水对环己烷-磷酸三丁酯体系γ辐解和脉冲辐解的影响(英文)

为确定辐解体系中烷烃单重态的来源,研究了水对环己烷(C6H12)-磷酸三丁酯(TBP)体系γ辐解和脉冲辐解的影响.水显著地抑制C6H12-TBPγ辐解体系中TBP酸式辐解产物的生成,酸式辐解产物的G值从无水体系的8.2降至水饱和体系的1.9,表明水分子既抑制了TBP自身辐解生成的TBP单重态,又通过阻断单重态C6H12与TBP之间的能量转移,消除了C6H12自身辐解对单重态TBP的酸式辐解产物的敏化作用.但在以二苯酮(Bp)为探针的TBP-Bp和C6H12-TBP-Bp脉冲辐解体系中,水的加入并未抑制辐解产物羰自由基的产额,其机理是,水分子通过与偕离子对反应而抑制C6H12单重态和TBP单重态的产生,但不影响羰自由基的生成.这也许是辐解体系中大部分(G=1.3)单重态C6H12和部分(G=0.8)单重态TBP来源于偕离子对[C6H12·+…e-]和[TBP·+…e-]的复合的直接证据.由于极性较大,水可用作偕离子对的高效捕捉剂.     

正己烷—TBP体系的光化学研究

用低压汞灯照射, 研究了n-C_6H_(14)—TBP体系的光化学反应。通过与γ辐解结果对比和动力学分析, 证实了γ辐解n-C_6H_(14)—TBP体系中, 激发能转移是能量传递的主要形式, 并讨论了亚激电子在能量传递中的作用。     

N,N-二正丙基丁酰胺对辐照磷酸三丁酯的保护效应

本文研究N,N-二正丙基丁酰胺(DPBA)对辐照磷酸三丁酯(TBP)的保护作用, 实验发现在~(60)Coγ辐照下, 它对TBP~*。具有双重能量转移效应, DPBA本身辐解, 属于“自我牺牲”机理。应用稳态原理得出辐解TBP的两种激发态分子的能量抑制方程。     

二氟沙星在中性水溶液中的光化学性质(英文)

对二氟沙星在中性水溶液中的光化学性质进行了研究.在pH值为7.17的水溶液中二氟沙星的紫外吸收峰位于273 nm(摩尔消光系数ε=33000 dm3·mol-1·cm-1),323 nm(ε=15500 dm3·mol-1·cm-1),335 nm(ε=15500 dm3·mol-1·cm-1)处.荧光吸收和发射光谱均显示二氟沙星具有pH效应,其pKa(电离平衡常数)测定分别为5.9和9.8.二氟沙星的荧光量子产额较低,在pH=3.00时达到最大值,为0.06.同时对二氟沙星在中性水溶液中的激光光解和脉冲辐解进行详细研究.激光光解研究发现在水溶液中二氟沙星的三重激发态位于620nm,其摩尔消光系数为7900 dm3·mol-1·cm-1.通过能量转移的方法得到其三重激发态的能量为263.5 kJ·mol-1,三重激发态的量子产额为0.21.在激光激发下,二氟沙星进行单光子电离其量子产额为0.02.脉冲辐解研究表明二氟沙星可以与水合电子(e-aq)及羟基自由基(·OH)快速反应,其二级反应动力学常数分别为1.72×1010和1.0×1010dm3·mol-1·s-1.本文对二氟沙星光化学性质的研究有助于确定其光敏毒性的产生机理.     

