中国自由基捕获技术发展30年

本文简要回顾了30年来国内在自由基捕获技术（spin trapping）领域的研究进展,其中包括新型自由基捕获探针的分子设计与合成,探针结合EPR波谱方法在光、电化学反应以及生物领域的应用实例. 最后,结合国内外自由基捕获技术现状讨论了它的未来发展前景.     

Pd(OAc)_2与有机双膦在氯代烷中的反应机理(Ⅱ)研究

在前文[1 ,2 ] 基础上 ,扩展了有机双膦系列 .应用电子自旋捕获技术 (EPR ST)研究了Pd(OAc) 2 与系列有机双膦dppm(二 (二苯基膦甲烷 ) )、dppe(二 (二苯基膦乙烷 ) )及dppp(二(二苯基膦丙烷 ) )在氯代烷中反应的反应机理 ,所用捕获剂为PBN ,得到EPR实验谱并进行了模拟 .提出了反应机理并进行了讨论 .并对影响反应的一些因素进行了探讨 .Pd(OAc) 2 在此反应中既是反应物又是引发剂 ,在反应中起分子诱导作用 .当Pd(OAc) 2 与非自由基物种有机双膦配体及氯代烷共存时 ,引发了自由基反应 .     

配合物PdCl2[(PPh2)2CHCl]的合成、结构及反应机理

合成了新配合物PdCl₂[(PPh₂)₂CHCl],用核磁、红外光谱、元素分析等表征了其结构,X-rax衍射确定了单晶结构.应用电子顺磁共振-自旋捕获(EPR-ST)对技术研究了其反应的机理.捕获到PPh₂及含碳自由基中间体,提出了反应机理.     

Pd(OAc)2与PPh3在氯代甲烷中的反应研究

用Pd(OAc)₂与PPh₃在四氯甲烷中反应,合成了配合物PdCl₂(PPh₃)₂?CCl₄,得到单晶,用X-ray衍射确定了单晶结构.应用电子顺磁共振-自旋捕获(EPR-ST)技术研究了其反应的机理.捕获了含碳自由基中间体,提出了反应机理.     

新型饱和烷基类自由基捕捉剂的合成及ESR研究

设计合成了新的饱和烷基类线型硝酮捕捉剂N-（亚乙基）-t-丁胺-N-氧化物(EBN)和N-（亚乙基）-1-二乙氧基磷酰基-1-甲基乙基胺N-氧化物(EPN),并运用ESR、MS、IR、UV等一系列手段对其结构进行了表征,同时对Fenton体系中产生的羟基及不同类型的氧中心、碳中心和硫中心自由基的捕获能力进行了系统的研究. 结果表明,这两种捕捉剂合成方法比较简单,产率较高,对羟基等自由基有比较强的捕捉能力. 期望本文的工作能为自由基捕捉剂的研究提供一个新的思路.     

自由基ClO和ClO_2的解析势能函数

运用密度泛函(B3LYP)方法,分别选用6-311+G(3df)和aug-cc-pV6Z基组,对ClO自由基和O_2分子进行了计算,并拟合了其M-S势能函数.采用密度泛函方法(B3LYP)在6-311G(3df)基组下对ClO_2自由基的结构进行了优化计算,得到:ClO_2自由基的稳态结构为C_(2v)构型,电子态为~2B_1、平衡核间距R_(clo)=0.14785 nm、键角/OClO=117.3107°、离解能D_e=2.7552 eV、基态振动频率ν_1(a_1)=451.3423 cm~(-1),v_2(a_1)=970.8289 cm~(-1),ν_3(b_2)=1123.5023 cm~(-1).采用多体项展式理论推导了ClO_2自由基的基态解析势能函数,其等值势能图准确再现了该分子的结构特征及其势阱深度与位置.分析讨论势能面的静态特征时得到:在ClO+O→ClO_2反应中存在两个对称的鞍点,分别位于(0.248 nm,0.152 nm)和(0.152 nm,0.248 nm)处,活化能为5.614 kcal/mol     

二苯甲酮与2-芳基-1,3-二噻烷衍生物光化夺氢反应中产生的活泼自由基的ESR研究

本文用自旋捕捉技术与ESR相结合的方法,研究了九种2-芳基-1,3-二噻烷衍生物与二苯甲酮光化夺氢反应中产生的活泼自由基。结果表明,与硫原子相联的两个碳上的C-H键(即2位和4或6位碳的C-H键),都能发生均裂而生成较稳定的自由基。并均可为ND和TBN捕获而生成两种自由基加合物,其浓度比约为1:1。     

