Successive Reaction Cycles Research Articles

Co-production of tannase and pectinase by free and immobilized cells of the yeast Rhodotorula glutinis MP-10 isolated from tannin-rich persimmon (Diospyros kaki L.) fruits

Hyper tannase and pectinase-producing yeast Rhodotorula glutinis MP-10 was isolated from persimmon (Diospyros kaki L.) fruits. The main pectinase activity of yeast was exo-polygalacturonase. No pectin methyl esterase and too low pectin lyase activities were detected for this yeast. The maximum exo-activities of tannase and polygalacturonase were determined as 15.2 and 26.9 U/mL for free cells and 19.8 and 28.6 U/mL for immobilized cells, respectively. Immobilized cells could be reused in 13 successive reaction cycles without any loss in the maximum tannase and polygalacturonase activities. Besides, too little decreases in activities of these enzymes were recorded between 14 and 18 cycles. At the end of 18 successive reaction cycles, total 503.1 U/mL of polygalacturonase and 349.6 U/mL of tannase could be produced using the same immobilized cells. This is the first report on the use of free and/or immobilized cells of a microorganism for the co-production of tannase and pectinase.

Hydrogen by glycerol steam reforming on a nickel–alumina catalyst: Deactivation processes and regeneration

Hydrogen energy has attracted considerable attention because of its efficiency and environmental benefits, and the increasing demand requires finding renewable sources of raw materials to produce it. Glycerol, by-product of biodiesel production and coming from renewable raw materials, could be a bio-renewable substrate to produce hydrogen. The glycerol steam reforming to obtain hydrogen was evaluated using a 5.1 wt% Ni impregnated on Al2O3 catalyst, characterized by nitrogen adsorption, XRD, and FTIR. Deactivation processes were analyzed in successive cycles of reaction at 700 °C, atmospheric pressure, 5 h−1 WHSV, and 3:1 water:glycerol molar ratio, during 12 h. Between reaction cycles, regenerating took place using a He/Air stream. Hydrogen was the main product on the fresh catalyst, following by CO and CH4; during reaction, carbonaceous deposits deactivated catalyst, decreasing H2 and increasing both CO and CH4. Carbonaceous deposits were characterized by TPO, showing a main peak centered at 690 °C; the carbon content reached 11.9%.

Carbon-supported Ru and Pd nanoparticles: Efficient and recyclable catalysts for the aerobic oxidation of benzyl alcohol in water

Ru NPs and Pd NPs were firstly synthesized and further supported on mesoporous carbon materials. Spherical and homogenously dispersed MNPs displaying mean sizes in the range 1.2–2.2nm were thus achieved. The catalytic activity as well as the recyclability of these carbon-supported Ru and Pd NPs in the aerobic oxidation of benzyl alcohol to benzaldehyde in water was investigated, showing excellent conversions and high selectivity to the aldehyde. The selectivity towards aldehyde is particularly relevant since usually the oxidation of primary alcohols in water mainly yields the carboxylic acid. Moreover, these nanocatalysts present good recyclability in terms of conversion with up to eight successive reaction cycles. However, the selectivity to the aldehyde decreased, in some cases significantly, after the third cycle. The catalytic activity of these systems was found to be influenced by the hydrophilicity of the carbon support surface. However, the significance of this influence depends on the ligand used to stabilize the MNPs.

A universal pathway for kinesin stepping

Kinesin-1 is an ATP-driven, processive motor that transports cargo along microtubules in a tightly regulated stepping cycle. Efficient gating mechanisms ensure that the sequence of kinetic events proceeds in proper order, generating a large number of successive reaction cycles. To study gating, we created two mutant constructs with extended neck-linkers and measured their properties using single-molecule optical trapping and ensemble fluorescence techniques. Due to a reduction in the inter-head tension, the constructs access an otherwise rarely populated conformational state where both motor heads remain bound to the microtubule. ATP-dependent, processive backstepping and futile hydrolysis were observed under moderate hindering loads. Based on measurements, we formulated a comprehensive model for kinesin motion that incorporates reaction pathways for both forward and backward stepping. In addition to inter-head tension, we find that neck-linker orientation is also responsible for ensuring gating in kinesin.

