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Auteur : Grafiati
Publié le 7 juillet 2024
Mis à jour le 7 juillet 2024

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1

Rajesh, Nimmakuri, et Dipak Prajapati. « Indium(iii) catalysed regio- and stereoselective hydrothiolation of bromoalkynes ». RSC Adv. 4, no 61 (2014) : 32108–12. http://dx.doi.org/10.1039/c4ra04359f.

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Hydrothiolation of bromoalkynes has been reported for the first time under metal catalysed conditions. Indium(iii) trifluoromethanesulfonate was demonstrated as the first catalyst which can catalyse the hydrothiolation of bromoalkynes with absolute regio- and stereoselectivity to generate synthetically valuable (Z)-β-bromo vinyl sulfides in good yields.
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2

Khan, Mohammad Niyaz, et Ibrahim Isah Fagge. « Kinetics and Mechanism of Cationic Micelle/Flexible Nanoparticle Catalysis : A Review ». Progress in Reaction Kinetics and Mechanism 43, no 1 (mars 2018) : 1–20. http://dx.doi.org/10.3184/146867818x15066862094905.

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The aqueous surfactant (Surf) solution at [Surf] > cmc (critical micelle concentration) contains flexible micelles/nanoparticles. These particles form a pseudophase of different shapes and sizes where the medium polarity decreases as the distance increases from the exterior region of the interface of the Surf/H2O particle towards its furthest interior region. Flexible nanoparticles (FNs) catalyse a variety of chemical and biochemical reactions. FN catalysis involves both positive catalysis ( i.e. rate increase) and negative catalysis ( i.e. rate decrease). This article describes the mechanistic details of these catalyses at the molecular level, which reveals the molecular origin of these catalyses. Effects of inert counterionic salts (MX) on the rates of bimolecular reactions (with one of the reactants as reactive counterion) in the presence of ionic FNs/micelles may result in either positive or negative catalysis. The kinetics of cationic FN (Surf/MX/H2O)-catalysed bimolecular reactions (with nonionic and anionic reactants) provide kinetic parameters which can be used to determine an ion exchange constant or the ratio of the binding constants of counterions.
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3

Avigliano, L., V. Carelli, A. Casini, A. Finazzi-Agrò et F. Liberatore. « Oxidation of NAD dimers by horseradish peroxidase ». Biochemical Journal 226, no 2 (1 mars 1985) : 391–95. http://dx.doi.org/10.1042/bj2260391.

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Horseradish peroxidase catalyses the oxidation of NAD dimers, (NAD)2, to NAD+ in accordance with a reaction that is pH-dependent and requires 1 mol of O2 per 2 mol of (NAD)2. Horseradish peroxidase also catalyses the peroxidation of (NAD)2 to NAD+. In contrast, bacterial NADH peroxidase does not catalyse the peroxidation or the oxidation of (NAD)2. A free-radical mechanism is proposed for both horseradish-peroxidase-catalysed oxidation and peroxidation of (NAD)2.
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4

ABBADI, Amine, Monika BRUMMEL, Burkhardt S. SCHüTT, Mary B. SLABAUGH, Ricardo SCHUCH et Friedrich SPENER. « Reaction mechanism of recombinant 3-oxoacyl-(acyl-carrier-protein) synthase III from Cuphea wrightii embryo, a fatty acid synthase type II condensing enzyme ». Biochemical Journal 345, no 1 (17 décembre 1999) : 153–60. http://dx.doi.org/10.1042/bj3450153.

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A unique feature of fatty acid synthase (FAS) type II of higher plants and bacteria is 3-oxoacyl-[acyl-carrier-protein (ACP)] synthase III (KAS III), which catalyses the committing condensing reaction. Working with KAS IIIs from Cuphea seeds we obtained kinetic evidence that KAS III catalysis follows a Ping-Pong mechanism and that these enzymes have substrate-binding sites for acetyl-CoA and malonyl-ACP. It was the aim of the present study to identify these binding sites and to elucidate the catalytic mechanism of recombinant Cuphea wrightii KAS III, which we expressed in Escherichia coli. We engineered mutants, which allowed us to dissect the condensing reaction into three stages, i.e. formation of acyl-enzyme, decarboxylation of malonyl-ACP, and final Claisen condensation. Incubation of recombinant enzyme with [1-14C]acetyl-CoA-labelled Cys111, and the replacement of this residue by Ala and Ser resulted in loss of overall condensing activity. The Cys111Ser mutant, however, still was able to bind acetyl-CoA and to catalyse subsequent binding and decarboxylation of malonyl-ACP to acetyl-ACP. We replaced His261 with Ala and Arg and found that the former lost activity, whereas the latter retained overall condensing activity, which indicated a general-base action of His261. Double mutants Cys111Ser/His261Ala and Cys111Ser/His261Arg were not able to catalyse overall condensation, but the double mutant containing Arg induced decarboxylation of [2-14C]malonyl-ACP, a reaction indicating the role of His261 in general-acid catalysis. Finally, alanine scanning revealed the involvement of Arg150 and Arg306 in KAS III catalysis. The results offer for the first time a detailed mechanism for a condensing reaction catalysed by a FAS type II condensing enzyme.
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5

Ortega-Caballero, Fernando, et Mikael Bols. « Cyclodextrin derivatives with cyanohydrin and carboxylate groups as artificial glycosidases ». Canadian Journal of Chemistry 84, no 4 (1 avril 2006) : 650–58. http://dx.doi.org/10.1139/v06-039.

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Two cyclodextrin derivatives (1 and 2) were prepared in an attempt to create glycosidase mimics with a general acid catalyst and a nucleophilic carboxylate group. The catalysts 1 and 2 were found to catalyse the hydrolysis of 4-nitrophenyl β-D-glucopyranoside at pH 8.0, but rapidly underwent decomposition with loss of hydrogen cyanide to convert the cyanohydrin to the corresponding aldehyde. The initial rate of the catalysis shows that the cyanohydrin group in these molecules functions as a good catalyst, but that the carboxylate has no positive effect. The decomposition product aldehydes display little or no catalysis. A mechanism for the decomposition is suggested.Key words: biomimicry, enzyme model, kinetics, intramolecular reaction.
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6

Jia, Yunhua, Takeo Tomita, Kazuma Yamauchi, Makoto Nishiyama et David R. J. Palmer. « Kinetics and product analysis of the reaction catalysed by recombinant homoaconitase from Thermus thermophilus ». Biochemical Journal 396, no 3 (29 mai 2006) : 479–85. http://dx.doi.org/10.1042/bj20051711.

