取代脲类除草剂的微生物降解

取代脲类除草剂主要用来防除一年生禾本科杂草和阔叶杂草,自20世纪中期推入市场以来,在世界范围内被广泛使用,已成为重要的除草剂之一。随着取代脲类除草剂的持续施用,其在环境中的残留严重超标,危害日益凸显。因此,取代脲类除草剂在环境中的吸附、迁移和降解等行为备受关注。研究表明细菌降解N,N-二甲基取代脲类除草剂主要是通过连续脱甲基作用后断脲桥降解,而降解N-甲氧基-N-甲基取代脲类除草剂是通过脲桥的直接断裂。真菌降解取代脲类除草剂的途径则较为复杂,尚需进一步阐明。本文综述了近年来分离筛选的取代脲类除草剂降解菌株及其降解途径的最新研究进展,为取代脲类除草剂污染环境的生物修复研究提供参考。     

β-胡萝卜素氧化降解及产物对SGC-7901细胞的抑制作用

本文对β-胡萝卜素的不同氧化降解方法以及氧化降解产物的生理活性进行了研究。用AIBN、NaClO、紫外以及OsO4对β-胡萝卜素进行了氧化降解研究,并用OsO4-H2O2-Ether体系进行控制型氧化降解的产物进行薄层分离后,采用体外细胞培养技术观察β-胡萝卜素氧化降解产物对SGC-7901癌细胞增殖的影响。结果发现不同的氧化方法的氧化速率不同,并且氧化的产物也不同。通过OsO4氧化得到的β-胡萝卜素氧化降解产物对SGC-7901细胞有抑制作用,0.1000 g/L时抑制率达26.15%。分离的AB混合主份对癌细胞的抑制作用呈浓度依赖关系。随着浓度的增加,抑制作用增强,在0.2000 g/L下抑制率达23.31%。主份C对癌细胞也有抑制作用,但效果不及混合主份A、B。     

Fe^2＋-H2O2体系降解壳聚糖

Fe2 -H2O2体系能够有效地降解壳聚糖,反应介质的pH值、反应时间、反应温度、Fe2 浓度及H2O2浓度等实验因素对壳聚糖的降解效果都有程度不同的影响,其中以反应介质的pH值和H2O2浓度对降解反应的影响为最大.在pH值为3～5时Fe2 -H2O2体系降解壳聚糖的活性最高.适当增大H2O2的用量可以增大壳聚糖的降解程度,但当其用量增大至一定程度后,壳聚糖降解产物分子量的下降趋势明显变缓.合理的Fe2 -H2O2体系降解壳聚糖的实验条件为:介质pH值3～5;温度,室温;时间60～90 min;壳聚糖:H2O2:Fe2 =240:12～24:1～2(摩尔比).     

乌骨鸡黑色素氧化降解工艺研究

采用碳酸钾-过氧化氢法、高锰酸钾法、氢氧化钠-过氧化氢法及氨水-过氧化氢法对乌骨鸡黑色素进行氧化降解,并获得可溶性的降解产物,运用GC-MS分析降解萃取产物中物质种类,并且分析了降解产物得率和分子量分布,发现降解方法不同,降解产物各指标也存在相应差异。其中高锰酸钾法得率最高为82.5%,碳酸钾-过氧化氢次之为61.5%,其余均在50%以上;降解产物分子量以氨水-过氧化氢法最高,高达12265.5 Da,其降解程度最小,其萃取物中的物质种类及含量较少,而强酸性环境下高锰酸钾氧化降解乌骨鸡黑色素程度最大,降解产物中存在许多被彻底氧化的有机酸类,进一步表明强酸、强碱介质中黑色素更容易被氧化断裂。     

