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Peroxyl radicals participate in multiple processes involved in critical changes to cells, tissues, pharmacueticals and foods. Some of these reactions explain their association with degenerative pathologies, including cardiovascular and neurological diseases, as well as cancer development. Azocompounds, and particularly AAPH (2,2′-Azobis(2-methylpropionamidine) dihydrochloride), a cationic water-soluble derivative, have been employed extensively as sources of model peroxyl radicals. A considerable number of studies have reported mechanistic data on the oxidation of biologically-relevant targets, the scavenging activity of foods and natural products, and the reactions with, and responses of, cultured cells. However, despite the (supposed) experimental simplicity of using azocompounds, the chemistry of peroxyl radical production and subsequent reactions is complicated, and not always considered in sufficient depth when analyzing experimental data. The present work discusses the chemical aspects of azocompounds as generators of peroxyl (and other) radicals, together with their contribution to our understanding of biochemistry, pharmaceutical and food chemistry research. The evidence supporting a role for the formation of alkoxyl (RO•) and other radicals during thermal and photochemical decomposition of azocompounds is assessed, together with the potential influence of such species on the reactions under study. Image 1 • Peroxyl radicals participate in critical processes of the human life. • Azocompounds are employed extensively as sources of model peroxyl radicals (ROO•). • The chemistry and contributions of azocompounds as generators of ROO• is discussed. • Formation of alkoxyl radicals (RO•) and their role in the tested systems is revised. [ABSTRACT FROM AUTHOR]

Control of selectivity is one of the central topics in organic chemistry. Although unprecedented alkoxyl‐radical‐induced transformations have drawn a lot of attention, compared to selective C−H activation, selective radical O−H activation remains less explored. Herein, we report a novel selective radical O−H activation strategy of diols by combining spatial effects with proton‐coupled electron transfer (PCET). It was found that DMSO is an essential reagent that enables the regioselective transformation of diols. Mechanistic studies indicated the existence of the alkoxyl radical and the selective interaction between DMSO and hydroxyl groups. Moreover, the distal C−C cleavage was realized by this selective alkoxyl‐radical‐initiation protocol. [ABSTRACT FROM AUTHOR]

Control of selectivity is one of the central topics in organic chemistry. Although unprecedented alkoxyl‐radical‐induced transformations have drawn a lot of attention, compared to selective C−H activation, selective radical O−H activation remains less explored. Herein, we report a novel selective radical O−H activation strategy of diols by combining spatial effects with proton‐coupled electron transfer (PCET). It was found that DMSO is an essential reagent that enables the regioselective transformation of diols. Mechanistic studies indicated the existence of the alkoxyl radical and the selective interaction between DMSO and hydroxyl groups. Moreover, the distal C−C cleavage was realized by this selective alkoxyl‐radical‐initiation protocol. [ABSTRACT FROM AUTHOR]

A mild and convenient method for the synthesis of reverse glycosyl fluorides (RGFs) has been developed that is based on the silver‐promoted radical dehydroxymethylative fluorination of carbohydrates. A salient feature of the reaction is that furanoid and pyranoid carbohydrates furnish structurally diverse RGFs bearing a wide variety of functional groups in good to excellent yields. Intramolecular hydrogen atom transfer experiments revealed that the reaction involves an underexploited radical fluorination that proceeds via β‐fragmentation of sugar‐derived primary alkoxyl radicals. Structurally divergent RGFs were obtained by catalytic C−F bond activation, and our method thus offers a concise and efficient strategy for the synthesis of reverse glycosides by late‐stage diversification of RGFs. The potential of this method is showcased by the preparation and diversification of sotagliflozin, leading to the discovery of a promising SGLT2 inhibitor candidate. [ABSTRACT FROM AUTHOR]

Alkoxyl radicals are highly reactive species which rapidly react by hydrogen atom transfer (HAT) or β-fragmentation to afford a carbon-centered radical. We discuss herein how these RO · radicals can be efficiently trapped in an intermolecular manner by styrene derivatives when they are generated by photoredox catalysis from the corresponding N -alkoxypyridinium salts. This allows for the synthesis of valuable ethers with complete anti-Markovnikov regioselectivity. 1 Introduction 2 Anti-Markovnikov Alkoxylation of Alkenes: Background 3 Addition of Alkoxyl Radicals to Styrenes 4 Summary and Outlook [ABSTRACT FROM AUTHOR]

A challenging deoxygenation of alkoxyl radicals from readily accessible alcohol derivatives was developed, affording facile synthesis of functionalized alkenes with good functional group tolerance under mild reaction conditions. Because alkoxyl radicals can easily undergo β‐fragmentations or hydrogen abstractions, this new strategy for deoxygenation of alkoxyl radicals is highly valuable. Moreover, mechanistic studies revealed that the electron‐neutral phosphine acts as the deoxygenation reagent. A challenging deoxygenation of alkoxyl radicals from readily accessible alcohol derivatives is described, affording facile synthesis of synthetic valuable alkenes with good functional group tolerance under mild reaction conditions. Because alkoxyl radicals can easily undergo β‐fragmentations or hydrogen abstractions, this new strategy for deoxygenation of alkoxyl radicals is of high significance. [ABSTRACT FROM AUTHOR]

