Showing papers on "Substrate (chemistry) published in 2014"

Nitrogen and Oxygen Dual‐Doped Carbon Hydrogel Film as a Substrate‐Free Electrode for Highly Efficient Oxygen Evolution Reaction

Abstract: A three-dimensional (3D) electrode composed of nitrogen, oxygen dualdoped graphene-carbon nanotube hydrogel film is fabricated, which greatly favors the transport and access of gas and reaction intermediates, and shows a remarkable oxygen-evolution catalytic performance in both alkaline and acidic solutions.

Ni-Catalyzed Carboxylation of C(sp2)– and C(sp3)–O Bonds with CO2

Abstract: In recent years a significant progress has been made for the carboxylation of aryl and benzyl halides with CO2, becoming convenient alternatives to the use of stoichiometric amounts of well-defined metal species. Still, however, most of these processes require the use of pyrophoric and air-sensitive reagents and the current methods are mostly restricted to organic halides. Therefore, the discovery of a mild, operationally simple alternate carboxylation that occurs with a wide substrate scope employing readily available coupling partners will be highly desirable. Herein, we report a new protocol that deals with the development of a synergistic activation of CO2 and a rather challenging activation of inert C(sp2)–O and C(sp3)–O bonds derived from simple and cheap alcohols, a previously unrecognized opportunity in this field. This unprecedented carboxylation event is characterized by its simplicity, mild reaction conditions, remarkable selectivity pattern and an excellent chemoselectivity profile using air-,...

Gold nanostar substrates for SERS-based chemical sensing in the femtomolar regime

Abstract: We report a novel approach for fabricating gold nanostar-functionalized substrates for highly sensitive surface enhanced Raman spectroscopy (SERS)-based chemical sensing. Gold nanostars immobilized on a gold substrate via a Raman silent organic tether serve as the SERS substrate, and facilitate the chemical sensing of analytes that can either be chemisorbed or physisorbed on the nanostars. Our SERS substrates are capable of detecting chemisorbed 4-mercaptobenzoic acid at a concentration as low as 10 fM with a reproducible SERS enhancement factor of 109, and enable the semi-quantitative multiplexed identification of analytes from mixtures in which they have been dissolved in variable stoichiometry. Most importantly, they afford the detection of physisorbed analytes, such as crystal violet, with an excellent signal-to-noise ratio, hence serving as a versatile platform for the chemical identification of in principle any molecular analyte. These characteristics make a strong case for the use of our nanostar-based SERS substrate in practical chemical sensing applications.

Substrate factors that influence the synergistic interaction of AA9 and cellulases during the enzymatic hydrolysis of biomass

Abstract: The polysaccharide monooxygenase enzyme AA9 (formerly known as GH61) was shown to interact synergistically with cellulases to enhance the enzymatic hydrolysis of a range of “commercially-relevant” pretreated and “model” cellulosic substrates. Although an exogenous source of reducing power was required when AA9 was added with cellulases to a “pure” cellulosic substrate, it was not required when added to pretreated lignocellulosic substrates. It appears that the non-cellulosic components such as soluble components, lignin, and possibly hemicellulose, can all act as AA9 reducing cofactor. Of the various substrate characteristics that influenced the efficacy of the enzyme mixture, the relative amount of accessible crystalline cellulose, assessed by the specific cellulose binding module (CBM), appeared to be the most critical. Cellulases and AA9 acted synergistically when hydrolysing cellulose I but it did not occur during the hydrolysis of cellulose II and III.

