非化学计量和掺杂对(Na_(1/2)Bi_(1/2))_(0.92)Ba_(0.08)TiO_3陶瓷电性能的影响

研究了非化学计量和掺杂对无铅压电陶瓷 (Na1 2 Bi1 2 ) 0 .92 Ba0 .0 8TiO3的压电性能及去极化温度的影响 .研究发现A位非化学计量可以提高陶瓷的压电性能 ;B位掺杂对材料电学性能的影响规律类似于Pb(Ti,Zr)O3系压电陶瓷的相关规律 ;由于非化学计量和掺杂会影响到A位离子对B位离子与氧离子形成的BO6 八面体的耦合作用 ,影响到畴的稳定性 ,从而影响到 (Na1 2 Bi1 2 ) 0 .92 Ba0 .0 8TiO3陶瓷的去极化温度 ;所研究的陶瓷样品的去极化温度越低 ,压电系数越高 .     

草酰胺分子构型、稳定性、IR光谱及分子轨道的密度泛函与从头算研究

运用多种密度泛函理论 (DFT)和从头算 (abinitio)方法研究了草酰胺顺、反异构体的分子几何构型 ,结果表明Beck88交换函数与LYP非局域相关函数形成杂化的DFT方法B3LYP与MP2方法计算结果比较吻合。在此基础上选择B3LYP方法对草酰胺分子电子结构、红外光谱和前线分子轨道组成进行了系统研究 ;与实验事实对比分析了气态草酰胺分子中配位原子的反应活性     

密度泛函理论研究Be_nNa(n=2~14)团簇的结构及其电子性质(英文)

基于密度泛函理论研究了BenNa(n=2~14)团簇的最低能量结构及其电子性质,具体采用的计算方法是B3LYP/6-311G(d).对于每一尺寸的团簇,我们从多个可能构型出发来寻找其最低能量结构.计算结果表明:钠原子易于附着在铍团簇的表面;Be4Na和Be9Na均具有较高的平均结合能及能隙,n=4,9是团簇的幻数;在所有的BenNa(n=2~14)团簇中,钠原子均失去电子;随着团簇尺寸n的增大,团簇内部原子间的相互作用是共价键和金属键共存.     

密度泛函理论研究碱金属原子在完美氧化镁(001)表面的吸附

基于平面波赝势法的密度泛函理论系统地研究了孤立碱金属原子(锂、钠、钾、铷、铯)在完美氧化镁(001)表面的吸附. 锂在氧位表面上的吸附能是0.72 eV,大约是其它碱金属的3倍. 锂和表面氧之间较强的相互作用主要是来源于共价键的作用,这可由态密度和差分电荷密度的分析所证实. 讨论碱金属在MgO(001)表面吸附的成键机理.     

MAS NMR with and without double-quantum filtration at and near the n=0 rotational resonance condition

Spectral lineshapes of MAS NMR spectra of dipolar (re)coupled spin pairs exhibiting considerable chemical shielding anisotropies at and near the so-called n=0 rotational resonance (R2) condition are considered. The n=0 R2 condition is found to be not extremely sharp. Anisotropic interaction parameters such as chemical shielding tensor orientations and the magnitude of the dipolar coupling constant remain sensitively encoded in such lineshapes even when differences in isotropic chemical shielding values of up to 400 Hz (corresponding to ca. half the size of the dipolar coupling constant) are present. Additional double-quantum filtration (DQF) may enhance the sensitivity of spectral lineshapes to anisotropic interaction parameters for even larger differences in isotropic chemical shielding values. The dependence of the DQF efficiency on spin-system parameters as well as on external parameters (Larmor and MAS frequencies) is investigated. Away from R2 conditions a trend to lower DQF efficiencies is found whereas some spin-system parameters are more sensitively encoded in the corresponding spectral lineshapes. Our study is based on numerical simulations, with the known parameters of the 31P spin pair in Na4P2O7.10H2O representing our model case.     

Influence of amphotericin B on liquid crystal state of the Cholesterol/Dipalmitoylphosphatidylcholine monolayer in the presence of different metal cations

