羟基自由基引起的脱氧核糖核酸损伤研究

以鲱鱼精脱氧核糖核酸(Herring sperm DNA)为研究对象,利用紫外光(UV,200～275 nm,66.4 Lx)激发纳米TiO2发生光催化作用介导产生羟基自由基(Hydroxyl radical,.OH),探讨.OH引发DNA氧化损伤特性。采用凝胶电泳和高效液相色谱(HPLC)分析法跟踪DNA损伤历程;应用电子自旋共振(Electron spinresonance,ESR)及分光光度法跟踪损伤过程氧化物种及H2O2相对浓度的变化;运用生物标准样8-羟基脱氧鸟苷(8-Hydroxy-2’-deoxyguanosine,8-OHdG)为内标物,通过HPLC分析DNA损伤产物,研究DNA损伤机理。结果表明,较单纯UV辐照或暗光(Dark)催化条件,DNA浓度10 mg/L,TiO2浓度1.5 g/L、pH 7～8,紫外光激发纳米TiO2介导产生.OH引发DNA损伤程度最大;DNA损伤为.OH氧化历程,并伴随有深度氧化过程;DNA结构中鸟嘌呤最易氧化损伤,8-OHdG为DNA氧化损伤中间产物及鸟嘌呤氧化损伤的特异产物。     

高频超声照射下血卟啉镓配合物对脱氧核糖核酸的损伤

用紫外-可见(UV-Vis)光谱和荧光(FL)光谱研究了高频超声波激活血卟啉镓(HP-Ga)配合物对脱氧核糖核酸(DNA)的损伤，并探讨了超声波照射时间、HP-Ga浓度、溶液酸度和离子强度等因素对DNA损伤的影响。结果表明，在一定条件下，DNA的损伤程度随着超声波照射时间的增加和HP-Ga浓度的增大而加剧，而溶液酸度和离子强度的影响则较为复杂。     

聚醚砜溶液流变性的研究

研究了聚醚砜（PES）/二甲基亚砜（DMSO）体系中PES的质量分数、原液温度对流变性的影响和原液中PES的质量分数对粘流活化能的影响,从而得出PES/DMSO体系属于切力变稀流体,非牛顿指数随着PES质量分数的增加而不断减小,随着溶液温度的升高而不断增大.     

铬(Ⅵ)-谷胱甘肽配合物诱导小牛胸腺DNA变性的新表征方法

本文采用电化学方法对铬(Ⅵ)-谷胱甘肽(GSH)配合物诱导DNA变性进行表征,同时运用原子力显微镜(AFM)对DNA损伤变性过程进行可视化探测.结果表明:在pH=5.6的HAc-NaAc缓冲溶液中,DNA溶液中加入Cr(Ⅵ)-GSH配合物后进行循环伏安扫描,+0.20 V和0.00 V(vs SCE)处出现一对新的氧化还原峰,该氧化还原峰随Cr(Ⅵ)-GSH配合物浓度增加峰电流上升.DNA热变性和表面活性剂SDS变性实验进一步证明了该峰为DNA变性后的氧化还原峰,且变性DNA的峰信号在修饰电极上比裸金电极上更为灵敏.电化学动力学表明在30 min内配合物诱导DNA变性的程度随时间的上升而增加,并通过AFM观察了配合物作用下DNA断链的过程.     

罗丹明S与热变性DNA作用的共振光散射光谱研究及其应用

研究了小分子染料罗丹明S与热变性脱氧核糖核酸(DNA)在弱酸性条件下共振光散射光谱的特征.考察了各种影响因素,在优化条件下确立了共振光散射强度与鱼精DNA和小牛胸腺DNA浓度之间的线性关系,相应的线性范围分别为0.024～3.00,0.018～3.50 mg·L-1;相关系数为0.998 6,0.999 0;检出限为24.0,18.3μg·L-1;基于共振光散射的增强,建立了一种测定DNA的方法.     