Electrocatalytic Oxygen Evolution on Iridium Oxide: Uncovering Catalyst-Substrate Interactions and Active Iridium Oxide Species

Abstract: The morphology, crystallinity, and chemical state of well-defined Ir oxide nanoscale thin-film catalysts prepared on Ti substrates at various calcination temperatures were investigated. Special emphasis was placed on the calcination temperature-dependent interaction between Ir oxide film and Ti substrate and its impact on the electrocatalytic oxygen evolution reaction (OER) activity. The Ir oxide films were characterized by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammetry. Furthermore, temperature programmed reduction was applied to study the Ir oxide species formed as a function of calcination temperature and its interaction with the Ti substrate. A previously unachieved correlation between the electrocatalytic OER activity and the nature and structural properties of the Ir oxide film was established. We find that the crystalline high temperature Ir oxide species is detrimental, whereas low temperature amorphous Ir oxy-hydroxides are highly active and efficient catalysts for the OER. Moreover, at the highest applied calcination temperature (550◦C), Ti oxides, originating from the substrate, strongly affect chemical state and electrocatalytic OER activity of the Ir oxide film. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0411409jes] All rights reserved.

Beyond the active site: the impact of the outer coordination sphere on electrocatalysts for hydrogen production and oxidation.

Abstract: ConspectusRedox active metalloenzymes play a major role in energy transformation reactions in biological systems. Examples include formate dehydrogenases, nitrogenases, CO dehydrogenase, and hydrogenases. Many of these reactions are also of interest to humans as potential energy storage or utilization reactions for photoelectrochemical, electrolytic, and fuel cell applications. These metalloenzymes consist of redox active metal centers where substrates are activated and undergo transformation to products accompanied by electron and proton transfer to or from the substrate. These active sites are typically buried deep within a protein matrix of the enzyme with channels for proton transport, electron transport, and substrate/product transport between the active site and the surface of the protein. In addition, there are amino acid residues that lie in close proximity to the active site that are thought to play important roles in regulating and enhancing enzyme activity. Directly studying the outer coordinat...

Film deposition method

Abstract: A film deposition method, in which a film of a reaction product of a first reaction gas, which tends to be adsorbed onto hydroxyl radicals, and a second reaction gas capable of reacting with the first reaction gas is formed on a substrate provided with a concave portion, includes a step of controlling an adsorption distribution of the hydroxyl radicals in a depth direction in the concave portion of the substrate; a step of supplying the first reaction gas on the substrate onto which the hydroxyl radicals are adsorbed; and a step of supplying the second reaction gas on the substrate onto which the first reaction gas is adsorbed.

Methods Of Etching Films Comprising Transition Metals

Abstract: Provided are methods for etching films comprising transition metals. Certain methods involve activating a substrate surface comprising at least one transition metal, wherein activation of the substrate surface comprises exposing the substrate surface to heat, a plasma, an oxidizing environment, or a halide transfer agent to provide an activated substrate surface; and exposing the activated substrate surface to a reagent comprising a Lewis base or pi acid to provide a vapor phase coordination complex comprising one or more atoms of the transition metal coordinated to one or more ligands from the reagent. Certain other methods provide selective etching from a multi-layer substrate comprising two or more of a layer of Co, a layer of Cu and a layer of Ni.

Amide Functionalized Microporous Organic Polymer (Am-MOP) for Selective CO2 Sorption and Catalysis

Abstract: We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (CONH) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N-2, Ar, and O-2. The CO2 molecule interacts with amide functional groups via Lewis acid base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.

Plasmon‐Assisted Water Splitting Using Two Sides of the Same SrTiO3 Single‐Crystal Substrate: Conversion of Visible Light to Chemical Energy

Abstract: A plasmon-induced water splitting system that operates under irradiation by visible light was successfully developed; the system is based on the use of both sides of the same strontium titanate (SrTiO3) single-crystal substrate. The water splitting system contains two solution chambers to separate hydrogen (H2) and oxygen (O2). To promote water splitting, a chemical bias was applied by regulating the pH values of the chambers. The quantity of H2 evolved from the surface of platinum, which was used as a reduction co-catalyst, was twice the quantity of O2 evolved from an Au-nanostructured surface. Thus, the stoichiometric evolution of H2 and O2 was clearly demonstrated. The hydrogen-evolution action spectrum closely corresponds to the plasmon resonance spectrum, indicating that the plasmon-induced charge separation at the Au/SrTiO3 interface promotes water oxidation and the subsequent reduction of a proton on the backside of the SrTiO3 substrate. The chemical bias is significantly reduced by plasmonic effects, which indicates the possibility of constructing an artificial photosynthesis system with low energy consumption.

