维生素C对紫外线诱发DNA损伤的保护作用

用拉曼光谱探讨维生素C对紫外线诱发DNA损伤的保护作用。测量了小牛胸腺DNA水溶液及其添加微量维生素C并经过9min和30min紫外辐射的拉曼光谱,紫外线的辐射照度为18．68W／m^2。实验结果表明：在浓度为O．2mmol／L的维生素C存在的条件下,全波段的紫外辐射对DNA只造成了轻微的损伤。DNA被保护可能是因为紫外辐射虽然产生了对DNA损伤很大的自由基,但维生素C具有清除自由基的能力。另外由于DNA和维生素C在260nm处对紫外线都有很强的吸收能力,因此也可能是维生素C对紫外线的吸收能力强于DNA,从而保护了DNA。     

不同浓度维生素C对DNA紫外损伤的影响

分别检测了DNA与不同浓度维生素C的混合物经10和30 min紫外辐射的拉曼光谱,紫外线的辐射照度为18.68 W·m-2。实验表明,维生素C对DNA损伤的影响与其浓度密切相关。低于0.35 mmol·L-1的维生素C对紫外线诱发的DNA损伤具有明显的保护作用,且保护效果随着其浓度的增大越来越好,0.35 mmol·L-1时保护效果最佳。当维生素C的浓度高于0.35 mmol·L-1时,在10 min的紫外辐射中,维生素C不仅没有保护DNA,反而促进了DNA的损伤,DNA被损伤的程度随着维生素C浓度的增加而增加;但在30 min的紫外辐射中,相对于不加VC的紫外辐射,维生素C对DNA仍起保护作用。     

UV-A区段紫外辐射对DNA影响的拉曼光谱研究

检测了小牛胸腺 DNA水溶液经 2 h和 16 h UV- A区段紫外辐射的拉曼光谱。实验结果表明 ,该区段紫外辐射对 DNA的影响要比全波段紫外辐射的影响小得多。主链构象基本上没有受到影响。经过较长时间的 UV- A区段紫外辐射后 ,DNA受到了较轻的损伤。 80 3— 816 cm-1间峰的变化表明 DNA链不同区段的构型处于不断的变化之中。脱氧核糖的特征峰 ,或强度有所下降 ,或峰发生了位移 ,或者两种变化皆有 ,表明 A区段紫外辐射对 DNA的脱氧核糖有所损伤。胸腺嘧啶的 6 81cm-1、75 2 cm-1和 1177cm-1谱线都发生了变化 ,表明胸腺嘧啶也受到了影响。但嘌呤碱基和胞嘧啶基本上没有受到影响。     

基于高光谱技术的甲烷层流预混火焰自由基特性研究

高光谱技术提供了空间和光谱维度的信息,同时基于传统黑体模型的实验技术和计算方法不适用于甲烷火焰的辐射特性,而火焰中自由基的高光谱信息反映了火焰结构、组分浓度分布等燃烧的多方面特征,能够为燃烧模型的完善提供依据。利用高光谱技术在不同当量比和不同流量下研究了甲烷预混火焰中自由基的空间和光谱特性。对不同当量比的研究表明,随着当量比的增加,火焰中心处的CH^*和C^*₂自由基的辐射强度先增加后降低,而燃烧区域内二者的平均辐射强度一直增加,火焰中心处的点可以表征局部的燃烧状态,而燃烧区域内辐射均值表征热释率等整体燃烧状态,定量给出了两种方法的不同趋势。火焰中心处的CH^*自由基辐射强度在当量比为1.01时达到峰值,而C^*₂自由基辐射强度在当量比为1.12时达到峰值,两种自由基的辐射峰值可以分别作为燃烧中反应强度和稳定性的判据。当量比可以由C^*₂和CH^*辐射强度之比来表征,修正了C^*     

西洋参60Co辐照损伤的ESR观测

用电子自旋共振(ESR)波谱技术对受⁶⁰Co辐照后的西洋参样品进行了较长时间的跟踪观测,发现γ辐射在西洋参内产生两种或两种以上的不稳定自由基,井测定了它们的衰减速率常数;当照射剂量过大时,还将出现异常稳定的自由基.这表明在西洋参内产生了永久性损伤.     

