Catalytic Functional Groups Research Articles

Concise Synthesis of (±)-Fortuneicyclidins and (±)-Cephalotine B Enabled by Pd-Catalyzed Dearomative Spirocyclization.

Total syntheses of C11-oxygenated Cephalotaxus alkaloids, fortuneicyclidins A and B, and cephalotine B, were achieved. The key for the synthesis is a Pd-catalyzed dearomative spirocyclization of bromofurans with N-tosylhydrazones, followed by acid-mediated tandem transformation to construct the tetracyclic skeleton with the C11-oxygen functional group. Chemo-selective and catalytic functional group conversions of the tetracyclic intermediate completed the synthesis of fortuneicyclidins and cephalotine B in 8 and 9 steps, respectively.

Amines as Catalysts: Dynamic Features and Kinetic Control of Catalytic Asymmetric Chemical Transformations to Form C-C Bonds and Complex Molecules.

Carbonyl transformations involving enolates and/or enamines have been used for various types of bond-forming reactions. In this account, catalysts and catalyst systems that have amino acids or primary, secondary, and/or tertiary amines as key catalytic functional groups that we have developed to accelerate chemical transformations, including regio-, diastereo- and enantioselective reactions, are discussed. Our chemical transformation strategies and methods that use amine derivatives as catalysts are also discussed. As amines can have different functions depending on protonation and on the species formed during the catalysis (such as enamines and iminium ions), dynamics and kinetic controls are the keys for understanding the catalysis. Further, strategies that harness dynamic steps and kinetic control in amine-catalyzed reactions have enabled the synthesis of complex molecules in stereocontrolled manners. Understanding the dynamic features and the kinetic controls of the catalysis will further the design of the catalysts and the development of chemical transformation strategies and methods.

Mutual leveraging of proximity effects and click chemistry in chemical biology.

Nature has the remarkable ability to realize reactions under physiological conditions that normally would require high temperature and other forcing conditions. In doing so, often proximity effects such as simultaneous binding of two reactants in the same pocket and/or strategic positioning of catalytic functional groups are used as ways to achieve otherwise kinetically challenging reactions. Though true biomimicry is challenging, there have been many beautiful examples of how to leverage proximity effects in realizing reactions that otherwise would not readily happen under near-physiological conditions. Along this line, click chemistry is often used to endow proximity effects, and proximity effects are also used to further leverage the facile and bioorthogonal nature of click chemistry. This review brings otherwise seemingly unrelated topics in chemical biology and drug discovery under one unifying theme of mutual leveraging of proximity effects and click chemistry and aims to critically analyze the biomimicry use of such leveraging effects as powerful approaches in chemical biology and drug discovery. We hope that this review demonstrates the power of employing mutual leveraging proximity effects and click chemistry and inspires the development of new strategies that will address unmet needs in chemistry and biology.

Nanostructured Carbon Electrocatalysts for Energy Conversions

The growing energy demand worldwide has led to increased use of fossil fuels. This, in turn, is making fossil fuels dwindle faster and cause more negative environmental impacts. Thus, alternative, environmentally friendly energy sources such as fuel cells and electrolyzers are being developed. While significant progress has already been made in this area, such energy systems are still hard to scale up because of their noble metal catalysts. In this concept paper, first, various scalable nanocarbon-based electrocatalysts that are being synthesized for energy conversions in these energy systems are introduced. Next, notable heteroatom-doping and nanostructuring strategies that are applied to produce different nanostructured carbon materials with high electrocatalytic activities for energy conversions are discussed. The concepts used to develop such materials with different structures and large density of dopant-based catalytic functional groups in a sustainable way, and the challenges therein, are emphasized in the discussions. The discussions also include the importance of various analytical, theoretical, and computational methods to probe the relationships between the compositions, structures, dopants, and active catalytic sites in such materials. These studies, coupled with experimental studies, can further guide innovative synthetic routes to efficient nanostructured carbon electrocatalysts for practical, large-scale energy conversion applications.

