共查询到20条相似文献,搜索用时 140 毫秒
1.
不同波段的紫外辐射对DNA构象影响的拉曼光谱研究 总被引:2,自引:0,他引:2
研究了小牛胸腺DNA水溶液经不同时问不同波段紫外辐射后的拉曼光谱。结果表明:仅仅经过9min强度为18.68W/m^2。的全波段紫外辐射,DNA就遭到了严重损伤:表征PO2^-对称伸张振动的1094cm^-1谱线分裂成4条谱线.说明DNA构象遭到破坏,构型发生了变化。UV—A&UV—B波段的紫外辐射对DNA的影响比全波段的紫外辐射对DNA的影响小得多,但经过较长时间辐射后,仍对DNA构型构象产生了影响,即A型构象增强,B型构象减弱.经过2h的UV—A辐射,出现了表征A型构象的805cm^-1和816cm^-1谱线,且816cm^-1峰与未经辐射的表征A型的803cm^-1峰相比,强度大得多。经过16h的UV—A辐射后,805cm^-1谱线消失,816cm^-1谱线移到了813cm^-1,且强度减弱50%,表明水溶液中的DNA在UV—A照射中A型构象不稳定,处于变化之中。 相似文献
2.
在天然产物Combretastatin A-4全合成的关键步骤——Wittig反应中,引入紫外(254nm)辐射,结果使得Wittig反应的产率从原有的65%提高到83.6%。特别是其产物的Z-式立体异构体选择性大大提高,从原来的Z/E之比为3.6提高到11.5,笔者推测这种光化学反应是按双自由基机理进行。 相似文献
3.
4.
北京、昆明地区太阳紫外辐射生物效应的评估 总被引:2,自引:0,他引:2
本文讨论了我国北京和昆明地区臭氧层减薄可能导致的紫外线生物有效辐射剂量季节和年度的变化情况。计算中采用表征一般植物危害和人体红斑效应的活跃光谱来评估紫外线的生物危害效应,对平均云顶对紫外线辐射的影响也进行了分析。臭氧浓度减少所引起的紫外辐射的增加对植物的危害大于对人体健康的影响。云层的存在改变了昆明地区晴天时地面紫外辐射的季节变化类型。并且使北京和昆明地区晴天时年均生物有效辐射剂量降低27%和33%。计算得到,在过去10年间,北京和昆明地区由于臭氧层减薄,地面紫外生物有效辐射剂量年增加率分别为1.4%和3.2%,这和测定结果相符。 相似文献
5.
6.
7.
8.
9.
微波辐射在制备竹节活性炭中的应用研究 总被引:11,自引:0,他引:11
研究了以竹节废料为原料,采用微波辐射氯化锌法制备优质活性炭的可行性.探讨了微波功率.活化时间及氯化锌浓度对产品各项指标的影响.得到了微波辐射氯化锌法制备活性炭的最佳工艺:微波功率350W、活化时间5min、氯化锌浓度40%.用此工艺制得的活性炭碘吸附值1088.4mg/g、亚甲基蓝脱色力22.0ml/0.1g.得率39.2%.该工艺所需活化时间为传统方法的1/36,产品活性炭亚甲基蓝脱色力为国家一级标准的1.83倍(GB/T13496.10-1999).微波辐射法所制活性炭比传统方法所制活性炭具有更加发达的孔隙结构,且孔隙的分布更加均匀. 相似文献
10.
11.
The chemical form of arsenic contained in the muscle of certain freshwater fish was examined using cultured specimens of rainbow trout (Salmo gairdneri) and wild specimens of Japanese smelt (Hypomesus nipponensis). More than 95% of the total arsenic of both species was extracted with methanol and recovered in the water-soluble fraction. The major arsenic compound of both species was purified by cation-exchange chromatography on Dowex 50, gel filtration on Bio-Gel P-2 and HPLC on Asahipak GS-220H. Behavior in the above purification procedure and analyses of the purified compounds by HPLC–ICP and TLC confirmed that the major arsenic compound of both species was arsenobetaine. Arsenobetaine found in cultured rainbow trout seems to be derived from the commercial assorted feed containing arsenobetaine as the major arsenical. On the other hand, the result with wild Japanese smelt suggested that arsenobetaine is a naturally occurring compound in the freshwater environment. 相似文献
12.