EPR and UV spectrometry investigation of sucrose irradiated with carbon particles

Solid state/EPR (SS/EPR) dosimeters of carbon ions irradiated sucrose are studied with EPR, and their water solutions – with UV spectroscopy. Doses between 20 and 200 Gy are used with linear energy transfer (LET) values for carbon ions of 63, 77, 96 and 230 keV μm^?1. After irradiation all samples show typical for irradiated sucrose EPR and UV spectra. The obtained data are compared with those previously reported for nitrogen particles and gamma rays irradiated sucrose. The identical shape of both the EPR and UV spectra of irradiated with various type radiation samples suggests that generated free radicals are not influenced by the nature of radiation. The lack of difference in the line width of the separate lines or the whole EPR spectrum, obtained for gamma and heavy particles irradiation, suggests negligible spin–spin interaction among the radiation-generated free radicals in the samples. The linear dependence of the EPR response on the absorbed dose radiation is found to be higher when generated by gamma rays, than by the same absorbed dose of heavy particles. In addition, the EPR response for carbon ions is higher than that for nitrogen ions. Water solutions of irradiated sucrose exhibit UV spectrum with absorption maximum at 267 nm, attributed to the recombination products of free radicals. The UV band intensity depends on the absorbed dose radiation. The UV spectra obtained for carbon, nitrogen and gamma rays irradiated sucrose are also compared.     

树脂基复合材料在连续激光作用下的损伤

 采用热压工艺制备了碳纤维布和高硅氧纤维布增强的环氧树脂和酚醛树脂基复合材料,研究了不同功率密度连续激光辐照下,复合材料的破坏形式及其组织结构与力学性能的变化。结果表明：当激光辐照功率密度大于0.1 kW/cm²后,树脂基体产生燃烧,碳纤维没有明显的损伤,而玻璃纤维布开始熔融,复合材料的拉伸性能降低30%~40%;当功率密度达到1 kW/cm²以后,除基体燃烧外,碳纤维复合材料产生明显的鼓泡分层,表层碳纤维有少量破断,而高硅氧纤维产生明显的熔融烧损,复合材料的拉伸性能降低80%以上。采用有限元计算方法,对碳纤维增强环氧树脂复合材料在连续激光辐照下的温度场进行了研究,计算结果与实验中复合材料的损伤行为相吻合。     

紫外辐射加速老化高温硫化硅橡胶的X射线光电子能谱研究

高温硫化硅橡胶具有优良的电气性能、机械性能、憎水性而广泛应用于特高压输电线路,但亦会受外界环境的影响而老化,其抗紫外老化性能受到关注.课题组模拟户外紫外辐射环境,设计搭建了可调式紫外辐射加速老化试验箱,对A、B两个厂家的高温硫化硅橡胶样品进行了紫外辐射(0,500和1000 h)加速老化实验,重点对辐射前后的试样进行X...     

臭牡丹黄酮类化合物提取及其抗氧化作用

研究臭牡丹中黄酮类化合物的最佳提取工艺条件及其抗氧化活性.以提取时间、料液比、提取温度、乙醇体积分数为主要影响因素,以黄酮类化合物提取率为考察指标,确定最佳提取工艺条件,并通过对亚硝酸盐、超氧阴离子自由基、羟自由基的清除效果及对猪油的抗氧化研究其抗氧化活性.结果表明,臭牡丹中黄酮类化合物的最佳提取工艺条件为提取时间2.0h、料液比1∶40（g/mL）、提取温度70℃、乙醇体积分数70％的条件下提取效果最好,臭牡丹中黄酮类化合物在各抗氧化体系中均表现出较强的抗氧化活性,且其作用具有剂量效应关系,其抗氧化活性均强于维生素C.     

Improved silica fiber with enhanced ultraviolet transmission

When a silica optical fiber is used for transmitting ultraviolet (UV) light, the problems associated with the damage and transmission deterioration of silica fiber in the UV region need to be solved in the fabrication process. In this paper, an improved silica fiber fabrication process was presented to enhance UV transmission, which combined the UV pre-irradiation on high-OH concentration preform with heat treatment while drawing fiber. The impact of the structural defects and color centers was diminished greatly by the new method of fabrication. The experimental results accorded with the theoretical analysis,and transmission was improved about 0.4-0.7 dB/m for wavelength from 350 to 400 nm.     

