New observations on the luminescence decay lifetime of Mn2+ in Zns: Mn2+ nanoparticles

A fast decay emission peaking at 645 nm with a decay lifetime within the experimental resolution of 0.14 micros is observed in ZnS:Mn2+ nanoparticles. This short-lived signal is also observed in pure ZnS and MgS: Eu3+ nanoparticles, which has nothing to do with Mn(2+)-doped ions but is from the deep trap states of the host materials. The short-lived component decreases in intensity relative to the Mn2+ emission at higher excitation powers, while it increases in intensity at low temperatures and shifts to longer wavelengths at longer time delays. Our observations demonstrated further that the emission of Mn2+ in ZnS: Mn2+ nanoparticles behaves basically the same as in bulk ZnS: Mn2+; the fast decay component is actually from the intrinsic and defect-related emission in sulfide compounds.     

高压下TiSi2可见光光热催化分解水制氢的研究

系统地研究了高压下一系列TiSi2催化剂的可见光光热催化分解水制氢行为.研究结果表明,压力增加显著提高了TiSi2催化剂光催化分解水制氢速率.添加NaOH和Na2CO3有利于水分解制氢的反应进行,在一定范围内,NaOH和Na2CO3浓度增加,放氢速率增加.研究还发现,担载贵金属Pt或Ru对反应速率没有显著影响.本文还采...     

适用于海洋沉积物间隙水中氧、锰(Ⅱ)、铁(Ⅱ)、硫分析的金汞齐微电极

用电化学方法在金微电极的基础上制成金汞齐微电极。研究了电极预处理方法、电镀以及强极化金汞齐微电极的条件、电极的校正方法以及实际测量电化学参数的选择等。采用三电极体系和方波伏安法,金汞齐微电极(vs.SCE)从-0.10～-1.75V电势范围内可同时测定沉积物间隙水中的溶解氧、Mn2 、Fe2 和S2-等氧化还原物的浓度。实验结果表明金汞齐微电极对溶解氧、Mn2 、Fe2 和S2-的灵敏度和检出限分别为0.16nA/(μmol/L)、6μmol/L,0.35nA/(μmol/L)、3μmol/L,0.22nA/(μmol/L)、5μmol/L和34nA/(μmol/L)、0.03μmol/L。在连续测定15个沉积物样品后,重新校正电极,测量相对误差<3%。     

Reactions of 2-chloro-2-(4-pyridyl)propane with nucleophiles. Substitution on tertiary carbon

The reaction of 2-chloro-2-(4-pyridyl)propane ( 2 ) with lithium 2-propanenitronate affords the C-alkylation product 2-nitro-3-(4-pyridyl)-2,3-dimethylbutane ( 3 ), the Michael-adduct 2-nitro-2-methyl-4-(4-pyridyl)pentane ( 4 ), 4-isopropenylpyridine ( 5 ) and 2-(4-pyridyl)-2-propanol ( 6 ). Of these four products, only the formation of 3 is suppressed when the reaction is performed in the presence of radical inhibitors. The reaction of compound 2 with sodium azide gives the tertiary substitution product 2-azido-2-(4-pyridyl)propane ( 8 ). The reaction is not influenced by radical inhibitors. This is also the case in the reaction of 2 with sodium benzenethiolate, which affords 2-mercaptophenyl-2-(4-pyridyl)propane ( 9 ) and 1-mercaptophenyl-2-(4-pyridyl)propane ( 10 ). Compound 5 , the product of an E₂-type elimination is also formed in the azide and thiolate reactions. A Michael type addition of sodium benzenethiolate to 5 explains the formation of 10 . Similarly, generation of 5 in reactions of 2 with sodium methanethiolate and sodium cyanide accounts for the formation of 1-mercaptomethyl-2-(4-pyridyl)propane ( 11 ) and 3-(4-pridyl)butanenitrile ( 12 ), respectively.     

