factors that differentiate base-assisted from base-free pathways. Emerging trends—including greener hydrogen donors, advanced catalyst architectures, and additive-minimized protocols—are discussed to guide future development of sustainable CTH processes. Full article

DFT study of graphene functionalized via carbene was performed to identify the preferred –OH adsorption sites and to assess how hydroxylation affects adsorption of NH₃ gas. The carbene attaches to the graphene basal plane through a [2+1] cycloaddition, producing a local cyclopropane-like motif with a C–C bond. This modification introduces localized mid-gap states and asymmetric charge redistribution that create chemically active anchoring sites for –OH groups. We systematically scanned possible –OH adsorption sites and identified site-dependent binding energies. NH₃ preferentially anchors at the carbene center and is further stabilized by multidentate hydrogen bonding with neighboring –OH groups. Calculated NH₃ adsorption energies range from moderate values (single –OH and some two –OH symmetric sites, E_ads ≈ −0.64 to −0.75 eV) to strong interaction for selected through-plane two –OH pairs (E_ads ≈ −1.78 to −1.83 eV), where synergistic hydrogen bonding amplifies the NH₃ interaction. Charge density difference and Bader analyses indicate polarization-dominated binding with minimal net charge transfer, consistent with hydrogen bonding rather than covalent bond formation. Desorption time estimation shows that moderate binding motifs provide rapid recovery at room temperature. We conclude that targeted placement of paired –OH groups on carbene-functionalized graphene offers a tunable route to balance sensitivity and reusability for NH₃ sensing. Full article

Chiral coordination compounds are of growing interest due to their structural diversity and wide applicability. Besides chirality, alcohol and especially oxime-functionalized limonene derivatives confer water solubility, stability, and the appropriate reactivity to enable their use in asymmetric catalysis—such as allylic substitution, alkynylation, transfer hydrogenation, and selective C–C bond formation. Biologically, they have shown promising anticancer, antibacterial, and antibiofilm activity. This review presents an integrated overview of the synthesis, properties, and applications of chiral transition metal complexes featuring ligands derived from inexpensive, naturally occurring R- and S-limonene substrates, and explore their roles in catalysis and biological activity. Full article

Two-dimensional transition metal dichalcogenides have attracted considerable attention in electrocatalytic hydrogen evolution due to their unique layered structures and tunable electronic properties. However, prior research has predominantly focused on the intrinsic catalytic activity of planar few-layer structures, which offer limited exposure of edge-active sites due to their restricted two-dimensional geometry. Moreover, van der Waals interactions between layers impose substantial barriers to electron transport, significantly hindering charge transfer efficiency. To overcome these limitations, this study presents the innovative synthesis of high-quality single-screw WS₂ with a 5° dislocation angle via physical vapor deposition. Second harmonic generation measurements revealed a pronounced asymmetric polarization response, while the selected area electron diffractionand atomic force microscopy elucidated the material’s distinctive screwed dislocation configuration. In contrast to planar monolayer WS₂, the conical/screw-structured WS₂—formed through screw-dislocation-mediated growth—exhibits a higher density of exposed edge-active catalytic sites and enhanced electron transport capabilities. Electrochemical performance tests revealed that in an alkaline medium, the screwed WS₂ nanosheets exhibited an overpotential of 310 mV at a current density of −10 mA/cm², with a Tafel slope of 204 mV/dec. Additionally, under a current density of 18 mA/cm², the screwed WS₂ can sustain this current density for at least 30 h. These findings offer valuable insights into the design of low-cost, high-efficiency, non-precious metal catalysts for hydrogen evolution reactions. Full article

A cocrystal of acridine with 2,4-dihydroxybenzaldehyde (2:1 stoichiometric ratio) was synthesized, spectrally and structurally characterized using TG, DSC, ATR-FTIR and Single-Crystal XRD methods and Hirshfeld surface analysis, and its nonlinear optical properties were investigated by DFT at the B3LYP/6-311++Glevel. The obtained compound crystallizes in the noncentrosymmetric P2₁ monoclinic space group, with two molecules of acridine and one molecule of 2,4-dihydroxybenzaldehyde in the asymmetric unit. The strong O_(aldehyde)–H⋯N_(acridine) and weak C_(aldehyde)–H⋯O_(aldehyde) and C_(aldehyde)–H⋯O_(aldehyde) hydrogen bonds, as well as π_(acridine)–π_(acridine) and C_(acridine)–H⋯π_(aldehyde) interactions, are present in the crystal lattice of the title compound. The calculated energy gap (ΔE) between the HOMO-LUMO surfaces shows charge transfer interactions due to the π-π* transitions among the molecules. The calculated first and second hyperpolarizability values indicate that obtained cocrystal is a promising candidate for nonlinear optical applications. Full article