Enhancing Tolerance to Short-Chain Alcohols by Engineering the Escherichia coli AcrB Efflux Pump to Secrete the Non-native Substrate n-Butanol

Abstract: The microbial conversion of sugars to fuels is a promising technology, but the byproducts of biomass pretreatment processes and the fuels themselves are often toxic at industrially relevant levels. One promising solution to these problems is to engineer efflux pumps to secrete fuels and inhibitory chemicals from the cell, increasing microbial tolerance and enabling higher fuel titer. Toward that end, we used a directed evolution strategy to generate variants of the Escherichia coli AcrB efflux pump that act on the non-native substrate n-butanol, enhancing growth rates of E. coli in the presence of this biofuel by up to 25%. Furthermore, these variants confer improved tolerance to isobutanol and straight-chain alcohols up to n-heptanol. Single amino acid changes in AcrB responsible for this phenotype were identified. We have also shown that both the chemical and genetic inactivation of pump activity eliminate the tolerance conferred by AcrB pump variants, supporting our assertion that the variants secrete ...

Oxidizing capacity of periodate activated with iron-based bimetallic nanoparticles.

Abstract: Nanosized zerovalent iron (nFe0) loaded with a secondary metal such as Ni or Cu on its surface was demonstrated to effectively activate periodate (IO4-) and degrade selected organic compounds at neutral pH. The degradation was accompanied by a stoichiometric conversion of IO4- to iodate (IO3-). nFe0 without bimetallic loading led to similar IO4- reduction but no organic degradation, suggesting the production of reactive iodine intermediate only when IO4- is activated by bimetallic nFe0 (e.g., nFe0-Ni and nFe0-Cu). The organic degradation kinetics in the nFe0-Ni(or Cu)/IO4- system was substrate dependent: 4-chlorophenol, phenol, and bisphenol A were effectively degraded, whereas little or no degradation was observed with benzoic acid, carbamazepine, and 2,4,6-trichlorophenol. The substrate specificity, further confirmed by little kinetic inhibition with background organic matter, implies the selective nature of oxidant in the nFe0-Ni(or Cu)/IO4- system. The comparison with the photoactivated IO4- system, in which iodyl radical (IO3•) is a predominant oxidant in the presence of methanol, suggests IO3• also as primary oxidant in the nFe0-Ni(or Cu)/IO4- system.

Immobilization of Horseradish Peroxidase on NH2-Modified Magnetic Fe3O4/SiO2 Particles and Its Application in Removal of 2,4-Dichlorophenol

Abstract: Fe3O4 nanoparticles were prepared by a co-precipitation method with the assistance of ultrasound irradiation, and then coated with silica generated by hydrolysis and condensation of tetraethoxysilane. The silica-coated Fe3O4 nanoparticles were further modified with 3-aminopropyltriethoxysilane, resulting in anchoring of primary amine groups on the surface of the particles. Horseradish peroxidase (HRP) was then immobilized on the magnetic core-shell particles by using glutaraldehyde as a crosslinking agent. Immobilization conditions were optimized to obtain the highest relative activity of the immobilized enzyme. It was found the durability of the immobilized enzyme to heating and pH variation were improved in comparison with free HRP. The apparent Michaelis constants of the immobilized HRP and free HRP with substrate were compared, showing that the enzyme activity of the immobilized HRP was close to that of free HRP. The HRP immobilized particles, as an enzyme catalyst, were used to activate H2O2 for degrading 2,4-dichlorophenol. The rapid degradation of 2,4-dichlorophenol indicated that the immobilized enzyme has potential applications for removing organic pollutants.

Chemotactic separation of enzymes.

