A Pulse Radiolysis Study of the Dynamics of Ascorbic Acid Free Radicals within a Liposomal Environment

The dynamics of free‐radical species in a model cellular system are examined by measuring the formation and decay of ascorbate radicals within a liposome with pulse radiolysis techniques. Upon pulse radiolysis of an N₂O‐saturated aqueous solution containing ascorbate‐loaded liposome vesicles, ascorbate radicals are formed by the reaction of OH^. radicals with ascorbate in unilamellar vesicles exclusively, irrespective of the presence of vesicle lipids. The radicals are found to decay rapidly compared with the decay kinetics in an aqueous solution. The distinct radical reaction kinetics in the vesicles and in bulk solution are characterized, and the kinetic data are analyzed.     

黄酮类化合物与α-羟乙基过氧自由基反应的脉冲辐解研究

由于脂质过氧化反应(LPO)是导致人体疾病(如肝炎、肝硬化、动脉硬化、脑溢血等)的主要原因, 而黄酮类化合物是一类很强的过氧化反应抑制剂, 因此有必要研究其化学结构与过氧化反应的关系及其抗氧化机理.本文选择α-羟乙基过氧自由基为脂质过氧自由基的模拟物, 采用脉冲辐解方法研究了乙醇溶液中4种典型的黄酮类化合物(槲皮素、芦丁、儿茶素以及黄岑甙)与α-羟乙基过氧自由基的反应动力学, 测得其反应活性顺序为:芦丁>槲皮素>黄岑甙>儿茶素. 同时以黄酮体和邻苯二酚为黄酮类化合物不同结构特征的模型化合物, 用脉冲辐解法测得二者与α-羟乙基过氧自由基的反应速率常数分别为(1.7±0.1)×10⁶和(2.9±0.1)×10⁵ mol^-1·dm³·s^-1.实验结果表明, 在黄酮类化合物与α-羟乙基过氧自由基的反应中, A环C₅位的羟基, C环C₂＝C₃或B-C环的大π键和B环邻二羟基共存时清除α-羟乙基过氧自由基活性最好, 而且C环C₂＝C₃或B-C环大π键的清除活性好于B环邻二羟基, 同时C环是否含有C₃-醣甙结构对清除作用没有明显影响. 因此我们推测在黄酮类化合物抑制脂质过氧化反应过程中, 起主要作用的是C环C₂＝C₃或B-C环的大π键与脂质过氧自由基的双键加成反应.     

胞嘧啶水溶液体系辐解的瞬态产物研究

Using the ns pulse radolysis, we studied the characteristic absorption spectrum and kinetic decay of cytosine anion radical (Cyt-). Results showed that the characteristic absorption of Cyt- was located at λ=355±5 nm, and decayed following the first order kinetics with τ1/2=265 ns at pH=7.0. The decay became slower and τ1/2 rapidly rised with the increment of pH value, Cyt- protonated at C6 in acidic solution, and the characteristic absorption was located at λ=310±5 nm, and decayed following the second order kinetics: Cyt- protonated at N3 in aqueous solution of pH≥7, and the characteristic absorption was located at λ=295±5 nm, and decayed following the second order kinetics.     

Reactions of Hydroxyl Radical with Salicylic Acid Derivatives： A Pulse Radiolysis Study

Based on pulse radiolysis of aqueous solutions of two salicylic acid derivatives including ethyl salicylate and benzylsalicylate the transient absorption spectra and the rate constants of hydroxyl radical with salicylic acid derivatives were determined for the first time. The results indicated that ethyl salicylate and benzylsalicylate have efficient activities to scavenge hydroxyl radical.     

水溶液中金属团簇的脉冲辐解研究进展

介绍了以脉冲辐解技术为手段研究水溶液中单金属团簇的形成机理,并对团簇的性质及其反应进行了简要的概括,对今后团簇的发展趋势进行了展望.     

