Catalysis In Aqueous Media Research Articles

Gold Nanoclusters Synthesized within Single-Chain Nanoparticles as Catalytic Nanoreactors in Water.

Metalloenzymes are able to catalyze complex biochemical reactions in cellular (aqueous) media with high efficiency. In recent years, a variety of metal-containing single-chain nanoparticles (SCNPs) have been synthesized as simplified metalloenzyme-mimetic nano-objects. However, most of the metal-containing SCNPs reported so far contained complexed metal ions but not metal nanoclusters (NCs) with diameter <5 nm, which could be used as powerful, emerging catalysts. Herein, we report the synthesis of gold nanoclusters (Au-NCs) within SCNPs and the further use of Au-NCs/SCNPs as catalytic nanoreactors in water. We demonstrate that a common motif contained in several drugs (i.e., the aminophenyl-oxazolidinone fragment present in Rivaroxaban, Sutezolid, and Linezolid) can be efficiently prepared in water from a hydrophobic precursor compound by using the Au-NCs/SCNPs as efficient catalytic nanoreactors. In summary, this work paves the way forthe synthesis of metal-NCs/SCNPs for advanced catalysis in aqueous media.

Adatom Surface Modification of Metal Nanoparticle Electrodes Though Underpotential Deposition for CO2 Electroreduction Catalysis

The electrocatalytic CO2 reduction reaction to form higher order carbon-coupled products is a complex interplay of CO binding energies, kinetic rate-constant branching ratios, CO2 solubility, and pH gradients. The result of this wide, and often uncontrolled parameter space is a distribution of CO2RR products, especially in carbon-coupled reactions. Designing electrocatalysts that promote any of these parameters individually is an attractive route to not only build selective CO2RR catalysts, but also to provide the framework of design principals for selective electrocatalysis. To this end, systematically varying the electrode kinetics of CO2 reduction reactions on model system substrates through minor surface modifications is an informative approach for understanding this complicated reaction and how certain products can be expressed or suppressed.Metal nanoparticle electrocatalysts are an interesting model system as recent advances in synthetic methods enable a large degree of size, shape, and facet control which allow systematic investigations of several well controlled parameters. Palladium nanoparticles are particularly interesting as Pd alloys with hydrogen prior to electroreduction catalysis in aqueous media. This alloying provides a continuous supply of reducing hydrogen equivalents for electrocatalysis. Pd surfaces can also be modified with submonolayer amounts of metal adatoms through underpotential electrodeposition. This surface modification can, in principal, tune both the binding energies of CO and the kinetic rate constants of the hydrogen evolution reaction, both critical parameters for CO2RR. This wide parameter space presents opportunities for applied and fundamental research. I will discuss recent results aimed at modifying the electrode kinetics of palladium nanocubes with 100 surface termination by modifying the surface with various metal adatoms in different amounts. I will show how Pd nanocube surface modification influences not only the surface, but bulk, hydrogen alloying properties of the nanocube as well.

Mapping the Surface Groups of Amine-Rich Carbon Dots Enables Covalent Catalysis in Aqueous Media

Summary Carbon nanodots stand as the missing link between the molecular and the nanoscale world, owing to the unique molecular-like behavior emerging from their synthetic precursors. A converging set of analytical and spectroscopic data yields a precise inventory of the surface reactive groups of amine-rich carbon dots (NCDs-1). As a result, NCDs-1 provide a multi-functional nano-platform that is able to covalently activate carbonyl groups, form iminium-ions and enamine intermediates, and efficiently promote diverse aminocatalytic transformations in water. Remarkably, the catalytic activity of carbon dots can also govern the stereoselectivity in the bond-forming event. Indeed, the use of chiral carbon dots (NCDs-7) as catalysts affords the final aldol products with significant enantiomeric excess. The successful implementation of carbon nanostructures into chemical roles so far restricted to molecular systems opens new avenues for advanced applications where the nanoscale and the molecular realms will merge and complement each other.

Aerobic Baeyer-Villiger Oxidation Catalyzed by a Flavin-Containing Enzyme Mimic in Water.

