OH自由基总反应性的实地测量

OH自由基作为大气氧化性的重要衡量指标,其去除途径仍无法完全准确地被量化,OH自由基总反应性作为描述OH自由基总去除能力和大气氧化性的重要参数,是OH自由基收支闭合分析的关键参数.OH自由基活性高、寿命短,其反应活性的准确测量具有挑战性.本综述总结了OH自由基总反应性的实地测量方法,并对移动注射-激光诱导荧光法、闪光光解-激光诱导荧光法、化学离子质谱法和相对反应活性法四种方法的测量原理、仪器架构等进行了系统阐述,综合分析认为闪光光解-激光诱导荧光法是目前OH自由基总反应性测量技术的发展方向.同时进一步总结了OH自由基总反应性在城市、森林和郊区等大气环境下的化学行为等,并对研究难点和可能的重点研究方向进行了探讨.     

氢氧根离子在TiO2薄膜电极上的吸附行为和光氧化动力学

在醇的水溶液中，应用电化学方法研究了OH－在TiO2薄膜电极上的吸附行为和光氧化动力学.实验结果表明，OH－在TiO2表面的吸附模型符合Langmuir等温吸附方程式，其光氧化动力学行为能用Langmuir-Hinshelwood动力学方程来描述.在光强足够大时，光电流和OH－在TiO2表面的吸附浓度成正比，这表明，光生空穴仅氧化吸附于TiO2表面的OH－，同时吸附的水分子则不能被氧化.在醇浓度足够高的溶液中，自由基OH•和电子之间的复合反应几乎不发生，这时整个光氧化反应的速控步骤是光生自由基OH•的生成.     

气体放电对SO_2和SO_3~(2-)氧化的影响

研究气体放电对SO2和亚硫酸盐氧化的影响,采用了直流电源和交直流叠加电源进行气体放电.结果表明,气体放电对于SO2氧化促进作用很少;但对溶液中的SO2-3的氧化则有明显促进作用.通过对两个反应过程的机理分析,认为亚硫酸盐溶液氧化快是因为气体放电产生的OH等自由基和液相里的亚硫酸根起作用,引发链反应,促进了溶液中四价硫被空气中的O2氧化为六价硫的过程.而气相中的SO2与OH等自由基作用不能形成链反应,所以影响不明显.实验表明,选择交直流叠加电源进行气体放电比用纯粹直流电源放电效果更好.     

气体放电对SO2和SO32－氧化的影响

研究气体放电对SO2和亚硫酸盐氧化的影响,采用了直流电源和交直流叠加电源进行气体放电.结果表明,气体放电对于SO2氧化促进作用很少;但对溶液中的SO32－的氧化则有明显促进作用.通过对两个反应过程的机理分析,认为亚硫酸盐溶液氧化快是因为气体放电产生的OH等自由基和液相里的亚硫酸根起作用,引发链反应,促进了溶液中四价硫被空气中的O2氧化为六价硫的过程.而气相中的SO2与OH等自由基作用不能形成链反应,所以影响不明显.实验表明,选择交直流叠加电源进行气体放电比用纯粹直流电源放电效果更好.     

掺硼金刚石膜电极表面产生羟基自由基的原位ESR研究

建立了原位电化学-电子顺磁共振(ESR)方法,系统研究了掺硼金刚石(BDD)膜电极表面在水溶液中的羟基自由基(·OH)产生规律.结果表明,在高于析氧电位时,·OH的生成速率随着阳极电位的升高、电流密度的增加而增大,增加速率逐渐减缓.与此同时,与氢终端的BDD膜电极相比,氧终端的BDD膜电极表面因具有较好的亲水性而具有更高的·OH产生能力.在电化学氧化处理有机废水的过程中,电极表面处于氧终端的状态,有利于·OH产生并保持较高的活性.溶液pH值也在一定程度上影响·OH生成反应,酸性溶液中,BDD膜电极表面的·OH产生能力强于在中性或碱性溶液中.进一步研究发现,BDD膜电极表面还可能生成O3-·0自由基.本研究为深入探索BDD膜电极表面·OH的产生机制提供了研究手段,为阐述BDD膜电极电极在污染物处理中高效性的本质提供了有效的证据.     

Nα-磷酰化二肽甲酯的氧化和氧化中电子转移的研究

用纳秒级脉冲辐解动态吸收光谱法研究了Ｂｒ２－自由基引发Ｎ－（Ｎ－二异丙氧基磷酰化甲硫氨酰）色氨酸甲酯的氧化和电子转移过程，结果表明：Ｂｒ２－自由基同步氧化Ｎα－磷酰化二肽中的甲硫氨酸和色氨酸部位，并发生由色氨酸向含硫三电子键自由基的分子内电子转移过程，求算了有关动力学参数，推导了氧化和电子转移机理     

