Degradation of rutin by Aspergillus flavus. Studies on specificity, inhibition, and possible reaction mechanism of quercetinase

1972 ◽  
Vol 18 (4) ◽  
pp. 493-508 ◽  
Author(s):  
T. Oka ◽  
F. J. Simpson ◽  
H. G. Krishnamurty
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Aspergillus Flavus ◽  
Chelating Agents ◽  
Enzymatic Oxidation ◽  
Maximal Rate ◽  
Carbonyl Groups ◽  
Sulfhydryl Reagents ◽  
Nitrogen Bases ◽  
Chelating Ability

The dioxygenase produced by Aspergillus flavus that oxidizes quercetin contains 2 moles of copper per mole of enzyme and binds at least 2 moles of substrate. The enzyme is not inhibited by sulfhydryl reagents or affected by H2O2, but is inhibited by copper-chelating agents and reducing agents. Nitrogen bases with chelating ability are more effective inhibitors than those that do not form metal chelates.The dioxygenase oxidizes flavones that possess a double bond between carbons-2 and -3 and a hydroxyl on carbon-3. Hydroxyls at other positions affect both the relative rates of enzymatic oxidation and the concentration of substrate required to attain half maximal rate (Km). The evidence indicates that the substrate binds to the copper of the enzyme via the 3-hydroxyl and 4-carbonyl groups of the substrate. A possible mechanism for the reaction is presented.

Atomic absorption spectrometry of cobalt in the presence of chelating agents

1980 ◽  
Vol 45 (12) ◽  
pp. 3313-3319 ◽  
Author(s):  
Josef Komárek ◽  
Dalibor Kolčava ◽  
Lumír Sommer
Keyword(s):  
Reaction Mechanism ◽  
Atomic Absorption Spectrometry ◽  
Atomic Absorption ◽  
Chelating Agents ◽  
Absorption Spectrometry ◽  
Donor Atom ◽  
Optimum Conditions

The effect of chelating agents on the determination of cobalt in various flames, in a graphite cuvette and tantalum boat was studied considering the expected reaction mechanism of the atomization of cobalt and the reagent donor atom. A marked increase in the sensitivity of the determination of cobalt was observed in the presence of 1-(2-pyridylazo)-2-naphthol, pyrrolidinedithiocarboxylate, diethyldithiocarbamate, 8-mercaptoquinoline, 8-hydroxyquinoline and thenoyltrifluoroacetone for atomization from a tantalum boat. The optimum conditions for the determination of cobalt in the presence of 1-(2-pyridylazo)-1-naphthol are given.

scholarly journals Asymmetric Hydrogenation of C=N Double Bond with Modified Raney Nickel 1. New Determination Method for the Reaction Mechanism Using Asymmetric Catalyst

1970 ◽  
Vol 43 (6) ◽  
pp. 1792-1795 ◽  
Author(s):  
Yoshiharu Izumi ◽  
Hidemitsu Takizawa ◽  
Kunio Nakagawa ◽  
Ryushichi Imamura ◽  
Masami Imaida ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Raney Nickel ◽  
Asymmetric Hydrogenation ◽  
Determination Method ◽  
Asymmetric Catalyst

Metal-Free Addition of Boronic Acids to Silylnitronates

Synlett ◽  
2020 ◽  
Vol 31 (09) ◽  
pp. 856-860
Author(s):  
Laurent El Kaïm ◽  
Mansour Dolé Kerim ◽  
Pakoupati Boyode ◽  
Julian Garrec
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Boronic Acids ◽  
Dft Study ◽  
Metal Free ◽  
Nitro Derivatives ◽  
Oxime Derivatives ◽  
Nitrogen Double Bond ◽  
First Time ◽  
Aryl Transfer

We report for the first time a metal-free addition of boronic acids to silylnitronates to afford oxime derivatives through aryl transfer on the carbon nitrogen double bond. A reaction mechanism has been proposed in relation with a DFT study on the key aryl transfer. This arylation process is effective for cycloalkenyl nitro derivatives leading to oximes that may be oxidatively converted into 3-arylisoxazole derivatives.

Isolation and characterization of a FAD-dependent NADH diaphorase from Methanospirillum hungatei strain GP1

1981 ◽  
Vol 59 (2) ◽  
pp. 83-91 ◽  
Author(s):  
R. C. McKellar ◽  
K. M. Shaw ◽  
G. D. Sprott
Keyword(s):  
Gel Electrophoresis ◽  
Superoxide Anion ◽  
Chelating Agents ◽  
Sodium Dodecyl ◽  
Sulfhydryl Reagents ◽  
Ph Optimum ◽  
Methanospirillum Hungatei ◽  
Isolation And Characterization ◽  
Nadh Diaphorase

Crude extracts of Methanospirillum hungatei strain GP1 contained NADH and NADPH diaphorase activities. After a 483-fold purification of the NADH diaphorase the enzyme was further separated from contaminating proteins by polyacrylamide disc gel electrophoresis. Two distinct activity bands were extracted from the acrylamide, each one having oxygen, 2,6-dichlorophenoiindophenol, and cytochrome c linked activities. In these preparations NADPH could not replace NADH as electron donor. During the initial purification steps all activity was lost due to the removal of a readily released cofactor. Enzyme activity was restored by either FAD or a FAD fraction isolated from M. hungatei. Oxidase activity exhibited a broad pH optimum from 7.0 to 8.5 and apparent Km values of 26 μM for NADH and 0.2 μM for FAD. Superoxide anion, formed in the presence of oxygen, accounted for all of the NADH consumed in this reaction. The molecular weight of the diaphorase was about 117 500 by sodium dodecyl sulfate gel electrophoresis. Sulfhydryl reagents and chelating agents were inhibitory. Inactivation, which occurred during storage in phosphate buffer at 4 °C, was delayed by dithiothreitol. The isolated NADH diaphorase lacked NADPH:NAD transhydrogenase and NAD reductase activities.

