各种自由基清除剂在γ射线辐照DNA损伤中的作用

为了对重离子辐照致DNA损伤中的自由基作用进行评估,本文利用γ射线对添加了各种自由基清除剂(甘露醇,维生素C和茶多酚)的质粒DNA进行辐照,凝胶电泳分析的结果表明,三种自由基清除剂对DNA均有很好的保护作用.在相同自由基清除剂浓度的情况下,甘露醇比维生素C具有更强的清除自由基的作用.与重离子辐照情况相比,这几种自由基清除剂对γ射线产生的自由基的清除作用更为明显.     

36 ^7Li离子辐射中直接和间接作用致pUC19 DNA损伤研究

电离辐射的直接和间接作用（自由基）可引起DNA分子的碱基损伤、链断裂（包括单链和双链断裂）和交联等多种损伤。其中，双链断裂（DSB）是辐射引起的各种生物效应中最重要的原初损伤。在液态环境下，辐射诱导产生的自由基可能是单链和双链断裂发生的主要原因。因此，建立适当的体外模式系统来研究自由基诱导单链和双链断裂的反应动力学是十分必要的。本实验利用原子力显微镜（AFM）开展了重离子辐射中直接和间接作用致DNA链断裂的反应动力学研究。     

质子剂量和DNA浓度对DNA损伤的影响

利用HI-13串列加速器产生的16 MeV质子,使用凝胶电泳技术对添加和未添加甘露醇的pUC19质粒DNA溶液中DNA分子形态变化进行了观测,研究了同一剂量下不同DNA浓度及同一DNA浓度下不同剂量对DNA链断裂产额的影响.结果表明,未添加甘露醇溶液中DNA浓度效应较明显.两种体系下DNA均表现出明显的剂量响应,即分子...     

电离辐射致DNA双链断裂研究方法及统计模型

DNA既是生命物质中信息的载体,也是辐射生物效应最主要的靶分子.电离辐射通过射线的直接作用和间接作用引起DNA分子的多类型损伤,其中DNA双链断裂(Double-strand breaks,DSB)是辐射引起的各种生物效应中最重要的原初损伤之一,成为辐射生物学研究的重点.目前DSB研究的主要方法包括拉曼光谱技术、原子力显微镜、单细胞凝胶电泳、脉冲场凝胶电泳、γH2AX分析技术、早熟染色体凝集等,研究DSB的统计模型包括随机断裂模型、Moment法、Tsallis熵模型、平均分子量法,在此均得到总结,最后探讨了DSB辐照热点的研究前景.     

电离辐射诱导体外DNA链断裂机理研究进展

概述了电离辐射诱导体外DNA单链断裂（SSB）和双链断裂（DSB）的形成机理。研究结果表明,DNA链断裂产额与DNA浓度和自由基清除剂的清除有力有关。并受DNA超螺旋度的影响。DNAαDSBB除可由直接作用形成外,还可分别由单自由基传递机制和LMDS机制产生;对LET辐射,αDSB主要由LMDS机制产生,而硫醇类化合物对DNA的辐射保护作用则随其电荷态的增加而增加;由于次级自由基反应,体外DNA链断裂具有反向氧效应;非均一动力学的柱模型被广泛地应用于OH等自由基与DNA反应的理论研究。     

质子致DNA链断裂损伤的剂量效应研究

质子作为一种高传能线密度（LET）的辐射，具有能量沉积与局部剂量远大于低LET辐射（如X射线、γ射线和电子束等）的特点，通过物质时有完全不同的径迹结构，能够更有效的诱发DNA发生双链断裂，产生更多的不能修复性损伤，引起细胞的转化和死亡以及癌的发生等较高的相对生物效应（RBE）。在DNA分子水平上研究质子致生物损伤的机理，深入了解其辐射特点及危害程度，并研究相应的防护途径十分重要，     

