Methylsulfinyl Radical Research Articles

Antioxidant activity of two edible isothiocyanates: Sulforaphane and erucin is due to their thermal decomposition to sulfenic acids and methylsulfinyl radicals

Sulforaphane(SFN) and erucin(ERN) are isothiocyanates (ITCs) bearing, respectively, methylsulfinyl and methylsulfanyl groups. Their chemopreventive and anticancer activity is attributed to ability to modulate cellular redox status due to induction of Phase 2 cytoprotective enzymes (indirect antioxidant action) but many attempts to connect the bioactivity of ITCs with their radical trapping activity failed. Both ITCs are evolved from their glucosinolates during food processing of Cruciferous vegetables, therefore, we studied antioxidant behaviour of SFN/ERN at elevated temperature in two lipid systems. Neither ERN nor SFN inhibit the oxidation of bulk linolenic acid (below 100 °C) but both ITCs increase oxidative stability of soy lecithin (above 150 °C). On the basis of GC-MS analysis we verified our preliminary hypothesis (Antioxidants2020, 9, 1090) about participation of sulfenic acids and methylsulfinyl radicals as radical trapping agents responsible for the antioxidant effect of edible ITCs during thermal oxidation of lipids at elevated temperatures (above 140 °C).

A Lesson Learnt from Food Chemistry—Elevated Temperature Triggers the Antioxidant Action of Two Edible Isothiocyanates: Erucin and Sulforaphane

In this communication we demonstrate that two natural isothiocyanates, sulforaphane (SFN) and erucin (ERN), inhibit autoxidation of lipids at 140 °C but not below 100 °C. This effect is due to thermal decomposition of ERN and SFN to sulfenic acids and methylsulfinyl radicals, species able to trap lipidperoxyl radicals. Our observations shed new light on thermal processing of vegetables containing these two isothiocyanates.

Assessing the Viability of the Methylsulfinyl Radical-Ozone Reaction.

Although integral to remote marine atmospheric sulfur chemistry, the reaction between methylsulfinyl radical (CH3 SO) and ozone poses challenges to theoretical treatments. The lone theoretical study on this reaction reported an unphysically large barrier of 66 kcal mol-1 for abstraction of an oxygen atom from O3 by CH3 SO. Herein, we demonstrate that this result stems from improper use of MP2 with a single-reference, unrestricted Hartree-Fock (UHF) wavefunction. We characterized the potential energy surface using density functional theory (DFT), as well as multireference methodologies employing a complete active-space self-consistent field (CASSCF) reference. Our DFT PES shows, in contrast to previous work, that the reaction proceeds by forming an addition adduct [CH3 S(O3 )O] in a deep potential well of 37 kcal mol-1 . An O-O bond of this adduct dissociates via a flat, low barrier of 1 kcal mol-1 to give CH3 SO2 +O2 . The multireference computations show that the initial addition of CH3 SO+O3 is barrierless. These results provide a more physically intuitive and accurate picture of this reaction than the previous theoretical study. In addition, our results imply that the CH3 SO2 formed in this reaction can readily decompose to give SO2 as a major product, in alignment with the literature on CH3 SO reactions.

Photodissociation dynamics of the methylsulfinyl radical at 248 nm

The photodissociation dynamics of jet-cooled methylsulfinyl radicals, CH3SO, at 248 nm have been investigated using molecular beam photofragment translational spectroscopy. The primary channel is CH3S + O, which occurs via the initially prepared excited CH3SO state by rapid cleavage of the S-O bond to produce ground state products. The minor SO + CH3 channel has two components in comparable proportions: a fast feature corresponding to rapid C-S cleavage on the excited state to produce CH3 and electronically excited SO, and a slow feature due to internal conversion of CH3SO followed by statistical dissociation on the ground electronic state. Statistical ground state dissociation also produces small amounts of CH2SO, likely sulfine, and H-atoms.

Correction: The methylsulfinyl radical CH3SO examined.

Correction for 'The methylsulfinyl radical CH3SO examined' by Marissa L. Estep et al., Phys. Chem. Chem. Phys., 2016, 18, 22293-22299.

The methylsulfinyl radical CH3SO examined.

Methylsulfinyl radical, a key intermediate in marine atmospheric chemistry, plays a central role in the oxidation of dimethyl sulfide. CH3SO has been extensively studied here with ab initio quantum mechanical methods, with methods as complete as CCSDT(Q) in conjunction with basis sets as large as cc-pV(5+d)Z. In this research, we report high-level computations for the ground and first excited electronic states of the methylsulfinyl radical. The structures of the X[combining tilde] (2)A'' and à (2)A' states are quite different with S-O distances of 1.499 and 1.652 Å, respectively. The X[combining tilde] to à adiabatic energy difference is predicted to be 45.1 kcal mol(-1), compared to 21.1 kcal mol(-1) for the analogous well-characterized methylperoxy radical CH3OO. The CH3SO barrier to internal rotation is 0.92 kcal mol(-1). The unknown X[combining tilde] (2)A'' torsional vibrational frequency τ is predicted to be 142 cm(-1) (harmonic) and 128 cm(-1) (anharmonic). Our predictions of the à (2)A' excited state vibrational frequencies are the first to be reported.