Reported herein is a novel photoredox‐catalyzed approach for ether synthesis and it involves alkoxyl radicals generated from N‐alkoxypyridinium salts. A wide range of alkenes are smoothly difunctionalized in an anti‐Markovnikov fashion, affording various functionalized alkyl alkyl ethers. Notably, this mild process tolerates a number of functional groups and is efficiently carried out under both batch and flow conditions. Importantly, electron paramagnetic resonance (EPR) experiments by spin trapping were carried out to characterize the radical intermediates involved in this radical/cationic process. [ABSTRACT FROM AUTHOR]

Reported herein is a novel photoredox‐catalyzed approach for ether synthesis and it involves alkoxyl radicals generated from N‐alkoxypyridinium salts. A wide range of alkenes are smoothly difunctionalized in an anti‐Markovnikov fashion, affording various functionalized alkyl alkyl ethers. Notably, this mild process tolerates a number of functional groups and is efficiently carried out under both batch and flow conditions. Importantly, electron paramagnetic resonance (EPR) experiments by spin trapping were carried out to characterize the radical intermediates involved in this radical/cationic process. Falling into a trap: Alkoxyl radicals generated under visible light photoredox catalysis from N‐alkoxypyridinium salts were efficiently trapped by alkenes in an intermolecular fashion under either batch or flow conditions. This alkoxylation strategy provides access to a wide variety of functionalized alkyl alkyl ethers by the difunctionalization of alkenes with perfect anti‐Markovnikov selectivity. [ABSTRACT FROM AUTHOR]

4,7-Bis(4-hexyl-5-(trimethylstannane) -2-thienyl) −2,1,3-benzothiadiazole (HTBT) coupled with 2,5-bis (decyloxy)-1,4-dibromobenzene to afford the donor-π-bridge-donor-acceptor conjugated poly (4,7-bis (4-hexyl-2-thienyl) −2,1,3-benzothiadiazole-co-p-didecyloxybenzene) (PTBTB). Further, copolymerization of fluorine-functionalized HTBT moiety with alkoxyl benzene π-bridge using Stille crossing-coupling reaction yield PTBTB-F. The optical, electrochemical, fluorescent, spectroelectrochemical and electrochromic switching properties of two polymers with different acceptors are studied in detail. Both polymers exhibit excellent solubility in conventional organic solvents, high thermal stability and favorable fluorescence properties. The combination of a strong electron withdrawing pendant group (fluorine atoms) with benzothiadiazole (BT) backbone significantly influences the electrochemical redox, optical and electrochromic behaviors of conducting polymers. The introduction of fluorine atoms to BT lead to a higher oxidation onset potential, but an improved electrochemical n-doping process. The optical band gaps (E g ) of PTBTB and PTBTB-F films are calculated to be 2.02 eV and 1.91 eV, respectively. PTBTB and PTBTB-F films exhibited obvious and reversible color switching between their neutral and oxidized states with high optical contrasts as well as favorable response times, making the polymers unique candidates for flexible organic electrochromic device applications. [ABSTRACT FROM AUTHOR]

Abstract: An alkoxyl radical guided strategy for site‐selective functionalization of unactivated methylene and methine C−H bonds enabled by an FeII‐catalyzed redox process is described. The mild, expeditious, and modular protocol allows efficient remote aliphatic fluorination, chlorination, amination, and alkynylation of structurally and electronically varied primary, secondary, and tertiary hydroperoxides with excellent functional‐group tolerance. The application for one‐pot 1,4‐hydroxyl functionalization of non‐oxygenated alkane substrates initiated by aerobic C−H oxygenation is also demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: An alkoxyl radical guided strategy for site‐selective functionalization of unactivated methylene and methine C−H bonds enabled by an FeII‐catalyzed redox process is described. The mild, expeditious, and modular protocol allows efficient remote aliphatic fluorination, chlorination, amination, and alkynylation of structurally and electronically varied primary, secondary, and tertiary hydroperoxides with excellent functional‐group tolerance. The application for one‐pot 1,4‐hydroxyl functionalization of non‐oxygenated alkane substrates initiated by aerobic C−H oxygenation is also demonstrated. [ABSTRACT FROM AUTHOR]

Inert chemical bond cleavage and functionalization reactions provide expedient synthetic routes and are fundamental in organic synthesis. Alkoxyl radicals enable inert chemical bond cleavages by hydrogen atom transfer and β-fragmentation reactivity; however their further synthetic transformations and functional group compatibility are limited by traditional alkoxyl radical generation methods. Recently, visible-light-induced alkoxyl radical generation methods have emerged and led to new advancements in inert chemical bond cleavage reactions and subsequent functionalization, with excellent chemoselectivity and functional group compatibility. In this Feature Article, the generation of alkoxyl radicals by different visible-light-induced methods and their common or distinct reactivity are discussed, which are categorized by C(sp3)–H, C(sp3)–C(sp3), and C(sp3)–X bond cleavages and subsequent transformations. [ABSTRACT FROM AUTHOR]