Arene-Ruthenium(II) Complexes Containing 11H-Indeno[1,2-b]quinoxalin-11-one Derivatives and Tryptanthrin-6-oxime: Synthesis, Characterization, Cytotoxicity, and Catalytic Transfer Hydrogenation of Aryl Ketones.

A series of novel mono- and binuclear arene–ruthenium(II) complexes [(p-cym)Ru(L)Cl] containing 11H-indeno[1,2-b]quinoxalin-11-one derivatives or tryptanthrin-6-oxime were synthesized and characterized by X-ray crystallography, IR, NMR spectroscopy, cyclic voltammetry, and elemental analysis. Theoretical calculations invoking singlet state geometry optimization, solvation effects, and noncovalent interactions were done using density functional theory (DFT). DFT calculations were also applied to evaluate the electronic properties, and time-dependent DFT was applied to clarify experimental UV–vis results. Cytotoxicity for cancerous and noncancerous human cell lines was evaluated with cell viability MTT assay. Complexes demonstrated a moderate cytotoxic effect toward cancerous human cell line PANC-1. The catalytic activity of the complexes was evaluated in transfer hydrogenation of aryl ketones. All complexes exhibited good catalytic activity and functional group tolerance.

A Catalyst of Pd@MIL‐101@SGO Catalyzes Epoxidation and Hydroxymethoxylation Tandem Reactions of Styrene

AbstractBrönsted acid and metal nanoparticles are important catalytic functional groups. In this work, a bifunctional heterogeneous catalyst with both strong Brönsted acid and metal nanoparticles was prepared. First Brönsted acid groups were obtained by sulfonating graphene oxide, next metal organic frameworks MIL‐101 (Cr) grew on sulfonated graphene oxide (SGO), then palladium nanoparticles (NPs) were encapsulated in MIL‐101@SGO composites. The catalyst was characterized by a variety of different techniques including XRD, SEM, TEM, EDS, FT‐IR, TGA, and nitrogen physisorption measurements. Tandem heterogeneous catalysis of Pd@MIL‐101@SGO was investigated for the one‐pot direct conversion of styrene into β‐alkoxy alcohol. The catalyst retained high catalytic activity after 5 times of reuses in aqueous solutions. No loss of crystal structure was detected by PXRD and no leakage of Pd was detected by ICP‐AES. Therefore, Pd@MIL‐101@SGO proved to be an effective recyclable heterogeneous catalyst for synthesizing β‐alkoxy alcohol and exhibited potential application in industry.

Spatial Distribution of Silica-Bound Catalytic Organic Functional Groups Can Now Be Revealed by Conventional and DNP-Enhanced Solid-State NMR Methods

Understanding the spatial distribution of functionalities on surfaces with atomic-scale resolution is very important for catalytic applications, yet very challenging for analytical inquiry. Recent ...

Study on Sulfonic Acid Functional Group Modified Imidazole Ionic Liquids for Oxygen Concentration Detection

The ionic liquid is a kind of ionic salt capable of being liquid state at room temperature. As a new type of green organic solvent, ionic liquid has the advantages of good electrical conductivity, wide electrochemical window, very low vapor pressure, and is widely used in electrochemical, organic synthesis and other fields. The use of ionic liquids as electrolytes in electrochemical oxygen sensors can alter the shortcomings of the current sensor's inability to operate at high temperature and humidity conditions. Besides, ionic liquids with certain catalytic functional group could improve the response performance of sensing devices. Therefore, in this paper, ionic liquids based on imidazolium, 1-methyl-3-propanesulfonic acid imidazolium hydrogensulfate ([Psmim]HSO4) and 1-methyl-3-butpropanesulfonic acid imidazolium hydrogensulfate ([Bsmim]HSO4 )with sulfonic-acid catalytic functional group were studied. Both ionic liquids mentioned above were synthesized through a traditional two-step method. Electrochemical tests including linear scanning voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) of both ionic liquids were carried out with an electrochemical workstation to characterize the intrinsic electrochemical performance of both ionic liquids. On the other hand, cyclic voltammetry (CV) curves were tested, which shows a proportional linear relationship between oxygen reduction peak current and the oxygen concentrations from 0% to 100% O2 with the corresponding R2 (R2 >0.97), and chronoamperometric current tsests were also carried out to futher confirm the ionic liquids promising materials for oxygen sensing. (This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.)