Direct incorporation of molecular oxygen into small organic molecules has attracted much attention for the development of new environmentally friendly oxidation processes. In line with this approach, bioinspired systems mimicking enzyme activities are of particular interest since they may perform catalysis in aqueous media. Demonstrated herein is the incorporation of a natural flavin cofactor (FMN) into the specific microenvironment of a water-soluble polymer which allows the efficient reduction of the FMN by NADH in aqueous solution. Once reduced, this artificial flavoenzyme can then activate molecular dioxygen under aerobic conditions and result in the Baeyer-Villiger reaction at room temperature in water.

Substituted 1-(isoxazol-3-yl)methyl-1H-1,2,3-triazoles: Synthesis, palladium(II) complexes, and high-turnover catalysis in aqueous media

New substituted 3-((1H-1,2,3-triazol-1-yl)methyl)-5-arylisoxazoles (aryl = Ph, p-Tol) and 2-(5-phenylisoxazol-3-yl)-5-(2-(1-((5-(p-tolyl)isoxazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)ethyl)-1,3,4-oxadiazole were synthesized by means of click-chemistry procedures. The obtained compounds were used as ligands in preparation of palladium(II) complexes, and the latter proved to be high-turnover-number catalysts for CC cross-coupling reactions under Green Chemistry conditions. One of the ligands was structurally characterized by single crystal X-ray diffraction, and the structure of complexes was determined by 1H, 13C, 15N NMR spectroscopy and quantum-chemical modeling.

Resolving the Iron Phthalocyanine Redox Transitions for ORR Catalysis in Aqueous Media.

Metal macrocycles are among the most important catalytic systems in electrocatalysis and biocatalysis owing to their rich redox chemistry. Precise understanding of the redox behavior of metal macrocycles in operando is essential for fundamental studies and practical applications of this catalytic system. Here we present electrochemical data for the representative iron phthalocyanine (FePc) in both aqueous and nonaqueous media coupled with in situ Raman and X-ray absorption analyses to challenge the traditional notion of the redox transition of FePc at the low potential end in aqueous media by showing that it arises from the redox transition of the ring. Our data unequivocally demonstrate that the electron is shuttled to the Pc ring via the Fe(II)/Fe(I) redox center. The Fe(II)/Fe(I) redox transition of FePc in aqueous media is indiscernible by normal spectroscopic methods owing to the lack of a suitable axial ligand to stabilize the Fe(I) state.

Functionalized isoxazole and isothiazole ligands: design, synthesis, palladium complexes, homogeneous and heterogeneous catalysis in aqueous media

Homogenous and heterogeneous palladium catalysts with functionalized izoxazole and isothiazole ligands were developed for the cross-coupling reactions. The catalysts possessed high activity and were suitable for the repeated use. Compared with commonly used organic solutions, application of water and its mixtures with methanol as a reaction medium significantly intensifies catalysis with no side being formed. The obtained results are promising for the development of effective and ecologically friendly technologies of synthesis of important compounds such as polyfunctional biaryls, arylated olefins, acetylenes and their heterocyclic analogs.

Highly active, stable and self-antimicrobial enzyme catalysts prepared by biomimetic mineralization of copper hydroxysulfate.

A nature-inspired approach to encapsulate enzymes in spindle-like copper hydroxysulfate nanocrystals was developed by a biomimetic mineralization process. Several types of enzymes including glucose oxidase (GOx), horseradish peroxidase (HRP), Candida antarctica lipase B (CALB) and cytochrome c (Cyt c) were successfully encapsulated in copper hydroxysulfate nanocrystals quickly (within 1 hour) with maintained or even greatly enhanced catalytic efficiencies (kcat/KM of Cyt c showed a 143-fold increase) and high stabilities, demonstrating the feasibility of utilizing copper hydroxysulfate nanocrystals as a novel type of nanocarrier for enzyme immobilization. In addition, by this approach, for the first time, we showed that an immobilized enzyme can be endowed with self-antibacterial activity by an inorganic component. This self-antibacterial performance together with the improved catalytic efficiencies and stabilities can greatly benefit the enzymatic catalysis in aqueous media and promote the future development of novel biosensors.

State of Supported Nickel Nanoparticles during Catalysis in Aqueous Media.