芳香羧酸衍生物驱避剂的非线性定量构效关系

【目的】驱避剂可使害虫不敢接近受用者从而保护受用者免遭其害。建立高精度、可解释性强的非线性定量构效关系(quantitative structure activity relationship, QSAR)模型对设计合成新的高效昆虫驱避剂有重要意义。【方法】基于37个芳香羧酸类化合物对家蝇Musca domestica的驱避活性,以量子化学计算软件PCLIENT获取每一化合物初始描述符,以二元矩阵重排过滤器、多轮末尾淘汰实施特征非线性筛选,以支持向量回归(support vector regression, SVR)建立非线性QSAR模型,以SVR非线性解释体系分析各保留描述符对驱避活性的影响。【结果】1 542个初始描述符的SVR模型F=1.2,特征筛选后6个保留描述符的SVR模型F=184.6,特征筛选对QSAR模型精度有重要影响。6个保留分子描述符的重要性依次为p4BCD>GATS7v>T(O..O)> JGI8>SssO>nArCONR2。【结论】保留描述符与芳香羧酸类化合物对家蝇驱避活性的非线性关系明显,获得了高精度、普适性强的非线性SVR-QSAR模型。     

D- 型氨基酸氧化酶抑制剂的发展

D-型氨基酸氧化酶(D-Amino acid oxidase,DAAO)抑制剂可以阻止D-型氨基酸(主要是D-型丝氨酸)的降解和过氧化氢的生成,在治疗精神分裂症阴性症状和认知障碍与镇痛等方面均表现出较好的疗效。从第一个DAAO抑制剂芳香羧酸类的苯甲酸到经过烯醇互变的α-羟基酮喹类抑制剂喹诺林-2,3-二酮,DAAO抑制剂结构上总共经历了3代变化,抑制剂与酶之间的相互作用模式逐渐加强,其抑制活性升高了数万倍,脂溶性增加,酸性减弱,理化性质逐渐优化。本文就近10年DAAO抑制剂的结构发展与生物活性之间的关系进行综述。     

肠浒苔多糖的羧甲基化修饰及其抗氧化活性研究

该研究采用氢氧化钠-氯乙酸的化学反应体系制备羧甲基化肠浒苔多糖,以获得不同取代度的羧甲基化肠浒苔多糖,取代度的大小受氢氧化钠浓度、反应温度和反应时间的影响。结果表明:(1)当氢氧化钠浓度20%、反应温度60℃、反应时间3 h时,得到羧甲基化的最大取代度为0.781。(2)通过体外抗氧化来评价不同羧甲基化肠浒苔多糖的抗氧化活性。(3)当羧甲基化肠浒苔多糖的浓度为1.6 mg·mL~(-1)时,羧甲基化肠浒苔多糖清除羟基自由基、超氧阴离子自由基的能力分别为44.45%、51.98%,其清除DPPH自由基清除率和还原能力分别为16.75%、0.457 6。(4)与修饰前的相比,羟基自由基、超氧阴离子的清除能力均有较大幅度提高,羧甲基化修饰对肠浒苔多糖的DPPH自由基和还原力有减弱作用。以上结果表明,羧甲基化修饰引起的肠浒苔多糖的结构变化可以提高其抗氧化活性。     

用SDS．NaClO从重组大肠杆菌中分离聚-β-羟基丁酸酯

聚－β－羟基丁酸酯(PHB)是微生物合成的一种以颗粒状态存在于细胞中的高分子聚合物,由于它具有生物可降解性、生物相容性等特性,在医学上具有独特而广阔的应用前景。从微生物细胞中分离PHB的方法有溶剂萃取法⑵、化学试剂法〔2-4〕和酶法⑸。目前工业生产中以溶剂萃取法和酶法为主,但这两种方法成本均很高。用次氯酸钠破细胞壁从真养产碱杆菌中分离PFIB的化学试剂法具有操作简单、效率高等优点⑹,但次氯酸钠会引起PHB分子的严重降解〔7.8〕。Hahn等人⑼比较了用次氯酸钠作用于真养产碱杆菌和重组大肠杆菌的情况,发现低浓度的次氯酸钠对重组大肠杆菌中的PHB几乎不降解,高浓度的次氯酸钠降解作用也小于对真养产碱杆菌中PHB的降解。本文研究了用NaClO与SDS相结合的作用从重组大肠杆菌中分离PHB的方法,试图利用二者的互补作用．降低SDS用量,减少对PHB分子量的降解．以获得较高纯度和分子量的PHB。     