丁基锡系列化合物与脱氧核糖核酸的相互作用

通过紫外（ultraviolet,UV）光谱和圆二色（circular dichroism,CD）光谱,研究了丁基锡化合物（一丁基锡、二丁基锡和三丁基锡）与脱氧核糖核酸（deoxyribonucleic acid,DNA）的作用方式以及时间和浓度的影响。结果显示丁基锡化合物与DNA的作用是双重的,既作用于DNA的碱基,对双螺旋结构有一定影响,又作用于DNA的磷酸基团,使构象发生变化。但是,丁基锡化合物与脱氧核糖核酸作用的程度和方式与丁基锡种类、时间和浓度等因素有关。一丁基锡倾向于与磷酸基团作用,三丁基锡倾向于与碱基作用,而二丁基锡与两者作用程度相近。短时间内,丁基锡化合物的作用位点通常是DNA的碱基;长时间时,则作用位点往往是DNA的磷酸基团。低浓度的丁基锡化合物倾向与DNA的碱基结合,高浓度的丁基锡化合物倾向与DNA的磷酸基团结合。     

全反式维甲酸合钐（Ⅲ）配合物与DNA作用的研究

以荧光法，粘度法和圆二色谱法研究了全反式维甲酸合钐（Ⅲ）配合物与DNA 的作用，结果表明，该配合物可使DNA的粘度增加，引起DNA圆二色谱中的负峰发生 较大变化，使EB－DNA体的荧光强度降低，DNA热变性温度升高，该配合物的荧光强 度在DNA存在时有较大的增加，据此推断，该配合物主要以嵌入方式与DNA作用，这 咱作用方式可能是该配合物对HL－60，EJ癌细胞瘤株有较强抑制作用的原因之一。     

脱氧核糖核酸和核糖核酸与铽离子的荧光反应及其在分析中的应用

本文提出了一种简单灵敏的测定DNA和RNA的方法。实验结果表明RNA可直接与铽离子发生荧光反应,但DNA只有在发生变性之后才能发生同样的反应。酸变性的最佳pH范围在2.2～2.8之间,通过实验确定了荧光反应的最佳条件。在最佳条件下测定DNA和RNA的线性范围在0.5～20.0μg/ml,标准偏差在5％以內。小牛胸腺DNA和鱼精子DNA在酸变性时其对铽离子荧光增强效应提高数十倍,而RNA变性前后对铽离子荧光增强效应变化不大,这本身反映了DNA与RNA二级结构的不同。利用DNA和RNA在酸变性时对Tb(Ⅱ)荧光增强变化的不同可在一定量的DNA存在下测定RNA或在一定量的RNA存在下利用差减法测DNA。     

铬(VI)-谷胱甘肽配合物诱导小牛胸腺DNA变性的新表征方法

本文采用电化学方法对铬(VI)-谷胱甘肽(GSH)配合物诱导DNA变性进行表征，同时运用原子力显微镜(AFM)对DNA损伤变性过程进行可视化探测。结果表明：在pH=5.6的HAc-NaAc缓冲溶液中，DNA溶液中加入Cr(VI)-GSH配合物后进行循环伏安扫描，+0.20 V和0.00 V(vs SCE)处出现一对新的氧化还原峰，该氧化还原峰随Cr(VI)-GSH配合物浓度增加峰电流上升。DNA热变性和表面活性剂SDS变性实验进一步证明了该峰为DNA变性后的氧化还原峰，且变性DNA的峰信号在修饰电极上比裸金电极上更为灵敏。电化学动力学表明在30 min内配合物诱导DNA变性的程度随时间的上升而增加，并通过AFM观察了配合物作用下DNA断链的过程。     