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HACN (homoaconitase) is a member of a family of [4Fe-4S] cluster-dependent enzymes that catalyse hydration/dehydration reactions. The best characterized example of this family is the ubiquitous ACN (aconitase), which catalyses the dehydration of citrate to cis-aconitate, and the subsequent hydration of cis-aconitate to isocitrate. HACN is an enzyme from the α-aminoadipate pathway of lysine biosynthesis, and has been identified in higher fungi and several archaea and one thermophilic species of bacteria, Thermus thermophilus. HACN catalyses the hydration of cis-homoaconitate to (2R,3S)-homoisocitrate, but the HACN-catalysed dehydration of (R)-homocitrate to cis-homoaconitate has not been observed in vitro. We have synthesized the substrates and putative substrates for this enzyme, and in the present study report the first steady-state kinetic data for recombinant HACN from T. thermophilus using a (2R,3S)-homoisocitrate dehydrogenase-coupled assay. We have also examined the products of the reaction using HPLC. We do not observe HACN-catalysed ‘homocitrate dehydratase’ activity; however, we have observed that ACN can catalyse the dehydration of (R)-homocitrate to cis-homoaconitate, but HACN is required for subsequent conversion of cis-homoaconitate into homoisocitrate. This suggests that the in vivo process for conversion of homocitrate into homoisocitrate requires two enzymes, in simile with the propionate utilization pathway from Escherichia coli. Surprisingly, HACN does not show any activity when cis-aconitate is substituted for the substrate, even though other enzymes from the α-aminoadipate pathway can accept analogous tricarboxylic acid-cycle substrates. The enzyme shows no apparent feedback inhibition by L-lysine.
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7

Liu, Yansheng, Xinlin Li, Xuanduong Le, Wei Zhang, Hao Gu, Ruiwen Xue et Jiantai Ma. « Catalysis of the hydro-dechlorination of 4-chlorophenol by Pd(0)-modified MCM-48 mesoporous microspheres with an ultra-high surface area ». New Journal of Chemistry 39, no 6 (2015) : 4519–25. http://dx.doi.org/10.1039/c5nj00617a.

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8

Gu, Nina X., Gaël Ung et Jonas C. Peters. « Catalytic hydrazine disproportionation mediated by a thiolate-bridged VFe complex ». Chemical Communications 55, no 37 (2019) : 5363–66. http://dx.doi.org/10.1039/c9cc00345b.

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A heterobimetallic VFe complex is demonstrated to catalyse hydrazine disproportionation with yields of up to 1073 equivalents of NH3 per catalyst, comparable to the highest turnover known for any molecular catalyst.
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9

Boucher, Guillaume, Bilal Said, Elizabeth L. Ostler, Marina Resmini, Keith Brocklehurst et Gerard Gallacher. « Evidence that the mechanism of antibody-catalysed hydrolysis of arylcarbamates can be determined by the structure of the immunogen used to elicit the catalytic antibody ». Biochemical Journal 401, no 3 (12 janvier 2007) : 721–26. http://dx.doi.org/10.1042/bj20060551.

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A kinetically homogeneous anti-phosphate catalytic antibody preparation was shown to catalyse the hydrolysis of a series of O-aryl N-methyl carbamates containing various substituents in the 4-position of the O-phenyl group. The specific nature of the antibody catalysis was demonstrated by the adherence of these reactions to the Michaelis–Menten equation, the complete inhibition by a hapten analogue, and the failure of the antibody to catalyse the hydrolysis of the 2-nitrophenyl analogue of the 4-nitrophenylcarbamate substrate. Hammett σ–ρ analysis suggests that both the non-catalysed and antibody-catalysed reactions proceed by mechanisms in which development of the aryloxyanion of the leaving group is well advanced in the transition state of the rate-determining step. This is probably the ElcB (elimination–addition) mechanism for the non-catalysed reaction, but for the antibody-catalysed reaction might be either ElcB or BAc2 (addition–elimination), in which the elimination of the aryloxy group from the tetrahedral intermediate has become rate-determining. This result provides evidence of the dominance of recognition of phenolate ion character in the phosphate hapten in the elicitation process, and is discussed in connection with data from the literature that suggest a BAc2 mechanism, with rate-determining formation of the tetrahedral intermediate for the hydrolysis of carbamate substrates catalysed by an antibody elicited by a phosphonamidate hapten in which phenolate anion character is minimized. The present paper contributes to the growing awareness that small differences in the structure of haptens can produce large differences in catalytic characteristics.
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10

Giger, Rudolf, et Pascal Hoffmann. « Design and synthesis of a transition state analog of a metalloporphyrin-catalysed oxidation reaction ». Journal of Porphyrins and Phthalocyanines 06, no 05 (mai 2002) : 362–65. http://dx.doi.org/10.1142/s1088424602000439.

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A hapten that mimics the transition state of a metalloporphyrin-catalysed oxidation reaction was synthesized in order to generate antibodies that might be able to catalyse the regioselective metalloporphyrin-co-catalysed reaction of cyclosporin A to [D-Ser8]cyclosporin A.
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11

Zemek, Jiří, Štefan Kučár et Dušan Anderle. « Enzyme-catalyzed partial deacetylation of 1,6-anhydro-2,3,4-tri-O-acetyl-β-D-glucopyranose ». Collection of Czechoslovak Chemical Communications 52, no 9 (1987) : 2347–52. http://dx.doi.org/10.1135/cccc19872347.

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Various esterases, lipases, and proteases with esterolytic activity were investigated for their power to catalyse deacetylation of 1,6-anhydro-2,3,4-tri-O-acetyl-β-D-glucopyranose. Out of these, chymotrypsin, esterase ex liver, lipase ex pancreas, and lipase ex wheat-germ have been found to be selective catalysts of deacetylation; chymotrypsin and wheat-germ lipase preferably removed the acetyl at C(3), whereas liver esterase and pancreas lipase the acetyl at C(4). Compared to chemical catalysis, whether by methanolic hydrogen chloride or hydrazine hydrate, the locoselectivity of the enzyme-catalysed deacetylation appear to be much better.
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12

Bélières, M., N. Chouini-Lalanne et C. Déjugnat. « Synthesis, self-assembly, and catalytic activity of histidine-based structured lipopeptides for hydrolysis reactions in water ». RSC Advances 5, no 45 (2015) : 35830–42. http://dx.doi.org/10.1039/c5ra02853a.

