Mechanisms of hydrolysis and rearrangements of epoxides

Whalen, Dale L.

doi:10.1016/s0065-3160(05)40006-4

Cited by 35 publications

(48 citation statements)

References 112 publications

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“…For clarity concerning the position of nucleophilic addition, these mechanisms are drawn as sequential reaction (S N 1-like) mechanisms. While it is likely that these mechanisms are more accurately represented by concerted (S N 2-like) formalism, the actual mechanism may lie somewhere on a continuum between the sequential and concerted pathways (Whalen, 2005;Eddingsaas et al, 2010;. It should be noted, however, that the preceding hydrolysis kinetics analysis does not depend on the actual mechanistic pathway (since nucleophilic water is in excess and has an unchanging concentration in those experiments, the two mechanisms are experimentally indistinguishable).…”

Section: Identification Of Nucleophilic Addition Mechanismsmentioning

confidence: 99%

Mechanistic study of secondary organic aerosol components formed from nucleophilic addition reactions of methacrylic acid epoxide

et al. 2014

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Abstract.Recently, methacrylic acid epoxide (MAE) has been proposed as a precursor to an important class of isoprene-derived compounds found in secondary organic aerosol (SOA): 2-methylglyceric acid (2-MG) and a set of oligomers, nitric acid esters, and sulfuric acid esters related to 2-MG. However, the specific chemical mechanisms by which MAE could form these compounds have not been previously studied with experimental methods. In order to determine the relevance of these processes to atmospheric aerosol, MAE and 2-MG have been synthesized and a series of bulk solution-phase experiments aimed at studying the reactivity of MAE using nuclear magnetic resonance (NMR) spectroscopy have been performed. The present results indicate that the acid-catalyzed MAE reaction is more than 600 times slower than a similar reaction of an important isoprenederived epoxide, but is still expected to be kinetically feasible in the atmosphere on more acidic SOA. The specific mechanism by which MAE leads to oligomers was identified, and the reactions of MAE with a number of atmospherically relevant nucleophiles were also investigated. Because the nucleophilic strengths of water, sulfate, alcohols (including 2-MG), and acids (including MAE and 2-MG) in their reactions with MAE were found to be of similar magnitudes, it is expected that a diverse variety of MAE + nucleophile product species may be formed on ambient SOA. Thus, the results indicate that epoxide chain reaction oligomerization will be limited by the presence of high concentrations of nonepoxide nucleophiles (such as water); this finding is consistent with previous environmental chamber investigations of the relative humidity dependence of 2-MG-derived oligomerization processes and suggests that extensive oligomerization may not be likely on ambient SOA because of other competitive MAE reaction mechanisms.

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Section: Identification Of Nucleophilic Addition Mechanismsmentioning

confidence: 99%

Mechanistic study of secondary organic aerosol components formed from nucleophilic addition reactions of methacrylic acid epoxide

et al. 2014

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“…The basis for the observed regiospecificity in epoxide ring opening is difficult to rationalize even from ambitious structure-reactivity studies [28,29]. The carbon subjected to nucleophilic attack will be influenced by distinct intrinsic reactivities of the oxirane carbons as dictated by the substituents.…”

Section: Regiospecificitymentioning

confidence: 99%

“…In addition to the enzyme-afforded catalytic steps, a further level of reaction complexity is added with SO derivatives as substrates. The phenyl substituent of these compounds can assist in stabilizing electron-rich reaction intermediates, hence affecting the regioselectivity in the ring-opening half-reaction by directing the attack away from the otherwise more reactive, least substituted, of the two oxirane carbons [28,29].…”

mentioning

confidence: 99%

Substrate‐dependent hysteretic behavior in StEH1‐catalyzed hydrolysis of styrene oxide derivatives