Heterogeneous catalyst based on peroxo-niobium complexes immobilized over iron oxide for organic oxidation in water

Nb-doped iron oxides were used as heterogeneous catalyst to oxidize organic compounds in aqueous medium containing hydrogen peroxide. XRD data reveal that the composites contain hematite (α-Fe2O3), maghemite (γ-Fe2O3) and FeNb2O6. The H2O2 pretreatment of the solid catalyst promotes important surface and structural changes of the iron oxides mainly by peroxo-niobium complexes formation, which expressively enhances the catalytic properties of the composite. Transmission electron microscopy images show that the H2O2-treatment tends also to decrease the mean particle size of grains of the composite. Nb-doped iron oxides were found to impart an important role to the solid catalyst towards H2O2 reactions. The developed composites were confirmed to have remarkable catalytic activity on the oxidation of organic substrates and can be regenerated for several successive reaction cycles for degrading polluting organic in water.

Kinetics of hydrotalcite catalyzed transesterification of tricaprylin and methanol for biodiesel synthesis

Currently, biodiesel is a well-known alternative diesel fuel that can be derived from transesterification or esterification. This work focused on the transesterification of tricaprylin (TCP) and methanol (MeOH) on solid base hydrotalcite catalyst in order to investigate the reaction kinetics in the temperature range of 60 °C and 120 °C and 15:1 molar ratio of MeOH to TCP in a well-mixed batch reactor. The apparent activation energy obtained over this reaction temperature range was 38.4 kJ/mol. This value was proved to be without the effect from catalyst deactivation and the presence of hexane solvent, as well as the mass transport limitation. The power law rate expression showed that the reaction orders with respect to the TCP and methanol were 0.70 and 1.92, respectively, at 60 °C of reaction temperature while they were 0.54 and 1.10 at 120 °C. An Eley–Rideal mechanism was employed to explain the power law rate expression at 120 °C of reaction temperature. Along with the reactant-catalyst pre-contacting experiment, it can be concluded that the reaction started with methanol adsorption on a single basic site and then the reaction between adsorbed methanol and tricaprylin from liquid phase with surface reaction as the rate determining step. On the other hand, bimolecular pathway was used to explain the reaction mechanism at 60 °C of reaction temperature since the reaction order with respect to methanol was close to 2. In addition, catalyst deactivation was observed when the catalyst was used in two successive reaction cycles, especially after being used at high temperature.

A synergistic effect of microwave irradiation and ionic liquids on enzyme-catalyzed biodiesel production

Under microwave irradiation (MW), an ionic liquid (IL) was used as reaction medium to produce biodiesel (fatty acid methyl ester, FAME) with soybean oil and methanol through transesterification by Novozym 435. [EMIM][PF6] was proved to be a good reaction medium for biodiesel production because the enzyme exhibited excellent transesterification activity in it. Under MW, the enzyme activity in [EMIM][PF6] was about 1.8 folds higher than that in tert-butanol, and under conventional heating, about 1.2 folds higher than that in tert-butanol. Under the optimum conditions (microwave power of 480 W, [EMIM][PF6]/oil volume ratio of 2 : 1, methanol/oil molar ratio of 6 : 1, 6% amount Novozym 435 based on soybean oil weight, water activity of 0.33, agitation speed of 200 rpm, and 60 °C), a 92% yield of FAME was achieved in 6 h in [EMIM][PF6] under MW, whereas the yield of FAME in [EMIM][PF6] without MW and in a solvent-free system with MW was 70% and 28%, respectively. The results suggested that MW and IL might have a synergistic effect on improving enzyme activity. The enhancement of enzyme activity might be that the microwave acted directly on the IL because of its excellent microwave-absorbing ability, which created a compatible system for both the substrate and the product, and prevented the deactivation of enzyme with methanol and glycerol. The introduction of IL in microwave system might also increase the velocity of transacylation, and increase the enzyme activity indirectly. Furthermore, recovered IL and enzyme were used for five successive reaction cycles without any significant loss of enzyme activity.

Levan production using Bacillus subtilis natto cells immobilized on alginate

The immobilization of B. subtilis natto Takahashi on alginate matrix was attempted for repeated production of levan. Factors that influence the stability of the immobilized-cell beads and the levan production in the process of fermentation were also investigated. The levan production and the stability of immobilized beads were greatly affected by the sucrose concentration, medium pH, metal ions and agitation speed. When the immobilized cells were cultivated in the optimal conditions, high levan production (70.6 g/L) was obtained after 3 d of fermentation and no damaged beads were observed. In the repetitive cultivation, the supplement of organic nitrogen source and control of initial pH was critical for high levan production. Immobilized cells on alginate beads were reused in five successive reaction cycles (each cycle 72 h) without any loss of biocatalytic activity and 9 cycles with 72% residual activity.