对锰离子参与类Fenton反应机理的研究

锰主要以Mn2 形式存在,有人发现其具有与其他过渡性金属离子截然相反的抗氧化活性,采用自旋捕捉-ESR技术、芳环羟基化反应-高效液相色谱(HPLC)法和琼脂糖电泳法三种方法研究Mn2 参与类Fenton反应的情况时,均检测到Mn2 与H2O2反应产生.OH,Mn2 与H2O2反应可以发生类Fenton反应,产生.OH。这一现象的产生可能是Mn2 引起生物体内氧化损伤之故。同时显示,Mn2 的类Fenton反应是否产生.OH与反应过程Mn2 以及其他成分浓度有关(如高浓度抑制,低浓度促进),为诸多文献中Mn2 作为促氧化剂还是抗氧化剂的争论提供了可能解释。同时Mn2 能引起.OH持续低量的产生为一些慢性疾病的发生提供了合理的解释。     

薤白多糖的硫酸化修饰及体外抗氧化活性

为探讨薤白多糖硫酸化修饰的最佳条件,以及硫酸化修饰提高薤白多糖活性的可能性,采用氯磺酸-吡啶法对醇沉法得到的薤白多糖和柱层析纯化的3种分级薤白多糖进行硫酸化修饰,以氯磺酸-吡啶配比、反应温度和反应时间为自变量,修饰产物的硫酸基取代度(DS)为响应值,应用响应面设计法确定硫酸化修饰的最佳条件,用H2O2/Fe2+体系法和邻苯三酚自氧化法测定修饰产物的抗氧化活性。结果表明:薤白多糖氯磺酸-吡啶法修饰的最佳条件为氯磺酸∶吡啶=1∶3,反应温度65℃,反应时间2 h,此条件下硫酸根取代度为0.470,硫酸化修饰能提高薤白多糖的体外抗氧化活性。     

高铁酸钾氧化去除饮用水中微量苯酚的研究

采用次氯酸盐氧化法合成高铁酸钾,测试了其对水中苯酚的氧化去除效果及其影响因素.结果表明,苯酚的去除效率主要取决于高铁酸钾和苯酚的质量比.在酸性条件下高铁酸钾对苯酚的去除效果较好.高铁酸钾与苯酚反应主要发生在最初的几分钟时间内,是一个由快而慢的过程.     

Reactivity of potassium permanganate and tetraethylammonium chloride with mismatched bases and a simple mutation detection protocol

Many mutation detection techniques rely upon recognition of mismatched base pairs in DNA hetero-duplexes. Potassium permanganate in combination with tetraethylammonium chloride (TEAC) is capable of chemically modifying mismatched thymidine residues. The DNA strand can then be cleaved at that point by treatment with piperidine. The reactivity of potassium permanganate (KMnO4) in TEAC toward mismatches was investigated in 29 different mutations, representing 58 mismatched base pairs and 116 mismatched bases. All mismatched thymidine residues were modified by KMnO4/TEAC with the majority of these showing strong reactivity. KMnO4/TEAC was also able to modify many mismatched guanosine and cytidine residues, as well as matched guanosine, cytidine and thymidine residues adjacent to, or nearby, mismatched base pairs. Previous techniques using osmium tetroxide (OsO4) to modify mismatched thymidine residues have been limited by the apparent lack of reactivity of a third of all T/G mismatches. KMnO4/TEAC showed no such phenomenon. In this series, all 29 mutations were detected by KMnO4/TEAC treatment. The latest development of the Single Tube Chemical Cleavage of Mismatch Method detects both thymidine and cytidine mismatches by KMnO4/TEAC and hydroxylamine (NH2OH) in a single tube without a clean-up step in between the two reactions. This technique saves time and material without disrupting the sensitivity and efficiency of either reaction.     

高铁酸钾的制备及其降解苯二酚的研究

采用电解法经分离、提纯后,成功地制备了高铁酸钾,并进一步研究了不同高铁酸钾用量对降解苯二酚废水的影响。SEM结果表明高铁酸钾呈棱柱状,XRD结果表明高铁酸钾纯度较高,毛细管电泳检测结果表明,高铁酸钾对苯二酚具有良好的氧化去除效果。在其它条件相同的情况下,苯二酚的去除效率主要取决于高铁酸钾与苯二酚的物质的量比。     

Chemical reactivity of potassium permanganate and diethyl pyrocarbonate with B DNA: specific reactivity with short A-tracts