DNA分子及其双链断裂碎片的AFM观测

生物大分子DNA是生命信息的载体,是辐射生物学效应最重要的靶分子。为了进一步研究辐射致DNA损伤的机理,首先需要掌握观测DNA分子及其双链断裂(Double Strand Breaks,DSB)碎片的技术。在大气状态下,使用先进的原子力显微镜(AFM)技术获得了3种经过提纯的DNA分子的直观图像;在水溶液中,利用~(241)Am-α源辐照装置对其中一种DNA分子进行了低剂量照射,利用AFM     

高LET重离子照射人肿瘤细胞的DNA双链断裂及修复研究

依托兰州近代物理研究所的HIRFL装置对人肝癌细胞SMMC-7721进行高LET的重离子辐照,同时利用脉冲场凝胶电泳研究高LET辐射引起的细胞DSB及其修复的特点.对于不同离子的辐射进行了比较分析,探索重离子的辐射生物学效应机理.结果发现,随着剂量的增加,初始DSB在给定剂量范围内呈线性增长,LET较高的氩离子的剂量效应曲线具有较大的斜率.对于DSB分布情况的研究发现,LET不同,大小片段的分布随着剂量的变化呈现不同的变化情况.修复研究显示两种LET辐射的快修复在30 min左右都已经结束,此后都开始了慢修复,对于高LET的氩离子辐射来说,快修复和慢修复完成的修复量均高于较低LET的碳离子辐射.4 h时,两种辐射残余的DSB基本一致.结果证明了高LET辐射下初始DSB与剂量的线性依赖关系,且发现不同种类的离子辐射引起的DSB的剂量效应曲线的斜率不同.结果也显示了DSB的非随机分布现象和DSB修复的双阶段模式,发现LET、离子种类和剂量对于DSB的片段非随机分布同时存在影响,同时修复结果提示慢修复机制和错修复在高LET辐射引起损伤的修复研究中可能具有重要意义.     

加速12C6+离子照射诱发人肝癌细胞SMMC-7721的DNA双链断裂

重离子为高传能线密度(LET)辐射,在引起肿瘤细胞失活上有更大的相对生物学效应。DNA的双链断裂在细胞辐射损伤中是极其重要的,其最终导致细胞的失活。本实验研究检测细胞DNA的双链断裂(DSB),以探讨细胞失活的机理。用脉冲场凝胶电泳方法结合溴乙锭染色的荧光扫描技术,定量测定^12C^6 锈导人肝癌细胞SMMC-7721 DNA的DSB剂量效应关系。结果发现,DNA片段释放百分比随吸收剂量的增加而增加。     

辐射致DNA损伤中DNA浓度的影响

在水溶液中，DNA以微观的形态存在，由于布朗运动以及DNA之间的相互作用的存在，使得DNA的浓度可能影响着DNA的微观分布，从而影响DNA损伤，这在我们以前的实验中已有了初步的观测与发现。关于DNA浓度对DNA损伤的影响的报道很少，实验结果不统一，也不系统，且以前的报道均为低LET射线辐射后的结果。关于高LET的重离子的研究目前尚未见诸报道。     

14MeV单能中子致DNA链断裂及相应防护研究

利用中国原子能科学研究院600kV高压倍加器产生的14MeV的单能中子,以不同剂量对不含和含有甘露醇或香兰素衍生物VND3207的质粒DNA进行了照射,使用凝胶电泳技术观测了DNA分子的链断裂。结果表明,中子可诱发DNA分子发生单链和双链断裂,随剂量的升高,链断裂产额逐渐增加,具有明显的剂量响应。在含有甘露醇和VND3207的研究体系中,也存在一定的剂量响应,但相比不含两者的体系而言,剂量响应不明显,且在相同剂量下DNA分子的链断裂产额极低。此结果反映出研究中所选用浓度的甘露醇与VND3207可有效降低中子辐射所诱发的DNA单链和双链断裂的产生,对DNA分子起到极好的保护作用,具有一定的中子辐射防护能力。     