α-羟乙基过氧自由基的自身衰变及其与槲皮素和邻苯二酚反应的脉冲辐解动力学研究

脂质过氧化反应是人体内很多病理现象的原因 ,而槲皮素是一种很强的过氧化反应抑制剂 .本文选择α-羟乙基过氧自由基作为脂质过氧自由基的模拟物 ,研究了其与槲皮素和邻苯二酚的反应动力学 .首次得到纯乙醇体系中 α-羟乙基自由基的一级和二级自身衰变速率常数分别为 (4 0 .4± 2 .6) s- 1和 (6.9± 0 .9)×1 0 8mol- 1·L· s- 1 .用脉冲辐解方法得到槲皮素与 α-羟乙基过氧自由基反应的速率常数为 (2 .1± 0 .3 )× 1 0 7mol- 1·L· s- 1 .同时选择邻苯二酚作为多酚化合物的模型化合物 ,用脉冲辐解法研究了其与 α-羟乙基过氧自由基的反应 .得到邻苯二酚与α-羟乙基过氧自由基反应的速率常数为 (3 .1± 0 .1 )× 1 0 5mol- 1 · L· s     

Deconvolution of Complex Absorption Spectra Recorded in the Pulse Radiolysis of Aqueous Solutions of 3,5-Dihydroxytolyene

The optical absorption spectra of short-lived species generated in aerated aqueous solutions of 3,5-dihydroxytoluene, a representative of alkylhydroxybenzenes, by the action of single electron beam pulses were recorded. The decay curves recorded at different wavelengths differ from each other, thus suggesting that the transient species react with one another and with water via a complex mechanism and making it possible to discriminate between individual bands characterizing each particular species in the overall spectrum. Two procedures for analyzing complex absorption spectra were employed: (i) with the use of spectra observed at different time delays after the electron pulse and (ii) with deconvolution into a sum of Gaussians.     

脉冲辐解研究喹啉和异喹啉与瞬态粒子的反应

通过合理控制反应条件, 使体系在电子束脉冲作用后只剩下所需要的一种瞬态粒子, 用脉冲辐解研究了喹啉、异喹啉分别与水合电子、羟基自由基、氢自由基等几种典型的氧化还原瞬态粒子的反应过程, 研究了各种瞬态产物的吸收光谱及其变化规律, 测定了相关反应的速率常数. 喹啉、异喹啉与水合电子的反应速率常数分别为7.1×10⁹和3.4×10⁹ mol^-1·L·s^-1, 与羟基自由基的反应速率常数分别为7.2×10⁹和3.4×10⁹ mol^-1·L·s^-1, 与氢自由基的反应速率常数分别为5.7×10⁹和3.6×10⁹ mol^-1·L·s^-1. 这一结果表明, 喹啉、异喹啉均能够非常迅速地与水合电子、羟基自由基、氢自由基发生反应, 喹啉比异喹啉的反应速率更快. 运用电子理论分析了瞬态反应产物结构的稳定性差异, 结果表明, 喹啉的反应产物比异喹啉的稳定, 从而揭示了喹啉比异喹啉反应速率快的原因.     

Complexation of Macrocyclic Compounds with Silver Ions in Surfactant Media

This paper is a report on the complexation studies of silverions with certain water soluble crown ethers viz., 15-crown-5,18-crown-6, cyclam, diaza 15-crown-5 and certain water insolublecrown ethers viz., benzo 15-crown-5, dibenzodiaza 15-crown-4,dibenzyldiaza 18-crown-6 in some nonionic surfactants viz.,polyoxyethylated alkyl phenol (TX 100), polyoxyethylene (20)sorbiton monolaurate (Tween 20), polyoxyethylene (20) sorbitonmonoleate (Tween 80) and polyoxyethylated glyco monolaurylether (Brij 35) by potentiometry. In addition, conductometry wasalso used to study the complexation of oxa crown ethers to comparethe results obtained by potentiometry, which were found to be ingood agreement with each other. The complexation studies indicate1:1 complex formation between the silver ion and macrocycle, thelog_ML ⁿ⁺ values being in the range 1 to 9.     