The generation and fate of 2I–VII,3I–VII,6II–VII-icosa-O-methyl-β-cyclomaltoheptaos-6I-O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5VIIC. The radical can reach the anomeric hydrogen at 1VC three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at 5VIIC, 2VIC, and 4VIC to obtain β-CD with a β-l-Idop unit, acyclic hepta-, and hexa-saccharide structures, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Reported for the first time is a tertiary‐alcohol‐guided heteroarylation of remote C(sp3)−H bonds. The mild and direct generation of alkoxyl radicals from alcohols is enabled by visible‐light photocatalysis. A remote hydrogen atom and heteroaryl migration sequence are involved in the reaction. Many sensitive groups remain intact in the reaction, thus illustrating wide functional‐group compatibility. This protocol provides a practical strategy for the late‐stage modification of alkyl ketones. [ABSTRACT FROM AUTHOR]

The alkoxyl radical is an essential and prevalent reactive intermediate for chemical and biological studies. Here we report the first donor-acceptor complex-enabled alkoxyl radical generation under metal-free reaction conditions induced by visible light. Hantzsch ester forms the key donor-acceptor complex with N-alkoxyl derivatives, which is elucidated by a series of spectrometry and mechanistic experiments. Selective C(sp3)-C(sp3) bond cleavage and allylation/alkenylation is demonstrated for the first time using this photocatalyst-free approach with linear primary, secondary, and tertiary alkoxyl radicals. [ABSTRACT FROM AUTHOR]

Lipid oxidation has always been viewed as a simple free radical chain reaction with straightforward sequence of radicals → hydroperoxides → products. The first paper in this series proposed that alternate reactions of lipid peroxyl and alkoxyl radicals compete with hydrogen abstraction to make the process much more complex. This article provides experimental evidence for formation of epoxides as major products and shows how monitoring a broad spectrum of products is critical for accurate assessment of the extent of lipid oxidation, elucidating reaction pathways, and anticipating potential toxicity. [ABSTRACT FROM AUTHOR]

The novel derivatization of boron nitride nanotubes (BNNTs) with two organic peroxides (lauroyl peroxide and dicumyl peroxide) is presented. The functionalized-BNNTs (f-BNNTs) were characterized by FTIR, 1H NMR, TGA, and SEM. These thermally labile peroxides can decompose to generate an alkoxyl radical, or an alkyl radical (with the loss of CO2), which then acts as a Lewis base to attack the electron-deficient boron sites of BNNTs. This results in the covalent formation of R-O-BNNT or R-BNNT bonds. Thin films (15 to 35 μm thickness) of 0.5 to 1.0 wt% lauryl-BNNT/polycarbonate and 1 wt% BNNT-OH/polycarboante composites were fabricated, and their transparency was demonstrated. Semi-transparent, hot-pressed disks (200 μm thickness) of 1.0 wt% cumyloxy-BNNT/polycarbonate and 1.0 wt% lauryl-BNNT/polycarbonate composites were also fabricated and mechanically tested. The Young's modulus and the maximum tensile stress were increased by 12% and 8%, respectively, compared to the corresponding properties of BNNT-free polycarbonate samples. [ABSTRACT FROM AUTHOR]

3-Hydroxy-anthranilic acid (3-OHAA), a tryptophan metabolite produced in the kynurenine pathway, is an efficient antioxidant towards peroxyl radicals (ROO ) derived from the AAPH (2,2′-azobis(2-amidinopropane) dihydrochloride) thermolysis. However, self-reactions of ROO can give rise to alkoxyl radicals (RO ), which could strongly affect the fate of scavenging reactions. In the present work, we studied the influence of RO in the scavenging activity of 3-OHAA in three different systems: i) Monitoring of the direct reaction between 3-OHAA and AAPH-derived free radicals (kinetic studies); ii) Evaluation of the protective effect of 3-OHAA on the AAPH-induced consumption of fluorescein; and, iii) Inhibition, given by 3-OHAA, of the AAPH-initiated lipid peroxidation of both, rat brain synaptosomes and homogenate preparations (assessed by chemiluminescence). For such purposes, the fraction of free radicals ( f ) trapped per 3-OHAA molecule was determined in each system. Kinetic results show that the oxidation of 3-OHAA follows a process dominated by ROO with a zero order kinetic limit in 3-OHAA, and a fraction ( f ri ) equal to 0.88. From the induction times, elicited by 3-OHAA in the kinetic profiles of fluorescein consumption, a fraction ( f T ) of 0.28 was determined. 3-OHAA also generated induction times in the kinetic profiles of light emission during the AAPH-initiated lipid peroxidation of rat brain synaptosomes and homogenates. From such induction times, fractions of 0.61 and 0.63 were determined for rat brain synaptosomes ( f syn ) and homogenates ( f hom ), respectively. These results show that during the incubation of 3-OHAA and AAPH, a low fraction of ROO self-reacts to generate RO . Nevertheless, when 3-OHAA is employed to protect particular targets, such as fluorescein, rat brain synaptosomes and homogenates, reactions of ROO and/or RO should be considered. [ABSTRACT FROM AUTHOR]

A series of N-OR substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and benzo[1,2-b:4,5-b′]dithiophene (BDT) based copolymers are systematically investigated. The replacing CH2 with smaller size oxygen atom not only reduces the steric hindrance but also enhances the dipole moment (Δμge), which is in favor of charge separation. while the optical and electrochemical properties almost remain unchanged due to the alkoxyl chain on TPD unit not conjugated with the backbone. Consequently, the PBT-O8 based solar cell devices yield a remarkable short-circuit current density (JSC) of up to 14.3 mA/cm² and power conversion efficiency (PCE) of 8.22%, which exhibits an increase of 10% in comparison with that of PBT-C8 (PCE 7.50%). Furthermore, the PCEs increase almost linearly with decreasing side chain length from O12 to O10 to O8. Apart from the novel TPD analogues reported here, this work also provides a new insight into the ingenious use of alkoxyl side chain to improve the photovoltaic performance. [ABSTRACT FROM AUTHOR]

