Correct Classification and Identification of Autocatalysis

2021 ◽  
Author(s):  
Attila Horváth
Keyword(s):  
Correct Classification ◽  
Reaction Proceeds ◽  
Kinetic Phenomenon

It is generally accepted that autocatalysis is a kinetic phenomenon, where a product of a reacting system catalyzes its own formation. Consequently, the reaction proceeds faster upon adding the corresponding...

Observations of the Thermal Decomposition of Brucite

1968 ◽  
Vol 26 ◽  
pp. 446-447
Author(s):  
P. L. Burnett ◽  
W. R. Mitchell ◽  
C. L. Houck
Keyword(s):  
Thermal Decomposition ◽  
Magnesium Oxide ◽  
Basal Plane ◽  
Magnesium Ions ◽  
A Value ◽  
Reaction Proceeds

Natural Brucite (Mg(OH)2) decomposes on heating to form magnesium oxide (MgO) having its cubic ﹛110﹜ and ﹛111﹜ planes respectively parallel to the prism and basal planes of the hexagonal brucite lattice. Although the crystal-lographic relation between the parent brucite crystal and the resulting mag-nesium oxide crystallites is well known, the exact mechanism by which the reaction proceeds is still a matter of controversy. Goodman described the decomposition as an initial shrinkage in the brucite basal plane allowing magnesium ions to shift their original sites to the required magnesium oxide positions followed by a collapse of the planes along the original <0001> direction of the brucite crystal. He noted that the (110) diffraction spots of brucite immediately shifted to the positions required for the (220) reflections of magnesium oxide. Gordon observed separate diffraction spots for the (110) brucite and (220) magnesium oxide planes. The positions of the (110) and (100) brucite never changed but only diminished in intensity while the (220) planes of magnesium shifted from a value larger than the listed ASTM d spacing to the predicted value as the decomposition progressed.

Solar photocatalysis mediated by ZnO for the removal of last traces of Indigo carmine dye pollutant from water

2018 ◽  
Vol 4 (02) ◽  
Author(s):  
Veena Vijayan ◽  
Suguna Yesodharan ◽  
E. P. Yesodharan
Keyword(s):  
Indigo Carmine ◽  
Parent Compound ◽  
Oxygen Demand ◽  
Green Technology ◽  
Solar Photocatalysis ◽  
Reaction Proceeds ◽  
Transient Intermediates ◽  
Significant Chemical ◽  
Hydroxyl Free Radicals ◽  
Purification Of Water

Solar photocatalysis as a potential green technology for the removal of traces of the dye pollutant Indigo carmine (IC) from water is investigated using ZnO as the catalyst. Degradation/decolorization alone does not result in complete decontamination as seen from the significant Chemical Oxygen Demand (COD) of water even after the parent compound has disappeared completely. The degradation proceeds through many intermediates which also get mineralized eventually but slowly. Oxalic acid is identified as a stable slow mineralizing degradation product which itself is formed from other transient intermediates. Effect of various parameters such as catalyst dosage, concentration of the dye, pH, temperature, presence of contaminant salts etc. on the degradation is investigated and quantified. Oxidants such as S2O82- and H2O2 have only moderate influence on the degradation. The degradation follows variable kinetics depending on the concentration of the substrate. The reaction proceeds very slowly in the absence of O2 indicating the importance of reactive oxygen species and hydroxyl free radicals in photocatalysis. H2O2 formed insitu in the system undergoes concurrent decomposition resulting in stabilization in its concentration. The study demonstrates that solar photocatalysis can be used as a viable tool for the purification of water contaminated with traces of IC.

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

2019 ◽  
Author(s):  
Marharyta V. Laktsevich-Iskryk ◽  
Nastassia A. Varabyeva ◽  
Volha V. Kazlova ◽  
Vladimir N. Zhabinskii ◽  
Vladimir A. Khripach ◽  
...  
Keyword(s):  
Visible Light ◽  
Functional Groups ◽  
Ring Opening ◽  
Radical Intermediates ◽  
Reaction Proceeds

In this article, we report a photocatalytic protocol for the isomerization of 1,2-disubstituted cyclopropanols to linear ketones. The reaction proceeds <i>via</i> radical intermediates and tolerates various functional groups.

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

2019 ◽  
Author(s):  
Marharyta V. Laktsevich-Iskryk ◽  
Nastassia A. Varabyeva ◽  
Volha V. Kazlova ◽  
Vladimir N. Zhabinskii ◽  
Vladimir A. Khripach ◽  
...  
Keyword(s):  
Visible Light ◽  
Functional Groups ◽  
Ring Opening ◽  
Radical Intermediates ◽  
Reaction Proceeds

In this article, we report a photocatalytic protocol for the isomerization of 1,2-disubstituted cyclopropanols to linear ketones. The reaction proceeds <i>via</i> radical intermediates and tolerates various functional groups.