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13

Zhang, Yu Li, Xiang Ying Hao, Cui Zhang et De Yun Ma. « Application of SO42-/ Al-Fe-Activated Solid Acid Catalyst Prepared by Cross-Linking Method ». Applied Mechanics and Materials 448-453 (octobre 2013) : 2929–32. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.2929.

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SO42-/ Al-Fe-activated solid acid catalyst has been prepared using cross-linking method, and characterized by FTIR spectra, TG-DTA, XRD analysis. The catalyst is able to effectively catalyse the hydration of turpentine to α-terpineol, with the conversion up to 40% after > 4 uses.
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14

Tabita, F. Robert, Thomas E. Hanson, Sriram Satagopan, Brian H. Witte et Nathan E. Kreel. « Phylogenetic and evolutionary relationships of RubisCO and the RubisCO-like proteins and the functional lessons provided by diverse molecular forms ». Philosophical Transactions of the Royal Society B : Biological Sciences 363, no 1504 (16 mai 2008) : 2629–40. http://dx.doi.org/10.1098/rstb.2008.0023.

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Ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RubisCO) catalyses the key reaction by which inorganic carbon may be assimilated into organic carbon. Phylogenetic analyses indicate that there are three classes of bona fide RubisCO proteins, forms I, II and III, which all catalyse the same reactions. In addition, there exists another form of RubisCO, form IV, which does not catalyse RuBP carboxylation or oxygenation. Form IV is actually a homologue of RubisCO and is called the RubisCO-like protein (RLP). Both RubisCO and RLP appear to have evolved from an ancestor protein in a methanogenic archaeon, and comprehensive analyses indicate that the different forms (I, II, III and IV) contain various subgroups, with individual sequences derived from representatives of all three kingdoms of life. The diversity of RubisCO molecules, many of which function in distinct milieus, has provided convenient model systems to study the ways in which the active site of this protein has evolved to accommodate necessary molecular adaptations. Such studies have proven useful to help provide a framework for understanding the molecular basis for many important aspects of RubisCO catalysis, including the elucidation of factors or functional groups that impinge on RubisCO carbon dioxide/oxygen substrate discrimination.
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15

BERTOLDI, Mariarita, Virginia CARBONE et Carla BORRI VOLTATTORNI. « Ornithine and glutamate decarboxylases catalyse an oxidative deamination of their α-methyl substrates ». Biochemical Journal 342, no 3 (5 septembre 1999) : 509–12. http://dx.doi.org/10.1042/bj3420509.

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Ornithine decarboxylase (ODC) from Lactobacillus 30a catalyses the cleavage of α-methylornithine into ammonia and 2-methyl-1-pyrroline; glutamate decarboxylase (GAD) from Escherichia coli catalyses the cleavage of α-methylglutamate into ammonia and laevulinic acid. In our analyses, 2-methyl-1-pyrroline and laevulinic acid were identified by HPLC and mass spectroscopic analysis, and ammonia was identified by means of glutamate dehydrogenase. Molecular oxygen was consumed during these reactions in a 1:2 molar ratio with respect to the products. The catalytic efficiencies (kcat/Km) of the reactions catalysed by ODC and GAD were determined as 12500 and 9163 M-1˙min-1 respectively. When the reactions were performed under anaerobic conditions, no ammonia, 2-methyl-1-pyrroline or laevulinic acid was produced to a significant extent. The formation of ammonia and O2 consumption (in a 1:2 molar ratio with respect to ammonia) were also detected during the reaction of ODC and GAD with putrescine and γ-aminobutyrate respectively. Taken together, these findings clearly indicate that ODC and GAD catalyse an oxidative deamination of their decarboxylation products, a reaction similar to that catalysed by dopa decarboxylase (DDC) with α-methyldopa [Bertoldi, Dominici, Moore, Maras and Borri Voltattorni (1998) Biochemistry 37, 6552-6561]. Furthermore, this reaction was accompanied by a decarboxylation-dependent transamination occurring for GAD, DDC and ODC with a frequency of approx. 0.24%, 1% and 9% respectively compared with that of oxidative deamination.
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16

BAGGOTT, Joseph E., et Robert E. MacKENZIE. « 5,10-Methenyltetrahydrofolate cyclohydrolase, rat liver and chemically catalysed formation of 5-formyltetrahydrofolate ». Biochemical Journal 374, no 3 (15 septembre 2003) : 773–78. http://dx.doi.org/10.1042/bj20021970.

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The 5,10-methenyltetrahydrofolate (5,10-CH=H4folate) synthetase catalyses the physiologically irreversible formation of 5,10-CH=H4folate from 5-formyltetrahydrofolate (5-HCO-H4folate) and ATP. It is not clear how (or if) 5-HCO-H4folate is formed in vivo. Using a spectrophotometric assay for 5-HCO-H4folate, human recombinant 5,10-CH=H4folate cyclohydrolase, which catalyses the hydrolysis of 5,10-CH=H4folate to 10-HCO-H4folate, was previously shown to catalyse inefficiently the formation of 5-HCO-H4folate at pH 7.3 [Pelletier and MacKenzie (1996) Bioorg. Chem. 24, 220–228]. In the present study, we report that (i) the human cyclohydrolase enzyme catalyses the conversion of 10-HCO-/5,10-CH=H4folate into 5-HCO-H4folate (it is also chemically formed) at pH 4.0–7.0; (ii) rat liver has a very low capacity to catalyse the formation of 5-HCO-H4folate when compared with the traditional activity of 5,10-CH=H4folate cyclohydrolase and the activity of the 5,10-CH=H4folate synthetase; and (iii) a substantial amount of 5-HCO-H4folate reported to be present in rat liver is chemically formed during analytical procedures. We conclude that (i) the cyclohydrolase represents some of the capacity of rat liver to catalyse the formation of 5-HCO-H4folate; (ii) the amount of 5-HCO-H4folate reported to be present in rat liver is overestimated (liver 5-HCO-H4folate content may be negligible); and (iii) there is little evidence that 5-HCO-H4folate inhibits one-carbon metabolism in mammals.
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17

Martínez, Alejandro V., Fabio Invernizzi, Alejandro Leal-Duaso, José A. Mayoral et José I. García. « Microwave-promoted solventless Mizoroki–Heck reactions catalysed by Pd nanoparticles supported on laponite clay ». RSC Advances 5, no 14 (2015) : 10102–9. http://dx.doi.org/10.1039/c4ra15418e.