The palladium catalyzed borylation of a Boc protected aminobromoquinoline compound with bis(pinacolato)diboron yielded a biaryl compound, resulting from cross coupling, as the major product, instead of the intended boronate, even though no strong base was used. Such results indicate that under certain conditions and with certain substrates, cross coupling can be a major problem during borylation, leading to unintended consequences. 相似文献
13.
CHEN Pei ZHAO Feng-qi ** LUO yang HU Rong-zu GAO Sheng-li ZHENG Yu-mei DENG Min-zhi GAO Yin . Xi′an Modern Chemistry Research Institute Xi′an P. R. China . Shaanxi Key Laboratory of Physico-Inorganic Chemistry Department of Chemistry Northwest University Xi′an P. R. China . Shanghai Institute of Organic Chemistry Chinese Academy of Sciences Shanghai P. R. China 《高等学校化学研究》2005,21(1):100-103
IntroductionCopper( ) salt of4- hydroxy- 3,5 - dinitropy-ridine( 4 HDNPCu) is an energetic material contain-ing energetic_ NO2 groups,which can be used asan energetic auxiliary catalyzer substituting the in-ertia copper salt to improve the catalysis of themain catalyzer( lead salt) in propellant[1] .Thermalbehavior is one of the most important aspects af-fecting its catalytic efficiency for propellant.How-ever,its kinetic parameters of thermal decomposi-tion and its application in RDX- co… 相似文献
14.
Ogra Y Ishiwata K Ruiz Encinar J Łobiński R Suzuki KT 《Analytical and bioanalytical chemistry》2004,379(5-6):861-866
The major selenium compound in an aqueous extract of the most popular mushroom in Eastern Asian countries, shiitake (Lentinula edodes), fortified with selenium (Se) was identified by means of hyphenated techniques, i.e. HPLC-inductively coupled argon plasma mass spectrometry and HPLC-electrospray ionization mass spectrometry (HPLC–ICP MS and HPLC–ESI MS). Sixty-eight per cent of the total Se in the selenized shiitake was extracted with water, and 49.8% of the Se in the water extract was eluted in the high molecular mass fraction (>40,000 kDa) before incubation at 37 °C. After incubation, 40.6% of the Se in the water extract was eluted in a lower molecular mass fraction and the Se eluted in the high molecular mass fraction had decreased to 14.0%, suggesting that the major selenium compound in the water extract was initially in a form bound to macromolecule(s) and was then enzymatically liberated from the macromolecule(s). The retention time of the liberated selenium compound in HPLC–ICP MS matched that of selenomethionine (SeMet), and the masses of molecular and fragment ions detected by HPLC–ESI MS also suggested that the selenium compound was SeMet. The selenized shiitake accumulated Se as SeMet, and SeMet might be bound to the water extractable high molecular mass protein(s).Electronic Supplementary Material Supplementary material is available for this article at 相似文献
15.
An on-line supercritical fluid extraction (SFE) system coupled to a continuous flow manifold including a UV detector was used as a screening system to extract astaxanthin from crayfish, which was found to be the major carotenoid present in the samples. This compound constitutes the principal additive used to dye salmon flesh. The flow manifold was used to confirm the presence of astaxanthin in the crustacean samples. Also, an HPLC/UV-vis method was used to ascertain that this compound was the major carotenoid extracted under the optimum SFE conditions employed. The influence of SFE operating variables such as pressure, temperature, equilibration time, extraction time, trap temperature, and volume of CO2 modifier was examined in order to maximize the efficiency of analyte extraction. The use of supercritical CO2 enables the expeditious, selective, quantitative extraction of astaxanthin from crustaceans. 相似文献
16.
Melo MJ Sousa M Parola AJ de Melo JS Catarino F Marçalo J Pina F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(5):1417-1422
The compound 7,4'-dihydroxy-5-methoxyflavylium (dracoflavylium) was identified as the major red colorant in samples of the resin "dragon's blood", extracted from the tree Dracaena draco. The complex network of reversible chemical reactions that dracoflavylium undergoes in aqueous solution is fully described; for the first time, all the equilibrium constants that enable a complete characterisation of the system have been obtained (K'(a)=1.6 x 10(-4), K(a1)=1.0 x 10(-4), K(a2)=3.2 x 10(-8), K(Ct1)=1.0 x 10(-7), K(Ct2)=1.3 x 10(-10)). It is concluded that the red colour is due to a stable quinoid base, A, which is the major species at pH 4-7. It is further shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3-deoxyanthocyanidin. Similarly to synthetic flavylium salts, the natural compound 7,4'-dihydroxy-5-methoxyflavylium gives rise to several species (multistate system) reversibly interconverted by external stimuli, such as pH. 相似文献
17.