Methylglyoxal at a concentration of 5 mM caused a significant inhibition of superoxide anion radical (O ) comparable to the effect of Tirone. In the process of O generation in the system of egg phosphatidylcholine liposome peroxidation induced by the azo-initiator AIBN, a marked inhibition of chemiluminescence in the presence of 100 mM methylglyoxal was found. At the same time, methylglyoxal did not inhibit free radical peroxidation of low-density lipoprotein particles, which indicates the absence of interaction with methylglyoxal alkoxyl and peroxyl polyenoic lipid radicals. These findings deepen information about the role of methylglyoxal in the regulation of free radical processes. [ABSTRACT FROM AUTHOR]

High-level ab initio calculations have been used to compare prototypical thiyl, alkoxyl, and alkyl radical addition reactions. Thiyl radical addition to the sulfur center of thioketones is exothermic and rapid, occurring with negative enthalpic barriers and only weakly positive Gibbs free energy barriers. In stark contrast, alkoxyl radical addition to the oxygen center of ketones is highly endothermic and occurs with very high reaction barriers, though these are also suppressed. On the basis of analysis of the corresponding alkyl radical additions to these substrates and the corresponding reactions of these heteroatom radicals with alkenes, it suggested that addition reactions involving thiyl radicals have low intrinsic barriers because their unpaired electrons are better able to undergo stabilizing resonance interactions with the p* orbitals of the substrate in the transition state. [ABSTRACT FROM AUTHOR]

The alkoxyl radical is an important reactive intermediate in mechanistic studies and organic synthesis; however, its current generation from alcohol oxidation heavily relies on transition metal activation under strong oxidative conditions. Here we report the first visible-light-induced alcohol oxidation to generate alkoxyl radicals by cyclic iodine(III) reagent catalysis under mild reaction conditions. The β-fragmentation of alkoxyl radicals enables selective C(sp3)-C(sp3) bond cleavage and alkynylation/alkenylation reactions with various strained cycloalkanols, and for the first time with linear alcohols. [ABSTRACT FROM AUTHOR]

Reported herein is the first visible-light-induced formation of alkoxyl radicals from N-alkoxyphthalimides, and the Hantzsch ester as the reductant is crucial for the reaction. The selective hydrogen atom abstraction by the alkoxyl radical enables C(sp3)−H allylation and alkenylation reactions under mild reaction conditions at room temperature. Broad substrate variations, including a structurally complexed steroid, undergo the C(sp3)−H functionalization reaction effectively with high regio- and chemoselectivity. [ABSTRACT FROM AUTHOR]

Reported herein is the first visible-light-induced formation of alkoxyl radicals from N-alkoxyphthalimides, and the Hantzsch ester as the reductant is crucial for the reaction. The selective hydrogen atom abstraction by the alkoxyl radical enables C(sp3)−H allylation and alkenylation reactions under mild reaction conditions at room temperature. Broad substrate variations, including a structurally complexed steroid, undergo the C(sp3)−H functionalization reaction effectively with high regio- and chemoselectivity. [ABSTRACT FROM AUTHOR]

The development of an efficient and green catalytic system for recalcitrant pollutant removal is an attractive yet challenging research topic in the field of environmental catalysis. In the present work, the use of activated carbon fibers (ACFs) as a novel and excellent metal-free catalyst is proposed for peracetic acid (PAA) activation, constructing a pro-environmental and efficient catalytic system for the removal of organic pollutants. In this system, ACFs could effectively activate PAA to remove the dye Reactive Brilliant Red X-3B (RR X-3B) over a wide pH range (3–11), exhibiting a remarkable pH-tolerant performance. Moreover, the ACFs also displayed excellent sustained catalytic ability and regeneration capability, avoiding secondary contamination. A hybrid method that combines various radical scavengers with electron paramagnetic resonance (EPR) technology has been used to confirm that both hydroxyl radicals (HO ) and alkoxyl radicals (CH 3 C(O)O ) were generated in the ACFs/PAA catalytic system. Furthermore, a combination of EPR with density functional theory calculations has been employed to evaluate the role of ACFs in the ACFs/PAA system. The results suggested that the introduction of ACFs facilitated homolytic cleavage of the O–OH bond, resulting in the generation of HO and CH 3 C(O)O for the effective removal of organic dyes. Based on these results and analyses, a possible mechanism is proposed. [ABSTRACT FROM AUTHOR]