Abstract: We demonstrate a procedure for the separation of enzymes based on their chemotactic response toward an imposed substrate concentration gradient. The separation is observed within a two-inlet, five-outlet microfluidic network, designed to allow mixtures of active (ones that catalyze substrate turnover) and inactive (ones that do not catalyze substrate turnover) enzymes, labeled with different fluorophores, to flow through one of the inlets. Substrate solution prepared in phosphate buffer was introduced through the other inlet of the device at the same flow rate. The steady-state concentration profiles of the enzymes were obtained at specific positions within the outlets of the microchannel using fluorescence microscopy. In the presence of a substrate concentration gradient, active enzyme molecules migrated preferentially toward the substrate channel. The excess migration of the active enzyme molecules was quantified in terms of an enrichment coefficient. Experiments were carried out with different pairs of...

The exometabolome of Clostridium thermocellum reveals overflow metabolism at high cellulose loading

Abstract: Background: Clostridium thermocellum is a model thermophilic organism for the production of biofuels from lignocellulosic substrates. The majority of publications studying the physiology of this organism use substrate concentrations of ≤10 g/L. However, industrially relevant concentrations of substrate start at 100 g/L carbohydrate, which corresponds to approximately 150 g/L solids. To gain insight into the physiology of fermentation of high substrate concentrations, we studied the growth on, and utilization of high concentrations of crystalline cellulose varying from 50 to 100 g/L by C. thermocellum. Results: Using a defined medium, batch cultures of C. thermocellum achieved 93% conversion of cellulose (Avicel) initially present at 100 g/L. The maximum rate of substrate utilization increased with increasing substrate loading. During fermentation of 100 g/L cellulose, growth ceased when about half of the substrate had been solubilized. However, fermentation continued in an uncoupled mode until substrate utilization was almost complete. In addition to commonly reported fermentation products, amino acids - predominantly L-valine and L-alanine - were secreted at concentrations up to 7.5 g/L. Uncoupled metabolism was also accompanied by products not documented previously for C. thermocellum, including isobutanol, meso- and RR/SS-2,3-butanediol and trace amounts of 3-methyl-1-butanol, 2-methyl-1-butanol and 1-propanol. We hypothesize that C. thermocellum uses overflow metabolism to balance its metabolism around the pyruvate node in glycolysis. Conclusions: C. thermocellum is able to utilize industrially relevant concentrations of cellulose, up to 93 g/L. We report here one of the highest degrees of crystalline cellulose utilization observed thus far for a pure culture of C. thermocellum, the highest maximum substrate utilization rate and the highest amount of isobutanol produced by a wild-type organism.

Intrinsic peroxidase-like activity of mesoporous nickel oxide for selective cysteine sensing

Abstract: Mesoporous nickel oxide nanoflowers (NiO NFs) can be easily synthesized by a two-step synthetic procedure based on modified hydrothermal (MHT) treatment of nickel acetate and ethanol amine in water followed by thermal decomposition at 350 °C for 4 h. After thermal treatment, the porosity is increased by 18% with retention of parental nickel hydroxide size. In this study, for the first time, a new catalytic application of NiO NFs has been revealed in terms of peroxidase-like activity where colorless 3,3′,5,5′ tetramethylbenzidine (TMB) is oxidized to blue color product in the presence of H2O2 at room temperature. Comparative study confirms that mesoporous NiO NFs exhibit superior catalytic activity to the parent analogues, i.e. Ni(OH)2 or bulk NiO. This intrinsic peroxidase-like activity from an easily synthesized inorganic nanomaterial provides an alternative to horseradish peroxidase (HRP) enzyme. The lower Michaelis constant (Km) value indicates that the catalyst NiO NFs bind efficiently to the test substrate, i.e. TMB. Interestingly, the NiO NFs-catalyzed TMB oxidation, i.e. blue color formation, has been found to be selectively and successively inhibited by a variable amount of cysteine among a set of 21 congeners. Thus our adopted simple, low-cost and novel colorimetric assay stands to be a highly efficient approach for selective detection of cysteine with a limit of detection (LOD) value of ∼1.1 μM using a simple UV-vis spectrophotometer. The proposed method also exhibits outstanding selectivity and accuracy for N-acetyl cysteine (an analogue of cysteine) estimation in real pharmaceutical samples.