H-Bonded CH 3 SO/H 2 SO 4 /H 2 O Complexes: Quantum Chemical Study

The structural, electronic, and spectroscopic properties of complexes of the methyl sulfinyl radical, sulphuric acid and water molecules have been studied by density functional theory and ab initio methods. The hydrogen bond interactions between the CH(3)SO radical, H(2)SO(4) and H(2)O molecules have been characterised. The calculations predict relatively large binding energies for the complexes of 12.2 kcal mol-1 for the most stable CH(3)SO-H(2)SO(4) complex, 19.1 kcal mol-1 for CH3SO-H(2)SO(4)-H(2)O complex and 28.8 kcal mol-1 for CH(3)SO-H(2)SO(4)-2H(2)O complex at the CBS-QB3 level of theory. The relatively high stabilisation of the complexes is likely to have significant effects on the overall processes that lead to the formation of new-particles in the atmosphere. Infrared spectroscopy is suggested to be a potentially useful tool for the detection of these complexes either in laboratory experiments or in atmospheric observations. The electronic spectra of the complexes have been examined, and their photochemical spectral features are discussed. The hydrated CH(3)SO-H(2)SO(4) complexes can be expected to undergo photolysis in sunlight.

Reactions of the methylsulfinyl radical [CH3(O)S˙] with oxygen (3O2) in solid argon

The atmospherically highly relevant methylsulfinyl radical (CH3(O)S˙) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of (3)O2. Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed (3)O2 adduct has the structure of a peroxyl radical (CH3(O)SOO˙), which upon irradiation with UV light isomerizes to the methylsulfonoxyl radical (CH3SO3˙). The latter transforms into the methansulfonic acid radical (˙CH2SO3H) by irradiation with visible light. During the matrix photolysis small amounts of SO3 and the methyl radical were detected indicating competitive direct photodissociation.

Matrix isolation and spectroscopic properties of the methylsulfinyl radical CH3(O)S˙

The atmospherically highly relevant methylsulfinyl radical CH3(O)S˙ was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH3(O)S˙ and its D3- and (13)C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.

Formation of a Criegee intermediate in the low-temperature oxidation of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is the major sulfur-containing constituent of the Marine Boundary Layer. It is a significant source of H2SO4 aerosol/particles and methane sulfonic acid via atmospheric oxidation processes, where the mechanism is not established. In this study, several new, low-temperature pathways are revealed in the oxidation of DMSO using CBS-QB3 and G3MP2 multilevel and B3LYP hybrid density functional quantum chemical methods. Unlike analogous hydrocarbon peroxy radicals the chemically activated DMSO peroxy radical, [CH3S(=O)CH2OO*]*, predominantly undergoes simple dissociation to a methylsulfinyl radical CH3S*(=O) and a Criegee intermediate, CH2OO, with the barrier to dissociation 11.3 kcal mol(-1) below the energy of the CH3S(=O)CH2* + O2 reactants. The well depth for addition of O2 to the CH3S(=O)CH2 precursor radical is 29.6 kcal mol(-1) at the CBS-QB3 level of theory. We believe that this reaction may serve an important role in atmospheric photochemical and irradiated biological (oxygen-rich) media where formation of initial radicals is facilitated even at lower temperatures. The Criegee intermediate (carbonyl oxide, peroxymethylene) and sulfinyl radical can further decompose, resulting in additional chain branching. A second reaction channel important for oxidation processes includes formation (via intramolecular H atom transfer) and further decomposition of hydroperoxide methylsulfoxide radical, *CH2S(=O)CH2OOH over a low barrier of activation. The initial H-transfer reaction is similar and common in analogous hydrocarbon radical + O2 reactions; but the subsequent very low (3-6 kcal mol(-1)) barrier (14 kcal mol(-1) below the initial reagents) to beta-scission products is not common in HC systems. The low energy reaction of the hydroperoxide radical is a beta-scission elimination of *CH2S(=O)CH2OOH into the CH2=S=O + CH2O + *OH product set. This beta-scission barrier is low, because of the delocalization of the *CH2 radical center through the -S(=O) group, to the -CH2OOH fragment in the transition state structure. The hydroperoxide methylsulfoxide radical can also decompose via a second reaction channel of intramolecular OH migration, yielding formaldehyde and a sulfur-centered hydroxymethylsulfinyl radical HOCH2S*(=O). The barrier of activation relative to initial reagents is 4.2 kcal mol(-1). Heats of formation for DMSO, DMSO carbon-centered radical and Criegee intermediate are evaluated at 298 K as -35.97 +/- 0.05, 13.0 +/- 0.2 and 25.3 +/- 0.7 kcal mol(-1) respectively using isodesmic reaction analysis. The [CH3S*(=O) + CH2OO] product set is shown to form a van der Waals complex that results in O-atom transfer reaction and the formation of new products CH3SO2* radical and CH2O. Proper orientation of the Criegee intermediate and methylsulfinyl radical, as a pre-stabilized pre-reaction complex, assist the process. The DMSO radical reaction is also compared to that of acetonyl radical.

Angular dependence of proton hyperfine splittings in the electron spin resonance spectrum of the methylsulfinyl radical

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAngular dependence of proton hyperfine splittings in the electron spin resonance spectrum of the methylsulfinyl radicalKoichi Nishikida and Ffrancon WilliamsCite this: J. Am. Chem. Soc. 1974, 96, 15, 4781–4784Publication Date (Print):July 1, 1974Publication History Published online1 May 2002Published inissue 1 July 1974https://doi.org/10.1021/ja00822a010RIGHTS & PERMISSIONSArticle Views73Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (463 KB) Get e-Alerts Get e-Alerts