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Palladium nanoparticles supported on laponite efficiently catalyse solventless Mizoroki–Heck reactions activated by microwaves. High yields are obtained in a few minutes and the catalyst can be efficiently recovered and reused up to thirteen times.
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18

Mozaceanu, Cristina, Christopher G. P. Taylor, Jerico R. Piper, Stephen P. Argent et Michael D. Ward. « Catalysis of an Aldol Condensation Using a Coordination Cage ». Chemistry 2, no 1 (25 janvier 2020) : 22–32. http://dx.doi.org/10.3390/chemistry2010004.

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The aldol condensation of indane-1,3-dione (ID) to give ‘bindone’ in water is catalysed by an M8L12 cubic coordination cage (Hw). The absolute rate of reaction is slow under weakly acidic conditions (pH 3–4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of Hw is ca. 2.4 (±1.2) × 103 M−1, giving a ∆G for the binding of −19.3 (±1.2) kJ mol−1. The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage’s exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which—as the control experiments show—occurs at the exterior surface of the cage and not inside the cage cavity.
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19

Badarau, Adriana, Christian Damblon et Michael I. Page. « The activity of the dinuclear cobalt-β-lactamase from Bacillus cereus in catalysing the hydrolysis of β-lactams ». Biochemical Journal 401, no 1 (11 décembre 2006) : 197–203. http://dx.doi.org/10.1042/bj20061002.

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Metallo-β-lactamases are native zinc enzymes that catalyse the hydrolysis of β-lactam antibiotics, but are also able to function with cobalt(II) and require one or two metal-ions for catalytic activity. The hydrolysis of cefoxitin, cephaloridine and benzylpenicillin catalysed by CoBcII (cobalt-substituted β-lactamase from Bacillus cereus) has been studied at different pHs and metal-ion concentrations. An enzyme group of pKa 6.52±0.1 is found to be required in its deprotonated form for metal-ion binding and catalysis. The species that results from the loss of one cobalt ion from the enzyme has no significant catalytic activity and is thought to be the mononuclear CoBcII. It appears that dinuclear CoBcII is the active form of the enzyme necessary for turnover, while the mononuclear CoBcII is only involved in substrate binding. The cobalt-substituted enzyme is a more efficient catalyst than the native enzyme for the hydrolysis of some β-lactam antibiotics suggesting that the role of the metal-ion is predominantly to provide the nucleophilic hydroxide, rather than to act as a Lewis acid to polarize the carbonyl group and stabilize the oxyanion tetrahedral intermediate.
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20

MONTE, Massimo DAL, Ilaria CECCONI, Francesca BUONO, Pier Giuseppe VILARDO, Antonella DEL CORSO et Umberto MURA. « Thioltransferase activity of bovine lens glutathione S-transferase ». Biochemical Journal 334, no 1 (15 août 1998) : 57–62. http://dx.doi.org/10.1042/bj3340057.

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A Mu-class glutathione S-transferase purified to electrophoretic homogeneity from bovine lens displayed thioltransferase activity, catalysing the transthiolation reaction between GSH and hydroxyethyldisulphide. The thiol-transfer reaction is composed of two steps, the formation of GSSG occurring through the generation of an intermediate mixed disulphide between GSH and the target disulphide. Unlike glutaredoxin, which is only able to catalyse the second step of the transthiolation process, glutathioneS-transferase catalyses both steps of the reaction. Data are presented showing that bovine lens glutathione S-transferase and rat liver glutaredoxin, which was used as a thioltransferase enzyme model, can operate in synergy to catalyse the GSH-dependent reduction of hydroxyethyldisulphide.
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21

Han, Fei, Wenrui Wang, Danyi Li, Siyi Xu, Ying Sun, Lin Lin, Lin Ma, Jihao Li et Linfan Li. « Green preparation of silver nanocluster composite AgNCs@CF-g-PAA and its application : 4-NP catalytic reduction and hydrogen production ». RSC Advances 13, no 17 (2023) : 11807–16. http://dx.doi.org/10.1039/d3ra01245j.

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Silver nanocluster composites are obtained directly through radiation technology and can be used to catalyse 4-nitrophenol reduction and sodium borohydride. The catalyst is a candidate for the treatment of water contaminant 4-NP and the production of hydrogen from NaBH4.
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22

Xu, Mengxue, Hongpeng Zhang, Haiyan Zhu, Lianyuan Wang et Chaohua Zhou. « Soman hydrolysis catalysed by hypochlorite ions ». E3S Web of Conferences 267 (2021) : 02043. http://dx.doi.org/10.1051/e3sconf/202126702043.

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Sarin (GB) and soman (GD) are severely toxic nerve agents that react slowly in water, resulting in long-term poisoning of the water and a serious threat to personnel. Some ions can catalyse GB and GD hydrolysis in water; the relevant research for GB is detailed, whereas that for GD is relatively less so. In this paper, GD hydrolysis catalysed by hypochlorite (ClO−) ions was studied via kinetic experiments. A fluorite-ion-specific electrode was used to monitor F− ions produced, allowing the rate constant and half-life of the GD hydrolysis to be calculated. The results showed that ClO− ions promote GD hydrolysis well; the higher the concentration of ClO−, the faster the GD was hydrolysed. In NaClO solution at pH 8.0 with 3.22×10–3 M ClO− ions, the half-life of GD hydrolysis was 82.5 s, about 875 times shorter than that in water at pH 8.0. The rate constant for catalysis of GD hydrolysis by ClO- ions ++(kc1o−)++ was 2.6 M−1 s−1, about one quarter the value of ++koh− ++but over 1500 times greater than kB and ++kPO4,++ with B representing N-2-hydroxyethylpiperazine-N’-2-ethanesulfonic acid present as a free base; this result indicated that ClO− ions catalyse GD hydrolysis well.
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23

Chen, Gong-Jun, Chao-Qun Chen, Xue-Tian Li, Hui-Chao Ma et Yu-Bin Dong. « Cu3L2 metal–organic cages for A3-coupling reactions : reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery ». Chemical Communications 54, no 82 (2018) : 11550–53. http://dx.doi.org/10.1039/c8cc07208f.

