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在通空气条件下,回流竹红菌甲素(HA)(或乙素,HB)和Na~2SO~3的含1%NaOH强碱性水溶性生成14-脱羟基-15-脱乙酰基竹红菌甲素-13-位磺酸钠(13-SO~3Na-DDHA)(产率30%)和另一种红色的水溶性聚合物。当这一反应在吡啶-水(1:1/V:V)混合溶剂中进行,并用CuO作氧化剂时,只得到13-SO~3Na-DDHA一种水溶性产物(70%产率)。在后一体系中,由于改变了溶剂和氧化剂,使13-SO~3Na-DDHA的制备更加便利。反应体系的ESR研究表明,这一磺化反应首先是通过竹红菌素和Na~2SO~3之间热活化的电子转移进行的。电子转移的结果产生竹红菌素半醌负离子自由基和三氧化硫负离子自由基(SO~3^-)。硝基甲烷酸式负离子猝灭实验证明,由于竹红菌素的13位能在碱性、高温下活化,磺化的关键步骤是SO~3^-对其活化了的13位的亲电进攻。氧化剂在这一反应中的作用为:将产生的竹红菌素半醌负离子自由基氧化至其母体醌,增加反应物的相对浓度,同时使竹红菌素与SO~3^2^-之间的电子转移循环进行,加速SO~3^-的产生。 相似文献
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竹红菌乙素与BNAH及AcrH_2的光化学反应 总被引:2,自引:0,他引:2
BNAH与AcrH2 同为二氢吡啶类衍生物 ,但由于结构和电化学性质上的差异 ,造成了它们与竹红菌素的光化学反应历程上的差异 ,HB与BNAH的光化学反应是以电子转移为反应的初始步骤 ,吸收光谱及ESR谱均能检测到竹红菌素自由基负离子中间体HB-·.AcrH2 能以动态和静态两种方式猝灭HB的荧光 ,而在AcrH2 与HB的光化学反应过程中未能检测到竹红菌素自由基负离子中间体HB-·,1HCID NP研究表明反应的初始步骤为激发单线态1HB 夺取AcrH2 上氢原子而形成中性自由基对中间体 相似文献
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水溶性竹红菌素及电子转移中间体的光谱研究 总被引:1,自引:0,他引:1
本文详细研究了水溶性竹红菌素衍生物14-脱羟基-15-脱乙酰基-竹红菌甲素-13-磺酸钠(13-SO_3Na-DDHA)及光还原产物的吸收光谱和影响因素。通过吸收光谱随pH值的变化观察到13-SO_3Na-DDHA及两电子还原产物酚羟基的分步解离,并通过实验值与理论公式相拟合分别求出了解离的pK_a。此外,还比较了13-SO_3Na-DDHA在buffer溶液和在DMF-buffer溶液中的光还原特点。测定了13-SO_3Na-DDHA半醌负离子自由基质子化和歧化的动力学性质。 相似文献
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电子顺磁共振现场研究多孔电极表面自由基的电化学行为 总被引:1,自引:0,他引:1
本文建立了一套ESR-EC联合现场测试多孔电极表面顺磁粒子的方法, 并对多孔碳电极上吸附的醌化合物在电极上还原时的自由基中间产物的ESR进行了研究。首次获得了固体电极表面自由基有hfs的高分辨ESR信号。研究结果表明,醌在RB碳电极表面有多种行为各异的吸附态。在测量电位范围内, 观察到了四种吸附醌化合物是通过自由基过程还原的。其中两种通过可旋转单键吸附到碳电极表面, 给出有hfs的ESR谱; 另两种表现为各向异性ESR信号,可能是通过多个位置吸附在碳表面。 相似文献
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Thermodynamic and kinetic acidities of 6-tert-butyl-2-hydroxy-4-triphenylmethylphenoxyl during its interaction with triethylamine in toluene have been studied by ESR. It has been shown that the protolysis of this radical is a two-pathway process, since tautomeric transitions, i.e. ammonium ion migration between oxygen atoms of the semiquinone radical anion, have been detected in the reaction products, that is, in contact ion pairs of the corresponding semiquinone radicals.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 81–84, January, 1993. 相似文献
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H. Kurreck S. Aguirre H. Dieks J. Gtschmann J. v. Gersdorff H. Newman H. Schubert M. Speck T. Stabingis J. Sobek P. Tian A. Wiehe 《Radiation Physics and Chemistry》1995,45(6):853-865
Porphyrin quinones (P-Qs), covalently linked via different aliphatic bridges, have been synthesized and studies in their (porphyrin) cationic and (semiquinone) anionic radical states by EPR, ENDOR and TRIPLE resonance techniques. Electron transfer (ET) from the porphyrin donor to the quinone acceptor could be observed by time-resolved picosecond fluorescence spectroscopy (singlet ET) and by time-resolved EPR spectroscopy (triplet ET) in isotropic fluid solution and in anisotropic media (liquid crystals and reversed micelles). Steady-state in situ photoexcitation of P-Qs in CTAB cationic reversed micelles yielded the corresponding semiquinone radical anions. In TRITON X-100 reversed micelles both the radical cation of the porphyrin and the radical anion of the semiquinone could be detected, which occured in complete emission. In covalently linked porphyrin flavins ET from the photoexcited porphyrin fragment to the flavin and, in addition, energy transfer from the photoexcited flavin to the porphyrin could be observed. 相似文献
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Peter Boldt Detlev Bruhnke Fabina Gerson Markus Scholz Peter G. Jones Friedrich Br 《Helvetica chimica acta》1993,76(4):1739-1751
3,5,3″,5″-Tetra(tert-butyl)-p-terphenoquinone ( 12b ) was synthesized and characterized by its spectroscopic and X-ray structural data. The ground state of 12b is singlet with a strong contribution of a biradical structure. Paramagnetic derivative of 12b , such as the semiquinone radical anion (12bτ) and its O-protonated form, the phenoxy radical ( 18 ), were studied by ESR and ENDOR spectroscopy. 相似文献
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共轭聚合物中稳定自由基的ESR研究 总被引:2,自引:2,他引:2
通过ESR跟踪测试,研究了3种胺类化合物与聚(N,N-二甲基苯胺)(PDMA)中离域正离子自由基相线作用的过程,发现胺类化合物能使PDMA的ESR谱形发生不同程度的劈裂,信号强度随时间的变化与胺的结构有关,说明正离子自由基与亲核试剂作用后发生了定域化转变,通过进一步比较发现PDMA自由基的亲电活性不如聚苯上的正离子的自由基。 相似文献
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Ogata M Kaneya D Shin-Ya K Li L Abe Y Katoh H Seki S Seki Y Gonda R Urano S Endo T 《Chemical & pharmaceutical bulletin》2005,53(9):1167-1170