Xyloglucan xyloglucosyl transferases from barley ( Hordeum vulgare L.) bind oligomeric and polymeric xyloglucan molecules in their acceptor binding sites

Background Xyloglucan xyloglucosyl transferases (EC 2.4.1.207), known as xyloglucan endotransglycosylases (XETs) use a disproportionation reaction mechanism and modulate molecular masses of xyloglucans. However, it is not known precisely how these size modulations and transfer reactions occur with polymeric acceptor substrates. Methods cDNAs encoding three barley HvXETs were expressed in Pichia pastoris and reaction mechanism and molecular properties of HvXETs were investigated. Results Significant differences in catalytic efficiencies ( k cat· K m − 1) were observed and these values were 0.01, 0.02 and 0.2 s − 1·mg − 1·ml for HvXET3, HvXET4 and HvXET6, respectively, using tamarind xyloglucan as a donor substrate. HPLC analyses of the reaction mixtures showed that HvXET6 followed a stochastic reaction mechanism with fluorescently or radioactively labelled tamarind xyloglucans and xyloglucan-derived oligosaccharides. The analyses from two successive reaction cycles revealed that HvXET6 could increase or decrease molecular masses of xyloglucans. In the first reaction cycle equilibrium was reached under limiting donor substrate concentrations, while xyloglucan mass modulations occurred during the second reaction cycle and depended on the molecular masses of incoming acceptors. Deglycosylation experiments indicated that occupancy of a singular N-glycosylation site was required for activity of HvXET6. Experiments with organic solvents demonstrated that HvXET6 tolerated DMSO, glycerol, methanol and 1,4-butanediol in 20% (v/v) concentrations. Conclusions The two-phase experiments demonstrated that large xyloglucan molecules can bind in the acceptor sites of HvXETs. General significance The results characterise donor and acceptor binding sites in plant XET, report that HvXETs act on xyloglucan donor substrates adsorbed onto nanocrystals and that HvXETs tolerate the presence of organic solvents.

A Bayesian Hierarchical Model for Quantitative Real-Time PCR Data

We present a Bayesian hierarchical model for quantitative real-time polymerase chain reaction (PCR) data, aiming at relative quantification of DNA copy number in different biological samples. The model is specified in terms of a hidden Markov model for fluorescence intensities measured at successive cycles of the polymerase chain reaction. The efficiency of the reaction is assumed to depend on the abundance of the target DNA through fluorescence intensities, and the relationship is specified based on the kinetics of the reaction. The model incorporates the intrinsic random nature of the process as well as measurement error. Taking a Bayesian inferential approach, marginal posterior distributions of the quantities of interest are estimated using Markov chain Monte Carlo. The method is applied to simulated data and an experimental data set.

Ionic liquids as a reaction medium for lipase-catalyzed methanolysis of sunflower oil

Ionic liquids, 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIm][PF(6)]) and 1-ethyl-3-methyl imidazolium hexafluorophosphate ([EMIm][PF(6)]), were used for the methanolysis of sunflower oil using Candida antarctica lipase (Novozyme 435) and gave yields of fatty acid methyl esters at 98-99% within 10 h. The optimum conditions of methanolysis in hydrophobic ionic liquids are 2% (w/w) lipase, 1:1 (w/w) oil/ionic liquid and 1:8 (mol/mol) oil/methanol at 58-60 degrees C. Methanolysis using hydrophilic ionic liquids, 3-methyl imidazolium tetrafluoroborate ([HMIm][BF(4)]) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIm][BF(4)]), gave very poor yields. A hydrophobic ionic liquid thus protects the lipase from methanol. Recovered ionic liquids and lipase were used for four successive reaction cycles without any significant loss of activity.

A global kinetic model as a tool to reproduce the deactivation behaviour of the HZSM-5 zeolite in the catalytic cracking of low-density polyethylene

The deactivation behaviour of the HZSM-5 zeolite in the catalytic cracking of LDPE has been analysed. Four important properties of the partly deactivated catalysts have been measured: firstly, the activity of the fresh and partly coked zeolites in the pyrolysis reactions in TG; secondly, the amount of coke deposited on the catalysts after each reaction; thirdly the effect of the coke content of the catalyst on their acid properties and in the fourth place the effect of the coke content on their surface properties. The experimental study of the deactivation behaviour of HZSM-5 during the catalytic cracking of LDPE has permitted a new and simple kinetic model to be developed that takes into account the effect of the coke formation on the catalytic activity decay and the acid and surface properties of the zeolite. The model considered in the present work has been applied to simultaneously correlate the TG data of the successive reaction cycles, the NH3 TPD experimental curves and the nitrogen adsorption isotherms as a function of the amount of coke in the catalyst. Very good correlation results have been obtained, proving that the method suggested allows a quantitative and simultaneous correlation of the global deactivation behaviour of the HZSM-5 in the catalytic cracking of LDPE.

