Equal Catalytic Activity Research Articles

Preparation of Pt/CNT catalyst with high dispersion structure via plasma jet

A plasma jet (a high temperature jet formed by blowing a free arc through high pressure air) method based on free arc was carried out to disperse carbon nanotubes (CNTs) in gas phase while generating Pt nanoparticles (Pt-NPs) on them at the same time. The plasma jet is generated through the discharge between the cathode composed of CNTs, PtCl4 and DI water and the anode with a hole. Plasma jet prepares the Pt/CNT catalyst by directly spraying. The CNT carrier in the catalyst have good dispersion by SEM images. The mean size of Pt-NPs estimated by TEM images is 3.41 nm with the plasma jet method and about 4.77 nm with the commercial Pt/C respectively. It was showed that the bulk of Pt-NPs produced by plasma jet is in metal state in the analysis of XPS measurements. Compared with Pt/C, Pt/CNT have roughly equal catalytic activity and higher durability by cyclic voltammetry measurements. Based on these properties, the plasma injection method solves the problems of carrier dispersion and metal particle preparation at the same time, which greatly simplifies the catalyst preparation process.

Divalent metal activation of a GH43 β-xylosidase

Depolymerization of xylan, a major fraction of lignocellulosic biomass, releases xylose which can be converted into transportation fuels and chemical feedstocks. A requisite enzyme for the breakdown of xylan is β-xylosidase. A gene encoding the 324-amino acid β-xylosidase, RS223-BX, was cloned from an anaerobic mixed microbial culture. This glycoside hydrolase belongs to family 43. Unlike other GH43 enzymes, RS223-BX can be strongly activated by exogenously supplied Ca2+, Co2+, Fe2+, Mg2+, Mn2+ and Ni2+ (e.g., 28-fold by Mg2+) and it is inhibited by Cu2+ or Zn2+. Sedimentation equilibrium centrifugation experiments indicated that the divalent metal cations mediate multimerization of the enzyme from a dimeric to a tetrameric state, which have equal catalytic activity on an active-site basis. Compared to the determined active sites of other GH43 β-xylosidases, the predicted active site of RS223-BX contains two additional amino acids with carboxylated side chains that provide potential sites for divalent metal cations to reside. Thus, the divalent metal cations likely occupy the active site and participate in the catalytic mechanism. RS223-BX accepts as substrate xylobiose, arabinobiose, 4-nitrophenyl-β-d-xylopyranoside, and 4-nitrophenyl-α-l-arabinofuranoside. Additionally, the enzyme has good pH and temperature stabilities and a large Ki for d-glucose (1.3M), favorable properties for performance in saccharification reactors.

Ammoximation of Cyclohexanone to Cyclohexanone Oxime Catalyzed by Titanium Silicalite-1 Zeolite in Three-phase System

An innovative green process of producing ɛ-caprolactam was proposed by integrating ammoximation and Beckmann rearrangement effectively. As a first part of the new process, TS-1 molecular sieve-catalyzed synthesis of cyclohexanone oxime from cyclohexanone, ammonia and hydrogen peroxide was carried out in a batch plant. Cyclohexane was used as the solvent in the three-phase reaction system. The influences of essential process parameters on ammoximation were investigated. Under the reaction conditions as catalyst content of 2.5% (by mass); H2O2/yclohexanone molar ratio of 1.10; NH3/cyclohexanone molar ratio of 2.20; reaction temperature of 343 K; reaction time of 5 h, high conversion of cyclohexanone and selectivity to oxime (both>99%) were obtained. Thus, the three-phase ammoximation process showed equal catalytic activity as TS-1 but much more convenient and simpler for the separation of catalyst in comparison to the industrial two-phase system with t-butanol used as solvent.

Preparation of cyclodextrin-based carbonaceous catalyst and its application in the esterification

A new carbonaceous catalyst with sulfonic acid group (-SO3H) was prepared by incomplete carbonization of β-cyclodextrin followed by sulfonation. The sulfonated amorphous carbon was characterized by IR, elemental analysis, DSC-TGA and PXRD, and the catalytic activity was investigated to be an efficient catalyst for the esterification reactions with maximum yield of 87%. The sulfonated carbonaceous catalyst was readily separated from the reaction solution and keeps approximately equal catalytic activity. The results confirm that the active centre is the hydrophilic sulfonic acid functional group in the esterification reactions.