The state of Ni supported on HZSM-5 zeolite, silica, and sulfonated carbon was studied during aqueous-phase catalysis of phenol hydrodeoxygenation using in situ extended X-ray absorption fine structure spectroscopy. On sulfonated carbon and HZSM-5 supports, NiO and Ni(OH)2 were readily reduced to Ni(0) under reaction conditions (≈35 bar H2 in aqueous phenol solutions containing up to 0.5 wt. % phosphoric acid at 473 K). In contrast, Ni supported on SiO2 was not stable in a fully reduced Ni(0) state. Water enables the formation of Ni(II) phyllosilicate, which is more stable, that is, difficult to reduce, than either α-Ni(OH)2 or NiO. Leaching of Ni from the supports was not observed over a broad range of reaction conditions. Ni(0) particles on HZSM-5 were stable even in presence of 15 wt. % acetic acid at 473 K and 35 bar H2 .

ChemInform Abstract: Ionic Liquid Immobilized Organocatalysts for Asymmetric Reactions in Aqueous Media

AbstractReview: 84 refs.

2-Pyridyl-phosphine and -diphosphine complexes of nickel(II), and their aqueous solution chemistry

The cis, square planar NiII complexes NiX2[d(py)pe], where d(py)pe is the 2-pyridyl-diphosphine ligand py2P(CH2)2Ppy2, and X=Cl (1a), Br (1b), I (1c), NCS, and NO3, and the corresponding d(py)pcp complexes, where d(py)pcp is ▪ with a cyclopentane ring bridge, are synthesized via use of the NiX2(PPh3)2 precursors, and fully characterized, including five X-ray structures. An X-ray structure of d(py)pcp is also reported.Complexes 1a–c dissolve in water to form cis-{Ni(H2O)2[d(py)pe]}2+, which is isolated as the PF6 salt; the d(py)pcp analogues behave similarly. All the diaquo complexes decompose slowly in H2O to generate Ni(H2O)62+ and the dioxides of the pyridyl-diphosphines, likely due to the presence of trace O2. Known, tetrahedral complexes of the type NiX2(PPh3−npyn)2 (X=Cl, Br; py=2-pyridyl, and n=1–3) also dissolve in H2O, again with generation of 2:1 electrolyte species. An attempted synthesis of Ni(CO)2(Ppy3)2 from Ni(CO)2(PPh3)2 and Ppy3 in CH2Cl2 accidentally gives the known NiCl2(P,N-Ppy3)·H2O via a laboratory light-induced reaction; this species partially converts into [Ni(Ppy3)2]Cl2, and a crystal structure confirms the octahedral, tripodal N,N′,N″-coordination of the cation. The water-soluble systems, studied because of their potential for catalysis in aqueous media, are not effective for catalyzed olefin hydration, or transfer-hydrogenation of cyclohexanone.

Chemically stable magnetic nanoparticles for metal adsorption and solid acid catalysis in aqueous media

Magnetically collectable and reusable particles for concentrating heavy metal ions and solid acid catalysis in aqueous media were developed.

Transesterifications and Peracid‐Assisted Oxidations in Aqueous Media Catalyzed by Mycobacterium smegmatis Acyl Transferase

AbstractHydrolases catalyze synthetic reactions in nonaqueous media, whereas they perform hydrolysis under aqueous solutions. An acyl transferase from Mycobacterium smegmatis (MsAcT) is able to catalyze synthetic reactions in buffer because of its highly hydrophobic active site, which enables efficient transesterification reactions even at 99.9 % v/v buffer solution. This unique feature of MsAcT among hydrolases may open new opportunities to conduct synthetic (bio)catalysis in aqueous media. With these goals in mind, this paper explores some evidence of such potential: MsAcT can perform enantioselective transesterifications (e.g., (S)‐2‐octanol), which could be combined with other aqueous multistep (asymmetric) reactions; 5‐hydroxymethylfurfural (HMF) can be esterified to produce more hydrophobic and easily extractable HMF esters (e.g., for downstream processing or wastewater treatment); and upon addition of dilute H2O2, MsAcT works efficiently as a perhydrolase to form in situ peracids—in bulk water—that can be used for oxidations (e.g., furfural to furoic acid oxidation). Overall, these and many other new applications can be envisaged by using MsAcT in aqueous solutions.