硼中子俘获治疗癌症的基础性实验研究

分别利用²⁴¹Am放射源和HI-13串列加速器产生的α粒子和⁷Li离子来模拟硼中子俘获治疗中的核反应产物，对DNA水溶液进行辐照，然后利用原子力显微镜(AFM)对DNA碎片进行观测，最后通过大量的统计分析获取DNA碎片长度、DNA形态的实验数据。实验结果表明：DNA碎片的平均长度随剂量的增大逐渐减小；线性和开环的DNA分子所占的比例随着剂量的增大逐渐增多；⁷Li离子比α粒子具有更强的相对生物学效应。      

抗辐射菌lexA基因的克隆及在大肠杆菌中表达

研究了旨在克隆抗辐射菌Ｄｅｉｎｏｃｏｃｃｕｓ ｒａｄｉｏｄｕｒａｎｓ的ｌｅｘＡ基因并构建其表达载体,以便于进一步研究ｌｅｘＡ基因的功能及其在辐射抗性中的作用。主要的实验步骤包括分离提取抗辐射菌基因组ＤＮＡ,分离出ｌｅｘＡ基因并测定其序列,克隆于质粒载体ＰＵＣ１９,用电击穿孔法将重组的质粒导入在肠杆菌ＪＭ１０９,ＳＤＳ－ＰＡＧＥ检测基因的表达。用定点突变技术,改变ｌｅｘＡ基因核糖体结合位点（ＲＢＳ）     

Rutherford backscattering (RBS) with lithium ions

⁷Li ions at 4.5 MeV and ⁴He ions at 1.5 MeV were scattered at 170° from the same target under the same conditions. The distribution of elements as a function of distance from the surface is more clearly revealed with ⁷Li than ⁴He. We have rewritten our RBS analysis program to handle all ion beams and to take into account the normal isotopic abundance of the target elements. With 4.5 MeV ⁷Li ions the minority isotopes can not be ignored, even with silicon. At present, the accuracy for determining elemental depth profiles with ⁷Li is limited by the accuracy of Li ion stopping powers.     

Production and characterization of thin Li targets fabricated by ion implantation

Very high fluence implantation of ⁷Li⁺ ions was used to promote the formation of a thin and high density ⁷Li target in the surface region of Al samples. The implanted volume was characterized by particle induced gamma-ray emission, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and nuclear reaction analysis, revealing that the implanted surface is a combination of Li₂CO₃, metallic lithium, LiOH and C, with almost no Al present. Radiation damage effects by proton beams were studied by observing the evolution of the ⁷Li(p, α)⁴He nuclear reaction yield with the accumulated charge, at different proton energies, revealing high stability of the produced Li target.     

Dosimetric properties of UV irradiated calcium co-doped borate glass-ceramic

The thermoluminescence (TL) response of Dy and Li doped 20CaB₄O₇-80CaB₂O₄ (wt%) glass-ceramic irradiated with ultraviolet (UV) radiation was studied. In order to act as TL activator ions, the Dy and Li ions were included in the matrix during the melting process to increase its TL efficiency. A single crystalline CaB₂O₄ phase was present in the glass-ceramic as determined by X-ray diffraction (XRD). The glass-ceramic 20CaB₄O₇-80CaB₂O₄:Dy,Li wt% (named 20CBO7:Dy,Li) is a newly prepared TL material. Its thermoluminescent dosimetric characteristics have shown a linear response under UV radiation exposure and a good TL signal reproducibility, thus proving to be a promising material for using as an ultraviolet radiation dosimeter.     

Nitrogen Deposition Via N^＋ Implantation： Implications for Primordial Amino Acids Synthesis Revisited

In this paper amino acids synthesis in aqueous solution induced by ion implantation, which was possibly ubiquitous on primitive Earth, is investigated. As a discharge using a graphite rod as the anode under a nitrogen atmosphere was performed against ammonia water, it was found that three kinds of amino acids were produced. They were glycine, serine and alanine. By introducing ion implantation into the carboxylate solution, ammonia and amino acids were also formed via nitrogen deposition/fixation. Another isotopic experiment showed that both OH and H radicals played a crucial role in the arc-discharge-promoted reactions in aqueous solution Therefore, we believe that the impact of ions in the original atmospheric conditions might have functioned as a promoter in the chemical origin and evolution of life.     

