烯丙醇电还原自由基中间产物的ESR研究

烯丙醇电还原自由基中间产物的ＥＳＲ研究张敬东，旷亚非，黄树坤，谢乃贤（湖南大学化学化工系，长沙４１００８２）汪风珍，陈德文（中南工业大学测试中心，长沙４１００８３）（中国科学院化学研究所，北京１０００８０）Ｈｏｒａｎｙｉ［１］、陈剑［２］等人对酸性水...     

酸性化学镀镍中次亚磷酸钠阳极氧化行为的研究

采用线性电位扫描和交流阻抗法研究了酸性化学镀镍过程中还原剂次亚磷酸钠的阳极氧化行为。结果表明,次亚磷酸钠的氧化是一个复杂的电化学过程,其阳极氧化行为受本身浓度、溶液温度、阳极扫描速度以及Ｎｉ＾２＋的影响,在其氧化反应之前可能存在异相界面转化步骤,该步骤成为整个氧化过程的控制步骤。     

炔丙醇电还原自由基中间产物的ESR研究

Electrochemical-ESR technique (ex situ method) with spin traps phenyl tert-butyl nitrone (PBN) and 5,5-dimethyl-1-Pyrroline-1-oxide (DMPO) has been applied to the detection of radical intermediates produced during electroreduction of propargyl alcohol (PA) at platinized platinum electrode in an acidified alcohol-aqua solution. Propargyl radical and H have been detected by PBN and DMPO, respectively. As a result of the discovery of these radicals, an evidence for a radical mechanism of the electroreduction of PA put forward by some authors might be obtained beyond all doubt.     

ESR自旋稳定化技术在漆酶化学中的应用

用ESR自旋稳定化技术对十六个儿茶酚类底物的漆酶催化氧化反应进行了ESR追踪,捕获到相应的半醌自由基．结果表明,ESR自旋稳定化技术的运用,开辟了一条在静态条件下用漆酶／O2体系获取高稳态浓度半醌自由基的有效途径．     

荧光自旋捕获探针的合成及ESR捕获研究

设计合成了具有荧光基团的新型硝酮类自由基捕获探针并对其结构进行了表征.自由基捕获实验结果表明,该探针能实现对超氧阴离子自由基与碳中心自由基的捕获.此外,该自由基捕获探针反应产物的荧光强度与被捕获自由基浓度之间存在相关性,有望建立依据荧光强度分析被捕获自由基浓度的新方法.     

碳纳米管表面的无钯活化化学镀镍研究

本文提出碳纳米管表面无钯活化的化学镀镍方法.碳纳米管经硝酸氧化和碱中和后表面生成羧基,利用羧基吸附镍离子,之后吸附的镍离子被化学还原为镍的纳米微粒并成为化学镀镍的催化活性中心.红外吸收光谱和电子显微镜观察等证实了上述活化过程的机理.实验表明,新的活化方法对碳纳米管表面化学镀是切实可行的,文中同时对化学沉积层的不同形貌进行讨论.     

含铁离子的XO/HX体系对糖类分子氧化作用的ESR研究

用自旋俘获方法直接检测含铁的黄嘌呤氧化酶/次黄嘌呤体系中由糖产生的自由基,发现该体系中除了产生羟基自由基外,还产生烷(氧)基自由基,且糖的浓度越高,体系中产生的烷(氧)基自由基也越多.这表明含铁的黄嘌呤氧化酶/次黄嘌呤体系对糖类分子有氧化作用,且糖的浓度越高,氧化作用越强,对机体的损伤越大.应用含硒抗体酶可有效清除烷(氧)基自由基,显示出很强的抗氧化能力.     

EMPO-酪氨酸共价链接物的合成与ESR研究

本文设计并试验了一种环状硝酮(5-乙酰基-5-甲基吡咯啉环氮氧化合物, EMPO)与酪氨酸氨基的共价链接方法, 并用ESR实验检验了链接后所得探针对自由基的捕获性能. 新探针的特色体现在以下两方面: (1) 对氨基酸氨基的链接方法几乎适用于所有多肽(或蛋白质); (2) 环状硝酮捕获自由基的效率更高.     

