二甲基羟胺水溶液的脉冲辐解研究

利用脉冲电子束进行二甲基羟胺(DMHAN)水溶液的脉冲辐解研究,对其瞬态光谱中的主要吸收峰作了归属,并初步考察了这些瞬态物种的生长、衰减等行为。研究结果表明,·OH与DMHAN反应生成(CH3)2NO·自由基,测得速率常数为(4.5±0.3)×109mol-1·L·s-1;eaq-与DMHAN反应生成(CH3)2N·自由基,测得速率常数为(1.3±0.04)×109mol-1·L·s-1。     

甲基肼水溶液的脉冲辐解研究

利用脉冲电子束进行甲基肼水溶液的脉冲辐解研究,对其瞬态光谱中的主要吸收峰作了归属,并初步考察了这些瞬态物种的生长、衰减等行为.结果表明,·OH与甲基肼反应生成CH3·NNH2,速率常数为(2.4±0.1)×1010mol-1·L·s-1;enq-与甲基肼反应生成CH3·NHNH2自由基,速率常数为(2.7±0.2)×1...     

4-氯酚的辐射降解机理研究

用纳秒级电子脉冲辐解技术研究了4-氯酚等四种单取代酚在不同pH条件下与水合电子(eaq)、氢自-由基(?H)、叠氮自由基(?N3)、羟基自由基(?OH)等活性粒子的反应[1],并对其瞬态吸收图谱进行归属,求得微观反应速率常数。研究表明:(1)4-氯酚/4-氯酚阴离子与eaq发生还原脱氯,形成p-羟苯基自由基/p--羟苯基自由基阴离子。4-氯酚与?H主要发生加成反应,形成环己二烯类的氢加成物。4-氯酚与?N3发生单电子转移,生成4-氯酚氧基。4-氯酚与?OH的反应途径与pH值有关:碱性条件下主要通过单电子转移形成4-氯酚氧基;中性条件下则通过苯环上的加成反应形成羟…     

水相中喹啉的辐解机理研究

利用纳秒级脉冲辐解技术对多种条件下喹啉水溶液的氧化还原机理进行了研究,并对瞬态粒子的主要吸收峰作了归属。探讨了喹啉在羟基、氢自由基、水合电子作用下所产生的瞬态粒子的生成、衰减行为。研究表明,·OH与喹啉在碱性条件下反应生成OH-加合物,速率常数为5.5×109L/mol?s?;在酸性条件下喹11啉先与氢离子反应生成喹啉阳离子,再与羟基发生加成反应,反应速率常数为7.9×109L/mol?s?;在中性条11件下和在碱性条件下反应相似,反应速率常数为7.2×109L/mol?s?;喹啉与水合电子反应生成的喹啉阴离子11自由基,其反应速率常数为7.05×109L/mol?s?;喹啉还可以与氢自由基的发生亲电加成反应。11     

环境雌激素己烯雌酚的流动池脉冲辐解瞬态谱

己烯雌酚(DES)是一种活泼的环境雌激素。利用流动池脉冲辐解手段对其活性瞬态粒子的动力学特性作了初步研究,发现己烯雌酚自由基的苯环间双键可能是羟自由基优先进攻破坏的一个位点。该化合物对高能电子束非常敏感,通过自由基机理被降解。研究结果对DES环境降解机理和生物毒理,对探索解毒、环境修复等,具有一定的指导意义。     

皮秒级脉冲辐解装置及其在抗氧化剂研究的应用

20世纪60代出现了微秒级脉冲辐解技术,开始了快速反应动力学的研究.其重要发现之一是溶剂化电子,它证实了人们早先的推测,并极大地促进了化学反应机理研究.随着加速器与电子学技术的发展,随后出现了纳秒、皮秒与飞秒级脉冲辐解装置.虽然纳秒时间分辨仍然是研究凝聚态化学反应机理的有效的手段,但在观察更快的化学反应和过程时,如超激发态、分子分裂和分子内电荷传递等过程,必须借助更快的时间分辨研究.我所于1990年建立了我国第一个纳秒级电子脉冲辐解装置,基于加速器技术与动态化学研究的良好基础,我所正在研制皮秒脉冲电子束装置,以将我国的脉冲辐解时间分辨研究推进到皮秒级水平,推动我国在自由基生物学、环境科学、高分子材料科学等领域的相关研究.生物体在呼吸和代谢过程都会产生活性氧自由基(ROS),同时电离辐射、紫外线及致癌物质等也会通过直接或间接作用产生活性氧自由基.体内一定浓度的自由基是机体进行正常生命活动的必要条件之一.但过多的自由基,会攻击生物膜的不饱和脂肪酸,引起膜脂质过氧化反应;或攻击蛋白质引起其结构与构象的改变,造成肽链断裂、聚合与交联;或攻击DNA,造成其永久性损伤.这些生物大分子结构与功能的改变,导致细胞功能的紊乱,导致细胞的衰老、畸变及死亡,是心脑血管疾病及癌症的祸首.随着人体年龄的增加,体内修复酶的活性不断下降,细胞中DNA氧化性损伤增多,受损伤的DNA不断积累,使人体患癌症的可能迅速上升(研究表明,癌症的发病率与年龄的4次方成正比).天然抗氧化剂是一类单电子氧化还原电位很低的活性物质,可清除活性氧自由基,又可通过电荷转移反应修复被氧化的DNA碱基及脂质过氧自由基等,因而是防止活性氧自由基对生物体损伤的有力措施.以往的研究表明,茶多酚、维生素C等天然抗氧化剂对心脑血管疾病等具有预防和保护作用.我们利用纳秒级脉冲辐解装置对抗氧化剂进行了研究(1)研究抗氧化剂与各种氧化性自由基[1,2].(2)研究抗氧化剂对受损伤的DNA及其碱基的修复过程[3].揭示了抗氧化剂不仅可以通过竞争反应清除体内有害自由基,而且可以对已受损伤的生物分子进行快速修复,减轻有害自由基对生物体的损伤.(3)研究抗氧化剂对受损伤的蛋白质及其氨基酸自由基的修复过程.这些研究为更好地了解和解释抗氧化剂在生物体内的作用机理提供了理论基础,也为开展其皮秒级脉冲辐解研究奠定了基础.     