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A novel Cu3L2 metal–organic cage, which features coordination interaction triggered solubility, can be a highly active and reusable catalyst to homogeneously catalyse the one-pot aldehyde–alkyne–amine A3-coupling reaction.
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24

Villemin, Didier, et Endo Schigeko. « Catalyse homogene : Synthese des benchrotrenylacetylenes catalysee par le palladium ». Journal of Organometallic Chemistry 293, no 1 (septembre 1985) : C10—C12. http://dx.doi.org/10.1016/0022-328x(85)80256-4.

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25

Zhang, Zhi, Zhihang Huang et Hong Yuan. « Direct conversion of cellulose to ethyl levulinate catalysed by modified fibrous mesoporous silica nanospheres in a co-solvent system ». New Journal of Chemistry 45, no 12 (2021) : 5526–39. http://dx.doi.org/10.1039/d0nj05433j.

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A KCC-1/Al–SO3H catalyst with Si/Al = 5 was prepared to directly catalyse the synthesis of ethyl levulinate from cellulose in an ethanol/toluene co-solvent system. A reaction yield of 28.8 mol% was achieved after 6 h at 200 °C.
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Ghosh, Shishir, Graeme Hogarth, Nathan Hollingsworth, Katherine B. Holt, Shariff E. Kabir et Ben E. Sanchez. « Hydrogenase biomimetics : Fe2(CO)4(μ-dppf)(μ-pdt) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) both a proton-reduction and hydrogen oxidation catalyst ». Chem. Commun. 50, no 8 (2014) : 945–47. http://dx.doi.org/10.1039/c3cc46456c.

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The diiron complex Fe2(CO)4(μ-dppf)(μ-pdt) is an active catalyst for both the reduction of protons to give hydrogen and also the reverse oxidation of hydrogen and thus mimics hydrogenases which are able to catalyse both reactions.
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27

Hiller, David A., et Scott A. Strobel. « The chemical versatility of RNA ». Philosophical Transactions of the Royal Society B : Biological Sciences 366, no 1580 (27 octobre 2011) : 2929–35. http://dx.doi.org/10.1098/rstb.2011.0143.

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The ability of RNA to both store genetic information and catalyse chemical reactions has led to the hypothesis that it predates DNA and proteins. While there is no doubt that RNA is capable of storing the genetic information of a primitive organism, only two classes of reactions—phosphoryl transfer and peptide bond formation—have been observed to be catalysed by RNA in nature. However, these naturally occurring ribozymes use a wide range of catalytic strategies that could be applied to other reactions. Furthermore, RNA can bind several cofactors that are used by protein enzymes to facilitate a wide variety of chemical processes. Despite its limited functional groups, these observations indicate RNA is a versatile molecule that could, in principle, catalyse the myriad reactions necessary to sustain life.
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Arabczyk, Walerian, Urszula Narkiewicz, Zofia Lendzion-Bieluń, Dariusz Moszyński, Iwona Pełech, Ewa Ekiert, Marcin Podsiadły et al. « Utilization of spent iron catalyst for ammonia synthesis ». Polish Journal of Chemical Technology 9, no 3 (1 janvier 2007) : 108–13. http://dx.doi.org/10.2478/v10026-007-0067-y.

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Utilization of spent iron catalyst for ammonia synthesis Several methods of the utilization of spent iron catalyst for ammonia synthesis have been presented. The formation of iron nitrides of different stoichiometry by direct nitriding in ammonia in the range of temperatures between 350°C and 450°C has been shown. The preparation methods of carbon nanotubes and nanofibers where iron catalyst catalyse the decomposition of hydrocarbons have been described. The formation of magnetite embedded in a carbon material by direct oxidation of carburized iron catalyst has been also presented.
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29

Banerjee, R., et M. Vlasie. « Controlling the reactivity of radical intermediates by coenzyme B12-dependent methylmalonyl-CoA mutase ». Biochemical Society Transactions 30, no 4 (1 août 2002) : 621–24. http://dx.doi.org/10.1042/bst0300621.

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Adenosylcobalamin or coenzyme B12-dependent enzymes are members of the still relatively small group of radical enzymes and catalyse 1,2-rearrangement reactions. A member of this family is methylmalonyl-CoA mutase, which catalyses the isomerization of methylmalonyl-CoA to succinyl-CoA and, unlike the others, is present in both bacteria and animals. Enzymes that catalyse some of the most chemically challenging reactions are the ones that tend to deploy radical chemistry. The use of radical intermediates in an active site lined with amino acid side chains that threaten to extinguish the reaction by presenting alternative groups for abstraction poses the conundrum of how the enzymes control their reactivity. In this review, insights into this issue that have emerged from kinetic, mutagenesis and structural studies are described for methylmalonyl-CoA mutase.
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30

Dembinski, Paul H. « Crise ou catalyse ? » Finance & ; Bien Commun 31-32, no 2 (2008) : 11. http://dx.doi.org/10.3917/fbc.031.0011.

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Ma, Yubo, Zhixian Gao, Tao Yuan et Tianfu Wang. « Kinetics of Dicyclopentadiene Hydroformylation over Rh–SiO2 Catalysts ». Progress in Reaction Kinetics and Mechanism 42, no 2 (mai 2017) : 191–99. http://dx.doi.org/10.3184/146867817x14821527549013.

