scholarly journals Effect of Methyl Group Substitution on the Kinetics of Vinyl Radical + O2 Reaction

2019 ◽  
Vol 123 (49) ◽  
pp. 10514-10519
Author(s):  
Satya P. Joshi ◽  
Timo T. Pekkanen ◽  
Raimo S. Timonen ◽  
Arkke J. Eskola
Keyword(s):  
Methyl Group ◽  
Vinyl Radical ◽  
Kinetics Of

Kinetics of the Imidazolium Ring-Opening of mRNA 5'-cap Analogs in Aqueous Alkali

2006 ◽  
Vol 71 (4) ◽  
pp. 567-578 ◽  
Author(s):  
Alicja Stachelska ◽  
Zbigniew J. Wieczorek ◽  
Janusz Stępiński ◽  
Marzena Jankowska-Anyszka ◽  
Harri Lönnberg ◽  
...  
Keyword(s):  
Electrostatic Interaction ◽  
Ring Opening ◽  
Nucleophilic Attack ◽  
Amino Groups ◽  
Hydroxide Ion ◽  
Methyl Group ◽  
Structural Modifications ◽  
Alkyl Groups ◽  
Imidazolium Ring ◽  
Kinetics Of

Second-order rate constants for the hydroxide-ion-catalyzed imidazolium ring-opening of several mono- and dinucleosidic analogs of mRNA 5'-cap have been determined. Intramolecular stacking of the two nucleobases in the dinucleosidic analogs, m7GpppN (m7G = 7-methylguanosine, N = 5'-linked nucleoside), and electrostatic interaction between the N-alkylated imidazolium ring and phosphate moiety have been shown to shield the m7G moiety against the nucleophilic attack of hydroxide ion. In addition, the effect of methylation of the nucleobase amino groups and replacement of the 7-methyl group with other alkyl groups have been studied. The influence of all the structural modifications studied turned out to be modest, the cleavage rates of the most and least reactive analogs (with the exception of non-phosphorylated nucleosides) differing only by a factor of 5.

Reactions of free radicals with aromatic compounds in the gaseous phase. I. Kinetics of the reaction of methyl radicals with toluene

1964 ◽  
Vol 17 (12) ◽  
pp. 1329 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Flow System ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Benzyl Radical ◽  
Toluene Molecule ◽  
Benzyl Radicals ◽  
Butyl Peroxide ◽  
Kinetics Of

The kinetics of abstraction of hydrogen atoms from the methyl group of the toluene molecule by methyl radicals at 430-540�K have been determined. The methyl radicals were produced by pyrolysis of di-t-butyl peroxide in a stirred-flow system. The kinetics ,agree substantially with those obtained by previous authors using photolytic methods for generating the methyl radicals. At toluene and methyl-radical concentrations of about 5 x 10-7 and 10-11 mole cm-3 respectively the benzyl radicals resulting from the abstraction disappear almost entirely by combination with methyl radicals at the methylenic position. In this respect the benzyl radical behaves differently from the iso-electronic phenoxy radical, which previous work has shown to combine with a methyl radical mainly at ring positions. The investigation illustrates the application of stirred-flow technique to the study of the kinetics of free-radical reactions.

scholarly journals Turning Cones Off: the Role of the 9-Methyl Group of Retinal in Red Cones

2006 ◽  
Vol 128 (6) ◽  
pp. 671-685 ◽  
Author(s):  
Maureen E. Estevez ◽  
Petri Ala-Laurila ◽  
Rosalie K. Crouch ◽  
M. Carter Cornwall
Keyword(s):  
Visual Pigment ◽  
Bright Light ◽  
Rapid Rate ◽  
Methyl Group ◽  
Cone Opsin ◽  
Rate Of Recovery ◽  
Kinetics Of ◽  
Flash Response

Our ability to see in bright light depends critically on the rapid rate at which cone photoreceptors detect and adapt to changes in illumination. This is achieved, in part, by their rapid response termination. In this study, we investigate the hypothesis that this rapid termination of the response in red cones is dependent on interactions between the 9-methyl group of retinal and red cone opsin, which are required for timely metarhodopsin (Meta) II decay. We used single-cell electrical recordings of flash responses to assess the kinetics of response termination and to calculate guanylyl cyclase (GC) rates in salamander red cones containing native visual pigment as well as visual pigment regenerated with 11-cis 9-demethyl retinal, an analogue of retinal in which the 9-methyl group is missing. After exposure to bright light that photoactivated more than ∼0.2% of the pigment, red cones containing the analogue pigment had a slower recovery of both flash response amplitudes and GC rates (up to 10 times slower at high bleaches) than red cones containing 11-cis retinal. This finding is consistent with previously published biochemical data demonstrating that red cone opsin regenerated in vitro with 11-cis 9-demethyl retinal exhibited prolonged activation as a result of slowed Meta II decay. Our results suggest that two different mechanisms regulate the recovery of responsiveness in red cones after exposure to light. We propose a model in which the response recovery in red cones can be regulated (particularly at high light intensities) by the Meta II decay rate if that rate has been inhibited. In red cones, the interaction of the 9-methyl group of retinal with opsin promotes efficient Meta II decay and, thus, the rapid rate of recovery.

