Multiphoton ionization of metal cluster complexes Os3(CO)12 and Ir4(CO)12: Determination of the ionization energy and coordination energy of the complex ions

Multiphoton ionization and the subsequent dissociation process of metal cluster complexes Os₃(CO)₁₂ and Ir₄(CO)₁₂, prepared in a supersonic jet, were studied by means of multiphoton ionization with time-of-flight (TOF) mass detection. The ionization energies of Os₃(CO)₁₂ and Ir₄(CO)₁₂ were determined to be 7.95 and 8.3 eV, respectively, from the laser wavelength at the ionization threshold. The coordination energies of Os₃(CO)₁₂⁺ and Ir₄(CO)₁₂⁺ ions were also determined to be 1.6 and 1.2 eV, respectively, from the excitation energy needed to cause the appearance of fragment ions. The observed values agreed reasonably well with the ones calculated by using the density functional theory method.     

手性赖氨酸基Gemini表面活性剂的表面性能

用表面张力法、电导法和稳态荧光法研究了手性Gemini表面活性剂[C₁₂-m-C₁₂] Na₂（m=2,4,6）和[C₁₂-T-C₁₂] Na₂的表面性能及临界胶束聚集数,并计算胶束形成的热力学参数,用圆二色谱法考察了[C₁₂-2-C₁₂] Na₂在不同浓度下的立体构型. 结果表明,手性Gemini表面活性剂的临界胶束浓度（cmc）和临界表面张力γ_cmc随着连接基链长增加或刚性增强而增大;ΔG_m⁰和ΔH_m⁰为负值,|ΔH_m⁰|比|-TΔS_m⁰|小很多,说明胶束化过程为熵驱动的自发放热过程;随着连接基链长增加或刚性增强,ΔG_m⁰和ΔH_m⁰逐渐增大,ΔS_m⁰和临界胶束聚集数逐渐减小,表明其胶束化能力随之降低;当浓度大于cmc时,手性Gemini表面活性剂可形成手性超分子聚集体.     

三岔共轭体系中的结构效应(Ⅱ)——分子轨道能量与键级

本文计算了双向型、合流型、分流型三岔共轭多烯链物的分子轨道能级,能级差量。它们的同系递变与相应线型共轭体系一样,也遵守同系线性规律。但它们的同系直线在截距和斜率上都表现有一定的差异,这些差异定量地表明了三岔共轭体系中一根分岔只起代基的作用。这样,由分子基态中轨道能级的同系直线的差异,即可找出作为代基的分岔基团的代基当量。 中心碳原子周围的p_2-3与p_2-N键级的同系直线和用能级因子考查三岔共轭体系的分子轨道能级和键级,所得结果也说明三岔共轭体系的侧链为代基。     

Thermal dissociation of the protein homodimer ecotin in the gas phase

The influence of charge on the thermal dissociation of gaseous, protonated, homodimeric, protein ecotin ions produced by nanoflow electrospray ionization (nanoES) was investigated using the blackbody infrared radiative dissociation technique. Dissociation of the protonated dimer, (E₂ + nH)ⁿ⁺ E₂ⁿ⁺ where n = 14–17, into pairs of monomer ions is the dominant reaction at temperatures from 126 to 175 °C. The monomer pair corresponding to the most symmetric charge distribution is preferred, although 50–60% of the monomer product ions correspond to an asymmetric partitioning of charge. The relative abundance of the different monomer ion pairs produced from E₂¹⁴⁺, E₂¹⁵⁺, and E₂¹⁶⁺ depends on reaction time, with the more symmetric charge distribution pair dominating at longer times. The relative yield of monomer ions observed late in the reaction is independent of temperature indicating that proton transfer between the monomers does not occur during dissociation and that the different monomer ion pairs are formed from dimer ions which differ in the distribution of charge between the monomers. For E₂¹⁷⁺, the yield of monomer ions is independent of reaction time but does exhibit slight temperature dependence, with higher temperatures favoring the monomers corresponding to most symmetric charge distribution. The charge distribution in the E₂¹⁵⁺ and E₂¹⁶⁺ dimer ions influences the dissociation kinetics, with the more asymmetric distribution resulting in greater reactivity. In contrast, the charge distribution has no measurable effect on the dissociation kinetics and energetics of the E₂¹⁷⁺ dimer.     