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The hydroformylation of dicyclopentadiene (DCPD) to monoformyltricyclodecenes (MFTD) represents a key intermediate step in the conversion of the C5 fraction derived from the petrochemical process to value-added fine chemicals, for example, diformyltricyclodecanes and tricyclodecanedimethylol. Although both heterogeneous and homogeneous catalysts can catalyse this reaction, the heterogeneously catalysed pathway has received significantly less attention due to its lower catalytic activities. We demonstrate in this work that a low Rh loaded heterogeneous 0.1% Rh–SiO2 catalyst can present a similar performance relative to the homogeneous Rh(PPh3)Cl, a reference catalyst for this reaction. Furthermore, an extensive kinetic study of DCPD hydroformylation to MFTD using heterogeneous 0.1% Rh–SiO2 catalysts has been performed. A series of kinetic experiments was carried out over a broad range of conditions (temperature: 100–120 °C; pressure: 1.5–5 MPa; catalyst-to-reactant mass ratio: 0.02–0.05; PPh3 concentration: 5–12.5 g L−1). A kinetic analysis was carried out, indicating the activation energy for the reaction to be 84.7 kJ mol−1. DCPD conversion and MFTD yield could be optimised to be as high as 99% at 0.1% Rh loading, a DCPD/catalyst mass ratio of 25, a PPh3 concentration of 10 g L−1, a reaction time of 4 h and a reaction pressure of 4 MPa.
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32

Wong, W.-Y., S. Lim, Y.-L. Pang, C.-H. Lim, F.-L. Pua et G. Pua. « Response surface optimisation of biodiesel synthesis using biomass derived green heterogeneous catalyst ». IOP Conference Series : Materials Science and Engineering 1257, no 1 (1 octobre 2022) : 012010. http://dx.doi.org/10.1088/1757-899x/1257/1/012010.

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Abstract Although homogeneous alkali-catalysed transesterification is the typical process used in biodiesel production, it caused complications in downstream separation processes and an oversupply of glycerol as a by-product. The present work studied the synthesis of a novel sulfonated biomass-derived solid acid catalyst and its application in biodiesel production via interesterification of oleic acid. Solid acid catalysts were prepared by direct sulfonation via thermal treatment with concentrated sulfuric acid. The design of experiments was conducted via four-factors central composite design (CCD) coupled with response surface methodology (RSM) analysis. The parameters considered for optimisation included carbonisation and sulfonation temperatures, catalyst loading and reaction time, each varied at five levels. The maximum yield of fatty acid methyl ester (FAME) was obtained using optimum parameters as carbonisation temperature of 586 °C, sulfonation temperature of 110 °C, catalyst loading of 10.5 wt.% and reaction time of 7 h was 54.3 % based on the theoretical ester formation. A quadratic mathematical model in RSM was successfully established that can make effective predictions about the anticipated biodiesel yield. This study proved that the low-cost heterogeneous catalyst derived from biomass waste with a simple production route could catalyse the interesterification process under moderate process conditions.
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Li, Feng, et Hao Li. « Spatial compartmentalisation effects for multifunctionality catalysis : From dual sites to cascade reactions ». Innovation & ; Technology Advances 2, no 1 (12 mars 2024) : 1–13. http://dx.doi.org/10.61187/ita.v2i1.54.

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Catalysis plays a key role in the production of fuels, industrial chemicals and the chemical transformation of fine chemicals. As society faces increasing environmental pollution and energy crises, tandem catalysis has attracted increasing attention as an outstanding model due to its sustainability and environmental friendliness. Compared with traditional stepwise synthesis methods, tandem catalysis not only can couple several different reactions together, but also does not require the separation of intermediates, which provides new ideas for improving reaction activity, regulating product selectivity and developing new methods for catalysis. In order to catalyse cascade reactions efficiently, it is crucial to design suitable multifunctional catalysts, which should contain at least two active sites and achieve spatial separation. Here, we introduce the realisation and application of spatial segregation of metal, acidic and basic sites with examples to provide further insight into the indispensable role of active site compartmentalisation effects in tandem catalysis. In addition, this study highlights the challenges and issues associated with such catalysts, emphasising the importance of effective catalyst enhancement and environmentally sustainable catalytic transformations. The results of the study are intended to provide guidance for the development of rational and efficient catalysts.
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34

Maia, Luisa B. « Bringing Nitric Oxide to the Molybdenum World—A Personal Perspective ». Molecules 28, no 15 (2 août 2023) : 5819. http://dx.doi.org/10.3390/molecules28155819.

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Molybdenum-containing enzymes of the xanthine oxidase (XO) family are well known to catalyse oxygen atom transfer reactions, with the great majority of the characterised enzymes catalysing the insertion of an oxygen atom into the substrate. Although some family members are known to catalyse the “reverse” reaction, the capability to abstract an oxygen atom from the substrate molecule is not generally recognised for these enzymes. Hence, it was with surprise and scepticism that the “molybdenum community” noticed the reports on the mammalian XO capability to catalyse the oxygen atom abstraction of nitrite to form nitric oxide (NO). The lack of precedent for a molybdenum- (or tungsten) containing nitrite reductase on the nitrogen biogeochemical cycle contributed also to the scepticism. It took several kinetic, spectroscopic and mechanistic studies on enzymes of the XO family and also of sulfite oxidase and DMSO reductase families to finally have wide recognition of the molybdoenzymes’ ability to form NO from nitrite. Herein, integrated in a collection of “personal views” edited by Professor Ralf Mendel, is an overview of my personal journey on the XO and aldehyde oxidase-catalysed nitrite reduction to NO. The main research findings and the path followed to establish XO and AO as competent nitrite reductases are reviewed. The evidence suggesting that these enzymes are probable players of the mammalian NO metabolism is also discussed.
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35

Miłek, J., M. Wójcik et W. Verschelde. « Thermal stability for the effective use of commercial catalase ». Polish Journal of Chemical Technology 16, no 4 (1 décembre 2014) : 75–79. http://dx.doi.org/10.2478/pjct-2014-0073.

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Abstract Catalase with the commercial catalase name Terminox Ultra is widely used in the textile industry in bleaching processes. This enzyme is used to catalyse the decomposition of residual hydrogen peroxide into oxygen and water. In this study catalase was kept for about 30 hours in water baths in a temperature range from 35 to 70°C. For the first time, the kinetics of thermal deactivation of this enzyme was examined using an oxygen electrode. Stability of the enzyme depends strongly on temperature and its half-life times are 0.0014 h and 7.6 h, at 35 and 70°C, respectively.
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Jankovič, Ľuboš, et Peter Komadel. « Catalytic Properties of a Heated Ammonium-Saturated Dioctahedral Smectite ». Collection of Czechoslovak Chemical Communications 65, no 9 (2000) : 1527–36. http://dx.doi.org/10.1135/cccc20001527.