Rnai Activity of Sirnas Modified with 2′-Aminoalkyl-Substituted Fluorinated Nucleobases

We recently reported that a 1′-deoxy-1′-(4,6-difluoro-1H-benzimidazol-1-yl)-2′-(β-aminoethyl)-β-d-ribofuranose nucleoside appears to be a universal nucleoside which does not differentiate between the four natural nucleosides A, C, G, and U in duplexes. Moreover, ribozymes modified with this nucleoside analog showed a better or at least equal catalytic activity relative to Watson-Crick mismatches.[ 1 ] Due to these data, we investigated the ability of this compound to tolerate Watson-Crick mismatches in order to avoid HIV escape mutations in RNA interference. The influence of this nucleoside analog on siRNA efficiency was analyzed with a proven siRNA targeting GFP.

The role of functionalized phosphines in the hydrogenation of carboxylic acids in the presence of phosphine substituted hydrido ruthenium complexes

Hydrido ruthenium carbonyl complexes substituted by functionalized phosphines such as H4Ru4(CO)8[P(CH2OCOR)3]4 have been synthesized and tested as catalysts in the hydrogenation of carboxylic acids. These complexes are more active than those reported previously, containing trialkyl- or triarylphosphines. On the basis of their behavior, their different activity has been explained in terms of an involvement of the phosphine ligand in the catalytic cycle. The ester group present in the phosphine P(CH2OCOR)3 is hydrogenated to produce an alcohol (RCH2OH) and a P(CH2OH) group which, in turn, reacts with the free acid present in solution to restore the P(CH2OCOR) group. This hypothesis has been confirmed by the reactivity of the possible intermediate H4Ru4(CO)8[P(CH2OH)3]4 with acetic acid. Another support to this statement is the almost equal catalytic activity, displayed by H4Ru4(CO)8[P(CH2OCOR)3]4 complexes, whatever the R group present, in the phosphine ligand, in the hydrogenation of carboxylic acids. These complexes, on the other hand, are less active than the corresponding tributylphosphine substituted ones in the hydrogenation of alkenes and ketones. Finally when the phosphine ligand is P(CH2CH2COOCH3)3 the ester group is not reduced and consequently the catalytic activity of this complex in the hydrogenation of carboxylic acids is very low.

Comparison of the catalytic activity of Ziegler-type catalysts based on Cp2ZrCl2 and (Cp2ZrCl)2O

The rates of ethylene polymerization catalyzed by Cp2ZrCl2-polymethylalumoxane and (Cp2ZrCl)2O-polymethylalumoxane are equal. According to NMR and ESR spectral data, the same precatalyst, presumably Cp2ZrMe2, is formed in both systems by the action of AlMe3. This accounts for the equal catalytic activity of the systems based on Cp2ZrCl2 and (Cp2ZrCl)2O. A scheme of reactions resulting in cleavage of the Zr-O-Zr bridge is proposed and confirmed by spectroscopic data.

Purification and properties of an 8-hydroxy-5-deazaflavin-reducing hydrogenase from Methanobacterium thermoautotrophicum.

A coenzyme F430-reducing hydrogenase from Methanobacterium thermoautotrophicum has been purified 25-fold, to approximately 50% homogeneity. Following anaerobic preincubation in high salt under reducing conditions, the purified enzyme exhibits equal catalytic activity (turnover number = 725 s-1) toward the artificial 1-electron acceptor, methyl viologen, and the physiological 2-electron acceptor, 7,8-didemethyl-8-hydroxy-5-deazaflavin (F420). The enzyme had the following Km values (micromolarity) under the described assay conditions: 420 (methyl viologen, pH 9.0), 19 (F420, pH 7.2), 34 (Fo, 7.8-didemethyl-8-hydroxy-5-deazariboflavin, pH 7.2), 10 (H2, Fo as co-substrate, pH 7.2), 2 (H2, methyl viologen as co-substrate, pH 9.0). The native protein is oligomeric (apparent Mr greater than 500,000) and is composed of three distinct subunits with Mr - 40,000, 31,000, and 26,000 in the ratio of 2:2:1, leading to a minimum Mr = 170,000. In addition to 33 atoms of Fe and 24 atoms of acid-labile sulfur, the F420-hydrogenase contains 2.3 mol of FAD/mol of Mr - 170,000. This activity is chromatographically distinct from a smaller methanogen hydrogenase capable of rapid viologen reduction, but which only very slowly reduces 5-deazariboflavins.