Mn3+/Mn2+氧化还原体系的旋转圆盘电极法性能

氧化还原液流电池的独特性能受到关注[1～4]。本文综合运用循环伏安法,旋转圆盘电极法研究锰离子浓度较高(0 25～0 35mol·L-1、转速范围较宽(400～4200rpm)、同时考虑过电位的条件下Mn(Ⅲ)/Mn(Ⅱ)电对在RDE铂盘电极上的电极过程动力学并确定有关的动力学参数,了解其影响因素,为该电对作为氧化还原液流电池正极活性材料提供动力学依据。1　实验部分铂电极使用前在铬酸洗液中浸10min,水冲洗干净,蒸馏水淋洗,然后在6 3mol·L-1H2SO4中超声清洗10min,再用CHI660电化学工作站(美国CH仪器公司)控制,以0 05V/s的扫速在-1 0～1 2V之间扫…     

高温高压水中干酪根热解的拉曼光谱原位研究

利用对顶砧压腔装置,以金刚石作为顶砧,通过观测和采用拉曼光谱对干酪根在高温高压水中热解的具体过程进行了原位研究.由于金刚石顶砧只在约1 332 cm-1波数出现一个很强很尖锐的峰,因此用于压 标的石英、介质水以及样品干酪根的拉曼峰都未受影响.测试了在450℃和850 MPa条件下干酪根变化的拉 曼峰.随着温度和压力的增加,干酪根在1 600 cm-1波数附近由于芳香环振动引起拉曼峰的最大峰位置 (vmax)和半高宽(FWHM)存在转折变化.在干酪根热解之前,其芳香环结构和无序结构之间的缺陷向有序化变化.而对于干酪根的热解过程,先是热解为液相碳氢化合物,随后进一步热解为更小分子的成分,如 CH4.干酪根的热解过程与压力密切相关,增加压力对热解存在抑制作用.     

非均相电解Mn^2＋的电极过程动力学研究

选择Ｐｂ－Ｓｂ－Ａｓ合金为研究电极，通过阳极极化曲线确定了非均相电解氧化Ｍｎ６２＋电极过程机理，即为在阳极上存在液相和固相两个反应；并确定了４０％Ｈ２ＳＯ４介质中Ｍｎ／Ｍｎ体系的条件电极电势为０．８８６Ｖ。采用旋转圆盘电极研究得到在非均相电解ＭｎＳＯ４过程中电极过程控制步骤为电荷传递－浓度极化混合控制步骤，并确定了电极反应的动力学参数。     

Mn2+在铝酸盐中的发光

用金属硝酸盐、稀土氧化物和乙酸锰为原料,用燃烧法合成了Ce³⁺、Tb³⁺、Mn²⁺共激活的铝酸盐绿色荧光粉,在Ce³⁺和Tb³⁺共激活的铝酸盐体系中掺入Mn²⁺后,发射峰中出现锰的特征峰.通过对其结构的分析,对Mn²⁺发光和最佳掺杂量给出了合理的解释.同时研究了不同碱金属和碱土金属离子代替Mg²⁺时,对Mn²⁺发光的影响.     

Theoretical investigation of electron paramagnetic resonance spectra and local structure distortion for Mn2+ ions in CaCO3:Mn2+ system: a simple model for Mn2+ ions in a trigonal ligand field

This paper reports on a novel application of a ligand field model for the detection of the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand field and the spin-orbit coupling for the d5 configuration ion in a trigonal ligand field, the local distortion structure of the (MnO6)10- coordination complex for Mn2+ ions doped into CaCO3, have been investigated. Both the second-order zero-field splitting parameter b(0)2 and the fourth-order zero-field splitting parameter b(0)4 are taken simultaneously in the structural investigation. From the electron paramagnetic resonance (EPR) calculations, the local structure distortion, DeltaR=-0.169 A to -0.156 A, Deltatheta=0.996 degrees to 1.035 degrees for Mn2+ ions in calcite single crystal, DeltaR=-0.185 A to -0.171 A, Deltatheta=3.139 degrees to 3.184 degrees for Mn2+ ions in travertines, and DeltaR=-0.149 A to -0.102 A, Deltatheta=0.791 degrees to 3.927 degrees for Mn2+ ions in shells are determined, respectively. These results elucidate a microscopic origin of various ligand field parameters which are usually used empirically for the interpretation of EPR and optical absorption experiments. It is found that the theoretical results of the EPR and optical absorption spectra for Mn2+ ions in CaCO3 are in good agreement with the experimental findings. Moreover, to understand the detailed physical and chemical properties of the doped CaCO3, the theoretical values of the fourth-order zero-field splitting parameters b(0)4 for Mn2+ ions in travertines and shells are reported first.     