自由基诱导的水溶液中氟西汀的降解:脉冲辐解及稳态辐照研究

The reactions of the pharmaceutical fluoxetine (FLX) with different radicals were investigated by pulse radiolysis. The reaction of hydroxyl radical (·OH) with FLX formed hydroxylated adduct of the aromatic ring, while oxidation of FLX by sulfate radical anion (SO₄^·-) formed benzene radical cation that further reacted with H₂O to yield the ·OH adduct. The determined rate constants of ·OH, hydrated electrons (e_aq^-), and SO₄^·- with FLX were 7.8×10⁹, 2.3×10⁹, and 1.1×10⁹ mol·L^-1·s^-1, respectively. In the steady-state radiolysis study, the degradation of FLX in different radiolytic conditions by electron beam irradiation was detected by HPLC and UV-Vis spectra techniques. It was found that FLX concentration decreased by more than 90% in both N₂O and air-saturated solutions after 1.5 kGy irradiation. In contrast, only 43% of FLX was decomposed in N₂-saturated solution containing 0.1 mol·L^-1 tert-butanol. The degradation rates of FLX in acidic and neutral solutions were higher than those in alkaline solutions. Our results showed that the degradation of FLX is optimal in air-saturated neutral solution, and ·OH-induced degradation is more efficient than SO₄^·- oxidation of FLX. The obtained kinetic data and optimal conditions give some hints to understand the degradation of FLX.     

超声辐照水体系下羟基自由基的检测

Fricke溶液在低频超声波辐照下产生羟基自由基,产生的羟基自由基可将溶液中的Fe2+氧化为Fe3+,用紫外-可见分光光度法测定Fricke溶液在235nm处的吸光度,根据吸光度变化值ΔA间接测定羟基自由基的产生量。初步研究了超声辐照时间、温度、频率和超声方式等因素对羟基自由基产量的影响。     

Gas-Phase Ion-Molecular Reactions of Free Ethylsilylium Ions with Ethylene

Gas-phase reaction of ethylsilylium ions with ethylene was studied by the radiochemical method. The reaction occurs via excited adduct C₄H₁₁Si⁺ which structurally is a complex of ethylsilylium cation with ethylene. The lifetime of this complex is long enough for the isotope exchange between tritium atoms of the cation and a proton of ethylene, as well as the isomerization of ethylsilylium cation to dimethylsilylium to occur. Decomposition of the complex results in predominant formation of labeled ethylene.     

ZnS胶体溶液中某些无机盐光化学过程中产生的阴离子自由基的ESR研究

本文用自旋捕捉与ＥＳＲ技术相结合的方法研究了ＺｎＳ胶体溶液中某些无机盐光化学过程中产生的无机阴离子自由基，并对自由基产生的机理进行了讨论     

二硫代乙酰丙酮和某些金属离子络合反应的研究

报导CH₃COCH₂COCH₃/H-2S/C₂H₅OH-HCl体系和十六种金属离子以及Fe(CO)₅的反应,用X射线衍射法测定了九种反应产物的分子和晶体结构.本文结果总结出了该反应的规律性.研究表明,在该反应条件下,钼是唯一能够形成原子簇化合物的元素.     

Trivalent Copper Complexes with 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane in Aqueous Solutions. A Pulse Radiolysis and Electrochemical Study

The mechanisms and kinetics of the formation and decomposition of the complexesCu^IIIL_aq and [LCu^IIIN₃]²⁺ are reportedand discussed.     

Aqueous Wittig Reactions of Aldehydes with In Situ Formed Semistabilized Phosphorus Ylides

The Wittig reactions of three semistabilized phosphorus ylides generated in situ from the corresponding phosphonium salts with aldehydes in water without any organic cosolvent were investigated. Most of the olefination reactions completed within between 5 min and 4.5 h in refluxing water containing 1.5 equiv of LiOH and 1.4 M LiCl to afford the products in 65–100% yields. The E∶Z selectivity depended not only on the substituent attached to the benzene ring of the ylides but also on the substituent bound to the aromatic aldehydes. LiCl promotes the aqueous Wittig reactions and suppresses decomposition of the ylide or the corresponding phosphonium salt.     

C-S Bond-Forming Reactions of Barbiturylbromide with Isothiocarbamides in Aqueous Media

The C-S cross coupling of pharmaceutically active barbituric acid derivatives has been achieved by the interaction of selective monobromobarbituric acid with thioureas in an aqueous medium. This method is applicable for simple thiourea as well as monosubstituted thioureas, and corresponding products are obtained in good yield.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

水溶液中金属铅诱发芳香醛的烯丙基化反应

超声辐射下,在Pb-THF-NH4C1-H2O体系中,烯丙基溴与一系列芳香醛室温反应4h,得62%～98%烯丙基化产物;而同样体系中搅拌20h,高烯丙基醇产率为63%～97%.