过渡金属卡宾正离子的从头算研究

过渡金属卡宾正离子被认为是如烯烃的聚合和烷基金属的分解过程等许多反应的中间体．较为稳定的环丁烷金属离子和环戊烷金属离子已从相应酮的脱羰反应获得［１］．Ｊａｃｏｂｓｏｎ等［２］研究了ＦｅＣＨ＋２和ＣｏＣＨ＋２与烯烃和环烷烃的气相反应．Ｍｃｋｅｅ［３］在...     

双核钴簇合物(C6H5C2R)Co2(CO)6的合成

羰基钴簇合物Co₂(CO)₈可用于有机合成的催化剂。但Co₂(CO)₈本身不稳定,易被氧化。因此,研究不向CO₂簇合物的稳定性及其催化性能具有一定的意义。     

尺寸效应对SiO2纳米管化学屏蔽张量的影响

运用密度泛函理论,对截面为三元环的有限长SiO2纳米管进行了研究.核磁共振(NMR)的结果表明,随着纳米管层数的增加,29Si和17O原子的各向同性化学屏蔽张量σiso和各向异性化学屏蔽张量△σ由两端向中间振荡直至趋于稳定值.对长度大于一定数值的有限长纳米管,中间层上原子的σiso和△σ值可作为更长的或无限长SiO2纳米管的理论预测值,这些结果对如何选取合理的有限长纳米管模型来研究无限长结构具有一定的指导意义.     

多氯联苯的定量结构－性质(活性)关系

多氯联苯(PCBs)是一类重要的持久性环境污染物.首先对所有209个PCB分子进行了HF/6-31G*水平上的结构优化, 在优化结构上获得了分子的表面静电势分布, 并在此基础上对其统计导出的参数进行了计算．其后, 运用多元线性回归方法对PCBs的水溶性、正辛醇/水分配系数、正辛醇/空气分配系数、土壤吸附性、水溶液活度系数、298 K超冷流体蒸汽压、总分子表面积、色谱保留指数、升华焓、蒸发焓、熔融焓、PCB结合芳烃受体活性数据、生物降解度以及生物降解速率参数等理化性质和生物活性与分子的结构参数进行了关联．结果表明:分子静电势参数结合分子表面积和常规的量子化学参数可以很好地用于表达多氯联苯分子理化性质和生物活性与其分子结构间的定量关系．     

稀土离子与硫氰酸根及硝酸根的络合作用

在25℃下,以2MNaClO₄维持水相的离子强度恒定,用离子交换法测定了除Ce和Pm以外的镧系元素及钇与CNS^-和NO₃^-的络合作用。用北京大学6912计算机处理了实验数据。结果表明:(1)RE³⁺与CNS^-的络合作用不大,当[CNS^-]≤1.5M时,主要以RECNS²⁺,RE(CNS)₂⁺及RE(CNS)₃三种络合物形式存在;镧系元素与CNS^-的络合度Y₍₁₎随原子序数Z的增大,总的趋向是增大,钇的Y₍₁₎值为最小。(2)RE²⁺与NO₂⁺的络合作用较弱,当[NO₂⁺]≤1.5M时,主要的络合物是RENO₃²⁺;各镧系元素与NO₃^-的Y₍₁₎随Z的增大,总的趋向是减小,钇的Y₍₁₎值最小。(3)在本实验中,稀土络合离子在树脂上的吸附量是可以忽略不计的。     