光谱法研究CTAB对木瓜酶酶活和构象的影响

采用荧光光谱、圆二色谱(CD)和紫外光谱研究了十六烷基三甲基溴化铵(CTAB)在NaHPO4-NaH2PO4缓冲溶液中对木瓜酶构象变化及其酶活的影响,并探讨了CTAB与木瓜酶的作用机理.荧光光谱表明,在CTAB存在下,木瓜酶的荧光强度增强,荧光峰发生红移,CTAB使木瓜酶分子链趋于伸展,酪氨酸等发色基团更多地暴露在水中.CD谱表明,当CTAB浓度(CCTAB)为0.5 mmol/L时,木瓜酶的a-螺旋构象和β-折叠构象含量比纯木瓜酶(Papain)体系分别增加了1.3％和0.1％,回转构象和无定型构象含量则分别减少了0.3％和1.2％.酶活测定结果表明,CTAB对木瓜酶的酶活有较大影响,当CCTAB由0增加到 1.5mmol/L时,木瓜酶酶活由11.2×105U/g增大到16.3×105U/g,当CCTAB由1.5mmol/L增加到3.5mmol/L时,木瓜酶的酶活又由峰值(16.3×105U/g)降到11.7×105U/g.CTAB使木瓜酶酶活增强与木瓜酶的构象有序度提高有关.     

A mathematical model of the evolution of free radical concentrations in a cell under ionizing radiation

A probabilistic mathematical model that describes the evolution of the free radical concentration in a cell under ionizing radiation is proposed. The model is of a stochastic character and allows one to describe the generation of free radicals in the process of radiolysis, as well as the interaction between the radicals of different types and between the radicals and the cell constituents (the latter is responsible for radiobiological effect). The possibility of the presence in the cell of a certain equilibrium quantity of radicals of nonradiative origin at the moment that the irradiation begins is taken into account. The results thus obtained show that under certain values of the model’s free parameters the total number of free radicals in a cell under radiation may decrease. This effect can explain the “positive” influence of small doses of ionizing radiation.     

Computational mechanistic investigation of radiation damage of adenine induced by hydroxyl radicals

The radiation damage of adenine base was studied by B3LYP and MP2 methods in the presence of hydroxyl radicals to probe the reactivities of five possible sites of an isolated adenine molecule. Both methods predict that the C8 site is the more vulnerable than the other sites. For its bonding covalently with the hydroxyl radicals, B3 LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the hydroxylation at the C2 site, the barrier was calculated to be 165.3 k J/mol using MP2 method. For the dehydrogenation reactions at five sites of adenine, B3 LYP method predicts that the free energy barrier decreases in the order of H8 H2 HN62 HN61 HN9.     

EPR of gamma irradiated solid sucrose and UV spectra of its solution. An attempt for calibration of solid state/EPR dosimetry

A simple new approach for independent calibration of solid state/EPR (SS/EPR) dosimetry system is reported. It is based on the fact that: (i) gamma-irradiation of solid sucrose (sugar) induces stable EPR detectable free radicals accompanied by UV detectable brown colour stable in the solid state and in solution; (ii) both the EPR intensity of gamma-irradiated solid sucrose and its solution UV absorbance linearly depend on the absorbed dose high energy radiation and may be independently used for dosimetric purpose; (iii) UV spectrometers are calibrated. The correlation between EPR response and absorbed dose radiation of solid sucrose and UV absorption of its solutions is used in the present communication for calibration purpose. The procedure of sucrose extraction from sucrose-paraffin dosimeters is described. The calibration procedure may be applied to any other (alanine, self-calibrated, etc.) SS/EPR dosimeters, simultaneously irradiated with sucrose.     

镍离子对DNA结构和导电性的影响

在碱性环境下,向DNA溶液中加入较低浓度的镍离子制备了金属DNA （M-DNA）,并分别对单根DNA和M-DNA的导电性进行了测量.结果表明,二者均表现出半导体性质;随镍离子浓度的增加导电性明显增强,伏特间隙减小;当镍离子浓度超过0.1 mmol/L时,DNA的电导几乎不随镍离子浓度变化.在中性环境下向DNA溶液中加入较高浓度的镍离子,实现了DNA从右手到左手螺旋结构的转变.利用STM观察到了左手螺旋结构的Z-DNA,Z构象可以分辨出大沟与小沟,并且螺旋结构不均匀,伴有局部的解旋和无序化;单根Z-DNA的导电性明显减弱.DNA,M-DNA,Z-DNA的电导大小关系为G_M-DNA>G_DNA>G_Z-DNA.通过紫外吸收和Raman光谱测量发现,使DNA发生右手到左手螺旋结构转变的镍离子浓度约为1.7 mol/L. 关键词： 镍离子 M-DNA Z-DNA 导电性     

紫外光诱导下的固体胆红素自由基性质的ESR研究

利用电子自旋共振方法对固体胆红素及其自由基在紫外照射下的变化进行了研究,发现在紫外光下仅引起胆红素超氧自由基及半醌自由基浓度的增加,而没有新的自由基形式生成,指出Foote提出的光氧化机理假说的中间体自由基即是由上述两种自由基构成,并通过电子计算机对ESR谱的摸拟,提出了紫外辐照下的胆红素自由基形成机理,推测胆红素光化学反应的途径及产物与这两种自由基浓度及在不同环境下的反应活性有关.     

