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一种测定主流卷烟烟气中固相自由基总量的新方法 总被引:1,自引:0,他引:1
研究了一种准确测定主流卷烟烟气中固相自由基总量的新方法. 通常人们采用剑桥滤片来捕集主流卷烟烟气中的固相自由基, 但它并不适合用于准确测定主流卷烟烟气中的固相自由基的总量, 研究发现有超过20%的主流卷烟烟气中的固相自由基可以透过剑桥滤片. 找到了一种电子顺磁共振波谱(EPR)信号很小的、适合用来捕集主流卷烟烟气中的固相自由基总量的过滤片. 采用了以在相同条件下测得的1,1-二苯基-2-苦基肼基(1,1-Diphenyl-2-picryl-hydrazyl, 简称DPPH)的EPR信号强度与强煤的EPR信号强度相比得到的相对EPR信号强度与自由基的自旋数建立校准曲线的方法来计算烟气固相自由基的量, 降低了使用不同的电子自旋共振波谱仪造成的对同一种检测样品测定结果的差异. 通过不同实验室内和实验室间的验证实验, 证明了此方法有很好的重复性和重现性. 相似文献
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以自旋标记荧光探针4-((9-acridinecarbonyl)amino)-2,2,6,6-tetramethylpiperidin-1-oxyl(TEMPO-9-AC)研究了卷烟主流烟气中的碳中心自由基。以吸烟机抽吸卷烟,以弱荧光的TEMPO-9-AC作为捕集剂捕集卷烟主流烟气中的碳中心自由基,生成稳定的强荧光的碳中心自由基捕集加合物,以高效液相色谱-三重四极杆串联质谱联用仪(HPLC-MS/MS)对其结构进行了确认,并建立了高效液相色谱-荧光检测(HPLC-FLD)的定量方法。结果表明,方法的检出限为0.318 nmol/cig,相对标准偏差(RSD)为3.5%~9.7%;利用TEMPO-9-AC捕集体系鉴别出了10种碳中心自由基;对5种代表性卷烟烟气中的碳中心自由基进行了定量计算,获得了它们在主流烟气中碳中心自由基的含量数据,并发现碳中心自由基总量与焦油释放量之间具有高度的相关性。本法检出限低,重复性好,适用于卷烟主流烟气中碳中心自由基的结构验证及释放量的检测分析。 相似文献
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自由基反应是环境化学教学过程中的重点和难点。为了达到良好的教学效果,本研究以量化计算结合三维可视化的图形手段,使用“自旋密度”对自由基反应中的单电子过程进行了教学展示,结合具体教情学情进行课堂教学内容和形式的优化调整。首先,通过分子轨道理论对羟基自由基的电子结构进行分析,明确自旋密度、单电子、半充满轨道等概念;其次,通过对自旋密度可视化,对经典自由基反应进行追踪;最后,建立自旋密度与静电势之间的呼应或互补的关系,加深对环境自由基过程的理解。这种与现代化学理论的有机融合,赋予了环境自由基反应更深刻的内涵,提供了更多可供研究或操作的“手柄”,提高了学生的学习兴趣,融洽了师生关系,实现了预期教学目标。 相似文献
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烟草中多酚热裂解产物研究 总被引:2,自引:0,他引:2
多酚类化合物对烟草品质、色泽和烟气生理强度等方面有着重要影响,因此是衡量烟草质量的一个重要因素[7],对卷烟的香气品质有很重要的作用.绿原酸、芸香苷和莨菪亭是烟草中最主要的酚类物质[7],有证据表明酚类物质的存在能显著提高多环芳烃的致癌活性[1,6].卷烟主流烟气中酚类物质的含量的多少直接影响到卷烟的安全性.另外某些酚类物质可能是影响卷烟的口感,引起涩味、辣味、余味不干净的一种因素.研究它们的裂解产物对探索降低卷烟烟气有害成分,提高卷烟的吸食品质十分必要[2,5]. 相似文献
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综述了荧光分析技术在卷烟烟气成分检测中的研究进展,包括自由基及其反应产物、酚类、多环芳烃、亚硝胺类等物质的荧光分析技术,指出了可以根据不同的烟气成分和分析测试对象合理选择荧光探针、同步荧光、时间分辨、衍生化、色谱联用等技术手段,提高分析检测效果,并对该技术的应用前景进行了展望(引用文献32篇)。 相似文献
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Chikayoshi Nagata Masahiko Kodama Teruyuki Kimura Tami Yamaguchi 《International journal of quantum chemistry》1979,16(4):917-930
A free radical was produced enzymatically by incubating benzo(a)pyrene with liver microsomes. This radical, identified as the 6-oxybenzo(a) pyrene radical, was sufficiently reactive to bind covalently with nucleic acid bases. Similar reactive free radicals were produced enzymatically from anthanthrene and 10-aza-benzo(a)pyrene, which are carcinogenic in spite of lacking so-called “bay regions.” Hepatocarcinogens such as 3′-methyl-4-dimethylaminoazobenzene and related compounds, naphthylamines, and 2-acetylaminofluorene yield free radicals after being incubated with liver microsomes. Thus, various kinds of chemical carcinogens are found to be converted to free radicals, suggesting causal significance for the formation of free radicals in chemical carcinogenesis. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(30):8927-8930
Anticancer modalities based on oxygen free radicals, including photodynamic therapy and radiotherapy, have emerged as promising treatments in the clinic. However, the hypoxic environment in tumor tissue prevents the formation of oxygen free radicals. Here we introduce a novel strategy that employs oxygen‐independent free radicals generated from a polymerization initiator for eradicating cancer cells. The initiator is mixed with a phase‐change material and loaded into the cavities of gold nanocages. Upon irradiation by a near‐infrared laser, the phase‐change material is melted due to the photothermal effect of gold nanocages, leading to the release and decomposition of the loaded initiator to generate free radicals. The free radicals produced in this way are highly effective in inducing apoptosis in hypoxic cancer cells. 相似文献
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The role of melanin as protector against free radicals in skin and its role as free radical indicator in hair 总被引:1,自引:0,他引:1
Herrling T Jung K Fuchs J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(5):1429-1435