Evidence for two-domain subunit structure of kidney lipoate acetyltransferase

1. Introduction Earlier studies on the inactivation of the mamma- lian pyruvate dehydrogenase (EC 1.2.4.1 f complex (PHD complex) by a thiol protease from rat liver [I] had shown that the lipoate acetyltransferase (EC 2.3.1 .12) was cleaved into two smaller fragments detectable on SDS-polyacryla~de gel electrophoresis [ 1,2]. Here we have studied the subunit structure of kidney lipoate acetyitransferase using trypsin (EC 3.4.21.4) which was found to yield also twa fragments with app. mol. wt 36 000 and 28 000. As will be shown here both fragments possess about equal catalytic activity for acetyl transfer, and each appar- ently contains p~ote~-bound lipoamide ~~est~g that the subunit of the mammalian lipoate acetyltransferase consists of two homologous if not identical domains. 2, Mate&Is and methods Bovine kidney pyruvate dehydrogenase complex (spec. act. 16-20 units/mg protein) was prepared by poly(ethylene glycol) precipitation [2] with some mo~~ca~ons to be detailed elsewhere. Lipoaie ace- tyltransferase was resolved according to [Z]. Marker proteins for molecular weight determination (LMW nrotein standards) were from Bio-Rad Labs., CA and poly(ethylene glycol) 6000 from Serva, Heidelberg. Bovine pancreatic trypsin (30 U/m&, other enzymes or eoenzymes came from ~oe~~ger~ Manner. Radiochemicals were purchased from New England Nuclear, Chicago. Laboratory chemicals, analytical grade, were from Merck,

Formate Dehydrogenase

Formate dehydrogenase (EC 1.2.1.2) prepared from peas (Pisum sativum) was a two-subunit enzyme. The enzyme accelerated the formation of an NAD+-cyanide compound having an adsorption band at 330 nm. The enzyme was able to bind one NAD+ molecule per each subunit but only 1 mole of NAD+-cyanide compound was formed per two subunits. The complex of NAD+, cyanide, and the enzyme was very stable and had no catalytic activity. Azide inhibited the formate dehydrogenase reaction in two different ways. By incubation of the enzyme with azide in the presence of NAD+, half of its catalytic activity was lost. The remaining activity was also inhibited by azide but this inhibition was removed competively by formate. Contrary to the case of cyanide the inhibition by azide could be removed by dialysis and no spectral species due to the addition compound of NAD+ and azide could be observed. The data from double recipricol plots of the initial velocity and the formate concentration led to a conclusion that formate dehydrogenase has two sites with about equal catalytic activity. The Km for formate was different for the two catalytic sites (1.67 and 6.25 mM) but the difference was not noticeable in the case of the Km for NAD+.

Catalytic Synthesis of Acetonitrile in Fluidized Bed. I

A method of preparation of alumina catalyst suitable for the synthesis of acetonitrile from acetylene and ammonia in fluidized bed and the activity of the catalyst was investigated. A quartz reaction tube of the diameter 1.5 inch was used and the grain size of the catalyst was 100-200 mesh. Under a definite fluidized synthetic condition, nearly equal catalytic activity was obtained in spite of the differences in the method of preparation of alumina, and when the catalyst prepared by addition of 3-4 wt% of Na2CO3 according to Murakami, Shiba etc, was used, the side reaction such as formation of pyridine base and hydrogen cyanide and another decomposition reaction was prevented, the selectivity for acetonitrile being increased. The activity of two kinds of alumina catalyst prepared by addition of alkali before or after calcining of aluminum hydroxide became nearly equal after repetition of reaction. This can explaine well that the effective site of activity for synthesis of acetonitrile is on the outer surfaceof the catalyst. The regeneration of catalyst prepared by addition of optimum amount of sodium carbonate is made easily by treatment with air at the same temperature range as at the synthesis.