Amphotericin B is a very effective antifungal drug,but it has an adverse reaction to the membrane of mammals' cells.The interaction between Am B and cholesterol(Chol) causes the formation of pores on the membrane to destroy its integrity.In particular,Am B has a significant effect on the permeability of membrane for K~+ions.It has been reported that Na+ions and Ca~(2+)ions may have some influence on the interaction between amphotericin B and lipid molecules.In this work,the effects of these metal cations on the physical state and intermolecular interaction of the Cholesterol/Dipalmitoylphosphatidylcholine(Chol/DPPC) monolayer with and without Am B have been investigated.The addition of Am B induces the change of physical state of the lipid monolayer from liquid-gel phase to liquid phase.Different metal cations could influence the phase transition of the Am B-lipid monolayer.The K~+ions and Ca2+ions make the obvious phase transition disappear.However,the presence of Na+ions has little influence on the phase transition of the Am B-lipid monolayer.The addition of Am B and the presence of different metal cations weaken the attractive force on the monolayers.After addition of Am B,the force between the molecules is the strongest in the environment of K+ions,thus is the weakest in the environment of Ca~(2+)ions,which may be due to the distribution of these metal cations inside and outside of cells.A large number of K+ions distribute inside of the cells,thus most of Na+and Ca~(2+)ions exist out of the cells.Hence,it may be possible that when Am B molecules are out of the cells,the reaction between the drug and lipid molecules is weaker than that inside the cells.These results may have a great reference value for further studying the toxicity mechanism of Am B and the influence of metal cations on the membrane.     

硼掺杂富勒烯储氢-从物理吸附到化学吸附的转变

本文采用密度泛函理论(DFT)中的局域密度近似(LDA)方法对硼(B)掺杂富勒烯(C_(35)B)储氢问题在前人的基础上做了进一步研究,结果表明被C_(35)B吸附的氢分子很容易解离,经历从物理吸附到化学吸附的转变,并且发现解离产物C_(34)BHCH有分子内氢转移反应发生,这时B原子仍能与氢分子有很强的相互作用,最终导致B位置以及与B最邻近的三个C原子上都有氢原子吸附.并利用过渡态理论从热力学上分析了这种反应的发生趋势.     

Strategies for extracting NMR parameters from 23Na MAS, DOR and MQMAS spectra. A case study for Na4P2O7

The 23Na magic-angle spinning (MAS), double rotation (DOR) and multiple-quantum magic-angle spinning (MQMAS) NMR spectra of anhydrous sodium pyrophosphate, Na4P2O7, measured at five different Larmor frequencies (nuL) ranging from 105.8 MHz (corresponding to 400 MHz 1H frequency) to 211.6 MHz (800 MHz) are analysed and the complete set of NMR parameters (C(qcc), etaQ and delta(iso)) of the four crystallographically inequivalent sodium sites were determined with high accuracy. Different approaches of spectra evaluation are discussed and their results are compared. The most reliable results are obtained from a combined evaluation of five DOR and three MQMAS spectra but also from two DOR and one MAS spectra or even from a single MQMAS spectrum all data can be derived. It is shown that Na4P2O7 may serve as a useful reference material for experimental set-up and reliability tests of the various NMR experiments.     

缺陷对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和缺陷石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,本征石墨烯中,钠原子的最佳吸附位置为H位,缺陷石墨烯中,钠原子的最佳吸附位置为T_D位.缺陷石墨烯对钠原子的吸附能是-4.423 eV,约为本征石墨烯对钠原子吸附能的2.5倍;钠原子与缺陷石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没有发生轨道杂化现象.缺陷石墨烯能够吸附10个钠原子,与本征石墨烯相比显著提高.因此,缺陷石墨烯有望成为一种潜在的储钠材料.     

钠分子B^1∏u与2^1∑g^＋间的碰撞激发转移

The B 1pi(u) electronic state of Na2 was excited by the 441.6 nm He-Cd laser line. The Na atomic transitions and the A 1sigma(u)+ --> X 1sigma(g)+ band of Na2 were recorded. From the intensities and spectra of the Na and Na2 fluorescence several collisional processes in the excited sodium atom-dimer system were identified. The Na atomic lines are the result of collisional energy transfer from Na2 (B 1pi(u)) to Na(3P). Predissociation process may also contribute to atomic fluorescence. The A 1sigma(u)+ --> X 1sigma(g)+ band is interpreted through a populating mechanism involving collisional transfer from B 1pi(u) to 2 1sigma(g)+ followed by a radiative transfer to the A 1sigma(u)+ state. From the decay constants and fluorescence intensities, the rate coefficient at 360 degrees C for collisional energy transfer from Na2 (B 1pi(u)) to Na2 (2 1sigma(g)+) was found to be 5.7 x 10(-10) cm3 x s(-1). The predissociation rate of the B 1pi(u) is 2.7 x 10(6) s(-1).     

Combined 17O NMR and 11B-31P double resonance NMR studies of sodium borophosphate glasses

17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B-31P heteronuclear correlation (HETCOR) NMR and 11B{31P} rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS. The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: P-O-P, Na...O-P, P-O-B, B-O-B, Na...O-B. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that P-O-B links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B{31P} REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that B-O-P bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B-31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups.     