化学镀镍过程中丙酸作用的机理研究

利用循环伏安法和红外漫反射光谱法研究化学镀镍过程中丙酸的作用机理. 不同丙酸浓度下的循环伏安曲线表明,丙酸能同时促进Ni^2＋的还原和H₂PO^-₂的氧化.根据丙酸分别与NaH₂PO₂和NiSO₄共存时镍基体上吸附物的红外漫反射光谱变化,推断丙酸是通过与NaH₂PO₂和Ni^2＋形成表面络合物来促进化学沉积的. 丙酸能与NaH₂PO₂形成分子间氢键,促使P-H键断裂并生成·PHO^-₂中间物,从而提高H₂PO^-₂的氧化速度; 同时,丙酸以其-OCO-官能团与Ni^2＋生成桥式配合物,有利于加速Ni^2＋的沉积. H₂PO^-₂氧化速度的提高有助于磷的沉积,从而增大了化学镀层中的磷含量.     

铝表面前处理及化学沉积镍初期行为

利用开路电位-时间(EOCP-t)曲线,研究铝表面经浸镍和化学预镀镍前处理后,化学沉积镍的初期行为;通过扫描电子显微镜(SEM)观察铝表面经前处理后的表面形貌.结果表明:未经及经前处理的铝表面,化学沉积镍的初期行为都经历去氧化膜、活化、混合控制以及化学沉积过程.经过浸镍和化学预镀镍前处理后的铝表面附着细小的镍颗粒.依据EOCP-t和SEM的最佳实验结果,在含有络合剂和还原剂的碱性预镀镍溶液中,经二次化学预镀镍前处理,成功实现铝基底弱酸性化学镀镍.所获得的化学镀镍层与铝基底结合牢固,呈团颗粒状形貌和非晶态结构.     

化学镀镍液中次磷酸钠在线检测仪的设计

基于次磷酸钠的化学性质和碘溶液的光谱吸收特征，将现有的分光光度计进行改造，采用流动注射光度分析法测定镀液中次磷酸钠的含量，借助于计算机控制，实现次磷酸钠的在线检测，能满足生产工艺分析的要求。     

毛细管柱GC/MS/ESR 联用研究自由基PBN加合物

采用硅烷化方法，并用石英毛细管柱气相色谱与双聚焦质谱仪组成的ＧＣ／ＭＳ联用系统，首次成功地分析鉴别了六种自由基的ＰＢＮ加合物，总结了这些自旋加合物的断裂规律。实验结果表明，硅烷化结合ＧＣ／ＭＳ和自旋捕捉ＥＳＲ联用技术是确定活泼自由基的一种有效方法。     

3-己炔-2,5-二醇电还原中间产物的ESR研究

3-己炔 - 2 ,5-二醇 ( HD)是半光亮电镀镍的一种添加剂 ,它在电镀镍时也发生电还原反应 .我们采用 GC- MS谱对其电还原产物作过分析 ,表明它与 1 ,4-丁炔二醇电还原类似 [1] ,在 p H值 1～ 2时 ,主产物为 3-己炔、己烷 ;p H值 >3.5时 ,主产物为 3-己烯 - 2 ,5-二醇和 2 ,5-己二醇 .对这类炔二醇电还原过程尚未见深入研究 ,为深入了解 HD在不同 p H值的溶液中的电还原过程 ,我们对其电还原中间产物作了电化学 - ESR研究 .1　实验部分PARC公司电化学测试系统 (美国 ) ,其中包括 Model 1 73恒电位 /恒电流仪 ,Model 30 3A汞电极装置 ;…     

Detection of the reduced forms of radical adducts on the ESR trace using HPLC‐electrochemical detector‐ultraviolet absorption detector‐electron spin resonance‐MS