Throughout the body, melanin is a homogenous biological polymer containing a population of intrinsic, semiquinone-like radicals. Additional extrinsic free radicals are reversibly photo-generated by UV and visible light. Melanin photochemistry, particularly the formation and decay of extrinsic radicals, has been the subject of numerous electron spin resonance (ESR) spectroscopy studies. Several melanin monomers exist, and the predominant monomer in a melanin polymer depends on its location within an organism. In skin and hair, melanin differs in content of eumelanin or pheomelanin. Its bioradical character and its susceptibility to UV irradiation makes melanin an excellent indicator for UV-related processes in both skin and hair. The existence of melanin in skin is strongly correlated with the prevention against free radicals/ROS generated by UV radiation. Especially in the skin melanin (mainly eumelanin) ensures the only natural UV protection by eliminating the generated free radicals/ROS. Melanin in hair can be used as a free radical detector for evaluating the efficacy of hair care products. The aim of this study was to investigate the suitability of melanin as protector of skin against UV generated free radicals and as free radical indicator in hair. 相似文献
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David N. -S. Hon 《Journal of polymer science. Part A, Polymer chemistry》1980,18(6):1857-1869
The formation and behavior of photo-and mechanoinduced free radicals in cellulose were studied by ESR spectroscopy and the capability of these free radicals to initiate graft copolymerization reactions was demonstrated. Although an 11-line ESR signal was detected from cellulose irradiated with ultraviolet (UV) light, a higher-intensity ESR signal with a five-line pattern was detected from a sample mechanically milled at 77 K. The decay of photoinduced free radicals when heated took place monotonously, whereas mechanoradicals exhibited an anomalous behavior with an increased signal intensity at 150 K before decaying at a higher temperature. Mechanoradicals have been found to react more efficiently and rapidly with oxygen and methyl methacrylate (MMA) than photoinduced free radicals. The peroxy mechanoradicals, however, were mobile and decayed more rapidly than the peroxy photoinduced radicals. Simultaneous graft copolymerizations of MMA to cellulose demonstrated that mechano-and photoinduced free radicals are capable of initiating grafting reactions, but a higher degree of grafting efficiency was obtained from cellulose treated mechanically. 相似文献
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Two cyclic alkoxyl radicals are formed as a result of peroxide bridge scission in artemisinin. Intramolecular reactions of these radicals induce the cascade of reactions of isomerization, decyclization, and decomposition of formed free radicals. It includes 14 reactions of intramolecular free radical hydrogen transfer, 17 reactions of decyclization of alkoxyl and alkyl radicals, and 4 reactions of decomposition of alkoxyl, acyl, and carboxyl radicals. The enthalpies of these 35 reactions are calculated. Using intersection parabolas method, activation energies and rate constants of all these reactions are calculated. The most rapid reactions are selected for every intermediate free radical. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 554–565, 2005 相似文献
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《International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry》1988,31(2):203-208
Important results obtained in our group in the field of ESR application to the study of irradiated polymers are summarized. They are the analysis of the decay reaction of the free radicals, spur-like trapping of the free radicals and the related discussions. A diffusion controlled bimolecular reaction scheme was a good way of analyzing the data of the decay reaction. Power saturation phenomenon of ESR spectra of the free radicals showed a circumstance of the spur-like trapping of the free radicals in irradiated polyethylene. The phenomenon of spur-like trapping was quite consistent with the interpretation of the decay reaction of the free radicals. 相似文献
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Nehal Gupta Kshitij Verma Sarath Nalla Alok Kulshreshtha Rajiv Lall Sahdeo Prasad 《Molecules (Basel, Switzerland)》2020,25(22)
Free radicals, generally composed of reactive oxygen species (ROS) and reactive nitrogen species (RNS), are generated in the body by various endogenous and exogenous systems. The overproduction of free radicals is known to cause several chronic diseases including cancer. However, increased production of free radicals by chemotherapeutic drugs is also associated with apoptosis in cancer cells, indicating the dual nature of free radicals. Among various natural compounds, curcumin manifests as an antioxidant in normal cells that helps in the prevention of carcinogenesis. It also acts as a prooxidant in cancer cells and is associated with inducing apoptosis. Curcumin quenches free radicals, induces antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), and upregulates antioxidative protein markers–Nrf2 and HO-1 that lead to the suppression of cellular oxidative stress. In cancer cells, curcumin aggressively increases ROS that results in DNA damage and subsequently cancer cell death. It also sensitizes drug-resistant cancer cells and increases the anticancer effects of chemotherapeutic drugs. Thus, curcumin shows beneficial effects in prevention, treatment and chemosensitization of cancer cells. In this review, we will discuss the dual role of free radicals as well as the chemopreventive and chemotherapeutic effects of curcumin and its analogues against cancer. 相似文献