二甲基亚砜及一些含氮环化合物与DNA的作用

通过实验探索了将既不溶于水又不能生成可溶性盐的一些含氮稠环化合物溶于二甲基亚砜（DMSO）水溶液中与小牛胸腺DNA作用的途径．溶解实验证明了DMSO及其水溶液对此类化合物极强的溶解性能，DMSO与小牛胸腺作用的紫外光谱（298 K）、圆二色谱（298 K）、~(31)P核磁谱（323 K）和摩尔焓变（298 K）数据均表明：在pH＝7.0的水溶液中，当DMSO浓度小于0．15 mol·L~(-1)时，其与DNA无作用．溶于DMsO水溶液中的八种含氮稠环化合物与小牛胸腺DNA作用的紫外光谱（298 K）、圆二色谱（298 K）和摩尔焓变（298 K）实验结果显示出两种化合物对DNA有较强的嵌插作用．通过对实验结果的分析，本文对具有相同含氮稠环骨架的化合物与DNA嵌播作用的规律和化合物本身微观结构的关系进行了讨论．     

A DSC study of the liquid crystalline phases of salmon sperm DNA

Thermodynamic stabilities of the liquid crystalline (LC) and gel (G) phases of salmon sperm DNA were investigated by differential scanning calorimetry (DSC). The enthalpic and the entropic components of the thermal denaturation free energy are briefly discussed. In order to evaluate the thermodynamic data for the denaturation of the gel (G) phase of DNA and compare it with those for the LC DNA phase, a hypothesis for the thermal denaturation mechanism of G DNA is proposed. A comparison between these two sets of data has shown that DNA in the LC phase is thermally and thermodynamically more stable than in the G phase over the temperature range which was investigated.     

DMSO对鸡蛋白溶菌酶溶液变性的影响

利用差示扫描量热(DSC)和温度调制差示扫描量热(MDSC)研究了鸡蛋白溶菌酶在纯水及二甲基亚砜(DMSO)/水混合溶剂中的热变性过程, 探讨了酶的浓度、扫描速率和共溶剂的含量对热变性行为的影响规律. 在纯水溶液中, 溶菌酶的变性焓(△Hm)随酶浓度的增大而增大. 而在DMSO/水混合溶剂中, 变性温度(Tm)随DMSO体积分数的增大向低温方向移动, 变性峰变低变宽; 当DMSO体积分数达到70%后, 热变性曲线变成了一条光滑的直线. 另外, 在纯水溶液中溶菌酶的MDSC图除了出现DSC中可观察到的主吸热峰(I)外, 在峰(I)的前面还出现一个小而对称的吸热峰(II), 并且当体系中有DMSO存在时也未能观察到此峰. 当溶菌酶浓度增大时, Tm(II)移向低温, △Hm(II)减小, Tm(I)与Tm(II)之间的距离变长. 吸热峰(II)的出现被认为是由于水溶液中溶菌酶二聚体的可逆离解造成的.     

甲壳素类液晶高分子的研究Ⅷ. N-邻苯二甲酰化壳聚糖/DMSO液晶溶液的热致相转变

合成了氮上完全取代的邻苯二甲酰化壳聚糖 (PhthCS) .用DSC研究了PhthCS DMSO液晶溶液的热致相转变 .偏光显微镜和DSC测定都表明临界浓度为 43wt% .在浓度高于 43wt%的溶液的DSC曲线中观察到了除了液晶 各向同性液体转变 (清亮点 )外还有一个明显的凝胶 溶胶转变 .凝胶 溶胶转变温度和转变焓均比文献报道的不规则取代的N 邻苯二甲酰化 O 乙酰化壳聚糖大得多 ,可见取代的规整性对凝胶 溶较转变有很大的影响 .根据DSC研究结果绘制了PhthCS DMSO体系的相图     

Gas phase thermal denaturation of an oligonucleotide duplex and its complexes with minor groove binders

Electrospray ionization with in-source collisionally induced dissociation has been used to probe the gas phase stability of an oligonucleotide duplex and its complexes with some minor groove binding drugs. On the basis of the arguments developed in detail by Drahos et al. (J. Mass Spectrom. 1999; 34:1373), this type of experiment can also be described as 'thermal denaturation in the gas phase'. We found that the gas phase denaturation curves were very similar to the solution phase denaturation curves determined by the traditional UV spectrophotometric method and, by analogy with the melting temperature T(m) which characterizes the stability in solution, we define a melting voltage V(m) to characterize the stability in the gas phase. A comparison of the T(m) and V(m) relative values suggests that the structure of the complexes is conserved during the electrospray process which transfers the ions from the solution to the gas phase.     

