initial reaction
Recently Published Documents





2022 ◽  
Mike J. Newland ◽  
Camille Mouchel-Vallon ◽  
Richard Valorso ◽  
Bernard Aumont ◽  
Luc Vereecken ◽  

Abstract. Reaction with ozone is an important atmospheric removal process for alkenes. The ozonolysis reaction produces carbonyls, and carbonyl oxides (Criegee intermediates, CI), which can rapidly decompose to yield a range of closed shell and radical products, including OH radicals. Consequently, it is essential to accurately represent the complex chemistry of Criegee intermediates in atmospheric models in order to fully understand the impact of alkene ozonolysis on atmospheric composition. A mechanism construction protocol is presented which is suitable for use in automatic mechanism generation. The protocol defines the critical parameters for describing the chemistry following the initial reaction, namely: the primary carbonyl / CI yields from the primary ozonide fragmentation; the amount of stabilisation of the excited CI (CI*); the unimolecular decomposition pathways, rates and products of the CI; the bimolecular rates and products of atmospherically important reactions of the stabilised CI (SCI). This analysis implicitly predicts the yield of OH from the alkene-ozone reaction. A comprehensive database of experimental OH, SCI and carbonyl yields has been collated using reported values in the literature and used to assess the reliability of the protocol. The protocol provides estimates OH, SCI and carbonyl yields with a root mean square error of 0.13 and 0.12 and 0.14, respectively. Areas where new experimental and theoretical data would improve the protocol and its assessment are identified and discussed.

2021 ◽  
Manvendra Singh ◽  
Bryce Gaskins ◽  
Daniel Johnson ◽  
Christopher Elles ◽  
Zarko Boskovic

We prepared a collection of complex cycloheptatriene-containing azetidine lactones by ap- plying two key photochemical reactions: “aza-Yang” cyclization and Buchner carbene insertion into aromatic rings. While photolysis of phenacyl amines leads to a rapid charge transfer and elimination, we found that a simple protonation of the amine enables the formation of azetidinols as single diastereomers. We provide evidence, through ultrafast spectroscopy, for the electron transfer from free amines in the excited state. Further, we characterize aza-Yang re- action by establishing the dependence of initial reaction rates on rates of photon absorption. Unanticipated change in reactivity in morpholine analogs is explained through interactions with the tosylate anion. Buchner reaction proceeds with slight preference for one diastereomer over the other, and successful reaction requires electron-donating carbene-stabilizing substituents. Overall, sixteen compounds were prepared over seven steps. Guided by an increase in structural complexity, efforts such as this one extend reach of chemists into unexplored chemical space and provide useful quantities of new compounds for studies focused on their properties.

Molecules ◽  
2021 ◽  
Vol 26 (24) ◽  
pp. 7663
Paulina Bednarczyk ◽  
Izabela Irska ◽  
Konrad Gziut ◽  
Paula Ossowicz-Rupniewska

This work involves the synthesis of hybrid oligomers based on the epoxy methacrylate resin. The EA resin was obtained by the modification of industrial-grade bisphenol A-based epoxy resin and methacrylic acid has been synthesized in order to develop multifunctional resins comprising both epoxide group and reactive, terminal unsaturation. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Monitoring of EA synthesis reactions over time using PAVs, MAAC and NV parameters, and the FT-IR method reveals that esterification reactions proceed faster at the start, exhibiting over 40% of conversion within the initial 60 min, which can be associated with a relatively high concentration of reactive sites and low viscosity of the reaction mixture at the initial reaction stage. With the further increase in the reaction time, the reaction rate tends to decrease.. The control of the EA synthesis process can guide how to adjust reactions to obtain EAs with desired characteristics. Based on obtained values, one can state that the optimum synthesis time of about 4–5 h should be adopted to prepare EAs having both epoxy groups and unsaturated double bonds. The structure of the obtained EA was confirmed by FT-IR and NMR methods, as well as the determination of partial acid value and epoxy equivalent. Samples at various stages of synthesis were cured with UV radiation in order to study the kinetics of the process according to cationic and radical polymerization determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) and then the properties of the cured coatings were tested. It turned out that the cationic polymerization was slower with a lower conversion of the photoreactive groups, as compared to the radical polymerization. All the obtained EA coatings were characterized by good properties of cured coatings and can be successfully used in the coating-forming sector.

Polymers ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 4309
Shufei Jiao ◽  
Zijie Liu ◽  
Min Liu ◽  
Yongxian Liu ◽  
Shuming Zhong ◽  

Selenium-functionalized starch (Se-starch80) is one of the main functional foods used for selenium supplementation. In traditional agriculture, Se-starch has some deficiencies such as long growth cycle and unstable selenium content that prevent its antioxidant performance. In this study, Se-starch was prepared by the nucleophilic addition between NaSeH and carbon-carbon double bond of octenyl succinic anhydride waxy corn starch ester (OSA starch). Some techniques such as 1HNMR, XPS, SEM-EDS, XRD and FT-IR were used to characterize the relevant samples and the results showed that the modification did not destroy the starch framework significantly and the catalytic center (negative divalent selenium) was anchored on the starch framework. The intensive distribution of catalytic center on the starch surface and the hydrophobic microenvironments derived from the OSA chains furnished the Se-starch80 with a high GPx-like catalytic activity (initial reaction rate = 3.64 μM/min). This value was about 1.5 × 105 times higher than that of a typical small-molecule GPx mimic (PhSeSePh). In addition, the Se-starch80, without any cytotoxicity, showed a saturated kinetic catalytic behavior that is similar to a typical enzyme. This work exemplifies a biodegradable selenium-functionalized polymer platform for the high-performing GPx mimic.