Kinetics of acid-catalyzed cyclization of substituted hydantoinamides to substituted hydantoins

1987 ◽  
Vol 52 (8) ◽  
pp. 1999-2004 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Gabriela Svobodová ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Hydrochloric Acid ◽  
Dissociation Constants ◽  
Amide Group ◽  
The Other ◽  
Methyl Group ◽  
Acid Catalyzed ◽  
Cyclization Rate ◽  
Kinetics Of

The kinetics of acid-catalyzed cyclization of the hydantoinamides type R3-N(5)H-CO-N(3)R2-CH2-CO-N(1)HR1 (R1, R2, R3 = H and/or CH3) has been studied in 0·5 to 5 mol l-1 hydrochloric acid. The cyclization rate is limited by the rate of the attack of nitrogen atom N(5) on the carbon atom of the protonated amide group. The dissociation constants of the protonated hydantoinamides and rate constants of their cyclizations have been determined. Replacement of hydrogen atom by methyl group at the N(5) nitrogen atom accelerates the cyclization about two times., the same substitution at N(3) accelerates about 50x, whereas at N(1) it results in a 300 fold retardation. With the hydantoinamides having R3 = CH3, the cyclization rate of the protonated hydantoinamide increases with increasing concentration of hydrochloric acid, whereas with the other derivatives this value is independent of the acid concentration.

scholarly journals Mechanistic and kinetics investigations of oligomer formation from Criegee intermediate reactions with hydroxyalkyl hydroperoxides

2019 ◽  
Vol 19 (6) ◽  
pp. 4075-4091 ◽  
Author(s):  
Long Chen ◽  
Yu Huang ◽  
Yonggang Xue ◽  
Zhenxing Shen ◽  
Junji Cao ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Organic Aerosol ◽  
Climate Forcing ◽  
Phase Reaction ◽  
Methyl Group ◽  
Consecutive Reactions ◽  
Mechanism And Kinetics ◽  
High Level ◽  
First Time ◽  
Kinetics Of

Abstract. Although secondary organic aerosol (SOA) is a major component of PM2.5 and organic aerosol (OA) particles and therefore profoundly influences air quality, climate forcing, and human health, the mechanism of SOA formation via Criegee chemistry is poorly understood. Herein, we perform high-level theoretical calculations to study the gas-phase reaction mechanism and kinetics of four Criegee intermediate (CI) reactions with four hydroxyalkyl hydroperoxides (HHPs) for the first time. The calculated results show that the consecutive reactions of CIs with HHPs are both thermochemically and kinetically favored, and the oligomers contain CIs as chain units. The addition of an −OOH group in HHPs to the central carbon atom of CIs is identified as the most energetically favorable channel, with a barrier height strongly dependent on both CI substituent number (one or two) and position (syn- or anti-). In particular, the introduction of a methyl group into the anti-position significantly increases the rate coefficient, and a dramatic decrease is observed when the methyl group is introduced into the syn-position. These findings are expected to broaden the reactivity profile and deepen our understanding of atmospheric SOA formation processes.

scholarly journals Oligomerization Reactions of Criegee Intermediates with Hydroxyalkyl Hydroperoxides: Mechanism, Kinetics, and Structure-Reactivity Relationship

2018 ◽  
pp. 1-35 ◽  
Author(s):  
Long Chen ◽  
Yu Huang ◽  
Yonggang Xue ◽  
Zhenxing Shen ◽  
Junji Cao ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Climate Forcing ◽  
Atmospheric Lifetime ◽  
Methyl Group ◽  
Criegee Intermediates ◽  
Sequential Addition ◽  
Structure Reactivity Relationship ◽  
High Level ◽  
First Time ◽  
Kinetics Of

<p><strong>Abstract.</strong> Although secondary organic aerosols (SOAs) are major components of PM<sub>2.5</sub> and organic aerosol (OA) particles and therefore profoundly influencing air quality, climate forcing and human health, the mechanism of SOAs formation via Criegee chemistry is poorly understood. Herein, we perform high-level theoretical calculations to study the reactivity and kinetics of four Criegee intermediates (CIs) reactions with four hydroxyalkyl hydroperoxides (HHPs) for the first time. The calculated results show that the sequential addition of CIs to HHPs affords oligomers containing CIs as chain units. The addition of -OOH group in HHPs to the central carbon atom of CIs is identified as the most energetically favorable channel, with a barrier height strongly dependent on both, CI substituent number (one or two) and position (<i>syn-</i> or <i>anti-</i>). In particular, the introduction of a methyl group into the <i>anti</i>-position significantly increase the rate coefficient, dramatic decrease is observed when the methyl group is introduced into the <i>syn</i>-position. Based on the collected data, the atmospheric lifetime of <i>anti</i>-CH<sub>3</sub>CHOO in the presence of HHPs is estimated as ~<span class="thinspace"></span>5.9<span class="thinspace"></span>×<span class="thinspace"></span>103<span class="thinspace"></span>s. These findings are expected to broaden the reactivity profile and deepen our understanding of atmospheric SOAs formation processes.</p>

Kinetics of the Reaction of Vinyl Radical With Molecular Oxygen

1995 ◽  
Vol 99 (8) ◽  
pp. 2247-2249 ◽  
Author(s):  
Vadim D. Knyazev ◽  
Irene R. Slagle
Keyword(s):  
Molecular Oxygen ◽  
Vinyl Radical ◽  
Kinetics Of
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