Reaction of N-Acyloxy-N-alkoxyamides with Biological Thiol Groups

Mutagenic N-acyloxy-N-alkoxyamides 1 react with thiols by an SN2 process at nitrogen with displacement of carboxylate. They react with glutathione 4 in [D6]DMSO/D2O and methyl and ethyl esters of cysteine hydrochloride, 11 and 12, in [D4]methanol but the intermediate N-alkoxy-N-(alkylthio)amides undergo a rapid substitution reaction at sulfur by a second thiol molecule to give hydroxamic esters and disulfides. Arrhenius activation energies and entropies of activation obtained for a series of different N-benzyloxy-N-(4-substitutedbenzoyloxy)benzamides 13–17 were similar to those found for the SN2 reaction of the same series with N-methylaniline. Entropies of activation were strongly negative in keeping with polar separation and attendant solvation in the transition state, and in keeping with this, bimolecular reaction rate constants at 298 K correlated with Hammett σ constants with a positive ρ-value of 1.1. The structure of model N-methoxy-N-(methylthio)acetamide has been computed at the B3LYP/6–31G(d) level and exhibits properties atypical of other anomeric amides with more electronegative atoms at nitrogen. Relative to N,N-bisoxyl substitution, the combination of a sulfur and an oxygen atom at the amide nitrogen results in a relatively small reduction in amide resonance.

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Detailed characterizations of the new Mines Douai comparative reactivity method instrument via laboratory experiments and modeling

Atmospheric Measurement Techniques ◽

10.5194/amt-8-3537-2015 ◽

2015 ◽

Vol 8 (8) ◽

pp. 3537-3553 ◽

Cited By ~ 21

Author(s):

V. Michoud ◽

R. F. Hansen ◽

N. Locoge ◽

P. S. Stevens ◽

S. Dusanter

Keyword(s):

Rate Constants ◽

Laboratory Experiments ◽

Reaction Rate ◽

Limit Of Detection ◽

Trace Gases ◽

Ambient Air ◽

Bimolecular Reaction ◽

Reaction Rate Constants ◽

Measurement Artifacts ◽

Comparative Reactivity

Abstract. The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime of most air quality- and climate-related trace gases. However, there are still uncertainties concerning its atmospheric budget, and integrated measurements of OH sinks have been valuable to improve this aspect. Among the analytical tools used for measuring total OH reactivity in ambient air, the comparative reactivity method (CRM) is spreading rapidly in the atmospheric community. However, measurement artifacts have been highlighted for this technique, and additional work is needed to fully characterize them. In this study, we present the new Mines Douai CRM instrument, with an emphasis on the corrections that need to be applied to ambient measurements of total OH reactivity. Measurement artifacts identified in the literature have been investigated, including (1) a correction for a change in relative humidity between the measurement steps leading to different OH levels, (2) the formation of spurious OH in the sampling reactor when hydroperoxy radicals (HO2) react with nitrogen monoxide (NO), (3) not operating the CRM under pseudo-first-order kinetics, and (4) the dilution of ambient air inside the reactor. The dependences of these artifacts on various measurable parameters, such as the pyrrole-to-OH ratio and the bimolecular reaction rate constants of ambient trace gases with OH, have also been studied. Based on these observations, parameterizations are proposed to correct ambient OH reactivity measurements. On average, corrections of 5.2 ± 3.2, 9.2 ± 15.7, and 8.5 ± 5.8 s−1 were respectively observed for (1), (2) and (3) during a field campaign performed in Dunkirk, France (summer 2014). Numerical simulations have been performed using a box model to check whether experimental observations mentioned above are consistent with our understanding of the chemistry occurring in the CRM reactor. Two different chemical mechanisms have been shown to reproduce the magnitude of corrections (2) and (3). In addition, these simulations reproduce their dependences on the pyrrole-to-OH ratio and on bimolecular reaction rate constants of gases reacting with OH. The good agreement found between laboratory experiments and model simulations gives us confidence in the proposed parameterizations. However, it is worth noting that the numerical values given in this study are suitable for the Mines Douai instrument and may not be appropriate for other CRM instruments. It is recommended that each group characterize its own instrument following the recommendations given in this study. An assessment of performances for the Mines Douai instrument, including a propagation of errors from the different corrections, indicates a limit of detection of 3.0 s−1 and total uncertainties of 17–25 % for OH reactivity values higher than 15 s−1 and NOx mixing ratios lower than 30 ppbv.

