Redox dependence of the reaction of alpha-alkoxyalkyl radicals with a series of oxidants.

Oxygen and oxidants enhance the sensitivity of cells to radiation. To understand this effect at the mechanistic level, the redox dependences for the reactivity of weakly reducing alpha-monoalkoxyalkyl radicals of 1,4-dioxane and tetrahydrofuran with a series of oxidants, for example, quinones, viologens, and nitro-arenes, with one-electron reduction potentials E71 values ranging from -80 to -640 mV, have been determined using the technique of pulse radiolysis. The second-order rate constants for these reactions with the alpha-monoalkoxyalkyl radicals of 1,4-dioxane and tetrahydrofuran are in the range (0.03-1.5) x 109 and (1.0-6.6) x 109 dm3 mol(-1) s(-1), respectively. The reactions of the alpha-alkoxyalkyl radicals of 1,4-dioxane with quinones and viologens involve an outer-sphere electron transfer, in contrast to a reaction with the nitro-arenes to give adducts. The resulting long-lived nitroaromatic adduct radicals were found to react with the reductant, TMPD, probably leading to the formation of hydroxylamine-type products. In cells, adducts formed on reaction of deoxyribose sugar radical with oxidants and subsequent reactions with reductants may contribute to the mechanisms involved in radiosensitization by oxygen and those oxidants that interact through adduct formation.

Ionic liquid supported three-phase liquid-liquid-liquid microextraction as a sample preparation technique for aliphatic and aromatic hydrocarbons prior to gas chromatography-mass spectrometry.

For the first time hollow fiber-protected ionic liquid supported three-phase (liquid-liquid-liquid) microextraction (HFM-LLLME) was developed for the gas chromatography-mass spectrometric (GC-MS) analysis of aromatic and aliphatic hydrocarbons. The hydrocarbons were extracted from 10 ml of aqueous samples though small volumes of ionic liquid and organic solvent in the hollow fiber membrane HFM) wall and channel, respectively. The ionic liquid was immiscible with both the aqueous sample and the organic solvent (toluene). After extraction, the enriched solvent was directly injected into a GC-MS system for analysis without any further pretreatment. Ionic liquid supported HFM-LLLME shows better extraction performance than two-phase HFM-liquid-phase microextraction, in which only organic solvent is involved, and solid-phase microextraction. The ionic liquid and organic solvent combination found most suitable for HFM-LLLME was 1-butyl-3-methylimidazolium hexafluorophosphate, and toluene, respectively. This new technique provided up to 210-fold enrichment of aliphatic and aromatic hydrocarbons in 40 min with good reproducibility (<11%) and limits of detection (1-7 ng l(-1)).

From alcohols to sugars-how does the reactivity of alpha-hydroxyalkyl radicals change with structure? A quantitative examination by pulse radiolysis.

Rate constants are reported for the 1-electron reduction of the azo dye Orange II in water (pH 7.0) by 10 different alpha-hydroxy radicals. The radicals were created by pulse radiolysis of aqueous solutions of the corresponding alcohol/sugar. The rate constants varied from 1 x 10(8) to 2.7 x 10(9) mol(-1) dm(3) s(-1) and radicals with beta-hydroxy groups had the lowest rate constant. The reaction was found to be controlled by the reduction potentials of the radicals, with steric influences having little effects. Good fits of the data were obtained using the Marcus equation with lambda =140 kJ/mol.