利用瞬态吸收光谱技术研究水体中苯与亚硝酸的交叉反应机理

利用瞬态吸收光谱技术进行了有氧、无氧条件下苯与亚硝酸水溶液复相体系的交叉反应机理研究 ,初步考察了这些瞬态物种的生长与衰减等行为 ;并对其光解产物进行了GC/MS分析 .研究表明 ,HNO2 在 3 5 5nm紫外光的照射下可产生·OH和NO+ ,·OH自由基和苯反应生成C6H6 OHadduct ,反应速率常数为 8 9× 10 9L·mol-1·s-1,在有氧条件下C6H6 OHadduct进一步氧化为C6H6 OHO2 ,反应速率常数 3 3× 10 8L·mol-1·s-1;NO+ 自由基和苯作用形成C6H6 NO+ πcomplex ,然后进一步分解     

某些还原性生物分子对竹红菌甲素敏化产生^1O~2的抑制作用

存在还原性的生物分手如甲硫氨酸、尿酸和还原性谷胱甘肽时,竹红菌甲素经受单电子还原形成甲素的半醌自由基、在去氧溶液中观察到了甲素半醌负离子自由基的ESR信号.在充氧的溶液中检测到了超氧负离子自由基.还原剂的存在降低了单重态氧的生成并引起了超氧负离子自由基的生成.     

某些还原性生物分子对竹红菌甲素敏化产生^1O~2的抑制作用

存在还原性的生物分子如甲硫氨酸、尿酸和 还原性谷胱甘肽时,竹红菌甲素经受单电子还原形成甲素的半醌自由基、在去氧溶液中观察到了 甲素半醌负离子自由基的ESR信号.在充氧的溶液中检测到了超氧负离子自由基.还原剂的存在降低了单重态氧的生成并引起超氧负离子自由基的生成.     

(SO4.-)诱导含硫三电子键自由基的生成机理研究

运用２４８ｎｍ激光光解瞬态吸收光谱,研究了ＳＯ４＾·－单电子氧化Ｄ－甲硫氨酸＊Ｍｅｔ）、Ｌ－甲硫氨酸甲酯（ＭＭＥ）和甲硫氨酰甲硫氨酸（Ｍｅｔ－Ｍｅｔ）的反应过程。观察到反应过程中生成３种含硫三电子键自由基中间体,［Ｓ∴Ｓ］＾＋、［Ｓ∴Ｎ］＾＋［Ｓ∴Ｏ］,并分析了反应机理。     

磷酰化与非磷酰化蛋氨酸水溶液的脉冲辅解研究

•OH radical induced oxidation of methionine and N-phosphoryl methionine in aqueous solutions has been investigated using optical pulse radiolytical technique, the influence of N-phosphoryl group on the radiolytical processes of methionine has been explained by molecular structure and the rate constants of oxidation of N-phosphoryl methionine (NDM) by the •OH radicals at different pH values have been determined. This research result suggests that the phosphonate ester has a coordinating effect on the radioprotection of methionine to the biological systems.     

磷酰化与非磷酰化蛋氨酸水溶液的脉冲辐解研究

蛋氨酸能快速清除导致辐射损伤的·OH自由基，在放射生物学上是一类很重要的辐射保护剂，因此，引起了人们的广泛关注［l一到．生物大分子的磷酸化作用亦越来越受到重视，特别是近年来基因调控研究发现，许多蛋白质和生物酶只有被磷酸化氧化才具有生理活性，文献［4－6］报导蛋     

Reactions of hydrated electron with various radicals: spin factor in diffusion-controlled reactions

The reactions of hydrated electron (eaq-) with various radicals have been studied in pulse radiolysis experiments. These radicals are hydroxyl radical (*OH), sulfite radical anion (*SO3-), carbonate radical anion (CO3*-), carbon dioxide radical anion (*CO2-), azidyl radical (*N3), dibromine radical anion (Br2*-), diiodine radical anion (I2*-), 2-hydroxy-2-propyl radical (*C(CH3)2OH), 2-hydroxy-2-methyl-1-propyl radical ((*CH2)(CH3)2COH), hydroxycyclohexadienyl radical (*C6H6OH), phenoxyl radical (C6H5O*), p-methylphenoxyl radical (p-(H3C)C6H4O*), p-benzosemiquinone radical anion (p-OC6H4O*-), and phenylthiyl radical (C6H5S*). The kinetics of eaq- was followed in the presence of the counter radicals in transient optical absorption measurements. The rate constants of the eaq- reactions with radicals have been determined over a temperature range of 5-75 degrees C from the kinetic analysis of systems of multiple second-order reactions. The observed high rate constants for all the eaq- + radical reactions have been analyzed with the Smoluchowski equation. This analysis suggests that many of the eaq- + radical reactions are diffusion-controlled with a spin factor of 1/4, while other reactions with *OH, *N3, Br2*-, I2*-, and C6H5S* have spin factors significantly larger than 1/4. Spin dynamics for the eaq-/radical pairs is discussed to explain the different spin factors. The reactions with *OH, *N3, Br2*-, and I2*- have also been found to have apparent activation energies less than that for diffusion control, and it is suggested that the spin factors for these reactions decrease with increasing temperature. Such a decrease in spin factor may reflect a changing competition between spin relaxation/conversion and diffusive escape from the radical pairs.     