Reorganization and caging of DPPC, DPPE, DPPG, and DPPS monolayers caused by dimethylsulfoxide observed using Brewster angle microscopy

The interaction between dimethylsulfoxide (DMSO) and phospholipid monolayers with different polar headgroups was studied using "in situ" Brewster angle microscopy (BAM) coupled to a Langmuir trough. For a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer, DMSO was shown to significantly impact the structure of the liquid expanded (LE) and gaseous phases. The domains reorganized to much larger domain structures. Domains in the liquid condensed (LC) phase were formed on the DMSO-containing subphase at the mean molecular area where only gaseous and LE phases were previously observed on the pure water subphase. These results clearly demonstrate the condensing and caging effect of DMSO molecules on the DPPC monolayer. Similar effects were found on dipalmitoyl phosphatidyl ethanolamine, glycerol, and serine phospholipids, indicating that the condensing and caging effect is not dependent upon the phospholipid headgroup structure. The DMSO-induced condensing and caging effect is the molecular mechanism that may account for the enhanced permeability of membranes upon exposure to DMSO.     

Gas‐phase behavior of noncovalent transmembrane segment complexes

Specific helix oligomerization between transmembrane segments (TMSs) is often promoted by motifs like GxxxG. Disruption of this motif in the transmembrane segments of vesicular stomatitis virus G‐protein and of glycophorin A results in a reduced dimerization level studied by in vivo systems like ToxR. This paper reports the influence of sequence motifs like GxxxG in solution and the gas phase. The transmembrane segments may behave differently in the gas and liquid phase, because of the absence of surrounding solvent molecules in the gas phase. Comparison of experiments depending on peptide properties performed in the gas and liquid phase discloses that the peptides retain ‘some memory’ of their liquid‐phase structure in the gas phase. A direct correlation has been found between helicity in solution as determined by circular dichroism and dimerization in the gas phase monitored by electrospray mass spectrometry. These results show that a proper folding in solution is required for oligomerization. On the other hand, sequence‐specific oligomerization depending on the GxxxG motif was not observed with the mass spectrometric detection. Further on, neither concentration‐dependent complex studies nor studies regarding complex stability in the gas phase – via collision‐induced dissociation (CID) – led to sequence‐specific differences. Finally, the findings show that in mass spectrometric measurements noncovalent interactions of studied TMSs is rather more dependent on the secondary structure and proper folding than on their primary structure. Copyright © 2008 John Wiley & Sons, Ltd.     

溶剂对PVDF铸膜液相转化和微孔膜皮-亚两层结构的不同影响

采用皮-亚分步凝固成膜机理分析了3种不同溶剂对聚偏氟乙烯(PVDF)铸膜液相转化和膜结构的影响,采用浊度法测定铸膜液体系的热力学性质,沉淀速度采用光透射仪测定.结果显示,3种膜的皮层分相主要由热力学性质控制,均发生延时液固分相,生成了相互融合的球粒组成的致密皮层.3体系的亚层分相行为由动力学扩散过程控制;对于二甲基亚砜(DMSO)、N,N-二甲基乙酰胺(DMAc)体系亚层发生瞬时液液分相,结晶化对动力学过程影响小,表现为光透射曲线上分相时间t2短,生成了大孔结构为主的亚层,膜厚度、孔隙率和气通量均高、结晶度低;N,N-二甲基甲酰胺(DMF)体系亚层发生延时液液分相,结晶化对动力学过程影响大,t2长,生成蜂窝状孔结构亚层,其膜厚度、孔隙率和气通量较低,但膜的结晶度高.     