Enzyme Kinetics: The Steady-State Approach

Abstract: One-substrate kinetics.- Inhibitors, activators and inactivators.- pH effects.- More than one substrate.- The King and Altman procedure.- Non-linear kinetics and the concept of allosteric interaction.

Enantiotopos-selective C-H oxygenation catalyzed by a supramolecular ruthenium complex.

Abstract: Spirocyclic oxindoles undergo an enantioselective oxygenation reaction (nine examples; e.r. up to 97:3) upon catalysis by a chiral ruthenium porphyrin complex (1 mol %). The catalyst exhibits a lactam ring, which is responsible for substrate association through hydrogen bonds, and an active ruthenium center, which is in a defined spatial relationship to the oxygenation substrate. DFT calculations illustrate the perfect alignment of the active site with the reactive C-H bond and suggest--in line with the kinetic isotope effect--an oxygen rebound mechanism for the reaction.

Three-dimensional interconnected network of nanoporous CoP nanowires as an efficient hydrogen evolution cathode

Abstract: For the first time we demonstrate the topotactic synthesis of a three-dimensional (3D) interconnected network of nanoporous CoP nanowires directly on a Ti substrate (np-CoP NWs/Ti) via low-temperature phosphidation of a Co2(OH)2(CO3)2/Ti precursor and its further use as a highly efficient hydrogen evolution cathode.

Borylation of Propargylic Substrates by Bimetallic Catalysis. Synthesis of Allenyl, Propargylic, and Butadienyl Bpin Derivatives

Abstract: Bimetallic Pd/Cu and Pd/Ag catalytic systems were used for borylation of propargylic alcohol derivatives. The substrate scope includes even terminal alkynes. The reactions proceed stererospecifically with formal SN2′ pathways to give allenyl boronates. Opening of propargyl epoxides leads to 1,2-diborylated butadienes probably via en allenylboronate intermediate.

A D-psicose 3-epimerase with neutral pH optimum from Clostridium bolteae for D-psicose production: cloning, expression, purification, and characterization.

Abstract: d-Tagatose 3-epimerase family enzymes can efficiently catalyze the epimerization of free keto-sugars, which could be used for d-psicose production from d-fructose. In previous studies, all optimum pH values of these enzymes were found to be alkaline. In this study, a d-psicose 3-epimerase (DPEase) with neutral pH optimum from Clostridium bolteae (ATCC BAA-613) was identified and characterized. The gene encoding the recombinant DPEase was cloned and expressed in Escherichia coli. In order to characterize the catalytic properties, the recombinant DPEase was purified to electrophoretic homogeneity using nickel-affinity chromatography. Ethylenediaminetetraacetic acid was shown to inhibit the enzyme activity completely; therefore, the enzyme was identified as a metalloprotein that exhibited the highest activity in the presence of Co2+. Although the DPEase demonstrated the most activity at a pH ranging from 6.5 to 7.5, it exhibited optimal activity at pH 7.0. The optimal temperature for the recombinant DPEase was 55 °C, and the half-life was 156 min at 55 °C. Using d-psicose as the substrate, the apparent K m, k cat, and catalytic efficiency (k cat/K m) were 27.4 mM, 49 s−1, and 1.78 s−1 mM−1, respectively. Under the optimal conditions, the equilibrium ratio of d-fructose to d-psicose was 69:31. For high production of d-psicose, 216 g/L d-psicose could be produced with 28.8 % turnover yield at pH 6.5 and 55 °C. The recombinant DPEase exhibited weak-acid stability and thermostability and had a high affinity and turnover for the substrate d-fructose, indicating that the enzyme was a potential d-psicose producer for industrial production.