乙醇辐解机理研究

本文研究了氧、温度和4-甲基-4-苯基-2-戊酮(Mpp)对乙醇辐解的影响。Mpp在实验使用的浓度范围内对乙醛的G值没有影响, G(2,3-丁二醇)值随Mpp浓度增加而下降, 最后达0.9恒值。使用Mpp求得原初过程形成的G_(H_2)=1.9, 动力学处理求得G_H=2.4, k_(12)/k_(11)=(11.9±1.8)×10~3。实验证明Mpp清除了体系中的H原子, 抑制了CH_3CHOH自由基的形成, 从而抑制了2,3-丁二醇的生成, 但不影响乙醛的产额。这一研究否定了传统文献所述的在γ辐解乙醇时相当量的羟乙基自由基歧化反应生成乙醛。本文还对乙醇γ辐解机理进行了讨论, 并求得了乙醇辐解的物料平衡。     

气相色谱法测定水中溴氰菊酯

采用气相色谱法-电子捕获检测器(GC- ECD)对水中溴氰菊酯进行检测.取10 mL水样,加入0.4g氯化钠,经环己烷萃取后,有机相干燥、氮吹浓缩,用带电子捕获检测器的气相色谱仪检测,外标法定量.结果表明,溴氰菊酯在2.0 ～40.0 μg/L范围内线性关系良好,相关系数为0.999 8.方法检出限为:0.40 μg/...     

鬼臼毒素及VP-16化学活性的激光光解与脉冲辐解研究

运用激光光解与脉冲辐解技术, 对用于肿瘤治疗的鬼臼毒素(PPT)和依托泊甙(VP-16)的化学活性进行了详细的研究. 结果表明: 鬼臼毒素及VP-16经248 nm的激光激发可光电离, 且光电离的量子产额比较高, 有很强的光敏性, 而且还有多个活性基团分别与水合电子、氢原子、羟基自由基作用生成不同的瞬态粒子, 并推断出相应的反应机理. 为医学工作者进一步了解、利用鬼臼毒素和VP-16, 探讨其抗肿瘤机理提供科学的参考, 也为化学工作者进一步合成高效、低毒的抗肿瘤药物提供新思路.     

TBP-DPPP两元体系辐射保护效应研究

本文报道磷酸三丁酯(TBP)-苯基膦酸二苯酯(DPPP)两元体系在γ-辐射作用下 DPPP 的辐射保护效应(a值),测定了该体系各类主要辐解产物的 G 值与 X_(DPPP)(DPPP mole 分数)的关系,并按 WAS 方程计算了 DPPP在两元体系中的辐射保护效应α值,还与其他辐射保护剂(苯、TOA、DBPP、DBBP)**的α值作了对比,表明DPPP 具有最大辐射保护能力。     

硝酸铀酰—硝酸—磷酸三丁酯体系的反萃取动力学研究

本文采用恒界面池法和上升单液滴法研究了UO_2(NO_3)_2/HNO_3/TBP-环己烷体系的反萃取动力学。得出扩散控制下的反萃速率方程为R=k_1[U]_(O)[TBP]_(O)~(-1.17)[HNO_3]~(-1.70;在恒定硝酸浓度下化学反应控制的反萃速率方程为R=k_2[U]_(O)[TBP]_(O)~0,并对二种速控类型下的反萃机制进行了讨论。     

AOT微乳液中通过水化电子产额调控合成BaSO_4纳米纤维

通过γ-辐照含有K2S2O8和BaCl2的二(2-乙基己基)琥珀酸酯磺酸钠(AOT)反相微乳液,将S2O82-通过辐射还原实现了SO42-的原位缓释,从而成功制备出BaSO4纳米纤维单晶,并进一步制得多层次的纳米纤维束结构.在此基础上,通过改变水与表面活性剂物质的量之比(ω值)、改变钡盐阴离子和在微乳液连续相添加芳香化合物等手段来调节水化电子(e-aq)产额,控制微乳液水池中S2O82-的还原和SO42-的缓释速率,成功实现了对BaSO4纳米粒子形貌的调控:随着ω值的增加或剂量率的增加,e-aq产额增加,从而加快了SO42-的释放,不利于BaSO4纳米纤维的生成;采用Ba(NO3)2为钡源时,NO3-能有效地降低e-aq产额和S2O82-的还原速率,因而在较高的剂量率和较高ω值下能得到BaSO4纳米纤维;在微乳液油相中加入甲苯来捕获油相中过量电子(e-oil),降低e-aq产额,从而在较高的剂量率下得到BaSO4纳米纤维.研究结果表明:通过e-aq产额调控纳米粒子形貌的机理在BaSO4纳米粒子的制备中得到很好体现.     