A paradigm study for assessment of phenylalanine’s damage under arc-discharge irradiation

Energetic ions induce important biological effects and the research into radiolysis of amino acids can help to clarify radiolysis of proteins. For this purpose, arc-discharge induced radiolysis of the benzyl-containing aromatic amino acid phenylalanine in aqueous solution was studied and the damage was assessed quantitatively. The energetic ions were produced by arc-discharge in nitrogen and argon atmosphere. The arc-discharge induced chemical reactions of the biomolecule in aqueous solution were detected and analyzed by means of UV-Vis absorption, fluorescence, Fourier transformation infrared (FTIR) spectroscopy and high performance liquid chromatography (HPLC). Based on the multiple spectroscopic approach, the damage can be evaluated in a more reliable and convenient way. The fluorescence analysis in this case appears to be a more direct indicator for the assessment of damage, where it reveals that the damage increases with the irradiation time exponentially. On the contrary, the ‘plateau region’ or ‘saddle-shape’ apparently shown both in our rough absorption analysis and ninhydrin reaction test, similar to the previously reported feature of the dose effect for low-energy-ion induced damage, may be just a consequence with varied reactions and processes involved at different stages. This work thus demonstrated that application of appropriate combination of spectroscopic tools can effectively dissect the diversity of the radiolysis reaction system and assess the biomolecular damage properly.     

Hydrothermal synthesis of Ni2FeBO5 in near-supercritical PWR coolant and possible effects of neutron-induced B fission in fuel crud

The hydrothermal synthesis of a nickel-iron oxyborate, Ni₂FeBO₅, known as bonaccordite, was investigated at pressures and temperatures that might occur at the surface of high-power fuel rods in PWR cores and in supercritical water reactors, especially during localized departures from nucleate boiling and dry-outs. The tests were performed using aqueous mixtures of nickel and iron oxides with boric acid or boron oxide, and as a function of lithium hydroxide addition, temperature and time of heating. At subcritical temperatures nickel ferrite NiFe₂O₄ was always the primary reaction product. High yield of Ni₂FeBO₅ synthesis started near critical water temperature and was strongly promoted by additions of LiOH up to Li/Fe and Li/B molar ratios in a range 0.1-1. The synthesis of bonaccordite was also promoted by other alkalis such as NaOH and KOH. The bonaccordite particles were likely formed by dissolution and re-crystallization by means of an intermediate nickel ferrite phase. It is postulated that the formation of Ni₂FeBO₅ in deposits of borated nickel and iron oxides on PWR fuel cladding can be accelerated by lithium produced in thermal neutron capture ¹⁰B(n,α)⁷Li reactions. The process may also be aided in the reactor core by kinetic energy of α-particles and ⁷Li ions dissipated in the crud layer.     

黄素类光核酸酶对DNA定位损伤的直接检测

近来研究人工合成能使ＤＮＡ定位损伤的光核酸酶成为光医学、光化学和光生物学领域的研究热点[1] 。然而 ,目前光核酸酶对癌细胞ＤＮＡ的作用机制尚不完全了解。尽管已公认ＤＮＡ碱基阳离子自由基 (或氧化性自由基 )是核酸光敏氧化反应的最初、最重要的瞬态产物 ,然而至今未能直接观察到光氧化产生的碱基阳离子自由基的瞬态吸收光谱。这一问题已成为国际同行关注的难题。因为它是激光束进入细胞时激发生物大分子动态过程的关键 ,是阐明电荷转移光氧化治疗畸变基因、调控基因表达机制的原初证据。现有的研究主要集中在稳态分析上[1.2 ] ,尽管…