Pollution of wastewater and natural waters by organic contaminants is a major health issue, yet actual remediation methods are limited by incomplete removal of recalcitrant contaminants and by secondary pollution by chlorinated contaminants and catalytic metals. To attempt to solve these issues, we tested the removal of acid orange by peracetic acid (PAA), a safe oxidant, activated by Fe-biochar that iron anchored on biochar to prevent secondary pollution by iron. Fe-biochar was synthesized using a simple, one-step pyrolysis method. We investigated the effects of PAA concentration, pH, humic acids, chloride, bicarbonate on the reaction. Radical quenching and electron paramagnetic resonance were used to identify reacting species. Results showed that the granulous structure of Fe-biochar and the presence of Fe, Fe 3 O 4 , Fe 2 O 3 , and Fe 3 C on Fe-biochar surface. The highest removal of acid orange of 99.9% was obtained with 1.144 mM PAA and 0.3 g/L Fe-biochar at pH 7. Acid orange removal increases with Fe-biochar dose, decreases with pH, is slightly inhibited by humic acids and bicarbonate, and is not modified by chloride. Our experimental results suggested that CH 3 C(O)OO· and CH 3 C(O)O· are the main radical species, but there may also be non-radical effects in Fe-biochar/PAA process. Fe-biochar displayed high re-usability, with 92.8% removal after five uses. [Display omitted] • The mechanism of the Fe-biochar/PAA process was investigated by removing acid orange. • CH 3 C(O)O· and CH 3 C(O)OO· act as the primary radicals. • There may also be non-radical effects in the process of acid orange removal. • Fe-biochar has a high recycling rate in the Fe-biochar/PAA process. [ABSTRACT FROM AUTHOR]

α-Hydrogen-substituted nitroxyl radicals are of considerable interest as catalysts for oxidation and polymerization, but are usually inherently unstable. We report herein the catalytic activity of a new family of stable iso-azaphenalene (IAPNO) α-hydrogen nitroxyl radicals in the copper/bipyridine/ N-methylimidazole co-catalyzed aerobic oxidation of alcohols. The nitroxyl radical Mes/TIPSO-IAPNO (TIPSO=triisopropyloxy, IAPNO=isoazaphenalene N-oxyl) displays higher activity than TEMPO in the oxidation of benzylic and allylic alcohols. Alkyl, benzyl, allyl, and propargyl alcohols are oxidized with yields up to 96 %. The readily prepared nitroxyl catalysts are recovered in 75-90 % yield after purification of the reaction mixture and are recycled. [ABSTRACT FROM AUTHOR]

Radical relay cyclizations initiated by alkoxy radicals are a powerful tool for the rapid construction of substituted tetrahydrofurans. The scope of these relay cyclizations has been dramatically increased with the development of two strategies that utilize an oxygen atom in the substrate to accelerate die desired hydrogen atom transfer (HAT) over competing pathways. This has enabled a chemoselective 1,6-HAT over a competing 1,5-HAT. Furthermore, this allows for a chemoselective 1,5-HAT over competing direct cyclizations and β-fragmentations. Oxygen atom incorporation leads to a general increase in cyclization diastereoselectivity over carbon analogues. This chemoselective relay cydization strategy was utilized in the improved synthesis of the tetrahydrofuran fragment in (-)-amphidinolide K. [ABSTRACT FROM AUTHOR]

Evidence is provided that the green leaf volatile 3-Z-hexenal serves as a precursor for biogenic secondary organic aerosol through the formation of polar organosulfates (OSs) with molecular weight (MW) 226. The MW 226 C6-OSs were chemically elucidated, along with structurally similar MW 212 C5-O0Ss, whose biogenic precursor is likely related to 3-Z-hexenal but still remains unknown. The MW 226 and 212 OSs have a substantial abundance in ambient fine aerosol from K-puszta, Hungary, which is comparable to that of the isoprene-related MW 216 OSs, known to be formed through sulfation of C5-epoxydiols, second-generation gas-phase photooxidation products of isoprene. Using detailed interpretation of negative-ion electrospray ionization mass spectral data, the MW 226 compounds are assigned to isomeric sulfate esters of 3,4- dihydroxyhex-5-enoic acid with the sulfate group located at the C-3 or C-4 position. Two MW 212 compounds present in ambient fine aerosol are attributed to isomeric sulfate esters of 2,3-dihydroxypent-4- enoic acid, of which two are sulfated at C-3 and one is sulfated at C-2. The formation of the MW 226 OSs is tentatively explained through photooxidation of 3-Z-hexenal in the gas phase, resulting in an alkoxy radical, followed by a rearrangement and subsequent sulfation of the epoxy group in the particle phase. [ABSTRACT FROM AUTHOR]

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF 3 CHFCF 2 OCF 3 with OH radicals and Cl atoms using M06-2X/6-31+G(d,p) level of theory. The energetic calculations were refined by using aug-cc-pVTZ basis set. Our calculations reveal that OH-initiated hydrogen abstraction is thermodynamically and kinetically more facile than that from the Cl-initiated hydrogen abstraction. Using group-balanced isodesmic reactions, the standard enthalpies of formation (Δ H f °) for species and bond dissociation energies for C H bond are also reported. The Δ H f ° for CF 3 CHFCF 2 OCF 3 and •CF(CF 3 )CF 2 OCF 3 species calculated from M06-2X/6-31+G(d,p) results are −523.15 and −471.65 kcal mol −1 , respectively. The rate constants evaluated by canonical transition state theory (CTST) are found to be 1.22 × 10 −15 and 3.40 × 10 −17 cm 3 molecule −1 s −1 which are in a reasonable agreement with the available experimental data of (1.43 ± 0.28) × 10 −15 and (4.09 ± 0.42) × 10 −17 cm 3 molecule −1 s −1 , respectively, for OH and Cl-initiated hydrogen abstraction reactions. The atmospheric life time of CF 3 CHFCF 2 OCF 3 is estimated to be 38.5 years. The atmospheric fate of the alkoxy radical, CF 3 CF(O•)CF 2 OCF 3 is also investigated for the first time using same level of theory. [ABSTRACT FROM AUTHOR]