Pd(OAc)2与有机双膦在氯代烷中的反应机理(Ⅱ)研究

在前文^[1,2]基础上,扩展了有机双膦系列.应用电子自旋捕获技术(EPR-ST)研究了Pd(OAc)₂与系列有机双膦dppm(二(二苯基膦甲烷))、dppe(二(二苯基膦乙烷))及dppp(二(二苯基膦丙烷))在氯代烷中反应的反应机理,所用捕获剂为PBN,得到EPR实验谱并进行了模拟.提出了反应机理并进行了讨论.并对影响反应的一些因素进行了探讨.Pd(OAc)₂在此反应中既是反应物又是引发剂,在反应中起分子诱导作用.当Pd(OAc)₂与非自由基物种有机双膦配体及氯代烷共存时,引发了自由基反应。     

用荧光探针法研究茶叶花粉黄酮对氧自由基致鼠红细胞膜氧化损伤的保护作用

应用1,6-二苯基-1,3,5-已三烯(DPH)为荧光探针,超氧阴离子自由基和羟基自由基致鼠红细胞膜氧化损伤为模型,研究了茶叶花粉黄酮对鼠红细胞膜氧化损伤的影响.结果表明,超氧阴离子自由基和羟基自由基均能引起鼠红细胞膜脂质过氧化反应,脂质过氧化产物丙二醛含量显著升高,膜脂流动性下降.将鼠红细胞膜预先用茶叶花粉黄酮处理后,膜脂的MDA含量明显下降,呈现剂量与效应关系,膜脂流动性显著提高,表明茶叶花粉黄酮对超氧阴离子自由基和羟基自由基引起的鼠红细胞膜的氧化损伤有保护作用.     

配合物PdCl_2[(PPh_2)_2CHC1]的合成、结构及反应机理

合成了新配合物PdCl2[(PPh2)CHCl]，用核磁、红外光谱、元素分析等表征了其结构，X－rax衍射确定了单晶结构.应用电子顺磁共振-自旋捕获（EPR－ST）对技术研究了其反应的机理．捕获到PPh2及含碳自由基中间体，提出了反应机理．     

Effect of radiation dose with low dose rate on degradation of propylene–ethylene copolymer

Medical grade propylene–ethylene (P–E) copolymer was irradiated by gamma rays. The radicals generated in the irradiated P–E copolymer were identified by using electron spin resonance (ESR) technique and the structural changes in the polymer were monitored with Fourier transform infrared spectroscopy (FTIR). The ESR spectra were analysed with computer simulations. The ESR studies show the formation of macro (～CH₂–?H–CH₂～), peroxy (POO˙), methyl and acyl (R–?=O) radicals and the asymmetric doublet, characteristic of peroxy radicals in the case of the sample irradiated at low dose (1 Mrad) and high doses (30 and 40 Mrad), respectively. The FTIR spectra of irradiated P–E copolymer indicate an increase in the concentration of peroxide groups. The absorption bands of –C=O and –OH groups were increased and the decline in the intensity of –CH₃ group absorption band is reported.     

脉冲强磁场高频电子自旋共振装置的研制

国内第一套脉冲强磁场高频电子自旋共振(ESR)装置由武汉国家脉冲强磁场科学中心研制成功.该装置的频率范围为210-370 GHz,样品温度范围为2-300 K, 磁场强度为0-50 T.在脉冲强磁场ESR装置上进行了红宝石ESR实验,获得了Cr³⁺ 离子的ESR谱.     

低密度聚乙烯光引发交联机理——Ⅰ.ND自旋捕捉ESR研究

本文使用2,3,5,6——四甲基亚硝基苯(ND)自旋捕捉ESR技术研究了由二苯甲酮(BP)光引发低密度聚乙烯(LDPE)交联自由基中间体。采用改变温度和熔融态检测到分辨得很好的氮氧自旋加合物自由基ESR谱的方法,鉴定了光引发LDPE交联前躯自由基主要为仲碳自由基,-CH_2-CH-CH_2-和叔碳自由基,由此可见,BP引发LDPE的光交联反应主要发生在仲碳和叔碳原子上。     

Characterization of free radicals generated from the reaction of Fe3+/Fe2+ withtert-butyl hydroperoxide and the effect of lanthanide ions

The inhibitory effects of lanthanide ions on the generation of free radicals from the reaction of Fe³⁺ and Fe²⁺ withtert-butyl hydroperoxide (^tBuOOH) were investigated by electron spin resonance (ESR) utilizing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. Peroxyl, alkoxyl, and carbon-centered free radicals generated from Fe³⁺-^tBuOOH system were successfully trapped by DMPO, whereas peroxyl radicals were not trapped in Fe²⁺-^tBuOOH system. Peroxyl and alkoxyl radicals are initial radical species generated from Fe³⁺ and Fe²⁺ systems, respectively. The carbon-centered radicals (^⋅CH₃) might be attributed to β-scission reaction of these alkoxyl radicals. The ESR signals of DMPO adducts of these radicals were quenched in the presence of lanthanides (Ln³⁺ or [Ln(cit)₂]³⁻), in concentration-dependent fashion. Moreover, the quenching effect of Ln³⁺ is closely related to the time the Ln³⁺ was added into the free-radical-triggered systems. The results reveal that there might be various mechanisms responsible for inhibiting generation and transformation of the free radicals. If Ln³⁺ and iron react with peroxide simultaneously, the complex formation of Ln³⁺ with^tBuOOH will be the main mechanism of the competitive inhibitory effect of Ln³⁺. Whereas if Ln³⁺ is added after iron, the inhibitory effect on the ESR signal of DMPO adducts might be interpreted preferentially by the coordination and magnetic dipole-dipole interaction between Ln³⁺ and DMPO adducts.     