To detect and identify the electron spin resonance (ESR) silent forms of the α‐(4‐pyridyl‐1‐oxide)‐N‐tert‐butylnitrone (4‐POBN) radical adducts, an electrochemical detector (ECD) was employed as a reactor in the HPLC‐ECD‐UV absorption detector‐ESR‐MS (HPLC‐ECD‐UV‐ESR‐MS). The ECD was employed to regenerate the radical forms from the reduced forms. The reduced forms of the 4‐POBN/pentyl radical adducts were analyzed using the HPLC‐ECD‐UV‐ESR‐MS. On addition of the ECD applied potential of +0.3 V, a peak appeared on the ESR trace of the HPLC‐ECD‐UV‐ESR‐MS analyses, indicating that the radical forms are regenerated from the reduced forms. The HPLC‐ECD‐UV‐ESR‐MS analyses were also performed for the reaction mixtures of phenylhydrazine with CuCl₂. Two peaks (peaks I and II) were detected on the UV trace (300 nm) of the HPLC‐ECD‐UV‐ESR‐MS. The mass spectra showed that the peak I and peak II compounds are radical and reduced forms of the 4‐POBN/phenyl radical adducts under the ECD applied potential of 0.0 V. Peak I was only detected on the ESR trace under the ECD applied potential of 0.0 V. In addition to peak I, peak II appeared on the ESR trace under the ECD applied potential of +0.3 V, indicating that the reduced forms are oxidized to the corresponding radical forms.     

ESR and quantum chemical studies of the structures and thermal transformations of the radical cations of vinylcyclopropane in irradiated frozen Freon matrices. Simulation of radical processes in solids

Thermal transformations of vinylcyclopropane radical cations (VCP^.+) in X-ray-irradiated frozen Freon matrices (CFCl₂CF₂Cl and CFCl₃) were studied by ESR; radical processes involving VCP^.+ in solid VCP were simulated.Gauche- andanti-VCP ^.+ were found to be the primary radical cations, however, the former, unlike the latter, is stable only under gas-phase conditions. The thermodynamic equilibrium betweenanti-VCP^.+ and its less stable distonic form,dist(90,0)-C ₅H₈ ^.+, is established in frozen Freon matrices and the VCP host matrix; the structure of dist(90,0)****-C ₅H₈ ^.+ is stabilized by a molecule ofanti-VCP. In CFC₃, along with dist(90,0)-C₅H₈ ^.+,-dimeric resonance [anti-VCP]₂ ^.+ complex was detected. A general scheme of the transformations of VCP^.+ in the solid phase has been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 11–21, January, 1994.     

Radical Products in the Chemical Oxidationof Amines. An ESR Study of Secondary CationRadicals from Aniline and Derivatives of 1,2-Phenylenediamine

Summary.  The oxidation of aniline and some derivatives of 1,2-phenylenediamine was performed by the system Pb(CH₃COO)₄—CF₃COOH—CH₂Cl₂. An ESR investigation of the oxidized aniline confirmed the presence of secondary cation radical. Its structure was determined by comparison of its ESR spectrum with those of cation radicals prepared from derivatives of 1,4-phenylenediamine. The oxidation of 1,2-phenylenediamine and its derivatives leads to the formation of either primary or secondary cation radicals, the latter having the character of substituted dihydrophenazinium cation radicals. Received August 17, 2000. Accepted (revised) October 16, 2000     

Controllable preparation of highly dispersed TiO2 nanoparticles for enhanced catalytic oxidation of dibenzothiophene in fuels

The aggregation of nanoparticle catalysts is one of the main problems in catalytic reactions. In this study, a series of TiO₂ nanoparticle catalysts with various dispersions were prepared and applied in the catalytic oxidation of dibenzothiophene (DBT) systems. Compositions and structures of the as‐prepared samples were analyzed by means of wide‐angle X‐ray diffraction, Raman and X‐ray photoelectron spectroscopies. The dispersions of TiO₂ nanoparticles were controlled by calcining at various temperatures and verified using transmission electron microscopy. It was found that the activities of TiO₂ nanoparticles in the catalytic oxidation of DBT were positively correlated with the dispersions. TiO₂ nanoparticles calcined at 500 °C (500‐TiO₂) showed the best catalytic activity and the oxidation of DBT reached 99.8% under mild conditions. Based on the results of GC–MS analysis, radical trapping experiments and electron spin resonance spectra, ^?O₂^? radicals were proved to be the main active species in the oxidation process, and a mechanism is proposed. Meanwhile, the recycling performance of 500‐TiO₂ was investigated, and no obvious decrease was observed after six recycles.