scholarly journals Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

2007 ◽  
Vol 461 (2) ◽  
pp. 159-168 ◽  
Author(s):  
Hui-Chun Yeh ◽  
Ah-Lim Tsai ◽  
Lee-Ho Wang
Keyword(s):  
Reaction Mechanisms ◽  
Acid Catalyzed ◽  
Hydroperoxyeicosatetraenoic Acid

scholarly journals BIS-DEACETYLATION OF TETRAACETYLGLYCOLURYL UNDER ACTION OF UREAS

2018 ◽  
Vol 61 (7) ◽  
pp. 50
Author(s):  
Ngoc Phuoc Hoang ◽  
Abdigali A. Bakibaev ◽  
Victor S. Malkov
Keyword(s):  
Reaction Mechanisms ◽  
Nucleophilic Addition ◽  
Specific Effect ◽  
Independent Effect ◽  
Similar Reaction ◽  
Urea Molecule ◽  
Acid Catalyzed ◽  
Integrated Intensities ◽  
Cis Isomer ◽  
Methyl Phenyl

It is established that tetraacetylglycoluril under the action of urea, some N-substituted ureas and benzylidenebisurea in the acid-catalyzed conditions undergoes only bis-deacetylation with the formation of syn- and anti-regio-substituted N,N-diacetylglycolurils, rather than N-acetylation as it was previously shown in a similar reaction for a number of aromatic and heterocyclic amines. In the course of individual experiments, the absence of independent effect of organic solvents during boiling for several hours (alcohols, dioxane, tetrahydrofuran, dimethylsulfoxide) on the deacetylation of tetraacetylglycoluril was revealed, since in these conditions the original substrate remained unchanged. Based on the NMR spectroscopy data, by comparison the integrated intensities of methine and acetyl protons of glycoluryl fragments, we found that the bis-deacetylation of tetraacetylglycoluril in the studied conditions occurs regioselectively with an overwhelming majority of anti-N,N-diacetylglycoluril (up to 92-94%) except for benzylidenebisurea, when the content of the trans-isomer reaches 75%. A marked increase in the cis-isomer (up to 25%) of N,N-diacetylglycoluril in the case of benzylidenebisurea seems to be dictated by the specific effect on the intermediates of reaction of phenylmethylureido carbocation from eliminating urea molecule in acid-catalyzed conditions. It is shown that N,N-diacetylglycoluril in similar conditions under the action of urea and its derivatives does not undergo further deacetylation to the progenitor of bicyclic bisureas – glycoluril, primarily related to the high hydrolytic and steric resistance of these compounds. On the basis of the above research results, the reaction mechanisms of bis-deacetylation of tetraacetylglycoluril in the acid-catalyzed conditions under the action of urea and its N-methyl (phenyl) derivatives through an intermediate process of nucleophilic addition of ureas is proposed.Forcitation:Hoang N.P., Bakibaev A.A., Malkov V.S. Bis-deacetylation of tetraacetylglycoluryl under action of ureas. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 49-53

scholarly journals NEW ASPECTS ON REACTION MECHANISMS IN THE FORMALDEHYDE HISTOFLUORESCENCE METHOD FOR MONOAMINES

1973 ◽  
Vol 21 (1) ◽  
pp. 17-25 ◽  
Author(s):  
ANDERS BJÖRKLUND ◽  
BENGT FALCK ◽  
OLLE LINDVALL ◽  
LEIF-ÅKE SVENSSON
Keyword(s):  
Mass Spectrometry ◽  
Reaction Mechanisms ◽  
Equal Importance ◽  
Freeze Dried ◽  
Subsequent Step ◽  
Fluorescent Products ◽  
Acid Catalyzed ◽  
Protein Models ◽  
Layer Chromatography ◽  
Mechanisms Of Reactions

The mechanisms of reactions underlying the fluorophore formation from indolylethylamines in the Falck-Hillarp histochemical formaldehyde method were investigated with the aid of thin layer chromatography and mass spectrometry of the fluorescent products formed in protein models and freeze-dried tissue. In the reaction of formaldehyde with tryptamine and 5-hydroxytryptamine, the main fluorophores formed were 3,4-dihydro-β-carboline and the 2-methyl-3,4-dihydro-β-carbolinium compound (from tryptamine), and 6-hydroxy-3,4-dihydro-β-carboline and the 2-methyl-6-hydroxy-3,4-dihydro-β-carbolinium compound (from 5-hydroxytryptamine). From these findings, it is concluded that the fluorophore formation in the Falck-Hillarp method proceeds as follows: In the first step of the reaction, the indolylethylamines react with formaldehyde to form low fluorescent 1,2,3,4-tetrahydro-β-carbolines. In a subsequent step, these products are converted to fluorophores in either of two ways: through an autoxidation to 3,4-dihydro-β-carbolines, or through a second, acid-catalyzed reaction with formaldehyde to yield 2-methyl-3,4-dihydro-β-carbolinium compounds. Experiments with radioactive tryptamine indicated that the two alternative fluorophore-forming pathways are of fairly equal importance. The latter of these fluorophore-forming reactions was not previously known, and the interesting properties and implications of this formaldehyde-induced and acid-catalyzed reaction are discussed.

scholarly journals The acid-catalyzed hydrolysis of an <i>α</i>-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact

2016 ◽  
Vol 16 (23) ◽  
pp. 15425-15432 ◽  
Author(s):  
Joel D. Rindelaub ◽  
Carlos H. Borca ◽  
Matthew A. Hostetler ◽  
Jonathan H. Slade ◽  
Mark A. Lipton ◽  
...  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Tropospheric Ozone ◽  
Organic Aerosol ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Particle Phase ◽  
Fine Aerosol ◽  
Acid Catalyzed

Abstract. The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO + NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long-range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, the hydrolysis mechanism and rate constants were elucidated for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the tertiary APN lifetime ranging from 8.3 min at acidic pH (0.25) to 8.8 h at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant data, product identification confirms that a unimolecular specific acid-catalyzed mechanism is responsible for organic nitrate hydrolysis under acidic conditions. The free energies and enthalpies of the isobutyl nitrate hydrolysis intermediates and products were calculated using a hybrid density functional (ωB97X-V) to support the proposed mechanisms. These findings provide valuable information regarding the organic nitrate hydrolysis mechanism and its contribution to the fate of atmospheric NOx, aerosol phase processing, and BSOA composition.

scholarly journals The Acid-Catalyzed Hydrolysis of an α-Pinene-Derived Organic Nitrate: Kinetics, Products, Reaction Mechanisms, and Atmospheric Impact

2016 ◽  
Author(s):  
Joel D. Rindelaub ◽  
Carlos H. Borca ◽  
Matthew A. Hostetler ◽  
Mark A. Lipton ◽  
Lyudmila V. Slipchenko ◽  
...  
Keyword(s):  
Gas Phase ◽  
Reaction Mechanisms ◽  
Tropospheric Ozone ◽  
Organic Aerosol ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Particle Phase ◽  
Fine Aerosol ◽  
Acid Catalyzed ◽  
Insight Into

Abstract. The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate, due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO+NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still very uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically-derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, this study elucidated the hydrolysis mechanism and rate constants for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the APN lifetime ranging from 8.3 minutes at acidic pH (0.25) to 8.8 hours at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant data, the identification of the products campholenic aldehyde, pinol, and pinocamphone confirms a unimolecular specific acid-catalyzed mechanism is responsible for organic nitrate hydrolysis under acidic conditions, where carbocation rearrangement is favored for α-pinene-derived species. The free energies and enthalpies of the isobutyl nitrate hydrolysis intermediates and products were calculated using a hybrid density functional (ωB97X-V) to support the proposed mechanisms. These findings provide valuable insight into the organic nitrate hydrolysis mechanism and its contribution to the fate of atmospheric NOx, aerosol phase processing, and BSOA composition.

Analyzing reactions of single mechanoenzyme molecules by light microscopy

1992 ◽  
Vol 50 (1) ◽  
pp. 426-427
Author(s):  
Jeff Gelles
Keyword(s):  
Image Processing ◽  
Reaction Mechanisms ◽  
Transient State ◽  
Nanometer Scale ◽  
Reaction Intermediates ◽  
Enzyme Molecule ◽  
Directed Movement ◽  
Enzyme Molecules ◽  
Individual Enzyme ◽  
Single Reaction

Mechanoenzymes are enzymes which use a chemical reaction to power directed movement along biological polymer. Such enzymes include the cytoskeletal motors (e.g., myosins, dyneins, and kinesins) as well as nucleic acid polymerases and helicases. A single catalytic turnover of a mechanoenzyme moves the enzyme molecule along the polymer a distance on the order of 10−9 m We have developed light microscope and digital image processing methods to detect and measure nanometer-scale motions driven by single mechanoenzyme molecules. These techniques enable one to monitor the occurrence of single reaction steps and to measure the lifetimes of reaction intermediates in individual enzyme molecules. This information can be used to elucidate reaction mechanisms and determine microscopic rate constants. Such an approach circumvents difficulties encountered in the use of traditional transient-state kinetics techniques to examine mechanoenzyme reaction mechanisms.

X-Ray Microanalysis of Nickel and Cobalt Intensified Peroxidase- Antiperoxidase For Verification of Reaction Sites

1985 ◽  
Vol 43 ◽  
pp. 468-469
Author(s):  
A. Angel ◽  
K. Miller ◽  
V. Seybold ◽  
R. Kriebel
Keyword(s):  
Reaction Mechanisms ◽  
Visual Discrimination ◽  
Osmium Tetroxide ◽  
Ultrastructural Level ◽  
Microscopic Level ◽  
Electron Microscopic Level ◽  
Electron Microscopic ◽  
X Ray ◽  
Insoluble Polymer ◽  
Cytochemical Reaction

Localization of specific substances at the ultrastructural level is dependent on the introduction of chemicals which will complex and impart an electron density at specific reaction sites. Peroxidase-antiperoxidase(PAP) methods have been successfully applied at the electron microscopic level. The PAP complex is localized by addition of its substrate, hydrogen peroxide and an electron donor, usually diaminobenzidine(DAB). On oxidation, DAB forms an insoluble polymer which is able to chelate with osmium tetroxide becoming electron dense. Since verification of reactivity is visual, discrimination of reaction product from osmiophillic structures may be difficult. Recently, x-ray microanalysis has been applied to examine cytochemical reaction precipitates, their distribution in tissues, and to study cytochemical reaction mechanisms. For example, immunoreactive sites labelled with gold have been ascertained by means of x-ray microanalysis.

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