Direct synthesis of acetic acid from CH 4 and CO 2 by a step-wise route over Pd/SiO 2 and Rh/SiO 2 catalysts

The theoretical and experimental feasibility of direct conversion of CH 4 and CO 2 to acetic acid by an isothermal step-wise route over Pd/SiO 2 and Rh/SiO 2 catalysts was investigated. The methyl radical formation from CH 4 dissociation and CO 2 inserting into the intermediate are regarded as two limiting steps. Preliminary experimental results have shown that the following step-wise route can circumvent the thermodynamic limitation of this direct synthesis at low temperatures. Pd catalysts are more active than Rh catalysts at 170 °C and 200 °C, while formic acid is only produced on Pd catalysts. The optimum contact time of CH 4 and CO 2 with catalysts is 1 min under the experimental conditions. And there is no apparent deactivation resulting from carbon deposition for catalysts during the successive reaction cycles.

The activity of chromia-promoted skeletal copper catalysts for the oxidative dehydrogenation of ethanolamine to sodium glycinate based on measurements in a modified autoclave

The activity of promoted and unpromoted skeletal copper catalysts for the oxidative dehydrogenation of ethanolamine to sodium glycinate in strong NaOH solutions has been studied using a modified stirred autoclave that allows the reactants to be brought to the reaction temperature of 160 °C separately prior to mixing. This enables the study of activity and kinetics without complication from partial reaction and catalyst deactivation at lower temperatures. First order plots based on the continuous measurement of hydrogen evolution are close to linear throughout reaction. Unpromoted catalysts show substantial deactivation in repeated experiments but this can be eliminated by pretreatment in NaOH alone at temperatures above that used for reaction. This lowers the initial activity but helps the stability with treatment at 200 °C in 9.7 M NaOH being particularly effective. Small amounts of Cr 2O 3, deposited from sodium chromate included in the NaOH solution used to prepare the catalysts by leaching of a CuAl 2 alloy, are a highly effective promoter. Catalysts containing 1–1.5 wt.% Cr 2O 3, pretreated in 9.7 M at 200 °C, are several times as active as their unpromoted counterparts through the course of six successive reaction cycles. The promoted catalysts exhibit a much higher surface area, which correlates with the retention of aluminium in used catalysts, but the connection to the improved activity is complex.

Kinetic Behavior of the SAPO-18 Catalyst in the Transformation of Methanol into Olefins

Kinetic behavior (production of olefins, selectivity) has been studied in the transformation of methanol into olefins on a catalyst prepared based on SAPO-18 in a fluidized bed reactor, for a wide range of operating conditions (temperature, space time, concentration of methanol in the feed, dilution of methanol with water, time on stream). Under certain conditions, an initiation period is observed, which is in agreement with the “carbon pool mechanism” and whose duration largely depends on the operating conditions and, particularly, on water content in the reaction medium. A study has been carried out on the role of water as an inhibiting agent in the formation of olefins and in coke deposition. The methanol/dimethyl ether ratio is higher than that corresponding to thermodynamic equilibrium under conditions in which the catalyst is active for olefin formation. The hydrothermal stability of SAPO-18 has been proven by using the catalyst in a series of 10 successive cycles of reaction−regeneration.

Activity and Reusability of Sol-Gel Encapsulated -Amylase and Catalase. Performance in Flow-Through Systems

A simple sol-gel procedure, based on the typical tetralkoxysilane-water-HCl reaction mixture, was used for the encapsulation of two enzymes of very different size in silica glasses. Optimization of the initial mixture composition, the hydrolysis time and the gelling and drying conditions led to the preparation of reusable porous biogels that preserved an interesting fraction of the native enzyme activity. Thus, the relative activities of the encapsulated enzymes, with respect to the enzymes in solution, were 20% for α-amylase and up to 57% for catalase. The lower performance of the former was probably due to the slow diffusion of the big substrate molecule (starch) within the gel. In the case of catalase, optimal results were obtained after washing the gel with a Triton X-100 solution; indeed, the surfactant treatment was indispensable to avoid a progressive blocking of the enzyme active sites during repeated uses of the same gel. Both biogels were packed in cartridges and tested during successive reaction cycles. Compared to batch experiments, the flow reactors were capable of transforming a higher substrate amount per unit time and, if appropriately regenerated, a practically constant efficiency was observed from cycle to cycle. These results open the way to envisage the use of the proposed sol-gel procedure for the preparation of different catalytic biogels with possible application in continuous high-throughput reactors.