Metathesis-active ligands enable a catalytic functional group metathesis between aroyl chlorides and aryl iodides.

Current methods for functional group interconversion have, for the most part, relied on relatively strong driving forces which often require highly reactive reagents to generate irreversibly a desired product in high yield and selectivity. These approaches generally prevent the use of the same catalytic strategy to perform the reverse reaction. Here we describe a catalytic functional group metathesis approach to interconvert, under CO-free conditions, two synthetically important classes of electrophiles that are often employed in the preparation of pharmaceuticals and agrochemicals-aroyl chlorides (ArCOCl) and aryl iodides (ArI). Our reaction design relies on the implementation of a key reversible ligand C-P bond cleavage event, which enables a non-innocent, metathesis-active phosphine ligand to mediate a rapid aryl group transfer between the two different electrophiles. Beyond enabling a practical and safer approach to the interconversion of ArCOCl and ArI, this type of ligand non-innocence provides a blueprint for the development of a broad range of functional group metathesis reactions employing synthetically relevant aryl electrophiles.

Recent Advances in Supramolecular Gels and Catalysis.

Over the past two decades, supramolecular gels have attracted significant attention from scientists in diverse research fields and have been extensively developed. This review mainly focuses on the significant achievements in supramolecular gels and catalysis. First, by incorporating diverse catalytic sites and active organic functional groups into gelator molecules, supramolecular gels have been considered as a novel matrix for catalysis. In addition, these rationally designed supramolecular gels also provide a variety of templates to access metal nanocomposites, which may function as catalysts and exhibit high activity in diverse catalytic transformations. Finally, as a new kind of biomaterial, supramolecular gels formed in situ by self-assembly triggered by catalytic transformations are also covered herein.

Screening the activity of Lewis pairs for hydrogenation of CO2

CO2 capture coupled with CO2 conversion to hydrocarbon fuels could reduce the overall anthropogenic carbon footprint but requires an efficient catalytic pathway for CO2 hydrogenation. In this work, we examine functional groups that can be integrated within nanoporous materials, such as metal organic frameworks, that could lead to the development of materials that can selectively adsorb CO2 from flue gas and convert it into a useful fuel. We focus on the use of Lewis pair (LP) moieties as catalytic functional groups because of their activity for heterolytic dissociation of H2 and subsequent hydrogenation of CO2. However, most LP functional groups also strongly bind CO2, such that the catalytic site can be poisoned if the binding energy of CO2 is much stronger than that of H2. In this work, we screen a variety of LP moieties using density functional theory to compute the adsorption energies of H2 and CO2. We consider five classes of LP functional groups, with each class designed to explore modifying the binding energies in different ways. We have developed a mathematical model for predicting the H2 adsorption energies on various Lewis pairs as a function of geometric and energetic properties of the functional moieties.

Aspartyl Oxidation Catalysts That Dial In Functional Group Selectivity, along with Regio- and Stereoselectivity.

A remarkable aspect of enzyme evolution is the portability of catalytic mechanisms for fundamentally different chemical reactions. For example, aspartyl proteases, which contain two active site carboxylic acid groups, catalyze the hydrolysis of amide bonds, while glycosyltransferases (and glycosyl hydrolases), which often also contain two active site carboxylates, have evolved to form (or break) glycosidic bonds. However, neither catalyst exhibits cross-reactivity in the intracellular environment. The large, macromolecular architectures of these biocatalysts tailor their active sites to their precise, divergent functions. The analogous portability of a small-molecule catalyst for truly orthogonal chemical reactivity is rare. Herein, we report aspartic acid containing peptides that can be directed to different sectors of a substrate for which the danger of cross-reactivity looms large. A transiently formed aspartyl peracid catalyst can participate either as an electrophilic oxidant to catalyze alkene epoxidation or as a nucleophilic oxidant to mediate the Baeyer–Villiger oxidation (BVO) of ketones. We show in this study that an appended peptide sequence can dictate the mode of reactivity for this conserved catalytic functional group within a substrate that has the potential to undergo both alkene epoxidation and BVO; in both cases the additional aspects of chemical selectivity (regio- and stereoselectivity) are high. This sequence-dependent tuning of a common catalytic moiety for functional group selective reactions constitutes a biomimetic strategy that may impact late-stage diversification of complex polyfunctional molecules.