Microbial hydroxylation of steroids. 10. Rearrangement during epoxidation and hydroxylation, and the stepwise nature of these enzymic reactions

1985 ◽  
Vol 63 (5) ◽  
pp. 1121-1126 ◽  
Author(s):  
Herbert L. Holland ◽  
Elly Riemland
Keyword(s):  
Double Bond ◽  
Product Formation ◽  
Enzymatic Oxidation ◽  
Allylic Rearrangement ◽  
Stepwise Mechanism ◽  
Microbial Hydroxylation ◽  
A Site

A series of unsaturated steroids has been incubated with fungi which are known to hydroxylate at a site corresponding to the allylic position in the analogous saturated steroids. In some cases, the anticipated hydroxylation occurred without rearrangement of the double bond. In a number of instances, however, products were obtained whose structures implied that allylic rearrangement had occurred during the reaction. The formation of these products is consistent with a stepwise mechanism of enzymatic oxidation. Possible routes for product formation are presented which incorporate this proposal.

scholarly journals Design of Boradecarboxylation Reaction

2020 ◽  
Author(s):  
Yuji Naruse ◽  
Atsushi Takamori ◽  
Kenji Oda
Keyword(s):  
Double Bond ◽  
Theoretical Calculation ◽  
Polar Solvent ◽  
Theoretical Calculations ◽  
Lone Pair ◽  
Carbonyl Groups ◽  
Orbital Theory ◽  
Enol Ethers ◽  
Decarboxylation Reaction ◽  
Boat Form

For mechanism of decarboxylation reaction, all textbooks show that the electron moves from the pi<sub>C=O</sub> bond. However, the most donating bond orbital in the carbonyl group should be the lone pair(s) on the oxygen. Thus, a picture of orbital theory with delocalization from a lone pair should be more appropriate than that from the pi<sub>C=O</sub> orbital. We confirmed our idea by theoretical calculation. In the TS, if we use 2-substituted b-ketoacids, the boat-form conformation should result in exclusively preferred generation of <i>E</i>-enolates. Normally, decarboxylation reaction performs in polar solvent, so that the resulting enols should be transformed to the corresponding ketones by tautomerization. Suppose we use the heteroatoms to obtain the enolate or enol ethers without tautomerization, it would offer a diastereoselective enol(ate) synthesis with regioselectivity, since the C=C double bond should always be introduced between two carbonyl groups. After screening the heteroatoms by the theoretical calculations, we found that boron is suitable for this purpose. We confirmed our idea by theoretical calculations, offering a new boradecarboxylation reaction to produce enolates diastereoselecitively and regioselectively.

Isotopic solvent effect in hydrogenation on a supported nickel catalyst

1983 ◽  
Vol 48 (9) ◽  
pp. 2609-2613
Author(s):  
Rostislav Kudláček ◽  
Alena Judlová
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Organic Compound ◽  
Nickel Catalyst ◽  
Heavy Water ◽  
Maleic Acid ◽  
Reaction Rate ◽  
Supported Nickel Catalyst ◽  
Light Water ◽  
Water Solvent

A supported nickel catalyst, commonly applied in industrial hydrogenation of fatts and oils, was used to study the effect of replacement of the light water solvent, with heavy water, on the addition of hydrogen on a double bond of maleic acid. The effect was investigated of the composition and temperature of the solution, on the reaction rate, as well as, the relation between the reaction rate and the amount of the acid absorbed on the catalyst. Reaction mechanism with respect to the hydrogenated organic compound is proposed.

Reactions of stabilized phosphoranes with enol lactones

1977 ◽  
Vol 30 (7) ◽  
pp. 1629 ◽  
Author(s):  
PJ Babidge ◽  
RA Massy-Westropp
Keyword(s):  
Double Bond ◽  
Carbonyl Group ◽  
Ester Group ◽  
Carbonyl Groups ◽  
Ketone Group ◽  
Mild Conditions ◽  
Lactone Carbonyl ◽  
Factors Influencing ◽  
Group Reaction

Enol lactones in which the double bond is conjugated with an ester group react with ethoxycarbonyl-methylenetriphenylphosphoraneunder mild conditions to yield the normal Wittig product, derivedfrom the lactone carbonyl group. When the double bond is conjugated with a ketone group reaction occurs at both carbonyl groups. Factors influencing reactivity are discussed.

THE MECHANISM OF POLYMERIZATION REACTIONS

1932 ◽  
Vol 7 (1) ◽  
pp. 113-114 ◽  
Author(s):  
William Chalmers
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Hydrogen Atoms ◽  
Chain Reaction ◽  
A Chain

Attention is called to an earlier, unpublished writing by the author wherein a chain-reaction mechanism was suggested for all polymerizations leading to macro-molecular products. It is further pointed out that the only scheme of reaction which is compatible with this mechanism is that which involves only the double bond, i.e., the possibility of the changes taking place by the transference of hydrogen atoms is practically excluded.

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