We have examined the reactivity of B DNA with two chemical probes of DNA structure, potassium permanganate (KMnO4; thymine specific) and diethyl pyrocarbonate (DEPC; purine specific, A greater than G). The DNA probed is from the beta-lactamase promoter region of the vector pBR322, and from the 3' noncoding region of a chicken embryonic myosin heavy chain gene. The chemical probes display variable reactivity with the susceptible bases in these fragments, suggesting that modification of these bases by KMnO4 and DEPC is quite sequence dependent. In contrast, these probes react with the short A-tracts present in these DNA fragments in a reproducible fashion, generating two related patterns of reactivity. In the majority of the A-tracts, all but the 3'-terminal thymine are protected from KMnO4 attack, while DEPC reacts significantly with all but the 3'-terminal adenine of the A-tracts. Some A-tracts also display a very high DEPC reactivity at the adenine adjacent to the 3'-terminal unreactive adenine. Little qualitative difference in the KMnO4 reactivity of the A-tracts was found between 12 and 43 degrees C. However, at lower temperatures the elevated KMnO4 reactivity at the 3'-terminal A-tract thymine is sometimes lost. Raising the temperature of the KMnO4 reaction can cause relatively large increases in the reactivity of some single thymines, suggesting that significant local changes in stacking occur at these thymines at elevated temperatures. The data presented suggest that many short A-tracts embedded in long fragments of DNA can assume a number of related structures in solution, each of which possess distinct junctions with the flanking DNA. This result is consistent with high-resolution structural studies on oligonucleotides containing short A-tracts. The relevance of these results to current models of A-tract structure and DNA bending is discussed. Our data also indicate that KMnO4 and DEPC are potentially useful reagents for the study of sequence-dependent variations in B DNA structure.     

Effect of oxidizing adulterants on human urinary steroid profiles

Steroid profiling is the most versatile and informative technique adapted by doping control laboratories for detection of steroid abuse. The absolute concentrations and ratios of endogenous steroids including testosterone, epitestosterone, androsterone, etiocholanolone, 5α-androstane-3α,17β-diol and 5β-androstane-3α,17β-diol constitute the significant characteristics of a steroid profile. In the present study we report the influence of various oxidizing adulterants on the steroid profile of human urine. Gas chromatography–mass spectrometry analysis was carried out to develop the steroid profile of human male and female urine. Oxidants potassium nitrite, sodium hypochlorite, potassium permanganate, cerium ammonium nitrate, sodium metaperiodate, pyridinium chlorochromate, potassium dichromate and potassium perchlorate were reacted with urine at various concentrations and conditions and the effect of these oxidants on the steroid profile were analyzed. Most of the oxidizing chemicals led to significant changes in endogenous steroid profile parameters which were considered stable under normal conditions. These oxidizing chemicals can cause serious problems regarding the interpretation of steroid profiles and have the potential to act as masking agents that can complicate or prevent the detection of the steroid abuse.     

Investigation of bacterial resistance to the immune system response: cepacian depolymerisation by reactive oxygen species

Reactive oxygen species (ROS) are part of the weapons used by the immune system to kill and degrade infecting microorganisms. Bacteria can produce macromolecules, such as polysaccharides, that are able to scavenge ROS. Species belonging to the Burkholderia cepacia complex are involved in serious lung infection in cystic fibrosis patients and produce a characteristic polysaccharide, cepacian. The interaction between ROS and bacterial polysaccharides was first investigated by killing experiments, where bacteria cells were incubated with sodium hypochlorite (NaClO) with and without prior incubation with cepacian. The results showed that the polysaccharide had a protective effect towards bacterial cells. Cepacian was then treated with different concentrations of NaClO and the course of reactions was followed by means of capillary viscometry. The degradation products were characterised by size-exclusion chromatography, NMR and mass spectrometry. The results showed that hypochlorite depolymerised cepacian, removed side chains and O-acetyl groups, but did not cleave the glycosidic bond between glucuronic acid and rhamnose. The structure of some oligomers produced by NaClO oxidation is reported.     