Geology ◽  
2021 ◽  
Krzysztof Sokół ◽  
Adrian A. Finch ◽  
William Hutchison ◽  
Jonathan Cloutier ◽  
Anouk M. Borst ◽  

Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth element (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage hydrothermal fluids associated with alkaline magmas is reported. However, the magnitude of the flux and the conditions are poorly constrained and yet essential to understanding the formation of REE-HFSE ores. We examined the alteration of country rocks (“fenitization”) accompanying the emplacement of a syenite magma at Illerfissalik in Greenland, through analysis of changes in rock chemistry, mineralogy, and texture. Our novel geochemical maps show a 400-m-wide intrusion aureole, within which we observed typically tenfold increases in the concentrations of many elements, including HFSEs. Textures suggest both pervasive and structurally hosted fluid flow, with initial reaction occurring with the protolith’s quartz cement, leading to increased permeability and enhancing chemical interaction with a mixed Ca-K-Na fenitizing fluid. We estimated the HFSE masses transferred from the syenite to the fenite by this fluid and found ~43 Mt of REEs were mobilized (~12% of the syenite-fenite system total rare-earth-oxide [TREO] budget), a mass comparable to the tonnages of some of the world’s largest HFSE resources. We argue that fenite can yield crucial information about the tipping points in magma evolution because retention and/or loss of volatile-bonded alkali and HFSEs are key factors in the development of magmatic zirconosilicate-hosted HFSE ores (e.g., Kringlerne, at Ilímaussaq), or the formation of the syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone deposits.

A.V. Shigapova ◽  
I.Kh. Vakhitov ◽  
R.S. Safin ◽  
I.R. Ibatullin ◽  

For the first time, studies were conducted to study the features of the heart rate response of laboratory animals exposed to various modes of motor activity when administered with β, α1 and α2-blockers. It was found that in all the experimental groups of animals studied, a decrease in the heart rate response was observed in the first week after the introduction of β, α1 and α2-adreno blockers. It was revealed that the initial reaction of the heart rate on the introduction of β, α1 and α2-blockers depends on the level of motor activity of laboratory animals. It was found that the most pronounced decrease in the heart rate response to the introduction of different subtypes of adreno-blockers is observed in the group of animals with limited motor activity. At the same time, the smallest decrease in the heart rate response occurs in the group of animals subject to enhanced motor mode. It was revealed that in the group of experimental animals, during further muscle training, by the end of the fourth week, there was a less pronounced decrease in the heart rate response to the administration of β, α1 and α2-adreno blockers. It was found that in a group of animals subject to a regime of limited motor activity, by the end of the fourth week of hypokinesia, the most pronounced decrease in the heart rate response to the introduction of β, α1-targeted blockers occurs.

O. M. Iniaghe ◽  
O. Ibukun

The effects of some alkali metal ions (Na+ and K+) and alkaline earth metal ions (Mg 2+ and Ba2+) on the initial reaction rates of Congregibacter litoralis KT71 β-lactamase hydrolysis of 4-nitrophenyl myristate was investigated by varying the concentrations of the metal ions in the assay mixture which comprised of 100 µl of standard enzyme solution, 200 µl of varying concentration of metal ions, 500 µl of 50 mM sodium phosphate buffer pH 7.5 and 200 µl of 4-nitrophenyl myristate (substrate) which was added last to the assay mixture after an incubation time of 10 minutes at 44 oC. The enzyme activity was measured spectrophotometrically using a UV-780 recording spectrophotometer at a wavelength of 405 nm. The hydrolysis of 4-nitrophenyl myristate to yield 4-nitrophenol was monitored by reading the absorbance at 25 minutes. Results showed that the alkaline earth metal ions (Ba2+ and Mg2+) had higher enzyme activation effect than the alkali metal ions (K+ and Na+) Also, all metal ions except Mg2+ showed enzyme stimulatory effect at low concentrations (<2 mM) but inhibitory at higher ion concentrations (2 mM - 3 mM). Mg 2+ caused a proportionate decrease in enzyme activity from its peak (when metal ion concentration was lowest). Results from this research is of great significance to the industrialist especially where the search for novel lipases with unique characteristics suitable for the industries are inevitable.

Reactions ◽  
2021 ◽  
Vol 2 (4) ◽  
pp. 486-498
Eva Vrbková ◽  
Adéla Šímová ◽  
Eliška Vyskočilová ◽  
Miloslav Lhotka ◽  
Libor Červený

Acid-treated montmorillonites (MMT) were used as catalysts of carvone isomerization to carvacrol. Mineral acids—sulfuric, hydrochloric, nitric acids and organic acids (acetic and chloroacetic)—were used for the acid treatment. Prepared materials were characterized by available characterization methods, namely XRD, EA, TPD, TPO, UV-Vis, laser light scattering and nitrogen physisorption. The structure of montmorillonite remained intact after treatment. However, TPD proved the increase of acidity of acid-treated materials comparing pure montmorillonite. All materials were tested in the isomerization of carvone, producing carvacrol as the desired product. The initial reaction rate increased using the materials in the row MMT-COOH < MMT-HNO3 < MMT-ClCOOH < MMT-H2SO4 < MMT-HCl, which is in accordance with the pKa of acids used for the treatment. The number of weak acid sites strongly influenced the selectivity to carvacrol. The optimal solvent for the reaction was toluene. Total conversion of carvone and the selectivity to carvacrol 95.5% was achieved within 24 h under 80 °C, with toluene as solvent and montmorillonite treated by chloroacetic acid as catalyst. The catalyst may be reused after calcination with only a low loss of activity.

Sign in / Sign up

Export Citation Format

Share Document