2008

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Soluble epoxide hydrolases (EC 3.3.2.10) make up a large group of enzymes catalyzing the hydrolysis of alkyl and aryl epoxides into the corresponding vicinal diols [1,2]. They fulfill various functions in host organisms, including detoxification by hydrolysis of endogenous and exogenous epoxides, regulation of cell signaling by hydrolysis of epoxide-containing bioactive lipids, or participation in the secondary metabolism of microorganisms. In plants, epoxide hydrolases have been suggested to contribute to pathogen defense systems through hydrolysis of epoxycontaining hydroxyl fatty acids. The diol products from the latter reaction show antifungal activity [3] and are established substrates for several plant isoenzymes as precursors in cutin synthesis [4]. The independence from cofactors in combination with, in some cases, high catalytic efficiencies and enantioselectivities has created an interest in using epoxide hydrolases as biocatalysts in the production of fine chemicals [5,6].Styrene oxide (SO) and derivatives thereof are important molecules as chiral and prochiral precursors in asymmetric synthesis. These compounds are also relevant for their toxicological impact [7]. Solanum tuberosum epoxide hydrolase 1 (StEH1) has previously been investigated using different SO derivatives as The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and presteady-state measurements on a series of styrene oxide derivatives. A preference for the (S)-or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide and trans-stilbene oxide was established, with E-values of 43, 160 and 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence, as did the rate of alkylenzyme formation in the reaction with the (R,R)-enantiomer. Such kinetic behavior is indicative of an additional, off-pathway step in the mechanism, referred to as hysteresis. On the basis of these data, a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13 C-NMR spectroscopy of 18 O-labeled diol products. The (S,S)-enantiomer is attacked exclusively at the C-1 epoxide carbon, whereas the (R,R)-enantiomer is attacked at either position at a ratio of 65 : 35 in favor of the C-1 carbon. On the basis of the results, we conclude that differences in efficiency in stabilization of the alkylenzyme intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans-stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency.Abbreviations 2-MeSO, 2-methylstyrene oxide; ES, enzyme-substrate; SO, styrene oxide; StEH1, Solanum tuberosum epoxide hydrolase 1; T...

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“…It is now established that the epoxides known to form in the oxidation of isoprene (Paulot et al, 2009b) (see Subsection 2.2.3) and monoterpenes (Iinuma et al, 2007a, b), react with sulfuric acid to form hydroxy sulfate esters by non-radical pathways. Epoxide ring opening and replacement by two hydroxy groups by acid-catalyzed hydrolysis is a well-known reaction (Whalen, 2005) as exemplified as follows: (95) The kinetics and products of the acid-catalyzed hydrolytic ring-opening of atmospherically relevant hydroxy epoxides has been studied by Cole-Filipiak et al (2010) and Eddingsaas et al (2010). In the case of isoprene, the gasphase formation of epoxides (IEPOX) has been fully characterized, as discussed in Subsection 2.2.3.…”

Section: Aqueous-phase Reactions Forming Organosulfatesmentioning

confidence: 99%

Fundamental Heterogeneous Reaction Chemistry Related to Secondary Organic Aerosols (SOA) in the Atmosphere

Akimoto¹

2016

Monogr. Environ. Earth Planets

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Citation: Akimoto, H. (2016), Fundamental heterogeneous reaction chemistry related to secondary organic aerosols (SOA) in the atmosphere, Monogr. Environ. Earth Planets, 4, 1-45, doi:10.5047/meep.2016.00401.0001. Abstract Typical reaction pathways of formation of dicarboxylic acids, larger multifunctional compounds, oligomers, and organosulfur and organonitrogen compounds in secondary organic aerosols (SOA), revealed by laboratory experimental studies are reviewed with a short introduction to field observations. In most of the reactions forming these compounds, glyoxal, methyl glyoxal and related difunctional carbonyl compounds play an important role as precursors, and so their formation pathways in the gas phase are discussed first. A substantial discussion is then presented for the OH-initiated aqueous phase radical oxidation reactions of glyoxal and other carbonyls which form dicarboxylic acids, larger multifunctional compounds and oligomers, and aqueous-phase non-radical reactions which form oligomers, organosulfates and organonitrogen compounds. Finally, the heterogeneous oxidation reaction of gaseous O 3 , OH and NO 3 with liquid and solid organic aerosols at the air-particle interface is discussed relating to the aging of SOA in the atmosphere.

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Mechanisms of hydrolysis and rearrangements of epoxides

Cited by 35 publications

References 112 publications

Mechanistic study of secondary organic aerosol components formed from nucleophilic addition reactions of methacrylic acid epoxide

Mechanistic study of secondary organic aerosol components formed from nucleophilic addition reactions of methacrylic acid epoxide

Substrate‐dependent hysteretic behavior in StEH1‐catalyzed hydrolysis of styrene oxide derivatives

Fundamental Heterogeneous Reaction Chemistry Related to Secondary Organic Aerosols (SOA) in the Atmosphere

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