皮秒级脉冲辐解装置及其在抗氧化剂研究中的应用

20世纪60代出现了微秒级脉冲辐解技术,开始了快速反应动力学的研究。其重要发现之一是溶剂化电子,它证实了人们早先的推测,并极大地促进了化学反应机理研究。随着加速器与电子学技术的发展,随后出现了纳秒、皮秒与飞秒级脉冲辐解装置。虽然纳秒时间分辨仍然是研究凝聚态化学反应机理的有效的手段,但在观察更快的化学反应和过程时,如超激发态、分子分裂和分子内电荷传递等过程,必须借助更快的时间分辨研究。我所于1990年建立了我国第一个纳秒级电子脉冲辐解装置,基于加速器技术与动态化学研究的良好基础,我所正在研制皮秒脉冲电子束装置,以将我国的脉冲辐解时间分辨研究推进到皮秒级水平,推动我国在自由基生物学、环境科学、高分子材料科学等领域的相关研究。     

一台微秒级脉冲辐解装置

本文介绍了一台自行研制的微秒级脉冲辐解实验装置。该装置利用一台5MeV辐照用电子直线加速器作脉冲辐射源,电子束脉宽2μs,流强200mA。采用动力学分光光度法探测瞬态产物的光吸收。利用单板机和瞬态信号记录仪进行数据采集和实施时序同步控制。整个装置的时间分辨率为2μs,探测的光谱范围为200—800nm,探测灵敏度为5×10~(-4)OD值。     

异喹啉的脉冲辐解和激光光解研究

用脉冲辐解和激光光解相结合,研究了异喹啉这种难降解杂环化合物在紫外光作用下的变化和与HO·的反应.结果表明,在波长为266nm的激光作用下,异喹啉不仅发生光激发,而且发生单光子电离,其量子产额为1.58×10-4.异喹啉光电离产生的阳离子自由基可以脱去质子,其pKa为5.50.异喹啉可以与HO·发生反应,其反应速率常数为3.4×109 mol-1·dm3·s-1.本工作的研究将为photo-Fenton法降解异喹啉提供理论上的依据.     

H_2MEHP水溶液的γ辐解

前言萃取剂磷酸三丁酯(TBP)和二(2-乙基己基)磷酸酯(H_2MEHP)的降解产物(如HDBP、H_2MBP和H_2MEHP)的水溶液的辐解情况很少报道。仅在五十年代,有人报道过几种单烷基磷酸酯水溶液的辐解情况,发现除了产生H_3PO_4外,还生成不稳定的酰基磷酸酯;后来,有人报道HDBP、H_2MEHP等在同水相搅拌或溶于水的情况下辐     

Pulse radiolysis study on aqueous solution of nicotine

Nicotine has been studied for the first time by pulse radiolysis techniques. It has been found that hydrated electrons, hydrogen radicals and hydroxyl radicals can react with nicotine to produce anion radicals and neutral radicals, respectively, and the related rate constants have been determined.     