Genotoxic activity of potassium permanganate in acidic solutions

Potassium permanganate (KMnO4) combined with sulfuric acid is a strongly oxidizing mixture which has been recommended for the destruction and the decontamination of various mutagens/carcinogens in the publication series of the International Agency for Research on Cancer. Evaluation of the genotoxicity of 4 potassium permanganate solutions was performed using a microtechnique of the Ames test with the tester strains TA97, TA98, TA100 and TA102 with and without metabolic activation. Presence of direct-acting mutagens was detected in all the samples with the tester strain TA102 without S9 mix (163-357 revertants/microliters of the solutions). Three samples containing either acetone or ethanol as an organic solvent also induced a mutagenic response on tester strain TA100 without S9 mix (167-337 revertants/microliters). In addition, DNA damage in human peripheral blood lymphocytes was also measured for one of the mixtures by a new technique: the single-cell gel assay (SCGA). A sample with no organic solvent induced DNA damage in human lymphocytes with a dose-response relationship as determined by SCGA. The major mutagenic agent generated by the permanganate solutions was found to be manganese ion (Mn2+). Both manganese sulfate (MnSO4) and manganese chloride (MnCl2) gave mutagenic dose-response relationships on tester strain TA102 without S9 mix. The mutagenic potencies were 2.8 and 2.4 revertant/nmole for MnSO4 and MnCl2 respectively. MnCl2 also induced DNA damage in human lymphocytes as determined by the SCGA. The genotoxic effects of KMnO4 in acidic conditions were probably mediated by the conversion of MnO4- to Mn2+. KMnO4 in alkaline solutions did not produce mutagenic species and may offer an alternative for the degradation of genotoxic compounds.     

Detection of an unusual distortion in A-tract DNA using KMnO4: effect of temperature and distamycin on the altered conformation.

The chemical probes potassium permanganate (KMnO4) and diethylpyrocarbonate (DEPC) can be used to study the conformational flexibility of short tracts of adenine (A-tracts) present in DNA. With these probes, we demonstrate that a novel distortion is induced in a 5 base pair A-tract at low temperature. Formation of this distorted A-tract structure, which occurs in a DNA fragment from the promoter region of the plasmid pBR322, is distinguished by a dramatic increase in the KMnO4 reactivity of the central thymines in this tract at 12 degrees C. This alteration occurs in the absence of any detectable rearrangement in the conformation of the adenines in the complementary strand. Induction of this low temperature A-tract structure is blocked by the minor groove binding drug distamycin. Hydroxyl radical footprinting of distamycin binding to the fragment containing the d(A)5 tract at 12 degrees C suggests that this drug has two different modes of binding to DNA in agreement with recent NMR data. These experiments show that short A-tracts are capable of forming more than one structural variant of B DNA in solution. The possible relationship between the intrinsic bending of DNA containing short phased A-tracts and the low temperature A-tract conformation is discussed.     

A structural analysis of the bent kinetoplast DNA from Crithidia fasciculata by high resolution chemical probing.

The chemical probes potassium permanganate (KMnO4) and diethylpyrocarbonate (DEPC) have been used to study the conformation of bent kinetoplast DNA from Crithidia fasciculata at different temperatures. Chemical reactivity data shows that the numerous short A-tracts of this bent DNA adopt a similar structure at 43 degrees C. This conformation appears to be very similar to the conformation of A-tracts in DNA exhibiting normal gel mobility. The A-tract structure detected by chemical probing is characterized by a high degree of base stacking on the thymine strand, and by an abrupt conformational change at the 3' end of the adenine strand. In general, no major alteration of this A-tract specific structure was detected between 4-53 degrees C. However, probing with KMnO4 revealed two unusual features of the C. fasciculata sequence that may contribute to the highly aberrant gel mobility of this DNA: 1) the B DNA/A-tract junction 5' dC/A3-6 3'. 5' dT3-6/G 3' is disproportionately represented and is conformationally distinct from other 5' end junctions, and 2) low temperature favors a novel strand-specific conformational distortion over a 20 base pair region of the bent kinetoplast DNA. Presence of the minor groove binding drug distamycin had little detectable effect on the A-tract conformation. However, distamycin did inhibit formation of the novel KMnO4 sensitive low temperature structure and partially eliminated the anomalous gel mobility of the kinetoplast DNA. Finally, we describe a simple and reproducible procedure for the production of an adenine-specific chemical DNA sequence ladder.