多次碰撞条件下金阳离子诱导的甲烷碳―碳偶联

The reactivity of atomic metal cations toward CH₄ has been extensively investigated over the past decades. Closed-shell metal cations in electronically ground states are usually inert with CH₄ under thermal collision conditions because of the extremely high stability of methane. With the elevation of collision energies, closed-shell atomic gold cations (Au⁺) have been reported to react with CH₄ under single-collision conditions to produce AuCH₂⁺, AuH⁺, and AuCH₃⁺ species. Further investigations found that the ion-source-generated AuCH₂⁺ cations can react with CH₄ to synthesize C―C coupling products. These previous studies suggested that new products for the reaction of Au⁺ with CH₄ can be identified under multiple-collision conditions with sufficient collision energies. However, the reported ion-molecule reactions involving methane were usually performed under single- or multiple-collision conditions with thermal collision energies. In this study, a new reactor composed of a drift tube and ion funnel is constructed and coupled with a homemade reflectron time-of-flight mass spectrometer. Laser-ablation-generated Au⁺ ions are injected into the reactor and drift 120 mm to react with methane seeded in the helium drift gas. The reaction products and unreacted Au⁺ ions are focused through the ion funnel and accumulate through a linear ion trap and are then detected by a mass spectrometer. In the reactor, the pressure is approximately 100 Pa, and the electric field between the drift tube and ion funnel can regulate the collision energies between ions and molecules. The reaction of the closed-shell atomic Au⁺ cation with CH₄ is investigated, and the C―C coupling product AuC₂H₄⁺ is observed under multiple-collision conditions with elevated collision energies. Density functional theory calculations are performed to understand the mechanism of the coupling reaction (Au⁺+ 2CH₄ → AuC₂H₄⁺ + 2H₂). Two pathways involving Au―CH₂ and Au―CH₃ species can separately mediate the C―C coupling process. The activation of the second C―H bond in each process requires additional energy to overcome the relatively high barrier (2.07 and 2.29 eV). Ion-trajectory simulations under multiple-collision conditions are then conducted to determine the collisional energy distribution in the reactor. These simulations confirmed that the electric fields between the drift tube and ion funnel could supply sufficient center-of-mass kinetic energies to facilitate the C―C coupling process to form AuC₂H₄⁺. The following catalytic cycle could then be postulated: $\mathrm{AuC}_{2} \mathrm{H}_{4}^{+}+\mathrm{CH}_{4} \stackrel{\Delta}{\longrightarrow} \mathrm{AuCH}_{4}^{+}+\mathrm{C}_{2} \mathrm{H}_{4}, \mathrm{AuCH}_{4}^{+}+\mathrm{CH}_{4} \stackrel{\Delta}{\longrightarrow} \mathrm{AuC}_{2} \mathrm{H}_{4}^{+}+2 \mathrm{H}_{2}$, and $\mathrm{CH}_{4} \stackrel{\mathrm{Au}^{+}, \Delta}{\longrightarrow} \mathrm{C}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2}$. Thus, this study enriches the chemistry of both gold and methane.     

Modification of 4-(2-pyridylazo)-resorcinol postcolumn reagent selectivity through competitive equilibria with chelating ligands

Aminopolycar☐ylate ligands were added to the 4-(2-pyridylazo)-resorcinol (PAR) postcolumn reagent to alter the reagent selectivity towards transition metals. Addition of ethylenediaminetetraacetic acid (EDTA) completely suppressed the reaction between PAR and the metal ions. Addition of 0.1 mM nitrilotriacetic acid (NTA) to 1 mM PAR lowered the response to specific transition metal ions, but completely suppressed the PAR response to the lanthanides. Increasing the NTA concentration to 8 mM resulted in complete suppression of the PAR response to all metal ions except Cu²⁺ and Co²⁺ for which the detection limits were 3 and 1 ng, respectively. The observed selectivity results from the slow rate of conversion of metal ions from the M(NTA)₂⁴⁻ form to M(PAR)₂.     