W-红色素的光褪色研究

红曲色素在自然光的作用下会逐渐褪色,紫外线是自然光中引起有机物褪色的主要光线。为了探明红曲色素光照褪色的机理,采用紫外灯照射一种红曲红色素(分子式C19H28N2O5)的水溶液至无色,经红外光谱、质谱和核磁图谱分析,鉴定其褪色后物质的分子式为C14H9NO6。根据光化学理论分析,提出了红曲红色素的光褪色机理:在紫外光作用下,红曲红色素分子中的脂肪族侧链首先在α-碳原子处发生NorrishⅠ型断裂,成为自由基,随后在碳7位甲基上发生相同反应,接着色素发生电子转移,双键转换,水溶液中产生羟自由基、超氧阴离子等自由基,与色素结构中双键发生加成反应,共轭双键消失,色素失去颜色。防止红曲红色素光褪色应首先考虑稳定其脂肪族侧链结构,其次可以在色素中添加自由基清除剂。     

大气HOx自由基湍流标定系统研究

HO_x(OH,HO₂)自由基是大气中重要的氧化剂, 准确测量大气HO_x自由基的浓度对研究大气光化学反应机理有着重要作用。气体扩张激光诱导荧光技术(FAGE)已广泛应用于HO_x自由基的外场观测, 准确标定是FAGE系统准确测量大气HO_x自由基的重要前提。介绍了一种可以产生准确OH和HO₂自由基浓度的便携式湍流标定系统。该系统是基于低压汞灯产生的185 nm线辐射处于湍流状态的H₂O和O₂产生一定浓度的HO_x自由基。该系统中产生的自由基浓度分布均匀, 适用于多种平台的系统标定。为了准确计算出湍流标定装置中产生HO_x自由基的浓度, 分别开展了氧气和水汽吸收截面的测量。利用高精度的腔衰荡光谱(CRDS)系统测量臭氧浓度, 并用冷镜式露点仪对温湿度计测量水汽的浓度进行修正, 提高标定系统HO_x自由基浓度计算的准确度。为了便携化湍流标定系统的外场应用, 快速获取标定系统中产生的HO_x自由基的浓度, 测量了用于探测汞灯光强的光电倍增管的灵敏度因子, 实现用汞灯光强代替标定系统中产生的臭氧浓度。考虑到HO_x自由基的活性比较高, 在湍流标定系统传输的过程中会有一定的壁碰撞损失, 通过改变汞灯和标定装置出气口之间的距离对HO_x自由基在标定系统中的壁碰撞损失进行定量测量。将搭建好的湍流标定系统应用于基于气体扩张激光诱导荧光技术HO_x自由基探测系统(FAGE-HO_x)的准确标定测试, 根据OH自由基在标定系统中的壁碰撞损失对FAGE系统中探测的OH自由基荧光数进行修正, 实验结果表明修正后的OH自由基荧光数和OH自由基浓度之间有着良好的相关性, 这说明HO_x自由基湍流标定系统具有很好的准确性, 并且体积小方便携带, 适用于外场复杂环境条件下的系统标定。     

ESR study on scavenging effect of nicotine on free radicals

Smokers have less risk to catch degenerative diseases such as Alzheimer’s disease and Parkinson’s disease that are both correlated with enhanced oxidative stress. The scavenging effect of nicotine on free radicals was investigated by electron spin resonance techniques. It was found that the scavenging effect of nicotine on hydroxyl radicals and superoxide free radicals was higher than that of vitamin C. It was also found that nicotine could scavenge free radicals in gas-phase cigarette smoke. The data indicate that nicotine may be a potential antioxidant.     

自发射荧光猝灭测定Gemini阴离子表面活性剂胶团聚集数

Gemini表面活性剂C11pPHCNa分子联接链上的对苯氧基在激发下自发射荧光。当浓度超过0.45 mmol·L-1时,激发光谱谱带的拓扑结构发生一系列变化,导致不同于对应的吸收光谱。由于联接链上的对苯氧基明显猝灭了外加探针芘发射的荧光,所以不能用传统的方法测定这类胶团的聚集数。文章利用甲基紫精(MV2+)可有效猝灭C11pPHCNa分子自发射荧光的原理,建立了测定这类胶团平均聚集数的方法。由该方法获得C11pPHCNa胶团平均聚集数为20.6;在溶液体相摩尔比为3∶7的C11pPHCNa/C₁₂-S₂-E₁-C₁₂·2Br体系中,混合胶团的平均聚集数为11.8。