INFLUENCE OF ELECTRON-WITHDRAWING SUBSTITUENTS IN THE OXAPHOSPHOLE RING ON THE AXIAL CONFORMATIONAL TRANSMISSION IN Pv COMPOUNDS

Abstract

A MNDO and 300-MHz ¹H NMR study of some trigonal-bipyramidal (TBP) five-coördinated phosphorus (P^v) compounds is reported. It is shown by the MNDO calculations that, in the oxaphosphole P^v TBP compounds 5a-c, the electron distribution in the axial bonds of the TBP is affected by the electronegativity of the substituent at C₄ of the oxaphosphole ring. With increasing electronegativity of the substituent at C₄, the electron density on the axial exocyclic oxygen atom O₁ decreases whereas the electron density on the axial endocyclic atom O₁ increases. This is supported by a ¹H NMR conformational analysis of the C₁[sbnd]C₂ bond of the oxaphosphole P^v TBP compounds 6–11. The gauche(-) rotamer fraction (O¹ and O¹ trans situated) of these compounds, which is correlated to the electron density on O₁, is reduced to 30% as compared to the absolute axial g^?rotamer fraction (59%) of the dioxaphosphole P^v TBP compound 13, most likely because of the presence of the carbonyl group at C₄ of the oxaphosphole ring. So, both the ¹H NMR and MNDO study show that electron withdrawing substituents on the oxaphosphole ring of P^v TBP compounds reverse the electron transfer in the axial P[sbnd]O bonds of the TBP (as compared to dioxaphosphole compounds), from exocyclic O₁ towards endocyclic O₁.     

ELECTROCHEMISTRY OF EXCITED MOLECULES: PHOTO-ELECTROCHEMICAL REACTIONS OF CHLOROPHYLLS*

Abstract— Semiconductors with a sufficiently large energy gap, in contact with an electrolyte, can be used as electrodes for the study of electrochemical reactions of excited molecules. The behavior of excited chlorophyll molecules at single crystal ZnO-electrodes has been investigated. These molecules inject electrons from excited levels into the conduction band of the electrode, thus giving rise to an anodic photocurrent. The influence of various agents on this electron transfer has been studied. In the presence of suitable electron donors (e.g., hydroquinone, phenylhydrazine) in the electrolyte chlorophyll molecules, absorbing quanta, mediate the pumping of electrons from levels of the reducing agents into the conduction band of the semiconductor-electron acceptor. The electron capture by the semiconductor electrode is irreversible, when an adequate electrochemical gradient is provided in the electrode surface. Some properties of excited chlorophyll at semiconductor electrodes (unidirectional electron transfer, highly efficient charge separation, chlorophyll as electron pump and able to convert electronic excitation into electric energy) show similarity to the behavior of chlorophyll in photosynthetic reaction centers.     

用甲基铝氧烷活化的氯化稀土催化剂合成高顺式窄分布聚丁二烯

以NdCl3.4L(配体L为膦酸三丁酯TBP、膦酸三苯酯TPP、膦酸二异辛酯P204)为主催化剂(简称[Nd])、甲基铝氧烷(MAO,简称[Al])为助催化剂和环己烷为溶剂,进行1,3-丁二烯聚合的研究.考察了配体对丁二烯聚合反应活性的规律及MAO用量、催化剂陈化时间、溶剂种类对聚合的影响;并对聚合物进行NMR,IR和GPC的表征.结果表明,3种配体的聚合活性顺序为TBP>P204>TPP;当[Al]/[Nd]为30时,聚合物的分子量分布指数达到1.20;30℃陈化时,聚丁二烯cis-1,4结构均大于97%;与正己烷、甲苯溶剂对比来看,环己烷体系所得聚合产物的分子量分布相对较窄、产率较高.     