从理论及实验上研究了2-芳基丙硅烷(1)的光物理及光化学特性.结果表明,在极性溶液中观察到的强荧光带来源于分子内电荷转移(ICT);在非极性溶液中,化合物1的光化学反应产物为亚甲硅基并伴随着1,3-甲硅烷基的迁移;而在乙醇-己烷溶液中,光化学反应主要导致Si-Si键的裂解,通过研究光化学反应与温度的关系可确认,亚甲硅基与1,3-甲硅烷基的迁移来源于化合物1的不同电子激发态,非谐振双光子光化学反应(NRTP)结果表明,亚甲硅基迁移来源于化合物1的La电子态. 相似文献
18.
MM Boyle JJ Gassensmith AC Whalley RS Forgan RA Smaldone KJ Hartlieb AK Blackburn JP Sauvage JF Stoddart 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(33):10312-10323
A trans isomer of a figure-of-eight (Fo8) compound was prepared from an electron-withdrawing cyclobis(paraquat-p-phenylene) derivative carrying trans-disposed azide functions between its two phenylene rings. Copper(I)-catalyzed azide-alkyne cycloadditions with a bispropargyl derivative of a polyether chain, interrupted in its midriff by an electron-donating 1,5-dioxynaphthalene unit acting as the template to organize the reactants prior to the onset of two click reactions, afforded the Fo8 compound with C(i) symmetry. Exactly the same chemistry is performed on the cis-bisazide of the tetracationic cyclophane to give a Fo8 compound with C(2) symmetry. Both of these Fo8 compounds exist as major and very minor conformational isomers in solution. The major conformation in the trans series, which has been characterized by X-ray crystallography, adopts a geometry which maximizes its C?H???O interactions, while maintaining its π???π stacking and C?H???π interactions. Ab initio calculations at the M06L level support the conformational assignments to the major and minor isomers in the trans series. Dynamic (1) H?NMR spectroscopy, supported by 2D (1) H?NMR experiments, indicates that the major and minor isomers in both the cis and trans series equilibrate in solution on the (1) H?NMR timescale rapidly above and slowly below room temperature. 相似文献
19.
Change of resole structures in a rubber compound by compounding and curing processes were investigated using ethylene-propylene-diene terpolymer (EPDM) compound and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). Resole structures were divided into three groups of reactive, pendent, and unreactive species to examine in detail the structural changes. Reasonable resole species of the major resole species having two possible structures were determined using variations of the relative abundances by compounding and curing. Of the major resole species, there was no resole species having both terminals of methylol. It was found that resole was not simply mixed in a rubber matrix and reactive resole species were diversified and activated through the compounding process. Almost all reactive resole species participated in crosslinking reactions, but some reactive resole species still remained in the vulcanizate. 相似文献
20.
Veronique Gilard Myriam Malet-martino Robert Martino Ulf Niemeyer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract In an attempt to clarify the alkaline hydrolytic pathway of the antitumor agent, cyclophosphamide (CP), the time course of its degradation was monitored by 31P NMR in 0.5 M KOH solution. After 16 hr at 25°C. 70% of CP is hydrolyzed (t½ 9 hr) leading to a mixture of 8 phosphorated compounds. among them only 4 represented more than 5% of the initial CP. The chemical shifts and the intensities of these compounds were as follows: 1 1 .1 ppm. 30% of the initial CP (compound 1); 9.5 ppm, 12% (compound 2); 6.4 ppm, 9% (unknown) and 4.8 ppm, 9% (compound 3). The structures of compounds 1–3 were identified by NMR (13C and IH) and mass spectrometry after their isolation. The major degradation compound formed, the nine-membered ring compound I, was also observed during CP hydrolysis at neutral or moderately acid pHsill and was detected in urine of patients treated with CP[2] Compounds 2 and 3 were also formed during the hydrolysis of compound I in 0.5 M KOH solution. Based on the formation in time of the 31P NMR signals in KOH solutions of CP and compound I, the following scheme was established for the major degradation alkaline pathway of CP. 相似文献