Reversible Binuclear Cu(II) Complex Formation in a New Sonogel−Cryptand Hybrid Material

New hybrid materials are obtained by embedding Cu(II) complexes of the open-chain triethylenetetraamine ligand (tren) or a related binucleating cryptand containing two tren subunits in sonogel matrixes prepared from tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS). The effectiveness of trapping depends on both the matrix and the nature of the complex. The chemical behavior and textural parameters of the different samples are explained according to a textural model with three different types of sites for trapping. The most promising samples for sensing purposes are TEOS-based silica sonogel matrixes containing the binuclear Cu(II) cryptate, where reversible reactions with small ions (H+, Cu2+, N3-) take place in a way similar to that observed in solution. However, successive reaction cycles lead to the partial loss of the trapped cryptand. Leaching becomes less important when the sonogel is prepared from TEOS and a salt of the protonated cryptand. In this case, the texture of the matrix is more suitable for cryptand trapping, and treatment with solutions containing Cu2+, N3-, or H+ leads to a larger number of reversible complex formation−decomposition processes.

The effect of macromolecular crowding on chaperonin-mediated protein folding.

The cylindrical chaperonin GroEL and its cofactor GroES mediate ATP-dependent protein folding in Escherichia coli. Recent studies in vitro demonstrated that GroES binding to GroEL causes the displacement of unfolded polypeptide into the central volume of the GroEL cavity for folding in a sequestrated environment. Resulting native protein leaves GroEL upon GroES release, whereas incompletely folded polypeptide can be recaptured for structural rearrangement followed by another folding trial. Additionally, each cycle of GroES binding and dissociation is associated with the release of nonnative polypeptide into the bulk solution. Here we show that this loss of substrate from GroEL is prevented when the folding reaction is carried out in the presence of macromolecular crowding agents, such as Ficoll and dextran, or in a dense cytosolic solution. Thus, the release of nonnative polypeptide is not an essential feature of the productive chaperonin mechanism. Our results argue that conditions of excluded volume, thought to prevail in the bacterial cytosol, increase the capacity of the chaperonin to retain nonnative polypeptide throughout successive reaction cycles. We propose that the leakiness of the chaperonin system under physiological conditions is adjusted such that E. coli proteins are likely to complete folding without partitioning between different GroEL complexes. Polypeptides that are unable to fold on GroEL eventually will be transferred to other chaperones or the degradation machinery.

Initial Activity of Reduced Chromia/Alumina Catalyst inn-Butane Dehydrogenation Monitored by On-Line FT–IR Gas Analysis

The initial activity of chromia/alumina catalyst (13 wt% Cr) inn-butane dehydrogenation was studied in a flow reactor at 853 K. The initial activity was determined by on-line FT–IR gas analysis, which enabled sampling of the gaseous product mixture at a time resolution of seconds. The catalysts were processed in repeated cycles of oxidation, reduction, and dehydrogenation usingn-butane, methane, hydrogen, or carbon monoxide as reducing agents. Withn-butane, methane, and hydrogen the dehydrogenation activity was associated with Cr3+species apparently formed in the reduction of high-valence Cr species. The catalyst reduced with carbon monoxide at 853 K showed poor initial selectivity for butenes and, relative to the other catalysts, stronger formation of coke in dehydrogenation. The initial selectivity for butenes increased with time on stream, however, and within 2 min reached the level obtained with the other catalysts. Simultaneous data relating the initial activity, coke content, and some of the physicochemical properties of the catalyst indicated that the surfaces of all catalysts were modified to some extent by the successive reaction cycles.

Influence of cyclic pumped diffusion on the morphology and microstructure of A15 layers in bronze processed multifilamentary wire

The authors have used a novel reaction method called cyclic-pumped diffusion (CPD) to achieve near uniform A15 reaction layers on filaments throughout the cross-section of a multifilamentary composite. A detailed investigation of the spatial variation of the lattice parameter during reaction in filaments and in the bronze matrix has enabled them to optimize the time and temperature for successive reaction cycles. A 61*61 filament Nb-7.5% wt Ta-bronze composite reacted using CPD in the range 600-800 degrees C shows a compound thickness variation between the inner and outer filaments of approximately 30%, while the same composite given a conventional isothermal heat treatment at 700 degrees C shows a corresponding layer thickness variation of approximately 200%. The consequences of the CPD reaction method for the design of composites containing tin reservoirs are discussed. >