Abstract: This account describes the results of our recent mechanistic studies on unimolecular C-C bond fragmentation (β-scission and O-neophyl rearrangement) and bimolecular hydrogen atom transfer (HAT) reactions of alkoxyl radicals. Particular attention is devoted to the study of solvent effects on these reactions by means of time-resolved techniques such as laser flash photolysis. Information is provided on the effect of ring substituents and of the solvent on the spectral properties of arylcarbinyloxyl radicals and on their reactivity in β-scission and O-neophyl rearrangement reactions, showing that a change in solvent can influence the fragmentation reactivity and selectivity. Detailed information has also been obtained on the role of the substrate structure and of the solvent on HAT reactions involving the cumyloxyl radical, showing the importance of solvent hydrogen bond interactions with the substrate and/or the radical on these processes, and providing a general mechanistic description of the kinetic solvent effects observed in HAT reactions from C-H bonds, as well as expanding on the previously available description for HAT from phenolic O-H bonds. The possible application of these findings to synthetically useful C-H functionalization procedures is discussed. 1 Introduction 2 C-C β-Scission Reactions 3 O-Neophyl Rearrangement 4 Hydrogen Atom Transfer (HAT) Reactions 5 Concluding Remarks. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of dihydroartemisinin (DHA) with solvated electrons ( ) generated under radiolytic conditions showed high pH dependence. The reduction performed under neutral conditions led to the formation of compound P1 deriving from the initial alkoxyl radical as the only detectable product. [Copyright &y& Elsevier]

A new general methodology for the synthesis of chiral vinylphosphonate and vinylphosphine oxide carbohydrate derivatives has been developed using the anomeric alkoxyl radical fragmentation reaction as the key step. The synthetic sequence proceeded via β-iodophosphonate and β-iodophosphine oxide intermediates, which may be interesting synthons for the introduction of phosphorus into organic molecules. These vinylphosphonates could be easily transformed into 2-methylene-1-phosphapentofuranoses (3-methylene-1,2-oxaphospholanes) and β-aminophosphonates, isosteres of biologically active α-methylene-γ-lactones and β-amino acids, respectively. [ABSTRACT FROM AUTHOR]

A time-resolved kinetic study on the effect of metal ions (Mn+) on hydrogen abstraction reactions from C-H donor substrates by the cumyloxyl radical (CumO•) was carried out in acetonitrile. Metal salt addition was observed to increase the CumO• β-scission rate constant in the order Li+ > Mg2+ > Na+. These effects were explained in terms of the stabilization of the β-scission transition state determined by Lewis acid-base interactions between Mn+ and the radical. When hydrogen abstraction from 1,4-cyclohexadiene was studied in the presence of LiClO4 and Mg(ClO4)2, a slight increase in rate constant (kH) was observed indicating that interaction between Mn+ and CumO• can also influence, although to a limited extent, the hydrogen abstraction reactivity of alkoxyl radicals. With Lewis basic C-H donors such as THF and tertiary amines, a decrease in kH with increasing Lewis acidity of Mn+ was observed (kH(MeCN) > kH(Li+) > kH(Mg2+)). This behavior was explained in terms of the stronger Lewis acid-base interaction of Mn+ with the substrate as compared to the radical. This interaction reduces the degree of overlap between the α-C-H σ" orbital and a heteroatom lone-pair, increasing the C-H BDE and destabilizing the carbon centered radical formed after abstraction. With tertiary amines, a >2-order of magnitude decrease in kH was measured after Mg(ClO4)2 addition up to a 1.5:1 amine/Mg(ClO4)2 ratio. At higher amine concentrations, very similar kH values were measured with and without Mg(ClO4)2. These results clearly show that with strong Lewis basic substrates variations in the nature and concentration of Mn+ can dramatically influence kH, allowing for a fine control of the substrate hydrogen atom donor ability, thus providing a convenient method for C-H deactivation. The implications and generality of these findings are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Alkoxyl radicals add 5-exo-trig selectively to cyano- and methoxycarbonyl-substituted carbon–carbon double bonds, to afford α-acceptor-α-tetrahydrofuryl-2-methyl radicals. Trapping of cyclized radicals by Bu3SnD furnishes products of site-specific deuterium-labeling in α-position to the acceptor group. In intramolecular competition experiments, alkoxyl radicals add similarly fast to a cyano-substituted double bond than to a terminal alkene, but by a factor >25 faster to an enol ether. The nucleophilic component of alkoxyl radical reactivity opens an interesting new access to tetrahydrofuryl amino acids via C,O-cyclization, as shown by synthesis of a N,O-protected 5-phenyltetrahydrofuryl-2-methyl glycine. [Copyright &y& Elsevier]

A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4-C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric D-furanoses. D-xylo- and D-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas D-arabino- and D-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively. [ABSTRACT FROM AUTHOR]