Many researchers have stated that eugenol might inhibit lipid peroxidation at the stage of initiation, propagation, or both, and many attempts have been made to elucidate the mechanism of its antioxidant activity. Nevertheless, details of its mechanism are still obscure. This study was carried out to investigate the trapping effect of eugenol on hydroxyl radical generated from L-3,4-dihydroxyphenylalanine (DOPA) in MiliQ water and the generation mechanism of the hydroxyl radical by this system which uses no metallic factor. This was studied by adding L-DOPA and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to phosphate buffered saline (PBS) or MiliQ water, and the generation of hydroxyl radical was detected on an ESR spectrum. By this method, the effect of antioxidants was detected as a modification of ESR spectra. We found that the eugenol trapped hydroxyl radicals directly, because it had no iron chelating action, did not trap L-DOPA semiquinone radical and inhibited hydroxyl radicals with or without iron ion. 相似文献
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Abstract— Irradiation of daunomycin (or adriamycin) and the spin trap 5,5-dimethyl-l-pyrroline-1-oxide (DMPO) at 490 nm in the presence or in the absence of air generated the hydroxyl radical adduct (DMPO-OH). The observed DMPO-OH signal was not affected by the addition of hydroxyl radical scavengers (ethanol, formate), suggesting that direct trapping of the hydroxyl radical was not involved. The DMPO-OH signal was insensitive to superoxide dismutase and catalase, which ruled out the possibility of superoxide or H2 O2 involvement. These findings demonstrate that daunomycin (or adriamycin) does not generate hydroxyl radicals or superoxide radical anions when subjected to 490-nm excitation. However, when daunomycin (or adriamycin) was irradiated at 310 nm DMPO adducts derived from two carbon-centered radicals, superoxide and the hydroxyl radical were detected. The superoxide adduct of DMPO was abolished by the addition of SOD, providing unequivocal evidence for the generation of the superoxide anion radical. The daunomycin semiquinone radical, observed upon 310-nm irradiation of daunomycin in the absence of DMPO, appears to be the precursor of the superoxide radical anion. One of the carbon-centered radicals trapped by DMPO exhibited a unique set of hyperfine parameters and was identified as an acyl radical. This suggests that the known photochemical deacylation of daunomycin occurs via a homolytic cleavage mechanism. The free radicals generated photolytically from adriamycin and daunomycin may be involved in the etiology of the skin ulceration and inflammation caused by these drugs. A knowledge of the dependence of these photogenerated radicals on the wavelength of excitation may be important in the development of adriamycin and daunomycin for photodynamic therapy. 相似文献
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Superoxide ion (O2˙-) forms a stable 1 : 1 complex with scandium hexamethylphosphoric triamide complex [Sc(HMPA)(3)(3+)], which can be detected in solution by ESR spectroscopy. Electron transfer from O2˙- -Sc(HMPA)(3)(3+) complex to a series of p-benzoquinone derivatives occurs, accompanied by binding of Sc(HMPA)(3)(3+) to the corresponding semiquinone radical anion complex to produce the semiquinone radical anion-Sc(HMPA)(3)(3+) complexes. The 1 : 1 and 1 : 2 complexes between semiquinone radical anions and Sc(HMPA)(3)(3+) depending on the type of semiquinone radical anions were detected by ESR measurements. This is defined as Sc(HMPA)(3)(3+)-coupled electron transfer. There are two reaction pathways in the Sc(HMPA)(3)(3+)-coupled electron transfer. One is a stepwise pathway in which the binding of Sc(HMPA)(3)(3+) to semiquinone radical anions occurs after the electron transfer, when the rate of electron transfer remains constant with the change in concentration of Sc(HMPA)(3)(3+). The other is a concerted pathway in which electron transfer and the binding of Sc(HMPA)(3)(3+) occurs in a concerted manner, when the rates of electron transfer exhibit first-order and second-order dependence on the concentration of Sc(HMPA)(3)(3+) depending the number of Sc(HMPA)(3)(3+) (one and two) bound to semiquinone radical anions. The contribution of two pathways changes depending on the substituents on p-benzoquinone derivatives. The present study provides the first example to clarify the kinetics and mechanism of metal ion-coupled electron-transfer reactions of the superoxide ion. 相似文献