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ChemInform Abstract: APPLICATION OF TRANSITION STATE THEORY TO ESTIMATE DIFFUSION CONTROLLED BIMOLECULAR REACTION RATE CONSTANTS

Chemischer Informationsdienst ◽

10.1002/chin.198208095 ◽

1982 ◽

Vol 13 (8) ◽

Author(s):

V. D. PARKER

Keyword(s):

Transition State ◽

Rate Constants ◽

Transition State Theory ◽

Reaction Rate ◽

Bimolecular Reaction ◽

State Theory ◽

Reaction Rate Constants ◽

Diffusion Controlled

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Detailed characterizations of a Comparative Reactivity Method (CRM) instrument: experiments vs. modelling

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-3803-2015 ◽

2015 ◽

Vol 8 (4) ◽

pp. 3803-3850 ◽

Cited By ~ 1

Author(s):

V. Michoud ◽

R. F. Hansen ◽

N. Locoge ◽

P. S. Stevens ◽

S. Dusanter

Keyword(s):

Reaction Rate ◽

Trace Gases ◽

Ambient Air ◽

Bimolecular Reaction ◽

Chemical Mechanism ◽

First Order ◽

Reaction Rate Constants ◽

First Order Kinetics ◽

Comparative Reactivity

Abstract. The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the lifetime of most trace gases, whose oxidation leads to the formation of harmful secondary pollutants such as ozone (O3) and Secondary Organic Aerosols (SOA). In spite of the importance of OH, uncertainties remain concerning its atmospheric budget and integrated measurements of the total sink of OH can help reducing these uncertainties. In this context, several methods have been developed to measure the first-order loss rate of ambient OH, called total OH reactivity. Among these techniques, the Comparative Reactivity Method (CRM) is promising and has already been widely used in the field and in atmospheric simulation chambers. This technique relies on monitoring competitive OH reactions between a reference molecule (pyrrole) and compounds present in ambient air inside a sampling reactor. However, artefacts and interferences exist for this method and a thorough characterization of the CRM technique is needed. In this study, we present a detailed characterization of a CRM instrument, assessing the corrections that need to be applied on ambient measurements. The main corrections are, in the order of their integration in the data processing: (1) a correction for a change in relative humidity between zero air and ambient air, (2) a correction for the formation of spurious OH when artificially produced HO2 react with NO in the sampling reactor, and (3) a correction for a deviation from pseudo first-order kinetics. The dependences of these artefacts to various measurable parameters, such as the pyrrole-to-OH ratio or the bimolecular reaction rate constants of ambient trace gases with OH are also studied. From these dependences, parameterizations are proposed to correct the OH reactivity measurements from the abovementioned artefacts. A comparison of experimental and simulation results is then discussed. The simulations were performed using a 0-D box model including either (1) a simple chemical mechanism, taking into account the inorganic chemistry from IUPAC 2001 and a simple organic chemistry scheme including only a generic RO2 compounds for all oxidized organic trace gases; and (2) a more exhaustive chemical mechanism, based on the Master Chemical Mechanism (MCM), including the chemistry of the different trace gases used during laboratory experiments. Both mechanisms take into account self- and cross-reactions of radical species. The simulations using these mechanisms allow reproducing the magnitude of the corrections needed to account for NO interferences and a deviation from pseudo first-order kinetics, as well as their dependence on the Pyrrole-to-OH ratio and on bimolecular reaction rate constants of trace gases. The reasonable agreement found between laboratory experiments and model simulations gives confidence in the parameterizations proposed to correct the Total OH reactivity measured by CRM. However, it must be noted that the parameterizations presented in this paper are suitable for the CRM instrument used during the laboratory characterization and may be not appropriate for other CRM instruments, even if similar behaviours should be observed. It is therefore recommended that each group characterizes its own instrument following the recommendations given in this study. Finally, the assessment of the limit of detection and total uncertainties is discussed and an example of field deployment of this CRM instrument is presented.

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Application of Transition State Theory to Estimate Diffusion Controlled Bimolecular Reaction Rate Constants.

Acta Chemica Scandinavica ◽

10.3891/acta.chem.scand.35b-0529 ◽

1981 ◽

Vol 35b ◽

pp. 529-531 ◽

Cited By ~ 1

Author(s):

Vernon D. Parker ◽

Ann-Marie Eklund ◽

Toshiaki Nishida ◽

Curt R. Enzell ◽

Curt R. Enzell

Keyword(s):

Transition State ◽

Rate Constants ◽

Transition State Theory ◽

Reaction Rate ◽

Bimolecular Reaction ◽

State Theory ◽

Reaction Rate Constants ◽

Diffusion Controlled

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STUDYING THE KINETIC CHARACTERISTICS OF THE EXTRACTION OF ANTHOCYANINS FROM THE SQUEEZE OF KRASNOSTOP ZOLOTOVSKY

STATE AND DEVELOPMENT PROSPECTS OF AGRIBUSINESS. In the frame of the XXIII Agribusiness Forum of the South of Russia and the Exhibition «Interagromash» Volume 1 ◽

10.23947/interagro.2020.1.525-528 ◽

2020 ◽

Author(s):

M.A. Egyan ◽

Keyword(s):

Reaction Rate ◽

Sugar Content ◽

Extraction Process ◽

Efficiency Coefficient ◽

Kinetic Characteristics ◽

Reaction Rate Constants ◽

Solids Content ◽

Kinetics Of ◽

Process Speed

The article shows studies characterizing the quality of the squeeze: the mechanical composition of the squeeze is determined, the structural moisture of each component is determined, the sugar content in the formed process of sedimentation of the juice and its acidity are determined refractometrically. The kinetics of anthocyanins extraction was determined in two ways, the solids content in the extract was calculated, and the reaction rate constants of the extraction process and the efficiency coefficient of ultrasonic amplification of the extraction process speed were calculated.

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