Phosphorous disulfide and its ions in the electronic ground state: a gas phase theoretical study

Ab initio molecular orbital theory and density functional theory calculations were performed on the electronic ground states of the open-shell PS₂ molecule and its singly charged ions. A comparison of the optimized molecular structures indicates as the stepwise one-electron reduction of the PS₂⁺ ion, to yield PS₂ and PS₂⁻, provokes a symmetric elongation of both PS bonds along with a bending of its linear equilibrium geometry. The ionization potential (IP), adiabatic electron affinity (EA_ad), and atomization energy (AE) of the open-shell PS₂ molecule were calculated at different levels of theory. The following values were obtained at the more realistic UMP4SDTQ/6-311+G(3df)//UHF/6-311+G(3df) level of theory: IP=8.32 eV, EA_ad=3.03 eV and AE=12.40 eV. At the same level of theory, the calculated vertical detachment energy (VDE) of the PS₂⁻ anion is 3.22 eV. The donor–acceptor complexes formed in the gas-phase upon interaction of either one or two ammonia molecules with PS₂⁺ were also investigated. The calculated gas-phase binding energies indicate that the formation of the bis-adduct is favored over that of the mono-adduct by a binding energy gain of about 20 kcal/mol.     

双铂电极交流示波双电位滴定法原理(Ⅱ)——荧光电位线理论公式的实验验证

本文对可逆体系滴定可逆体系时荧光电位线的理论公式做了进一步的实验验证,并对公式中的一些参数和性质进行了讨论。     

Pyrocatechol Violet immobilized Amberlite XAD-2: synthesis and metal-ion uptake properties suitable for analytical applications

Amberlite XAD-2 has been functionalized by coupling it, through the ---N=N--- group, with Pyrocatechol Violet (PV), and the resulting resin has been characterized by elemental analysis, thermogravimetric analysis (TGA) and IR spectra. The resin has been used for preconcentrating Zn(II), Cd(II), Pb(II) and Ni(II) ions prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption are 5, 5–7, 4, and 3 for Zn, Cd, Pb and Ni, respectively. The four metals can be desorbed (recovery ˜98%) with 4 M HNO₃; also, 4 M HCl is equally suitable except for Zn. The sorption capacity of the resin is 1410, 1270, 620 and 1360 μg g⁻¹ resin for Zn, Cd, Ni and Pb, respectively. The effect of F⁻, Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻ on the sorption of these four metal ions has been investigated. They are tolerable in the range 0.01–0.20 M, for Pb. In the sorption of Zn(II) and Ni(II), the tolerance limits of all these ions are upto 0.01 M, whereas for Cd(II), F⁻, NO₃⁻, and PO₄³⁻ have been found to be tolerable upto 0.50, 0.10 and 0.10 M, respectively. The preconcentration factors are 60, 50, 23 and 18 for Zn, Cd, Pb and Ni, respectively. Simultaneous collection and determination of the four metals are possible. Cations commonly present in drinking water do not affect the sorption of either metal ion if present at a concentration level similar to that of water. The method has been applied to determine Zn, Ni and Pb content of well-water samples (RSD ≤9%).     

Cellulose based macromolecular chelator having pyrocatechol as an anchored ligand: synthesis and applications as metal extractant prior to their determination by flame atomic absorption spectrometry

Pyrocatechol is immobilized on cellulose via ---NH---CH₂---CH₂---NH---SO₂---C₆H₄---N=N--- linker and the resulting macromolecular chelator characterized by IR, TGA, CPMAS ¹³C NMR and elemental analyses. It has been used for enrichment of Cu(II), Zn(II), Fe(III), Ni(II), Co(II), Cd(II) and Pb(II) prior to their determination by flame atomic absorption spectrometry (FAAS). The pH ranges for quantitative sorption (98.0–99.4%) are 4.0–7.0, 5.0–6.0, 3.0–4.0, 5.0–7.0, 5.0–8.0, 7.0–8.0 and 4.0–5.0, respectively. The desorption was found quantitative with 0.5 mol dm⁻³ HCl/HNO₃ (for Pb). The sorption capacity of the matrix for the seven metal ions has been found in the range 85.3–186.2 μmol g⁻¹. The optimum flow rate of metal ion solution for quantitative sorption of metal onto pyrocatechol functionalized cellulose as determined by column method, is 2–6 cm³ min⁻¹, whereas for desorption it is 2–4 cm³ min⁻¹. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. Ascorbic acid is tolerable up to 0.8 mmol dm⁻³ with Cu and Pb where as sodium tartrate does not interfere up to 0.6 mmol dm⁻³ with Pb. There is no interference of NaBr, NaCl and NaNO₃ up to a concentration of 0.5 mol dm⁻³, in the sorption of Cu(II), Cd(II) and Fe(III) on to the chelating cellulose matrix The preconcentration factors are between 75 and 300 and t_1/2 values ≤5 min for all the metal ions. Simultaneous sorption of Cu, Zn, Ni and Co is possible at pH 5.0 if their total concentration does not exceed lowest sorption capacity. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (relative standard deviation (R.S.D.) 1.05–7.20%) and synthetic certified water sample SLRS-4 (NRC, Canada) with R.S.D. 2.03%. The cobalt present in pharmaceutical vitamin tablets was also preconcentrated on the modified cellulose and determined by FAAS (R.S.D. 1.87%).     