吲哚荷尔蒙自由基脉冲辐解光谱及其酸基平衡和还原电位性质研究

The Absorption spectral, acid-base equilibrium potential properties and formation and decay kinetics of four kinds of radicals from natural existing indole hormones were studied by pulse radiolysis.One of the most important properties for these four indolyl hormones, melatonin, 5-methoxygramine (MTA),5-methoxy-N, N-dimethylthytrytamine (DMM TA) and 5-methoxy-N, N-diethylthytrytamine (DEMT A), which are involved in biochemical processes and play crucial roles in many neuropathy and cancer related diseases, is their facile one electron oxidation with formation of radical cations or their conjugated base, the indolyl radicals.Formation kinetics and properties of the radicals were investigated by pulse radiolysis using the Linac accelerator with fast time-resolving optical system in UTNL.In the present study, these radicals were generated through oxidation of the corresponding hormone with azide radical in radiation induced process. Their spectroscopic properties were investigated and it was found that the transient spectra in all these cases exhibit similar absorption and pH dependence: in acidic solution, the radicals are characterized with three absorption maxima around 320-350, 440-460, 520-550nm. The spectra of MTA at various pH were shown as an example. From the absorption changes as a function of pH, two pK values were determined to be around 5 and 9 for the indolyl radicals except for melatonin, in which, only one pK was distinguished to be 4.4. Formation kinetics of the radicals was measured by following the growth of their absorption peaks and it was found that these indolyl derivatives transfer an electron to N3, with different rate constants, i.e.1.2×1010, 4.5×109, 4.9×109, 1.6×109 dm3 mol-1 s-1 for melatonin, MTA, DMMTA, and DEMTA, respectively.Reduction potentials of the radicals vs their molecules were also determined and they are dependent on the pH of medium. At pH 7, the reduction potentials were estimated to be 1.10, 1.18, 1.18, 1.20eV for melatonin, MTA,DMMTA and DEMTA, respectively. Because of its relatively high contents in human brain cells, melatonin is the main antioxidant among hormones against the oxidizing species in brain cells.     

Phase relations and linear thermal expansion of cubic solid solutions in the Th1−xMxO2−x/2 (M = Eu, Gd, Dy) systems

Cell parameters and linear thermal expansion studies of the Th-M oxide systems with general compositions Th_1−xM_xO_2−x/2 (M = Eu³⁺, Gd³⁺ and Dy³⁺, 0.0 ? x ? 1.0) are reported. The XRD patterns of each product were refined to specify the solid solubility limits of MO_1.5 in the ThO₂ lattice. The upper solid solubility limits of EuO_1.5, GdO_1.5 and DyO_1.5 in the ThO₂ lattice under conditions of slow cooling from 1673 K are represented as Th_0.50Eu_0.50O_1.75, Th_0.60Gd_0.40O_1.80 and Th_0.85Dy_0.15O_1.925, respectively. The linear thermal expansion (293-1123 K) of MO_1.5 and their single-phase solid solutions with thoria were investigated by dilatometery. The average linear thermal expansion coefficients () of the compounds decrease on going from EuO_1.5 to DyO_1.5. The values of for EuO_1.5, GdO_1.5 and DyO_1.5 containing solid solutions showed a downward trend as a function of the dopant concentration. The linear thermal expansion (293-1473 K) of the solid solutions investigated by high-temperature XRD also showed a similar trend.     

Time-dependent radiolytic yields at room temperature and temperature-dependent absorption spectra of the solvated electrons in polyols

The molar extinction coefficients at the absorption maximum of the solvated electron spectrum have been evaluated to be 900,970,and 1000 mol~(-1).m~2 for 1,2-ethanediol (12ED),1,2-propanediol (12PD),and 1,3-propanediol (13PD),respectively.These values are two-third or three-fourth of the value usually reported in the published report. Picosecond pulse radiolysis studies have aided in depicting the radiolytic yield of the solvated electron in these sol- vents as a function of time from picosecond to microsecond.The radiolytic yield in these viscous solvents is found to be strongly different from that of the water solution.The temperature dependent absorption spectra of the solvated electron in 12ED,12PD,and 13PD have been also investigated.In all the three solvents,the optical spectra shift to the red with increasing temperature.While the shape of the spectra does not change in 13PD,a widening on the blue side of the absorption band is observed in 12ED and 12PD at elevated temperatures.     

低能X射线在正比管内产生脉冲幅度的分布

正比管对大于2keV X射线的探测,输出的脉冲幅度分布近似高斯分布。而对低能超软X射线、紫外线,它给出的脉冲幅度分布明显偏离高斯分布。本文从实验上和理论上研究单电子和少数日电子在正比管内产生脉冲的情况。认为在低气体放大倍数时,单能软X射线在正比管内产生脉冲幅度分布是Г分布的加权总和。     

Study of the pulsed working characteristics of the penning ion source for neutron tubes

The pulsed working characteristics of the neutron tube ion source were studied experimentally.The principle and method of selecting the gas pressure and anode voltage were determined.     

Fe-(Co6Ag94)颗粒膜磁光芯片的制备及研究

采用二分掩膜技术向溅射沉积的(Co6Ag94)薄膜中组合注入Fe离子,制备成具有不同Fe含量的16单元Fe-(Co6Ag94)颗粒膜磁光芯片。对制备态和退火态的Fe-(Co6Ag94)颗粒膜的物相进行了XRD研究。不同退火温度下,物相的演变反映出了退火过程中Co、Fe相和FeCo相纳米微晶的析出长大过程。采用原子力显微镜(AFM)对薄膜表面的研究结果表明,在退火过程中形成了嵌于基底中的纳米颗粒相。对制备态和不同温度退火后芯片各单元的磁光性能进行了测量,结果表明极向Kerr旋转角晚随着注入Fe含量的增加而增大,这可归因于颗粒膜中铁磁相的增多。在500℃以下,随着退火温度的增加,Fe-(Co6Ag94)颗粒膜的克尔磁光效应增加。对不同温度退火的样品进行穆斯堡尔谱测量,结果证明一定尺寸纳米Fe微晶颗粒的出现是磁光效应提高的主要原因之一。