Evidence of Sulfur Non-Innocence in [CoII(dithiacyclam)]2+-Mediated Catalytic Oxygen Reduction Reactions

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]²⁺ ( 1 ; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S₂N₂-cyclam)]²⁺ ( 2 ; S₂N₂-cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the Co^II centers in 1 and 2 point to the involvement of sulfur in the O₂ reduction process as the key for the improved catalytic ORR capabilities of 2 .     

Reactions of 2-nitro-2-(4-pyridyl) propane with nucleophiles. Substitution at tertiary carbon

The reaction of 2-nitro-2-(4-pyridyl) propane (I) with lithium 2-propanenitronate, lithium cyclohexanenitronate, and sodium thiophenoxide affords excellent yields of the C-alkylation products 2-nitro-3-(4-pyridyl)-2,3-dimethylbutane (II), 2-(4-pyridyl)-2-(1-nitrocyclohexyl) propane (V) and 2-thiophenyl-2-(4-pyridyl) propane (VI), respectively. In contrast, the reaction of compound I with sodium azide does not afford the expected tertiary azide; but instead gives the dimer 2,3-bis(4-pyridyl)-2,3-dimethylbutane (III), in near quantitative yield. Evidence has been obtained that all of these transformations proceed via electron transfer pathways.     

[2+2]环加成反应机理的理论研究

[2+2]环加成反应是有机化学中非常重要的一类反应,其机理的研究一直是实验和理论工作者关注的课题之一。本文从理论的角度综述了三类[2+2]环加成反应的反应机理,即简单烯烃或炔烃参与的环加成反应、累积双键体系参与的环加成反应以及稀土钍化合物参与的环加成反应, 得出对于简单的烯烃或炔烃之间的环加成反应一般是按双自由基机理进行,而其他两类反应主要按协同或两性离子方式进行,并且从前线分子轨道作用理论角度分析了产生不同反应机理的原因。     

Investigations on the electron paramagnetic resonance parameters for Mn2+ in the ABF3 fluoroperovskites

The electron paramagnetic resonance (EPR) parameters (g factor, the hyperfine structure constant A and the superhyperfine parameters A' and B') for Mn(2+) in the fluoroperovskites ABF(3) (A=K and Cs; B=Zn, Mg, Cd and Ca) are theoretically investigated from the perturbation formulas of these parameters for a 3d(5) ion under ideal octahedra. In the above treatments, not only the crystal-field mechanism but also the charge transfer mechanism is considered uniformly on the basis of the cluster approach. The theoretical EPR parameters are in good agreement with the experimental data. The charge transfer contribution to the g-shift Δg (≈g-g(s), where g(s)≈2.0023 is the spin-only value) is opposite (positive) in sign and comparable in magnitude to the crystal-field one. Nevertheless, the charge transfer contribution to the hyperfine structure constant shows the same sign and about 10% that of the crystal-field one. So, the conventional argument that the charge transfer contributions to the zero-field splittings are negligible for 3d(5) ions under low symmetrically distorted fluorine octahedra is proved no longer valid for the Δg analysis of ABF(3):Mn(2+) in view of the dominant second-order charge transfer perturbation terms. The unpaired spin densities of the fluorine 2s, 2p σ and 2p π orbitals are determined from the quantitative dependences upon the related molecular orbital coefficients, rather than obtained by fitting the observed superhyperfine parameters in the previous works.     

The binding of Mn2+ and ADP to myosin.