Enantiopure tetrahydroisoquinolines (THIQs), recognized as privileged skeletal structures in natural alkaloids, have attracted considerable attention from chemists due to their biological and pharmacological activities. Synthetic strategies for optically active THIQs have been rapidly and extensively developed in the past decades. In view of simplicity and atom economy, asymmetric reduction of N-heteroaromatics, imines, enamines, and iminium salts containing an isoquinoline (IQ) moiety should be the preferred approaches to obtain chiral THIQs. This review focuses on recent advances in the catalytic asymmetric synthesis of enantiopure THIQs via asymmetric reduction, including asymmetric hydrogenation, transfer hydrogenation, reductive amination, and deracemization. Highly enantioselective synthesis of THIQs was achieved via transition-metal-catalyzed asymmetric reduction and organocatalytic asymmetric reduction utilizing either catalyst activation or substrate activation strategy. Despite much progress in the enantioselective synthesis of THIQs, there still remain considerable opportunities and challenges for progress and developments in this field of research, particularly in the development of asymmetric catalytic systems for the direct reduction of IQs. Full article

The main purpose of this study is to characterize the nature of the low-energy singlet excited states of the anthranilic acid homodimer (AA₂) and their changes (symmetry breaking) caused by deformation of the centrosymmetric, ground state structure of AA₂ towards the geometry of the S₁ state. We employ both the correlated ab initio methods (approximate Coupled Clusters Singles and Doubles—CC2 and CASSCF/NEVPT2) as well as the DFT/TDDFT calculations with two exchange–correlation functionals, i.e., B3LYP and CAM-B3LYP. The composition of the wavefunctions is investigated using the one-electron transition density matrix and difference density maps. We demonstrate that in the case of AA₂, small asymmetric distortions of geometry bring about unproportionally large changes in the excited state wavefunctions. We further provide comprehensive characterization of the AA₂ electronic structure, showing that the excitation is nearly completely localized on one of the monomers, which stands in agreement with the experimental evidence. The excitation increases the π-electronic coupling of the substituents and the aromatic ring, but only in the excited monomer, while the changes in the electronic structure of the unexcited monomer are negligible (after geometry relaxation). The increased electronic density strengthens both intra- and intermolecular hydrogen bonds formed by the carbonyl oxygen atom of the excited monomer, making them significantly stronger than in the ground state. Although the overall pattern of changes remains qualitatively consistent across all methods employed, CC2 predicts more pronounced excitation-induced modifications of the electronic structure compared to the more routinely used TDDFT approach. The most important deficiency of the B3LYP functional in the present context is locating two charge-transfer states at erroneously low energies, in close proximity of the S₁ and S₂ states. The range-corrected CAM-B3LYP exchange–correlation functional gives a considerably improved description of the CT states at the price of overshot excitation energies. Full article

Chiral pincer complexes, characterized by their rigid tridentate coordination framework, have emerged as powerful catalysts in asymmetric synthesis. This review provides a comprehensive overview of recent advancements in the development of chiral pincer-type ligands and their corresponding transition metal complexes. We highlight the latest progress in their application across a range of catalytic asymmetric reactions, including the (transfer) hydrogenation of polar and non-polar bonds, hydrophosphination, alkynylation, Friedel-Crafts reactions, enantioselective reductive cyclization of alkynyl-tethered cyclohexadienones, enantioselective hydrosilylation, as well as Aza–Morita–Baylis–Hillman reactions. The structural rigidity and tunability of chiral pincer complexes enable precise control over stereoselectivity, resulting in high enantioselectivity and efficiency in complex molecular transformations. As the field advances, innovations in ligand design and the exploration of new metal centers are expected to expand the scope and utility of these catalysts, bearing significant implications for the synthesis of enantioenriched compounds in pharmaceuticals, materials science, and beyond. Full article

The (R,R)-Teth-TsDPEN-Ru(II) complex promoted the one-pot double C=O reduction of α-alkyl-β-ketoaldehydes through asymmetric transfer hydrogenation/dynamic kinetic resolution (ATH-DKR) under mild conditions. In this process, ten anti-2-benzyl-1-phenylpropane-1,3-diols (85:15 to 92:8 dr) were obtained in good yields (41–87%) and excellent enantioselectivities (>99% ee for all compounds). Notably, the preferential reduction of the aldehyde moiety led to the in situ formation of 2-benzyl-3-hydroxy-1-phenylpropan-1-one intermediates. These intermediates played a crucial role in enhancing both reactivity and stereoselectivity through hydrogen bonding. Full article