Energy Storage in Environmentally Stable Nanoscale Magnesium Hybrid Materials

Energy storage systems are confronted by a paradox: high-energy density materials are, by definition, metastable and able to release energy. However, technological advances require robust, reliable systems to store and deliver energy which mitigates safety concerns. In this talk, I focus on solving this dual challenge of storage vs. stability in a prototype system - nanoscale magnesium nanocrystals embedded in a graphene matrix for high density, stable, hydrogen storage for fuel cell systems. This work (reference below) was recently published in Nature Comms. Storage of hydrogen on board vehicles is one of the critical enabling technologies for creating hydrogen- fueled transportation systems that can reduce oil dependency and mitigate the long-term effects of fossil fuels on climate change. Stakeholders in developing hydrogen infrastructure (e.g., state governments, automotive OEMs, and industrial gas suppliers) are currently focused on high-pressure storage at 350 bar and 700 bar, in part because no viable solid-phase storage material has emerged. Nevertheless, solid-state materials remain of interest because of their unique potential to meet all DOE/FCTO targets and deliver hydrogen at lower pressures and higher on-board densities. A successful solution would significantly reduce costs and ensure the economic viability of a U.S. hydrogen infrastructure. In this talk, I present work highlighting advances in the performance and viability of nanoscale metal hydrides (Cho et al. Nature Communications, 2016) by using graphene-based materials as both hydrogen-specific barrier materials and catalytic functional groups to enhance the performance of nanoscale magnesium hydride. Historically, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. In this work, we report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage surpassing that of compressed hydrogen (we report 6.5wt% and 0.105kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments and have implications for other classes of energy storage devices. I will also discuss future and ongoing work using chemically synthesized versions of graphene nanobelts to co-localize dopant moieties on the surfaces of metal hydrides using a related materials architecture. Reference: “Graphene oxide/metal nanocrystal laminates: the atomic limit for safe, selective hydrogen storage”, Eun Seon Cho, Anne M. Ruminski, Shaul Aloni, and *Jeffrey J. Urban , Nature Communications (2016)

ChemInform Abstract: Catalysts Encapsulated in Molecular Machines

AbstractReview: 49 refs.

Catalysts Encapsulated in Molecular Machines.

Smart catalysts offer the control of chemical processes and sequences of transformations, and catalysts with unique catalytic behavior can afford chiral products or promote successive polymerization. To meet advanced demands, the key to constructing smart catalysts is to incorporate traditional catalytic functional groups with trigger-induced factors. Molecular machines with dynamic properties and particular topological structures have typical stimulus-responsive features. In recent years, scientists have made efforts to utilize molecular machines (molecular switches, rotaxanes, motors, etc.) as scaffolds to develop smart catalysts. This Minireview focuses on the achievements of developing catalysts encapsulated in molecular machines and their remarkable specialties. This strategy is believed to provide more potential applications in switchable reactions, asymmetric synthesis, and processive catalysis.

Electrochemical Treatment of Glassy Carbon for Label‐Free Detection of DNA Bases and Neurotransmitters

AbstractElectrochemically reduced glassy carbon (r‐GC) showed a superior electrochemical sensing performance, compared to oxidized GC (ox‐GC) and untreated GC for the oxidation of 4 DNA bases and neurotransmitters (epinephrine, norepinephrine and serotonin). r‐GC exhibited not only the largest current intensities of all redox biomolecules, but also displayed an excellent selectivity in detecting coexisting redox biomolecules. The enhanced performance of r‐GC was attributed to the improved surface cleanliness of electrode and its catalytic surface functional groups. The results presented herein imply that simple electrochemical treatments are a viable method to produce sensitive and selective electrodes for label‐free biosensing.