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This paper reports how free radicals generated in a liquid phase cross the boundary to an adjacent immiscible liquid phase as a function of the concentration of added surfactant. The yields of this crossing process are evaluated.If non-ionic free radicals are generated in the organic phase, this yield decreases with increasing occupation of the interphase by the surfactant, without vanishing however at saturation point.On the other hand, if ionic radicals are generated in an aqueous phase containing surfactant, transfer occurs generating non-ionic free radicals which, in turn, cross the interface more easily being insensitive to the Helmholtz electric double layer. If the organic phase contains styrene, the crossing free radicals form polystyrene which appears to be a mixture of two types of product, viz, a normal product for which DP is calculable in a classical kinetic manner, and another with very small DP which may result from the combination of growing polystyrene chains having their — OSO3K ends bound at the interface. 相似文献
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Percival PW Brodovitch JC Ghandi K McCollum BM McKenzie I 《Journal of the American Chemical Society》2005,127(39):13714-13719
There is a pressing need to identify and monitor reaction intermediates in water at high temperatures and pressures, but conventional techniques have limited capability for studying transient free radicals under such challenging conditions. Apparatus has now been developed to permit muon avoided-level crossing spectroscopy (muLCR) of organic free radicals in superheated water. The combination of muLCR with transverse-field muon spin rotation (TF-muSR) provides the means to identify and characterize free radicals via their nuclear hyperfine coupling constants. Because the radicals are derived from the addition of muonium (Mu = mu+ e-) to unsaturated compounds, the ensuing muoniated free radicals correspond to conventional organic free radicals but with a muon spin label substituted for one of the protons. Muon spin spectroscopy is the only technique presently being used to characterize transient free radicals under hydrothermal conditions in an unambiguous manner, free from interference from other reaction intermediates. This paper demonstrates how muoniated radicals can be used to monitor the species present in hydrothermal systems, and examples are presented from two classes of reaction: dehydration of alcohols and enolization of ketones. Spectra are displayed and hyperfine constants reported for muoniated forms of the following free radicals in superheated water (typically 350 degrees C at 250 bar): 2-propyl, 2-methyl-2-propyl (tert-butyl), and 2-hydroxy-2-propyl. The latter radical is the product of muonium addition to both the keto and the enol forms of acetone, but different isotopomers are produced according to which reaction channel is dominant. This should prove invaluable in future studies of the role of enols in combustion. 相似文献
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R. S. Pemberton M. C. Depew S. D. Pollington J. K. S. Wan 《Research on Chemical Intermediates》1995,21(3-5):425-439
The reactions of alkyl peroxyl radicals with cellulosic and lignin-containing papers have significance in both the problems of brightness reversion and paper aging phenomena. Since transient peroxyl radicals are elusive to ESR and other spectroscopic detection, we have explored the controlled study of the interactions of nitrogen oxides with paper and some model lignin compounds in solution as a comparable model of free radical oxidation. Formations of intermediate iminoxyl and nitroxide radicals are identified by ESR with products in some model systems analysed by GC/MS to elucidate the primary mechanisms of the interactions of these gaseous free radicals with papers and with some simple organic model lignin compounds. 相似文献