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A series of acid catalysts was prepared by heating of NH4-saturated montmorillonite at 200-600 °C for 24 h. Their catalytic activity was tested in acetylation of 3,4,5-trimethoxybenzaldehyde with acetic anhydride. This reaction is sufficiently sensitive to modification of the catalyst and thus suitable for testing catalytic activity of modified montmorillonites. Most of the prepared catalysts were able to catalyse the test reaction and produce diacetate in higher than 50% yields. The most active catalyst was obtained after heating at 300 °C. It was slightly less effective than commercially available acid-activated K10 catalyst.
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37

Pineda, J. R. E. T., et S. D. Schwartz. « Protein dynamics and catalysis : the problems of transition state theory and the subtlety of dynamic control ». Philosophical Transactions of the Royal Society B : Biological Sciences 361, no 1472 (12 juillet 2006) : 1433–38. http://dx.doi.org/10.1098/rstb.2006.1877.

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This manuscript describes ongoing research on the nature of chemical reactions in enzymes. We will investigate how protein dynamics can couple to chemical reaction in an enzyme. We first investigate in some detail why transition state theory cannot fully describe the dynamics of chemical reactions catalysed by enzymes. We describe quantum theories of chemical reaction in condensed phase including studies of how the symmetry of coupled vibrational modes differentially affects reaction dynamics. We make reference to previous work in our group on a variety of condensed phase chemical reactions (liquid and crystalline) and a variety of enzymatically catalysed reactions including the reactions of lactate dehydrogenase and purine nucleoside phosphorylase. All the protein motions we have studied have been quite rapid. We will propose methods to find motions over a broad range of time-scales in enzymes that couple to chemical catalysis. We report recent findings which show that conformational fluctuations in lactate dehydrogenase can strongly affect its ability to catalyse reactions through protein motion, and that only a tiny minority of conformations appear to be catalytically competent.
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38

Nadirova, Maryana, Joel Cejas-Sánchez, Rosa María Sebastián, Marcin Wiszniewski, Michał J. Chmielewski, Anna Kajetanowicz et Karol Grela. « Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support ». Catalysts 13, no 2 (28 janvier 2023) : 297. http://dx.doi.org/10.3390/catal13020297.

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Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then immobilised on the metal–organic framework (MOF) solid support (Al)MIL-101-NH2. The catalytic activity of such a heterogeneous system was tested, showing that, while the heterogeneous catalyst is less active than the corresponding homogeneous catalyst in solution, it can catalyse selected olefin metathesis reactions, serving as the proof-of-concept for the immobilisation of catalytically active complexes in MOFs using a phenolic tag.
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39

Lalanne-Tisné, Michael, Audrey Favrelle-Huret, Wim Thielemans, João P. Prates Ramalho et Philippe Zinck. « DFT Investigations on the Ring-Opening Polymerization of Trimethylene Carbonate Catalysed by Heterocyclic Nitrogen Bases ». Catalysts 12, no 10 (20 octobre 2022) : 1280. http://dx.doi.org/10.3390/catal12101280.

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Organocatalysts for polymerization have known a huge interest over the last two decades. Among them, heterocyclic nitrogen bases are widely used to catalyse the ring-opening polymerization (ROP) of heterocycles such as cyclic carbonates. We have investigated the ring-opening polymerization of trimethylene carbonate (TMC) catalysed by DMAP (4-dimethylaminopyridine) and TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) as case studies in the presence of methanol as co-initiator by Density Functional Theory (DFT). A dual mechanism based on H-bond activation of the carbonyl moieties of the monomer and a basic activation of the alcohol co-initiator has been shown to occur more preferentially than a direct nucleophilic attack of the carbonate monomer by the heterocyclic nitrogen catalyst. The rate-determining step of the mechanism is the ring opening of the TMC molecule, which is slightly higher than the nucleophilic attack of the TMC carbonyl by the activated alcohol. The calculations also indicate TBD as a more efficient catalyst than DMAP. The higher energy barrier found for DMAP vs. TBD, 23.7 vs. 11.3 kcal·mol−1, is corroborated experimentally showing a higher reactivity for the latter.
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40

Wijayati, Nanik, Harno Dwi Pranowo, Jumina Jumina et Triyono Triyono. « SYNTHESIS OF TERPINEOL FROM α-PINENE CATALYZED BY TCA/Y-ZEOLITE ». Indonesian Journal of Chemistry 11, no 3 (20 décembre 2011) : 234–37. http://dx.doi.org/10.22146/ijc.21386.

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The hydration of a-pinene has been studied in the presence of TCA/Y-Zeolite catalyse. The catalyst was prepared by impregnating trichloroacetic acid (TCA) on support of Y-Zeolite. The TCA/Y-Zeolite catalyst converted a-pinene into hydrocarbons, while the TCA/Y-Zeolite catalyst was active and selective for producing alcohols, with a conversion of 66% and showed 55% selectivity for α-terpineol at 10 min. The reaction taken place in a solid-liquid mode and most of the α-terpineol is extracted out by the organic phase during the course of the reaction. TCA/Y-Zeolite was found as good catalyst for hydration of α-pinene to produce α-terpineol.
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41

Villemin, Didier, et Endo Schigeko. « Catalyse homogéné : synthèse d'organométalliques σ-acétylèniques catalysée par le cuivre(I) ». Journal of Organometallic Chemistry 346, no 1 (mai 1988) : C24—C26. http://dx.doi.org/10.1016/0022-328x(88)87018-9.

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42

Dubied, Annik. « Catalyse et parenthèse enchantée ». Le Temps des médias 10, no 1 (2008) : 142. http://dx.doi.org/10.3917/tdm.010.0142.

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43

Kentish, Sandra. « Embedded enzymes catalyse capture ». Nature Energy 3, no 5 (23 avril 2018) : 359–60. http://dx.doi.org/10.1038/s41560-018-0146-8.

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44

Kruyt, H. R., et C. F. van Duin. « Catalyse Hétérogène et Adsorption ». Recueil des Travaux Chimiques des Pays-Bas 40, no 5 (3 septembre 2010) : 249–80. http://dx.doi.org/10.1002/recl.19210400502.