Oxidation of tyrosine moieties by radicals involved in lipid peroxidation is of current interest; while a rate constant has been reported for reaction of lipid peroxyl radicals with a tyrosine model, little is known about the reaction between tyrosine and alkoxyl radicals (also intermediates in the lipid peroxidation chain reaction). In this study, the reaction between a model alkoxyl radical, the tert-butoxyl radical and tyrosine was followed using steady-state and pulse radiolysis. Acetone, a product of the β-fragmentation of the tert-butoxyl radical, was measured; the yield was reduced by the presence of tyrosine in a concentration- and pH-dependent manner. From these data, a rate constant for the reaction between tert-butoxyl and tyrosine was estimated as 6 ± 1 × 107 M−1 s−1 at pH 10. Tyrosine phenoxyl radicals were also monitored directly by kinetic spectrophotometry following generation of tert-butoxyl radicals by pulse radiolysis of solutions containing tyrosine. From the yield of tyrosyl radicals (measured before they decayed) as a function of tyrosine concentration, a rate constant for the reaction between tert-butoxyl and tyrosine was estimated as 7 ± 3 × 107 M−1 s−1 at pH 10 (the reaction was not observable at pH 7). We conclude that reaction involves oxidation of tyrosine phenolate rather than undissociated phenol; since the p Ka of phenolic hydroxyl dissociation in tyrosine is ∼ 10.3, this infers a much lower rate constant, about 3 × 105 M−1 s−1, for the reaction between this alkoxyl radical and tyrosine at pH 7.4. [ABSTRACT FROM AUTHOR]

The fragmentation of anomeric alkoxyl radicals (ARF) and the subsequent intramolecular cyclization promoted by hypervalent iodine reagents provide an excellent method for the synthesis of tetrazolo-sugars. This new reaction offers additional advantages for the synthesis of these compounds, including the ready availability of the starting materials, experimental simplicity, mild conditions, and good yields. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of Artemisinin with solvated electrons () generated by radiolytic methods led to the formation of acid 2 as the only detectable product. A possible mechanism leading to the formation of compound 2 is discussed. [Copyright &y& Elsevier]

Abstract: Nitric oxide ( NO) is thought to react with fatty acid alkoxyl radical, which is generated from fatty acid hydroperoxide via one-electron reduction. However, detail in the reaction remains obscure. In the present study, we examined the reaction of nitric oxide with fatty acid alkoxyl radical generated in the lipoxygenase/linoleate/13-hydroperoxyoctadecadienoate (13-HpODE) system under anaerobic conditions via HPLC equipped with mass spectrometry and photodiode array detections. In this reaction system, nitric oxide can scavenge linoleate alkoxyl radical, producing 13-ONO-9Z,11E-ODE. However, instead of 13-ONO-9Z,11E-ODE, 13-NO-9E,11E-ODE and 9-NO-10E,12E-ODE were alternatively detected in the reaction solution. To explain this contradiction, we proposed a mechanism as follows: (1) 13-ONO-9E/11Z-ODE undergoes homolytic cleavage at >CHinto the linoleate allyl radical and nitrogen dioxide, (2) the allyl radical undergoes resonance stabilization into the E/E-form, and (3) nitric oxide scavenges the E/E-pentadiene radical at C9 or C13 position. Consequently, we concluded that nitric oxide immediately converts fatty acid alkoxyl radical into allyl radical. [Copyright &y& Elsevier]

Exposure of proteins to radicals in the presence of O2 gives both side-chain oxidation and backbone fragmentation. These processes can be interrelated, with initial side-chain oxidation giving rise to backbone damage via transfer reactions. We have shown previously that alkoxyl radicals formed on the C-3 carbons of Ala, Val, Leu, and Asp residues undergo β-scission to give backbone α-carbon radicals, with the release of the side- chain as a carbonyl compound. We now show that this is a general mechanism that occurs with a wide range of oxidants. The quantitative significance of this process depends on the extent of oxidation at C-3 compared with other sites. HO⋅, generated by γ radiolysis, gave the highest total carbonyl yield, with protein-bound carbonyls predominating over released. In contrast, metal ion/H2O2 systems, gave more released than bound carbonyls, with this ratio modulated by EDTA. This is ascribed to metal ion – protein interactions affecting the sites of initial oxidation. Hypochlorous acid gave low concentrations of released carbonyls, but high yields of protein-bound material. The peroxyl radical generator 2,2′-azobis(2-amidinopropane) hydrochloride, and a peroxynitrite generator, 3-morpholinosydnonimine hydrochloride, gave lower overall carbonyl yields, with released carbonyls predominating over protein-bound species similar to that observed with metal ion/H2O2 systems. [Copyright &y& Elsevier]

Structure activity relationship (SARs) have been developed for the estimation of rate data for the decomposition of RO to alkyl radical and carbonyl fragments. The SARs are based upon strong, non-linear, correlations between the logarithm of measured room temperature rate coefficients and the average measured ionisation potential (IP) of the reaction products, for the decomposition of a range of simple unsubstituted, β-chlorinated and β-hydroxylated alkoxyl radicals. The role of chemical activation in the decomposition chemistry of substituted-alkoxyl radicals is briefly discussed. Distinct correlations are observed for simple and for lone pair-bearing β-substituted radicals, and each is rationalised in terms of simple Marcus theory. By assuming an Arrhenius A-factor of 1×1013 s−1, for a single decomposition pathway, activation barriers (Ea) have been estimated from selected room temperature rate coefficient data taken from the literature. These estimated Ea values, and barriers obtained directly from recent temperature-dependent experimental studies, are also shown to correlate with the average product IP. The correlation expressions presented allow the prediction of decomposition rate data with a precision comparable to, or within, that of the experimental data. Of the 10 simple and 11 heteroatom-substituted RO. species used to construct the correlations, 18 (85%) of the predicted room temperature rate coefficients are within a factor of two of their measured (or theoretically calculated) values, and 100% are within a factor of three. [Copyright &y& Elsevier]