The metal ion requirement of myosin-ADP binding was investigated by use of Mn2+. Mn2+ binds to two sets of noninteracting sites on myosin which are characterized by affinity constants of 10(6) and 10(3), M(-1) at 0.016 M KCl concentration. The maximum number of sites is 2 for the high affinity and 20-25 for the low affinity set. Binding of Mn2+ to the high affinity sites increases the affinity of ADP binding to myosin. F-actin inhibits ADP binding (Kiely, B., and Martonosi, A., Biochim. Biophys. Acta 172: 158-170 [1969]), but even at F-actin concentrations much higher than that required to saturate the actin binding sites of myosin or its proteolytic fragments, significant ADP binding remained. The actin insensitive portion of ADP binding was inhibited by 10(-4) M inorganic pyrophosphate or ATP. The results are discussed on the basis of a model in which actin and ADP bind to myosin at distinct but interacting sites.     

Reactions of Charged Substrates. 5. The Solvolysis and Sodium Azide Substitution Reactions of Benzylpyridinium Ions in Deuterium Oxide

Second-order rate constants and activation values were measured for the reactions with NaN(3) of a series of 4-Y-substituted (Y = MeO, Me, H, Cl, and NO(2)) benzyl 3'-Z-substituted (Z = CN, CONH(2), H, F, Ac) pyridinium chlorides in deuterium oxide. 3'-Cyanopyridine substrates reacted much faster than nicotinamide and pyridine substrates; in the pyridine series the 4-Me, 4-H, and 4-Cl benzyl analogs did not react for up to 6 months at 96()() degrees C in 1.7 M NaN(3). The 3'-cyanopyridine substrates do not exhibit borderline kinetic behavior, but the nicotinamide substrates do. The Hammett plot is flat for the NaN(3) reaction of 3'-cyanopyridine substrates and increasingly V-shaped for the nicotinamide and pyridine substrates. The values of beta(LG) (four-point plot) for the NaN(3) reaction of the 4-MeO benzyl substrates is -1.45, which is usually interpreted as being a very "late" activated complex. Two-point Br?nsted "plots" for the other benzyl derivatives and for two N-methylpyridinium ions give values of beta(LG) in the same range. The second-order rate constant and activation values for N-methyl-3'-cyanopyridinium iodide are within the same range as those for the benzyl substrates. For the hydrolysis reaction, the Hammett plot is linear for 3'-cyanopyridine substrates (rho(+) = -1.24) and flat for the nicotinamide substrates. The extent of hydrolysis of 0.005-0.05 M solutions of the 3'-cyanopyridinie substrates depended on the initial concentration of substrate, and hydrolysis was slowed significantly or stopped completely in the presence of exogenous 3-cyanopyridine. These results show that an equilibrium is established among the products for the 4-MeO, 4-Me, 4-H, and 4-Cl substrates; the 4-NO(2) substrate reacted too slowly to discern any difference. Data for the extent of hydrolysis were fitted by an equation derived assuming the equilibrium. Despite this limitation on a classic test of mechanism, the rates and rho values are consistent with direct displacement by solvent and not with a unimolecular process. These results, which are rationalized in terms of the Pross-Shaik model, suggest that there are no ion-dipole complex intermediates in the benzyl series and show that borderline kinetic behavior is a function of leaving group ability and is not necessarily related to a change in mechanism. A computational approach was used to evaluate anomalous beta(LG) values for the hydrolysis and nucleophilic substitution reactions of the methypyridinium ion substrates. It was found that neither the Nu-substrate bond lengths nor the difference in charge matched the beta(LG) values. The value of DeltaDeltaS() of -15 gibbs/mol between (4-methoxybenzyl)-3'-cyanopyridinium chloride and the corresponding dimethylsulfonium chloride in the NaN(3) reaction, which is the result of the solvation of the pyridine at the transition state and the lack of solvation of SMe(2), is used to argue that the source of NAD(+) glycohydrolase "catalysis" of NAD(+) bond cleavage is the result of desolvation of the leaving group upon binding.