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45

Newsholme, Philip. « Mapping life's reactions : A brief history of metabolic pathways and their regulation ». Biochemist 31, no 3 (1 juin 2009) : 4–7. http://dx.doi.org/10.1042/bio03103004.

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It is now recognized that almost all chemical reactions that take place in a living cell require an enzyme to catalyse the reaction. An enzyme catalyses one (or, in rare cases, more than one closely related) chemical reaction. The complete synthesis or degradation of complex biological substances such as glycogen, nucleic acids, proteins and lipids requires a series of linked sequences of reactions. A chain of such reactions is referred to as a ‘metabolic pathway’.
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46

Thomas, Stephen, Nate Ang, Cornelia Buettner, Scott Docherty, Alessandro Bismuto, Jonathan Carney, Jamie Docherty et Michael Cowley. « Borane-Catalysed Hydroboration of Alkynes and Alkenes ». Synthesis 50, no 04 (20 novembre 2017) : 803–8. http://dx.doi.org/10.1055/s-0036-1591719.

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Simple, commercially available borane adducts, H3B·THF and H3B·SMe2, have been used to catalyse the hydroboration of alkynes and alkenes with pinacolborane to give the alkenyl and alkyl boronic esters, respectively. Alkynes and terminal alkenes underwent highly regioselective hydroboration to give the linear boronic ester products. Good functional group tolerance was observed for substrates bearing ester, amine, ether and halide substituents. This catalytic process shows comparable reactivity to transition-metal-catalysed hydroboration protocols.
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47

Guette-Marquet, Simon, Christine Roques et Alain Bergel. « Catalysis of the electrochemical oxygen reduction reaction (ORR) by animal and human cells ». PLOS ONE 16, no 5 (5 mai 2021) : e0251273. http://dx.doi.org/10.1371/journal.pone.0251273.

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Animal cells from the Vero lineage and MRC5 human cells were checked for their capacity to catalyse the electrochemical oxygen reduction reaction (ORR). The Vero cells needed 72 hours’ incubation to induce ORR catalysis. The cyclic voltammetry curves were clearly modified by the presence of the cells with a shift of ORR of 50 mV towards positive potentials and the appearance of a limiting current (59 μA.cm-2). The MRC5 cells induced considerable ORR catalysis after only 4 h of incubation with a potential shift of 110 mV but with large experimental deviation. A longer incubation time, of 24 h, made the results more reproducible with a potential shift of 90 mV. The presence of carbon nanotubes on the electrode surface or pre-treatment with foetal bovine serum or poly-D-lysine did not change the results. These data are the first demonstrations of the capability of animal and human cells to catalyse electrochemical ORR. The discussion of the possible mechanisms suggests that these pioneering observations could pave the way for electrochemical biosensors able to characterize the protective system of cells against oxidative stress and its sensitivity to external agents.
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48

Tai, Xi-Shi, Peng-Fei Li et Li-Li Liu. « Synthesis, Crystal Structure, and Catalytic Activity of a Calcium(II) Complex with 4-Formylbenzene-1,3-disulfonate-isonicotinic Acid Hydrazone ». Bulletin of Chemical Reaction Engineering & ; Catalysis 13, no 3 (4 décembre 2018) : 429. http://dx.doi.org/10.9767/bcrec.13.3.1961.429-435.

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A new calcium(II) complex was synthesized by one-pot synthesis method from disodium 4-formylbenzene-1,3-disulfonate, isonicotinic acid hydrazide and Ca(ClO4)2•2H2O. The structure of calcium(II) complex was determined by elemental analysis, IR and single crystal X-ray diffraction. The results show that the Ca(II) complex molecules form 3D network structure by the interactions of π-π stacking and hydrogen bonds. The Ca(II) complex catalyst could efficiently catalyse oxidation of benzylic alcohol with good conversion of benzyl alcohol (78 %) and excellent selectivity of benzaldehyde (98 %).Copyright © 2018 BCREC Group. All rights reserved.Received: 13rd December 2017; Revised: 23rd May 2018; Accepted: 23rd May 2018How to Cite: Tai, X.S., Li, P.F., Liu, L.L. (2018). Synthesis, Crystal Structure, and Catalytic Activity of a Calcium(II) Complex with 4-Formylbenzene-1,3-disulfonate-isonicotinic Acid Hydrazone. Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3): 429-435 (doi:10.9767/bcrec.13.3.1961.429-435)Permalink/DOI: https://doi.org/10.9767/bcrec.13.3.1961.429-435
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49

Lilley, David M. J. « Mechanisms of RNA catalysis ». Philosophical Transactions of the Royal Society B : Biological Sciences 366, no 1580 (27 octobre 2011) : 2910–17. http://dx.doi.org/10.1098/rstb.2011.0132.

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Ribozymes are RNA molecules that act as chemical catalysts. In contemporary cells, most known ribozymes carry out phosphoryl transfer reactions. The nucleolytic ribozymes comprise a class of five structurally-distinct species that bring about site-specific cleavage by nucleophilic attack of the 2′-O on the adjacent 3′-P to form a cyclic 2′,3′-phosphate. In general, they will also catalyse the reverse reaction. As a class, all these ribozymes appear to use general acid–base catalysis to accelerate these reactions by about a million-fold. In the Varkud satellite ribozyme, we have shown that the cleavage reaction is catalysed by guanine and adenine nucleobases acting as general base and acid, respectively. The hairpin ribozyme most probably uses a closely similar mechanism. Guanine nucleobases appear to be a common choice of general base, but the general acid is more variable. By contrast, the larger ribozymes such as the self-splicing introns and RNase P act as metalloenzymes.
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Mantle, T. J. « Haem degradation in animals and plants ». Biochemical Society Transactions 30, no 4 (1 août 2002) : 630–33. http://dx.doi.org/10.1042/bst0300630.

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Two enzyme systems have evolved for the reduction of linear tetrapyrroles: one family, found in plants, algae and cyanobacteria, uses ferredoxin and catalyses the reduction of the terminal pyrrole rings (A and D) and one of the vinyl side chains to form various light-harvesting and light-sensing chromophores. The other group (biliverdin reductases A and B) utilize NAD(P)H and catalyse reduction at C10 (hydride addition) to form the ‘bile’ pigments bilirubin-IXα and bilirubin-IX.
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