ESR investigations of burnt soil

Electron spin resonance (ESR) of transition metal ions (Mn^2?, Fe³⁺), radiation induced centres and pyrolytically formed radicals was studied to distinguish between burnt and unburnt soil. A testfire place and samples from an archaeological site were analyzed. The concentration of radiation induced centres decreases and pyrolytically formed radicals appear in a thermal annealing experiment. The spectral pattern of iron and manganese resonances changes during the heating process. These signals are useful to estimate temperature and atmosphere of the heating event. Chemithermoluminescence (CTL) of the soil was studied and could reveal its thermal history, too.     

Synthesis,Spectroscopic Characterization and Redox Reactivity of Some New N-(2,6-Di-Tert-Butyl-L-Hydroxyphenyl) Salicylaldimines

New substituted N- (2,6-Di-tert-butyl-l-hydroxyphenyl) Salicylaldimines (L_xH) were prepared by the condensation of various hydroxy and methoxy salicylaldehyde derivatives and 2,6-Di-tert-butyl-4-aminophenol and characterized by elemental analysis, IR, UV-Vis, ¹H NMR spectroscopy, as well as ESR studies of the oxidation products of L_xH. It was found that L_xH, unlike analogous electron-withdrawing C1, Br, NO₂ bearing derivatives, in the solid state exist both in associated and non-associated forms. UV-Vis and ¹H, NMR studies show that L_xH in solutions exists both in phenolimine and ketoamine tautomer forms. In addition, alcohol solutions of L_xH exhibited a new band in the region of 630-675 run. The ESR studies of one -electron oxidation of L_xH, in the condition of THF, CHC1₃ and toluene solutions at 300 K, indicate the formation of corresponding primary or secondary phenoxyl radicals. It was found that the stability and conversion pathway of the primary phenoxyl radicals are dependent upon both kind and position of the substituents in salicylaldehyde moiety of L_xH. For some L_xH without observation of primary phenoxyl radicals, the secondary Coppinger's type radical was detected. The ESR parameters of all radical intermediates have been determined.     

Decomposition of the angular ESR spectra of fossil tooth enamel fragments

The ESR spectra of a fragment of fossil tooth enamel were measured by rotating it in 10° increments over 360° around its three major axes. We used an automated simulated annealing (SA) procedure for the mathematical decomposition of the spectra. The SA approach is particularly robust in finding global solutions rather than getting stuck in local minima. All angular measurements could be fitted with four Gaussian lines, all of which could be attributed to components of CO₂^? radicals. The results imply that the tooth enamel fragment contains at least two different types of oriented CO₂^? radicals, plus about 9% of non-oriented CO₂^? radicals. The oriented components were tentatively attributed to axial and orthorhombic CO₂^? radicals. Their explicit locations in the crystal domains of the tooth enamel remain unresolved.     

Proton exchange in stable nitroxyl radicals of the imidazoline and imidazolidine series

The influence of pH on the ESR spectra of six nitroxyl radicals was studied. Hyperfine splitting constants, a_N, and g factors differ in protonated (RH⁺) and nonprotonated (R) forms of the radicals. Proton exchange rates between R and RH⁺ are either fast, moderate, or slow on the ESR time scale, depending on the pK_a of the radical. For moderate exchange rates, the temperature dependence of the proton exchange rate was studied. Quantum chemical methods were used to calculate the magnetic parameters of ESR spectra in R and RH⁺ forms for four of the radicals studied. All the radicals studied may be used as “pH probes.” One of the radicals was covalently bound to protein to give a macromolecular probe, which is recommended for pH studies in biological systems.     

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu²⁺-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu²⁺ lattice sites, Cu²⁺(I) and Cu²⁺(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: g_x ?=?2.0201?±?0.002, g_y ?=?2.0900?±?0.002, g_z ?=?2.1634?±?0.002, A_x ?=?(30?±?2)?×?10^?4?cm^?1, A_y ?=?(40?±?2)?×?10^?4?cm^?1 and A_z ?=?(154?±?2)?×?10^?4?cm^?1. It was found that Cu²⁺ enters the lattice substitutionally. The ground-state wavefunction of the Cu²⁺ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.