Catalytic Enantioselective Benzylation Directly from Aryl Acetic Acids

2018 ◽  
Author(s):  
Patrick Moon ◽  
Zhongyu Wie ◽  
Rylan Lundgren
Keyword(s):  
Functional Group ◽  
Terminal Event ◽  
Radical Intermediates ◽  
Carbon Carbon Bond ◽  
Or Groups ◽  
Reaction Proceeds ◽  
Wide Availability ◽  
Metal Catalyzed ◽  
The Stability ◽  
Acetic Acids

The stability and wide availability of carboxylic acids make them valuable reagents in chemical synthesis. Most transition metal catalyzed processes using carboxylic acid substrates are initiated by a decarboxylation event that generates reactive carbanion or radical intermediates. Developing enantioselective methodologies relying on these principles can be challenging, as highly reactive species tend to react indiscriminately without selectivity. Furthermore, anionic or radical intermediates generated from decarboxylation can be incompatible with protic and electrophilic functionality, or groups that undergo trapping with radicals. We demonstrate that metal-catalyzed enantioselective benzylation reactions of allylic electrophiles can occur directly from aryl acetic acids. The reaction proceeds via a pathway in which decarboxylation is the terminal event, occurring after stereoselective carbon–carbon bond formation. The mechanistic features of the process enable enantioselective benzylation without the generation of a highly basic nucleophile. Thus, the process has broad functional group compatibility that would not be possible employing established protocols.<br>

Purine nucleoside phosphorylase: Isolation and characterization

1990 ◽  
Vol 55 (12) ◽  
pp. 2987-2999 ◽  
Author(s):  
Katarina Šedivá ◽  
Ivan Votruba ◽  
Antonín Holý ◽  
Ivan Rosenberg
Keyword(s):  
Molecular Weight ◽  
Purine Nucleoside Phosphorylase ◽  
Purine Nucleoside ◽  
Leukemia Cells ◽  
Ph Optimum ◽  
Nucleoside Phosphorylase ◽  
Isolation And Characterization ◽  
Reaction Proceeds ◽  
The Matrix ◽  
Sepharose 4B

Purine nucleoside phosphorylase (PNP) from mouse leukemia cells L1210 was purified to homogeneity by a combination of ion exchange and affinity chromatography using AE-Sepharose 4B and 9-(p-succinylaminobenzyl)hypoxanthine as the matrix and the ligand, respectively. The native enzyme has a molecular weight of 104 000 and consists of three subunits of equal molecular weight of 34 000. The results of isoelectric focusing showed that the enzyme is considerably microheterogeneous over the pI-range 4.0-5.8 and most likely consists of eight isozymes. The temperature and pH-optimum of phosphorolysis, purine nucleoside synthesis and also of transribosylation is identical, namely 55 °C and pH 7.4. The transribosylation reaction proceeds in the presence of phosphate only. The following Km-values (μmol l-1) were determined for phosphorolysis: inosine 40, 2'-deoxyinosine 47, guanosine 27, 2'-deoxyguanosine 32. The Km-values (μmol l-1) of purine riboside and deoxyriboside synthesis are lower than the values for phosphorolysis (hypoxanthine 18 and 34, resp., guanine 8 and 11, resp.). An affinity lower by one order shows PNP for (-D-ribose-1-phosphate, (-D-2-deoxyribose-1-phosphate (Km = 200 μmol l-1 in both cases) and phosphate (Km = 805 μmol l-1). The substrate specificity of the enzyme was also studied: positions N(1), C(2) and C(8) are decisive for the binding of the substrate (purine nucleoside).

scholarly journals The Use of Artificial Neural Networks and a General Discriminant Analysis for Predicting Culling Reasons in Holstein-Friesian Cows Based on First-Lactation Performance Records

Animals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 721
Author(s):  
Krzysztof Adamczyk ◽  
Wilhelm Grzesiak ◽  
Daniel Zaborski
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Discriminant Analysis ◽  
Multilayer Perceptrons ◽  
Correct Classification ◽  
Correct Classification Rate ◽  
Classification Rate ◽  
Holstein Friesian ◽  
Artificial Neural ◽  
Friesian Cows

The aim of the present study was to verify whether artificial neural networks (ANN) may be an effective tool for predicting the culling reasons in cows based on routinely collected first-lactation records. Data on Holstein-Friesian cows culled in Poland between 2017 and 2018 were used in the present study. A general discriminant analysis (GDA) was applied as a reference method for ANN. Considering all predictive performance measures, ANN were the most effective in predicting the culling of cows due to old age (99.76–99.88% of correctly classified cases). In addition, a very high correct classification rate (99.24–99.98%) was obtained for culling the animals due to reproductive problems. It is significant because infertility is one of the conditions that are the most difficult to eliminate in dairy herds. The correct classification rate for individual culling reasons obtained with GDA (0.00–97.63%) was, in general, lower than that for multilayer perceptrons (MLP). The obtained results indicated that, in order to effectively predict the previously mentioned culling reasons, the following first-lactation parameters should be used: calving age, calving difficulty, and the characteristics of the lactation curve based on Wood’s model parameters.