The Three-Piece Oil Control Ring (TPOCR) is becoming a viable option for heavy duty gas and hydrogen engines due to the low particle concentration in these engines. Although direct oil leakage from the gap is not likely to happen with the misalignment of the upper and lower rail gaps, there exist other less-apparent oil leaking mechanisms through the TPOCR. This work is targeted at understanding the oil leakage’s source and destination through the rail and liner interfaces across the whole cycle. The 2D Laser Induced Fluorescence technique was applied on an optical engine to study the oil transport behavior. Combined with a TPOCR model for dynamics and lubrication, the mechanisms that cause rail twist and oil scraping by the upper rail were analyzed. It was found that the symmetrical rail can scrape the oil up in the up-strokes. The scraped oil first accumulates in the clearance between the upper rail and groove, as well as at the upper corner of the rail Outer Diameter before being transferred to both the third land and liner when the piston changes direction at Top Dead Center. Rails with an asymmetrical profile can reduce or enhance these effects depending the orientation of the rails. This study provides findings that could help design the engine to better control Lubricate Oil Consumption and properly lubricate the Top Dead Center’s dry region at the same time. Full article

Catalytic transfer hydrogenation has emerged as a pivotal chemical process with transformative potential in various industries. This review highlights the significance of catalytic transfer hydrogenation, a reaction that facilitates the transfer of hydrogen from one molecule to another, using a distinct molecule as the hydrogen source in the presence of a catalyst. Unlike conventional direct hydrogenation, catalytic transfer hydrogenation offers numerous advantages, such as enhanced safety, cost-effective hydrogen donors, byproduct recyclability, catalyst accessibility, and the potential for catalytic asymmetric transfer hydrogenation, particularly with chiral ligands. Moreover, the diverse range of hydrogen donor molecules utilized in this reaction have been explored, shedding light on their unique properties and their impact on catalytic systems and the mechanism elucidation of some reactions. Alcohols such as methanol and isopropanol are prominent hydrogen donors, demonstrating remarkable efficacy in various reductions. Formic acid offers irreversible hydrogenation, preventing the occurrence of reverse reactions, and is extensively utilized in chiral compound synthesis. Unconventional donors such as 1,4-cyclohexadiene and glycerol have shown a good efficiency in reducing unsaturated compounds, with glycerol additionally serving as a green solvent in some transformations. The compatibility of these donors with various catalysts, substrates, and reaction conditions were all discussed. Furthermore, this paper outlines future trends which include the utilization of biomass-derived hydrogen donors, the exploration of hydrogen storage materials such as metal-organic frameworks (MOFs), catalyst development for enhanced activity and recyclability, and the utilization of eco-friendly solvents such as glycerol and ionic liquids. Innovative heating methods, diverse base materials, and continued research into catalyst-hydrogen donor interactions are aimed to shape the future of catalytic transfer hydrogenation, enhancing its selectivity and efficiency across various industries and applications. Full article

The stoichiometric ratio 2:1 mix of 1-phenylpiperazine and oxalic acid dihydrate followed by slow evaporation results in a new material, bis(4-phenylpiperazin-1-ium) oxalate dihydrate, with the general chemical formula (C₁₀H₁₅N₂)₂(C₂O₄).2H₂O, indicated by PPOXH. The title compound’s asymmetric unit and three-dimensional network have been determined by single crystal X-ray diffraction. Intermolecular O-H…O, N-H…O and C-H…O hydrogen bonding assist in maintaining and stabilization of the crystal structure of this new compound. Hirshfeld surface analysis and two-dimensional fingerprints have been performed to quantify the non-covalent interactions in the PPOXH structure. The vibrational modes of the different characteristic groups of the title chemical were identified using infrared spectrum analysis. The thermal characterization of this product was studied by a coupled TG/DTA analysis. The ultraviolet-visible absorption spectrum has been used to study the optical properties and the energy gap of this compound. DFT calculations were employed to evaluate the composition and properties of PPOXH. The analysis of HOMO-LUMO frontier orbitals analysis allows us to understand the chemical reactivity of this supramolecular compound and to determine the electrophilic and nucleophilic sites responsible for electron transfer. Topological analysis (AIM), reduced density gradient (RDG), molecular electrostatic potential surface (MEPS) and Mulliken population were analyzed to evaluate the types of non-covalent interactions, localization of electrons in space, atomic charges and molecular polarity in depth. Full article