Ionic Liquid Immobilized Organocatalysts for Asymmetric Reactions in Aqueous Media

Ionic liquids are organic salts with melting points typically below ambient or reaction temperature. The unique combination of physical properties of ionic liquids, such as lack of measurable vapor pressure, high thermal and chemical stability, make them ideal to be used as reusable homogenous support for catalysts. In addition, the solubility of ionic liquids in various reaction media can be controlled and easily fine-tuned by modification of the structures of their cations and anions. As a result, ionic liquid immobilized organocatalysts are very effective in aqueous media and can be separated easily from organic solvents, as well as aqueous phases by simply adjusting the polarity of the media. Ionic liquid immobilized organocatalysts are not only very versatile compounds that are effective catalysts for a wide spectrum of reactions, but are also environmentally friendly and recyclable organocatalysts. Herein, we provide a summary of the past decade in the area of asymmetric catalysis in aqueous media for a wide variety of reactions in which ionic liquid and related ammonium salt immobilized organocatalysts are used.

Synthesis and cytotoxic evaluation of novel 2,3-di-O-alkyl derivatives of l-ascorbic acid

A new series of 2,3-di-O-alkyl derivatives of 5,6-O-isopropylidene-l-ascorbic acid were synthesized using phase transfer catalysis in aqueous media. These derivatives were screened for their superoxide radical scavenging activity and anticancer activity against human breast cancer cell line (MCF-7), leukemic cell line (HL-60), and cervical cell line (HeLa). All these derivatives exhibited enhanced scavenging effect than l-ascorbic acid except for the 4-fluorobenzyl or 2/4-chlorobenzyl alkyl group either at 3-O and/or 2-O position displayed pro-oxidant activity. These pro-oxidant derivatives (2c–e, m) exhibited potent anticancer activities against all the cell lines (IC50 = 25.79–57.21 μM). However, these compounds were also cytotoxic to human normal leukemic macrophages THP-1. On the other hand, antioxidant derivatives displayed albeit slight (2k, IC50 = 57.96–63.45 μM), but selective inhibitory effect toward all tumor cell lines. Thus, pro-oxidant and antioxidant properties can be used to predict the cytotoxic selectivity of drug against normal and cancer cells.

Green Chemistry, Biofuels, and Biorefinery

In the current climate of several interrelated impending global crises, namely, climate change, chemicals, energy, and oil, the impact of green chemistry with respect to chemicals and biofuels generated from within a holistic concept of a biorefinery is discussed. Green chemistry provides unique opportunities for innovation via product substitution, new feedstock generation, catalysis in aqueous media, utilization of microwaves, and scope for alternative or natural solvents. The potential of utilizing waste as a new resource and the development of integrated facilities producing multiple products from biomass is discussed under the guise of biorefineries. Biofuels are discussed in depth, as they not only provide fuel (energy) but are also a source of feedstock chemicals. In the future, the commercial success of biofuels commensurate with consumer demand will depend on the availability of new green (bio)chemical technologies capable of converting waste biomass to fuel in a context of a biorefinery.

ChemInform Abstract: Activation of Carbonyl‐Containing Molecules with Solid Lewis Acids in Aqueous Media

AbstractReview: 250 refs.

N-heterocyclic carbene transition metal complexes for catalysis in aqueous media

The last decade has seen an increasing number of reports on the use of NHC-metal complexes for catalysis in water, therefore this review is aimed to introduce the whole research on this area, in which the use of water or aqueous/organic media is to be applied. Since the first discovery of the NHC carbenes by Arduengo, work on the synthesis of NHC-metal organometallic compounds has revolutionized the field of catalysis, gradually displacing the typical phosphine and amine-type ligands in view of their higher stability and reactivity. Aqueous catalysis has become a hot topic in Green Chemistry due to the positive implications for the use of water as reaction media.

Activation of Carbonyl-Containing Molecules with Solid Lewis Acids in Aqueous Media

Current interest in reacting carbonyl-containing molecules in aqueous media is primarily due to the growing emphasis on conversion of biomass to fuels and chemicals. Recently, solid Lewis acids have been shown to perform catalytic reactions with carbonyl-containing molecules such as sugars in aqueous media. Here, catalysis mediated by Lewis acids is briefly discussed, Lewis acid solids that perform catalysis in aqueous media are then described, and the review is concluded with a few comments on the outlook for the future.

ChemInform Abstract: Catalysis in Aqueous Media for the Synthesis of Drug‐like Molecules

AbstractReview: 61 refs.