Catalytic fluoride triggers dehydrative oxazolidinone synthesis from CO2

Herein, catalytic fluoride (F−) is demonstrated to be a trigger for dehydrative immobilization of atmospheric pressure CO2, such that reaction of CO2 with β-amino alcohols derived from natural amino acids gives optically pure oxazolidinones in high yields. A synergistic combination of fluoride and organosilicon agents (e.g., Bu4NF + Ph3SiF or siloxanes) enhances the catalytic activity and functional group compatibility. This system lies at the interface between homogenous and heterogeneous catalysis, and may prove useful for the development of recoverable/reusable siloxane-based CO2 immobilization materials.

Stability and catalytic properties of porous acidic (organo)silica materials for conversion of carbohydrates

Sulfonic acid-modified mesoporous SBA-15-type silica and hybrid organosilica catalysts were prepared using the co-condensation and grafting functionalization methods. The catalytic activity of these materials for fructose dehydration to 5-hydroxymethylfurfural was studied in aqueous medium and in DMSO. The prepared materials were characterized by XRD, SEM, elemental analysis, nitrogen physisorption and 29Si CP MAS NMR. Special focus was on evaluating the influence of the structural modification of the mesoporous catalysts on their stability under the conditions of catalytic conversion of carbohydrates. In aqueous medium all catalysts show very low activity and HMF selectivity. However, when the reaction is carried out in DMSO, HMF yields of up to 88% can be achieved with a minimum amount of sulfonic acid-modified catalyst. Among the materials tested, the hybrid organosilica-based catalyst shows the highest dehydration rate. It is demonstrated that pure silica-based catalysts degrade strongly under the catalytic conditions. The hydrothermal stability of the mesoporous catalysts is improved in the presence of organic moieties in their structure. The co-condensed organic–inorganic catalysts retain much better the mesoporosity and are less susceptible to the loss of catalytic functional groups anchored to their surface compared to their pure silica counterparts. The methodology for the introduction of functional groups has also a profound impact on the catalyst stability. Species incorporated into the catalysts via the direct co-condensation method show much higher stability than those introduced via a post-synthetic grafting procedure.

Chemical modification of β-endoglucanase from Trichoderma viridin by methanol and determination of the catalytic functional groups

β -Endoglucanase from Trichoderma viride was modified by methanol to explore the catalytic functional groups of cellulase. Crude cellulase was produced, and the conditions of saturation and pH by salting out with ammonium sulfate were optimized. Under optimal conditions, crude cellulase was isolated and purified. The pure cellulase was modified by excess methanol, and it was found that the carboxyl in the side-chain radical of cellulase proved to be the catalytic functional group by analysis of the infrared spectrum of modification of cellulase. Modification of cellulase with different concentrations of methanol was carried out and results show that the modified side-chain radical lies at the active site of cellulase or on essential groups. Sodium carboxymethyl cellulose (CMC-Na) which protected the cellulase from inactivation by methanol indicated that the carboxyl modified by methanol is not only a structural radical but also lies at the active site. The inactivation degree of cellulase modified by methanol could be decreased by glucose and it showed that the modification occurred in the active site of cellulase. The kinetic analysis according to Keech and Farrant equation demonstrated that one carboxyl was an essential group for cellulase activity. Keywords: Chemical modification, cellulase, methanol, carboxyl

A trifluoroacetic acid adduct of a trifluoroacetate-bridged μ4-oxo-tetranuclear zinc cluster, Zn4(OCOCF3)6O·CF3CO2H: synthesis under mild conditions and catalytic transesterification and oxazoline formation

Synthesis of a trifluoroacetate-bridged tetranuclear zinc cluster and its trifluoroacetic acid (TFA) adduct under mild conditions (∼110 °C) was achieved. The catalytic activity and functional group tolerance of the TFA adduct in transesterification and oxazoline formation were almost identical to those of the original zinc cluster.