Reactions of 4-Pyrones with Azomethine Ylides as a Chemo­selective Method for the Construction of Multisubstituted Pyrano[2,3-c]pyrrolidines

Synthesis ◽  
2021 ◽  
Author(s):  
Dmitrii L. Obydennov ◽  
Vyacheslav D. Steben’kov ◽  
Konstantin L. Obydennov ◽  
Sergey A. Usachev ◽  
Vladimir S. Moshkin ◽  
...  
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Azomethine Ylides ◽  
Azomethine Ylide ◽  
Dipolar Cycloaddition ◽  
Computational Studies ◽  
Carbon Double Bond ◽  
Reactivity Indexes ◽  
Reaction Proceeds

Abstract4-Pyrones bearing electron-donating and electron-withdrawing groups react with nonstabilized azomethine ylides to form pyrano[2,3-c]pyrrolidines in moderate to good yields. The reaction proceeds chemoselectively as a 1,3-dipolar cycloaddition of the azomethine ylide at the carbon–carbon double bond of the pyrone activated by the electron-withdrawing substituent. The reactivity of 4-pyrones toward azomethine ylides was rationalized by computational studies with the use of reactivity indexes. The pyrano[2,3-c]pyrrolidine moiety could be modified, for example by a ring-opening transformation under the action of hydrazine to provide pyrazolyl-substituted pyrrolidines.

scholarly journals Nickel-Catalyzed Asymmetric Reductive Cross-Coupling of α-Chloroesters with (Hetero)Aryl Iodides

2021 ◽  
Author(s):  
Travis DeLano ◽  
Sara Dibrell ◽  
Caitlin R. Lacker ◽  
Adam Pancoast ◽  
Kelsey Poremba ◽  
...  
Keyword(s):  
Cross Coupling ◽  
Mild Conditions ◽  
Aryl Iodides ◽  
Reaction Proceeds

An asymmetric reductive cross-coupling of α-chloroesters and (hetero)aryl iodides is reported. This nickel-catalyzed reaction proceeds with a chiral BiOX ligand under mild conditions, affording α-arylesters in good yields and enantioselectivities....

Validation of the CASUS score in Tunisian patients: a quality management tool in intensive care units

2020 ◽  
Vol 30 (Supplement_5) ◽  
Author(s):  
T Besbes ◽  
S Mleyhi ◽  
J Sahli ◽  
M Messai ◽  
J Ziadi ◽  
...  
Keyword(s):  
Cardiac Surgery ◽  
Roc Curve ◽  
Goodness Of Fit ◽  
Cardiovascular Surgery ◽  
Management Tool ◽  
Medical Decision ◽  
Tunisian Population ◽  
Correct Classification ◽  
Goodness Of Fit Test ◽  
A Value

Abstract Background Early prediction of patients at highest risk of a poor outcome after cardiovascular surgery, including death can aid medical decision making, and adapt health care management in order to improve prognosis. In this context, we conducted this study to validate the CASUS severity score after cardiac surgery in the Tunisian population. Methods This is a retrospective cohort study conducted among patients who underwent cardiac surgery under extracorporeal circulation during the year 2018 at the Cardiovascular Surgery Department of La Rabta University Hospital in Tunisia. Data were collected from the patients hospitalization records. The discrimination of the score was assessed using the ROC curve and the calibration using the Hosmer-Lemeshow goodness of fit test and then by constructing the calibration curve. Overall correct classification was also obtained. Results In our study, the observed mortality rate was 10.52% among the 95 included patients. The discriminating power of the CASUS score was estimated by the area under the ROC curve (AUC), this scoring system had a good discrimination with AUC greater than 0.9 from postoperative Day 0 to Day 5.From postoperative day 0 to day 5, the Hosmer-Lemeshow's test gave a value of chi square test statistic ranging from 1.474 to 8.42 and a value of level of significance ranging from 0.39 to 0.99 indicating a good calibration. The overall correct classification rate from postoperative day 0 to day 5 ranged from 84.4% to 92.4%. Conclusions Despite the differences in the profile of the risk factors between the Tunisian population and the population constituting the database used to develop the CASUS score, we can say that this risk model presents acceptable performances in our population, attested by adequate discrimination and calibration. Prospective and especially multicentre studies on larger samples are needed before definitively conclude on the performance of this model in our country. Key messages The casus score seems to be valid to predict mortality among patients undergoing cardiac surgery. Multicenter study on larger sample is needed to derive and validate models able to predict in-hospitals mortality.

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