A mild and highly efficient one-pot synthesis of aryl glycines from easily available serine derivatives is described. This methodology is also applied to the synthesis of other uncommon amino acids. [Copyright &y& Elsevier]

A novel fluorogenic probe for tert-butoxy radicals based on the hydrazino-naphthalimide system is reported. Interestingly, different regioisomers exhibited significantly different optical properties toward ROS, which suggested 4-hydrazinyl naphthalimide as a potential new platform for the in vitro and in cellulo detection of alkoxyl radicals. [ABSTRACT FROM AUTHOR]

Lipids containing polyunsaturated fatty acids are primary targets of oxidation, leading to the formation of a variety of reactive products (1). The new oxidised products are generated with different number of oxygen molecules bound to the acyl chain, increasing the lipid molecular weight. However, the alkoxyl radicals can generate short-chain oxidation products including short-chain aldehydes, which can covalently modify proteins in a process called lipoxidation (2). Acrolein, with only three carbons, is the shortest alkenal identified as a short-chain oxidation product. It is also by far the strongest electrophile and therefore the most reactive, especially with thiol groups on proteins (3). These oxidative post-translational modifications influence cell behaviour and can be involved in inflammatory diseases (4). The exact nature of many of these adducts, and their relationship with cellular effects are still unclear. There is also a need to develop sensitive mass spectrometry (MS) methods that are well-adapted for the identification of these adducts in complex biological systems. The aim of this work was to develop a mass spectrometry approach for the analysis of protein-aldehyde adducts. Lysozyme from chicken egg white was used to investigate the formation of short-chain aldehyde-containing lipoxidation products. The protein was first reduced with dithiothreitol to break disulphide bounds between cysteine residues, generating free thiols available for modification. Acrolein was then added to modify the reduced protein. The protein-aldehyde adducts formed were stabilized by reduction with sodium borohydride and identified using mass spectrometry to analyse the intact protein and tryptic digests. Analysis of intact acrolein-modified lysozyme showed that multiple sites (up to 8) could be modified. All modifications were found to be Michal adducts, increasing the protein mass by 58 Da per adduct. Analysis of tryptic digests allowed the localization of the adducts to specific amino acid residues. Six cysteine and two lysine residues were shown to be modified, which corroborates observation of up to 8 acrolein adducts per protein in the intact protein analysis. By the same proteomic approach, it was possible to identify amino acid-specific fragmentations that may be helpful in the identification of specific acrolein adducts. In summary, this study can be seen as a model testing mass spectrometry for the analysis of protein-aldehyde adducts. The combined use of direct infusion and LC-MS/MS methods helped to identify the type, the number and the location of acrolein modifications in lysozyme. This shows that MS methods provide a powerful tool for the evaluation of these modifications and further aldehydes are now being investigated. Potentially, this MS approach can be applied to discover biomarkers of adductions in cells and tissues under pathophysiological environments. [ABSTRACT FROM AUTHOR]

This article demonstrates that ionizing radiation induces simultaneous crosslinking and scission in poly(trimethylene carbonate-co-d-lactide) diblock and random copolymers. Copolymer films were electron-beam (EB) irradiated up to 300 kGy under anaerobic conditions and subsequently examined by evaluation of their structure (FT-IR, NMR), molecular weight, intrinsic viscosities, and thermal properties. Radiation chemistry of the copolymers is strongly influenced by the content of ester linkages of the lactide component. At low lactide content, crosslinking reaction is the dominant one; however, as the lactide ratio increases, the ester linkages scission becomes more competent and exceeds the crosslinking. Electron paramagnetic resonance (EPR) measurements indicate that higher content of amorphous carbonate units in copolymers leads to a reduction in free radical yield and faster radical decay as compared to lactide-rich compositions. The domination of scission of ester bonds was confirmed by identifying the radiolytically produced alkoxyl and acetyl radicals, the latter being more stable due to its conjugated structure. [ABSTRACT FROM AUTHOR]

The article discusses the direct synthesis of 1,4-diols from alkenes with iron-catalyzed aerobic hydration and C-H hydroxylation, focusing on the study by doctor Tsuyoshi Taniguchi of the Kanazawa University in Japan and colleagues. Doctor Taniguchi states that they hypothesized that the alkoxyl radical might induce a 1,5-hydrogent transfer to transform an inert C-H bond into another functional group, with the help of students Takuma Hashimoto and Daisuke Hirose.

The visible-light-induced alcohol oxidation generates alkoxyl radicals through cyclic iodine(III) reagent catalysis. [ABSTRACT FROM AUTHOR]

Chemical equation related to "Generation of Alkoxyl Radicals by Photoredox Catalysis Enables Selective C(sp3)-H Functionalization under Mild Reaction Conditions" by J. Zhang and colleagues published in "Angewandte Chemie" is presented.