Water effect on the gelation behavior of polyacrylonitrile/dimethyl sulfoxide solution

The gelation behavior of polyacrylonitrile (PAN)/dimethyl sulfoxide (DMSO) solution containing different amounts of water has been investigated using various methods. The ternary phase diagram of PAN/DMSO/water system indicated that water enhanced the temperature at which phase separation of PAN/DMSO solution occurred. Intrinsic viscosities [η] of dilute PAN/DMSO solution and PAN/DMSO/water solution at varied temperatures were measured to examine the influence of water on the phase behavior of PAN/DMSO solution. The presence of water in the solution gave rise to elevated critical temperature T_c. The gelation temperature T_g obtained by measuring the loss tangent tan δ at different oscillation frequencies in a cooling process was found to increase with increased water content in the solution. The critical relaxation exponent n value, however, changed little with varied concentration. During the aging process, the gelation rate of PAN/DMSO solution increases with the water level. The n values of the PAN/DMSO solutions with 2 wt% and 4 wt% water were a little larger than that of the solution without water, which may be explained by the turbid gel resulted from phase separation. The n values obtained in the aging process were larger than those obtained in the cooling process for the same three solutions, ascribed to the weaker gel with less cross-linking points formed in long time. Water led to the formation of denser gel structure. The coarser gel surface can also be attributed to the phase separation promoted by water.     

Protein Conformation and Supercharging with DMSO from Aqueous Solution

The efficacy of dimethyl sulfoxide (DMSO) as a supercharging reagent for protein ions formed by electrospray ionization from aqueous solution and the mechanism for supercharging were investigated. Addition of small amounts of DMSO to aqueous solutions containing hen egg white lysozyme or equine myoglobin results in a lowering of charge, whereas a significant increase in charge occurs at higher concentrations. Results from both near-UV circular dichroism spectroscopy and solution-phase hydrogen/deuterium exchange mass spectrometry indicate that DMSO causes a compaction of the native structure of these proteins at low concentration, but significant unfolding occurs at ~63% and ~43% DMSO for lysozyme and myoglobin, respectively. The DMSO concentrations required to denature these two proteins in bulk solution are ~3–5 times higher than the concentrations required for the onset of supercharging, consistent with a significantly increased concentration of this high boiling point supercharging reagent in the ESI droplet as preferential evaporation of water occurs. DMSO is slightly more basic than m-nitrobenzyl alcohol and sulfolane, two other supercharging reagents, based on calculated proton affinity and gas-phase basicity values both at the B3LYP and MP2 levels of theory, and all three of these supercharging reagents are significantly more basic than water. These results provide additional evidence that the origin of supercharging from aqueous solution is the result of chemical and/or thermal denaturation that occurs in the ESI droplet as the concentration of these supercharging reagents increases, and that proton transfer reactivity does not play a significant role in the charge enhancement observed.     

Lithium ion induced stabilization of the liquid crystalline DNA

A comparative study of the effects of alkali metal ions Li(+), Na(+), K(+), Rb(+), and Cs(+) on the liquid crystalline organization of high-molecular-weight calf thymus DNA using polarized light microscopy was performed. Major differences in the behavior of Li(+) as compared to the other ions were found. Critical DNA concentration expected to exhibit anisotropic behavior was found to be the same for all the monovalent ions, except for Li(+). DNA initially showed cholesteric textures, which later changed to higher ordered columnar phase for all ions, with the cholesteric-columnar transition facilitated upon increasing the size of the counterion. For Li(+) ion, a nematic schlieren-like texture was formed initially, which after a few days changed to a highly stable (for more than 2 months) biphasic cholesteric-columnar arrangement. The observed differences between Li(+) and other alkali metal ions could be rationalized on the basis of the higher number of hydration water molecules of Li(+) and its complexation behavior. Highly stable DNA mesophases may find applications in the field of nanoelectronics, in designing biosensing units, and in DNA chips.