Methanesulfinic acid reaction with OH: mechanism, rate constants, and atmospheric implications

The mechanism for the atmospheric oxidation of methanesulfinic acid (MSIA) has been studied. This is the first theoretical study of the reaction between MSIA and the OH radical. All the possible channels in this reaction have been studied theoretically, and their corresponding rate constants have been evaluated under the variational transition-state theory (VTST) formalism. Two different products can be formed: the CH3S(O)2 radical (which had been experimentally proposed as the only one), and sulfurous acid (H2SO3). The CH3S(O)2 radical can be formed directly or can form via an intermediate adduct, which yields to the radical through the elimination of a water molecule. For the first time, it is theoretically demonstrated that SO2 is formed in the addition channel of the DMS + OH reaction. The consequences of this result in the interpretation of the T-dependence of the SO4(2-)/MSA (methanesulfonic acid) quocient are analyzed. The competition between the unimolecular dissociation of the CH3S(O)2 radical and OH-addition to yield MSA is proposed as one of the possible multiple branching points (along the DMS + OH degradation scheme) influencing the T-dependence of the SO4(2-)/MSA relation.     

Reaction of the hydroxyl radical with phenol in water up to supercritical conditions

The rate constants for the reactions of phenol with the hydroxyl radical (OH*) in water have been measured from room temperature to 380 degrees C using electron pulse radiolysis and transient absorption spectroscopy. The reaction scheme designed to fit the data shows the importance of an equilibrium, giving back reactants (OH* radical and phenol) from the dihydroxycyclohexadienyl radical formed by their reaction, and the non-negligible contribution of the hydroxycyclohexadienyl radical absorption from H* atom addition. The accuracy of the reaction scheme and the reaction rate constants determined from it have been determined by the analysis of two different experiments, one under pure N2O atmosphere and the second under a mixture a N2O and O2. We report reaction rates for the H* and OH* radical addition to phenol, the formation of phenoxyl, the second-order recombination, the reaction of dihydroxycyclohexadienyl with O2, and the decay of the peroxyl adduct. Nearly all of the reaction rates deviate strongly from Arrhenius behavior.     

CH(A^2Δ)自由基被醇类分子猝灭动力学的温度效应研究

用266nm激光光解CHBr3产生CH自由基, 利用精密控温仪控制反应温度, 测定CH(A→X)荧光的时间分辨信号, 测量了290K至653K范围内CH(A)被乙醇、丙醇、丁醇猝灭的速率常数, 利用修正的碰撞配合物模型, 定性解释了在多极吸引势与活化势垒的双重影响下, 猝灭截面与温度间的关系。     

Mechanism for degradation of Nafion in PEM fuel cells from quantum mechanics calculations

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism.     

Resonance Raman spectrum of the solvated electron in methanol: simulation within a cluster model

The microsolvation of the CH(3)OH(2) hypervalent radical in methanol clusters has been investigated by density functional theory. It is shown that the CH(3)OH(2) radical spontaneously decomposes within methanol clusters into protonated methanol and a localized solvated electron cloud. The geometric and electronic structures of these clusters as well as their vibrational frequencies have been characterized. Resonance Raman intensities, associated with the s --> p transition of the unpaired electron, have been estimated for CH(3)OH(2)M(n) (M = CH(3)OH, n = 1-3) clusters. It is shown that with increasing cluster size the simulated spectra converge toward the resonance Raman spectrum of the solvated electron in methanol measured recently by Tauber and Mathies (J. Am. Chem. Soc. 2004, 126, 3414). The results suggest that CH(3)OH(2)M(n) clusters are useful finite-size model systems for the computational investigation of the spectroscopic properties of the solvated electron in liquid methanol.     

Ab initio prediction of the structure and vibration-rotation spectroscopic properties of Li2OH and Li2OH+

The equilibrium structures and potential energy surfaces of the Li2OH radical and the Li2OH+ cation in their ground electronic states have been determined from accurate ab initio calculations. The vibration-rotation energy levels and spectroscopic constants of three isotopic species (Li2OH, Li2OD, 6Li2OH) were calculated by a perturbational approach. The predicted spectroscopic constants may serve as a useful guide for detecting these species by vibration-rotation spectroscopy and for assigning their spectra.     

Matrix isolation infrared spectroscopic and theoretical study of the hydrolysis of boron dioxide in solid argon

The reaction of boron dioxide with water molecule has been studied using matrix isolation infrared spectroscopy. The boron dioxide molecules produced by codeposition of laser-evaporated boron atoms with dioxygen react spontaneously with water molecules to form OB(OH)2, which is characterized to have a doublet ground-state with two OH groups in the cis-trans form. Isotopic substitution results indicate that the hydrolysis process proceeds via a concerted two hydrogen atom transfer mechanism. The cis-trans-OB(OH)2 molecule is photosensitive; it decomposes to the OH x OB(OH) complex upon broadband UV-visible irradiation. The OH x OB(OH) complex is determined to have a (2)A' ground-state with a bent C(s) symmetry, in which the terminal oxygen atom of the OB(OH) fragment is hydrogen bonded with the hydroxyl radical. The OH x OB(OH) complex recombines to the cis-trans-OB(OH)2 molecule upon sample annealing.