Improved electrochemical properties in the Li3Fe2(PO4)3 by titanium and vanadium doping

Ti⁴⁺ ions were introduced to the VO₄^3- substituted Li₃Fe₂(PO₄)₃ by sol-gel method. Simultaneous substitution of Ti⁴⁺ for Fe³⁺ and VO₄^3- for PO₄^3- in the Li₃Fe₂(PO₄)₃ resulted in a net improvement in the rate capability and cycling performance, as compared with the single Ti⁴⁺ or VO₄^3- substituted compound.     

基于第一性原理计算的铁电材料BaTiO3相关振动光谱指认

通过固相反应烧结法在1400 ℃下烧结4 h合成了BaTiO₃陶瓷, 并用X衍射确定了其为四方晶系. 进行了拉曼谱和红外谱的测量, 并采用洛仑兹函数以及四参数方法分别对上述光谱进行了拟合. 基于第一性原理的计算, 并考虑了横模纵模劈裂, 对拉曼和红外光谱进行了指认. 为了更好地分析振动模式, 所有振动模用群论的对称坐标进行了分解. 在12个光学模中, 仅具有拉曼活性的B₁模式是O4和O5沿着z轴的相对运动. A₁模式和E₁软模式是从立方BaTiO₃相的F_1u模式劈裂出来的, 对于四方相BaTiO₃的铁电性有着重要作用, 其体现在A₁⁽¹⁾模式造成了铁电z轴的极化, E₁模式导致了大介电常数. 这两个模式都可以看成是Ti 原子相对于O₆八面体笼子沿着z轴或者是xy平面的振动.     

反气相色谱测定非对称双阳离子型离子液体的溶解度参数

在343.15~363.15 K下采用反气相色谱法对实验室合成的3种非对称双阳离子型离子液体[PyC₅Pi]NTf₂]₂、[MpC₅Pi]NTf₂]₂和[PyC₆Pi]NTf₂]₂的溶解度参数进行了测定。以正辛烷、正癸烷、正十二烷、正十四烷和正十六烷作为探针溶剂,计算了在不同温度下探针溶剂在3种离子液体中的特性保留体积(V_g⁰)、摩尔吸收焓(ΔH₁^S)、无限稀释摩尔混合焓(ΔH_l^∞)、摩尔蒸发焓(ΔH_v)、无限稀释活度系数(Ω₁^∞)以及探针溶剂与3种离子液体的Flory-HuggirIs相互作用参数(χ₁₂^∞),得到了室温下3种离子液体的溶解度参数(δ₂)为28.52~32.66 (J·cm^-3)^1/2。分子结构中含有4-甲基吗啉比含有吡啶时溶解度参数更大。随着两个阳离子间连接基碳数的增加,溶解度参数增大。这一结果对研究离子液体的溶液性质和应用有指导作用。     

Activation free energy of Zn（Ⅱ）,Co（Ⅱ） binding to metallo-β-lactamase ImiS

In an effort to understand the recombination of a B2 metallo-β-lactamase（MβL）,the binding of metals to apo-ImiS was studied by isothermal titration calorimetry and fluorescence spectra.The binding of Zn（Ⅱ）,Co（Ⅱ） to apo-lmiS resulted in activation free energies △G_≠~θ values of 93.719 and 92.948 kJ mol~（-1）,respectively,and increasing of fluorescence intensity at maxima emission of 340 nm.