THERMODYNAMICS OF THE PRIMARY REACTIONS OF PHOTOSYNTHESIS

Abstract. It appears to be widely believed that fundamental thermodynamic limitations prevent the products of the primary electron transfer reactions of photosynthesis from exceeding the reactants in energy by more than about 0.7 hv ₀ where v ₀ is the frequency of the lowest energy absorption band of the reaction center. Specifically, in photosynthetic bacteria, where hv ₀ 1.34 eV, it is often said that the midpoint redox potentials of the primary electron donor and acceptor cannot differ by more than about 0.9 eV. This is incorrect. A simple expression is developed for δμ, the increase in the partial molecular free energy of an absorber under illumination. The magnitude of δμ gives one no information about the nature of the photochemical reactions that can result from excitation of the absorber. It puts no limits on the midpoint redox potentials of the reactants. However, knowing δμ does allow one to calculate the concentrations of the products if the system comes to equilibrium during illumination.     

PHOTO-INDUCED ELECTRON TRANSFER FROM TRANSITION METAL CATIONS TO EXCITED STATES OF THE 10-METHYLACRIDINIUM ION

Abstract— Photo-induced electron transfer from cuprous ion to electronically excited 10-methyiacridinium tetrafluoroborate in acetonitrile-water solutions is described. The final photoproducts are Cu²⁺ (aq) and 10,10'-dimethyl-9,9'-biacridane. The proposed mechanism, based on microsecond flash excitation and fluorimetry experiments, is one-electron transfer from Cu⁺ to the 10-methylacridinium ion triplet state (and possibly the singlet state), followed by dimerization of the neutral acridinyl radical. Because the high energy photoproducts revert slowly to reactants, the system may have potential for storage and controlled recovery of light energy.     

TEMPERATURE DEPENDENCE OF PHOTOSYNTHETIC EXCITATION TRANSFER—ACTIVATIONLESS TRANSFER

Abstract— We have investigated the temperature dependence of photosynthetic excitation transfer by quantum-mechanical treatment. Our theoretical analyses predict that the temperature dependence of most excitation transfers is quite weak in the relatively high temperature range (kT 100cm^-1), whereas some excitation transfers exhibit complex temperature dependence in the low temperature range due to the environmental effect. The temperature-independency in the high temperature range results from the fact that most excitation transfers among various Chi forms characterized by different absorption peaks almost satisfy the activationless condition where the energy gap for the excitation transfer matches with the nuclear rearrangement energy. This activationless condition, which has already been noticed in the electron transfers in the reaction center, is suggested to play central roles in the efficient energy conversion in the primary stage of photosynthesis.     

Using 4-methyl-4-phenyl-2-pentanone as a singlet probe of benzene,cyclohexane, tributylphosphate and its multiple scavenger effects

A special probe of excited singlet states was established. The Norrish type II elimination reaction of 4-methyl-4-phenyl-2-pentanone (MPP) induced by γ-rays was reinvestigated. By measuring the G value of the sensitization radiolytic product α-methylstyrene (α-MS), we obtained the G value of excited singlet states. It was found that the G value of benzene excited singlets is 1.4±0.2, the rate constant of excitation energy transfer from benzene excited singlets to MPP is (5.2±0.5)×10⁹dm³mol^-1s^-1; the G value of excited tributylphosphate singlets is 1.4±0.3, the lifetime of its excited singlets is (1.3±0.1)×10^-7s; the G value of excited cyclohexane singlets is 1.5±0.2, the rate constant of excitation energy transfer from cyclohexane excited singlets to MPP is (4.1±0.4)×10¹⁰dm³mol^-1s^-1. It was found that MPP has multiple effects in quenching the active species formed in the radiolysis of benzene and tributylphosphate, both excitation energy transfer and reaction with subexcitation electrons have occured. A yield of subexcitation electrons of benzene 4.0, that of tributylphosphate 5.0, was obtained. The kinetics of both processes were also discussed.