Oxidations by a H2O2-VO3 −-pyrazine-2-carboxylic acid reagent

Alkanes (cyclohexane, hexane, heptane isomers) are effectively oxidized in CH₃CN at 20–70°C by hydrogen peroxide when catalyzed by a Bu₄NVO₃-pyrazine-2-carboxylic acid system. Alkyl hydroperoxide is the main product; an alcohol and a ketone or an aldehyde are also formed. Under these conditions benzene is oxidized to give phenol, while alkyl benzenes yield oxygenation products both of the ring and the side chain. It has been assumed that the interaction of H₂O₂ with VO₃ ^– gives rise to generation of HO radicals and other radical-like vanadium containing species that abstract a hydrogen atom from an alkane, RH. The radical R^. formed reacts with O₂ to produce ROO^. which is then transformed to alkyl hydroperoxide.Presented at the VIII International Symposium on Homogeneous Catalysis (Amsterdam, 1992).Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 64–68, January, 1993.     

不同加成数C60精氨酸衍生物的合成及其清除活性氧自由基的性能

通过控制反应配比, 首次合成了三种具有不同加成数目的水溶性C₆₀精氨酸衍生物, C₆₀[HNC(NH)NH(CH₂)₃CH(NH₂)COOH]_nH_n (n＝2, 6, 8). 采用FT-IR, UV, RF, ¹H NMR, ¹³C NMR, LC-MS, EA, 粒径分析, 透射电镜等手段对其结构进行了表征. 同时采用化学发光法考察了三种具有不同加成数目的C₆₀精氨酸衍生物对活性氧自由基(超氧阴离子O₂^－.及羟自由基•OH)清除能力, 结果表明, C₆₀精氨酸衍生物对活性氧自由基具有优良的清除能力, 且清除能力与加成基团供电效应、空间位阻及C₆₀精氨酸衍生物在水中的聚集形态等因素密切相关.     

Preparation of Cs2ZrO3 and Cs2ThO3 Through Sol-gel Method and Their Characterization

Cesium zirconate and cesium thorate were prepared by sol-gel method following citrate-nitrate route. The compounds were characterized by X-ray diffraction, chemical analysis and simultaneous TG-DTA. The methods of preparation of Cs₂ZrO₃ and Cs₂ThO₃ reported in literature involve difficult steps and require stringent experimental conditions for obtaining the compounds. In this work we report an easier method for the preparation of these compounds at relatively low temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of isomeric spin adducts of Leu-Tyr and Tyr-Leu free radicals using liquid chromatography-tandem mass spectrometry

Free radical species are generally short-lived due to their high reactivity and thus direct measurement and identification are often impossible. In this study we used a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), to trap radical intermediates formed during the oxidation of isomeric dipeptides tyrosine-leucine (Tyr-Leu) and leucine-tyrosine (Leu-Tyr), induced by the hydroxyl radical. To investigate the influence of the amino acid position in the peptide chain on the oxidation and free radical generation, the spin adducts were characterized using LC-MS and MS(n) . We detected carbon and oxygen DMPO adducts and adducts bearing two DMPO, which were analyzed by MS(n) . Both alkoxyl and peroxyl radicals were identified. Radical intermediates were localized in Tyr during oxidation of Tyr-Leu, while radicals were identified in Leu and Tyr during oxidation of Leu-Tyr. DMPO adducts of acyl radical species formed from cleavage of the peptide backbone, promoted by the alkoxyl radical in α carbon of the N-terminal amino acid were observed. The results show that the amino acid position has an influence in the oxidation process, at least on small peptides, and that the α carbon of the N-terminal amino acid is more vulnerable to the attack of the electrophilic hydroxyl radical.     

Rationally Designed Fluorescence .OH Probe with High Sensitivity and Selectivity for Monitoring the Generation of .OH in Iron Autoxidation without Addition of H2O2

The first sensitive fluorescence ^.OH probe ( 1 ) that is capable of monitoring the generation of trace ^.OH in iron autoxidation is presented. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of ^.OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for ^.OH. Reaction of 1 with ^.OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off–on response. The capability of probe 1 has been demonstrated by imaging ^.OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of ^.OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace ^.OH in some critical physiological and pathological processes associated with iron autoxidation.     

Newly Detected Hydroxyls in Zeolite Mordenite by 1H MAS Spin Echo NMR Spectroscopy

The study of the acidic sites in zeolites is important to understand the nature of the acidic catalytic function.     

An HPLC assay of hydroxyl radicals by the hydroxylation reaction of terephthalic acid

An HPLC assay for hydroxyl radicals is described. The hydroxyl radical was trapped by terephthalic acid (non-fluorescent), and 2-hydroxyl terephthalic acid (fluorescent) was quantitated by HPLC-fluorescence detection. At a terephthalic acid concentration of 4.25 mmol/L, the hydroxyl radical formed in the Fenton reaction was successfully assayed in the concentration range of hydrogen peroxide of 2.5-50 micro mol/L, where the concentration of Fe(II) was 50 micro mol/L. The fluorescence of 2-hydroxy terephthalate was stable at 24 h, and its detection limit by this method was 5 nmol/L (100 fmol).     

Highly Efficient CH Hydroxylation of Carbonyl Compounds with Oxygen under Mild Conditions

A transition‐metal‐free Cs₂CO₃‐catalyzed α‐hydroxylation of carbonyl compounds with O₂ as the oxygen source is described. This reaction provides an efficient approach to tertiary α‐hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp³)? H bond cleavage.     

高氯酸介质中2—羟基—4—仲辛基—二苯甲酮肟萃取钯热力学的研究

２－羟基－４－仲辛基－二苯甲酮肟（Ｎ５３０）曾用于金属钴、镍的分离［１］。但对其萃钯热力学研究尚未见报道。为此本文对Ｎ５３０在高氯酸介质中萃取钯的热力学进行了研究,测定了该萃取反应的表观平衡常数和热力学函数。１实验部分１．１试剂与溶液Ｎ５３０由中国科...     

原位合成H2O2在水处理技术中的应用研究进展

从过氧化氢(H₂O₂)的原位生成技术角度总结了近年来利用原位合成H₂O₂处理水中污染物的研究,分析了当前可充当氢源材料的种类及不同的氢源材料对于提高H₂O₂产率的影响,以及不同的催化剂材料和催化反应环境提高H₂O₂利用率对污染处理效果的影响因素,并对原位合成H₂O₂在水处理领域中面临的挑战和发展前景做了展望,从而为该技术的大规模应用提供指导和借鉴。