Chemoenzymatic Dynamic Kinetic Resolution of Primary Amines Catalyzed by CAL-B at 38–40 °C

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Coniferyl Alcohol Radical Detection by the Dirigent Protein At DIR6 Monitored by EPR

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Nanostructured Silicas, a Platform for the Observation of Transient Radicals: Application to Sulfinyl Radicals

Diazenes, precursors of sulfinyl radicals, were used to functionalize nanostructured SBA-15 silicas either in the framework or on the pore by formation of covalent links, or by simple adsorption on the surface. Depending on their design and on the experimental conditions, these materials proved to be effective tools to study the behavior and the reactivity of arylsulfinyl radicals made persistent because of confinement effects. When the covalently linked precursors were irradiated at room temperature, a spectacular increase of the lifetime of the expected sulfinyl radicals was registered (up to 17 h). At higher temperature, upon thermal initiation at 473 K, the decomposition of the adsorbed precursor enabled visualization of the rearrangement of the corresponding arylsulfinyl radicals into sulfonyl radicals via O–S coupling

Design of Wall-Functionalized Hybrid Silicas Containing Diazene Radical Precursors. EPR Investigation of Their Photolysis and Thermolysis

Bis-silylated diazenes were designed to prepare wall-functionalized hybrid silicas via the sol–gel process. These precursors enabled the straightforward generation of arylsulfanyl radicals by either photolysis or thermolysis. Their location in the framework of the mesoporous materials was evidenced by spin trapping experiments. The incidence of confinement on the radical lifetime was investigated by electron paramagnetic resonance (EPR). An amazing persistence (<i>t</i>_1/2 = 27 min) was recorded at 473 K

Kinetic Studies on the Formation of Sulfonyl Radicals and Their Addition to Carbon–Carbon Multiple Bonds

The reactions of α-hydroxyl and α-alkoxyl alkyl radicals with methanesulfonyl chloride (MeSO₂Cl) have been studied by pulse radiolysis at room temperature. The alkyl radicals were produced by ionizing radiation of N₂O-saturated aqueous solution containing methanol, ethanol, isopropanol, or tetrahydrofuran. The transient optical absorption spectrum consisted of a broad band in the region 280–380 nm with a maximum at 320 nm typical of the MeSO₂^• radical. The rate constants in the interval of 1.7 × 10⁷–2.2 × 10⁸ M^–1 s^–1 were assigned to an electron-transfer process that leads to MeSO₂Cl^•–, subsequently decaying into MeSO₂^• radical and Cl^–. The rate constants for the addition of CH₃SO₂^• to acrolein and propiolic acid were found to be 4.9 × 10⁹ M^–1 s^–1 and 5.9 × 10⁷ M^–1 s^–1, respectively, in aqueous solutions and reversible. The reactivity of tosyl radical (<i>p</i>-CH₃C₆H₄SO₂^•) toward a series of alkenes bearing various functional groups was also determined by competition kinetics in benzene. The rate constants for the addition of tosyl radical to alkenes vary in a much narrower range than the rate constants for the reverse reaction. The stabilization of the adduct radical substantially contributes to the increase of the rate constant for the addition of tosyl radical to alkenes and, conversely, retards the β-elimination of tosyl radical