碰撞诱导钠分子A1Σ+u→X1Σ+g的荧光光谱

用532.0 nm激光激发Na2分子到B1Πu电子态,记录了Na(3P)原子的跃迁和Na2分子的A1Σ+u-Χ1Σ+g的谱带.由Na与Na2激发态发射的光谱及其强度可以认定在Na-Na2系统中的碰撞过程,Na(3P)原子线是Na2(B1Πu)到Na(3P)的碰撞能量转移产生的,预解离过程也可产生原子线.而A1Σ+u-Χ1Σ+g谱带是由B1Πu到21Σ+g的碰撞转移后再由21Σ+g到A1Σ+u的辐射而引起的.在360℃,根据辐射衰变率和荧光强度,得到Na2(B1Πu)到Na2(21Σ+g)碰撞转移率系数为7.1×10-10 cm3s-1,而B1Πu的预解离率为2.3×106 s-1.     

Rotor-encoded heteronuclear MQ MAS NMR spectroscopy of half-integer quadrupolar and spin I=1/2 nuclei

A new two-dimensional heteronuclear multiple-quantum magic-angle spinning (MQ MAS) experiment is presented which combines high resolution for the half-integer quadrupolar nucleus with information about the dipolar coupling between the quadrupolar nucleus and a spin I=1/2 nucleus. Homonuclear MQ coherence is initially created for the half-integer quadrupolar nucleus by a single pulse as in a standard MQ MAS experiment. REDOR recoupling of the heteronuclear dipolar coupling then allows the creation of a heteronuclear multiple-quantum coherence comprising multiple- and single-quantum coherence of the quadrupolar and spin I=1/2 nucleus, respectively, which evolves during t1. Provided that the t1 increment is not rotor synchronized, rotor-encoded spinning-sideband patterns are observed in the indirect dimension. Simulated spectra for an isolated IS spin pair show that these patterns depend on the recoupling time, the magnitude of the dipolar coupling, the quadrupolar parameters, as well as the relative orientation of the quadrupolar and dipolar principal axes systems. Spectra are presented for Na2HPO4, with the heteronuclear 23Na-1HMQ MAS experiments beginning with the excitation of 23Na (spin I=3/2) three-quantum coherence. Coherence counting experiments demonstrate that four- and two-quantum coherences evolve during t1. The heteronuclear spinning-sideband patterns observed for the three-spin H-Na-H system associated with the Na(2) site are analyzed. For an IS2 system, simulated spectra show that, considering the free parameters, the spinning-sideband patterns are particularly sensitive to only, first, the angle between the two IS internuclear vectors and, second, the two heteronuclear dipolar couplings. It is demonstrated that the proton localization around the Na(2) site according to the literature crystal structure of Na2HPO4 is erroneous. Instead, the experimental data is consistent with two alternative different structural arrangements, whereby either there is a deviation of 10 degrees from linearity for the case of two identical Na-H distances, or there is a linear arrangement, but the two Na-H distances are different. Furthermore, the question of the origin of spinning-sidebands in the (homonuclear) MQ MAS experiment is revisited. It is shown that the asymmetric experimental MQ sideband pattern observed for the low-C(Q) Na(2) site in Na(2)HPO4 can only be explained by considering the 23Na chemical shift anisotropy.     

Application of low energy ion blocking for adsorption site determination of Na Atoms on a Cu(111) surface

Ion blocking in the low keV energy range is demonstrated to be a sensitive method for probing surface adsorption sites by means of the technique of time-of-flight scattering and recoiling spectroscopy (TOF-SARS). Adsorbed atoms can block the nearly isotropic backscattering of primary ions from surface atoms in the outmost layers of a crystal. The relative adsorption site position can be derived unambiguously by simple geometrical constructs between the adsorbed atom site and the surface atom sites. Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) and molecular dynamics (MD) simulations provide the detailed ion trajectories. Herein we present a quantitative analysis of the blocking effects produced by sub-monolayer Na adsorbed on a Cu(111) surface at room temperature. The results show that the Na adsorption site preferences are different at different Na coverages. At a coverage θ = 0.25 monolayer, Na atoms preferentially populate the fcc threefold surface sites with a height of 2.7 ± 0.1 Å above the 1st layer Cu atoms. At a lower coverage of θ = 0.10 monolayer, there is no adsorption site preference for the Na atoms on the Cu(111) surface.     

碳纳米锥吸附Na的第一性原理计算

本文采用第一性原理计算结合从头算分子动力学的方法,研究了碳纳米锥(CNC)、B和N掺杂碳纳米锥(B-CNC和N-CNC)的稳定性,结果表明CNC、B-CNC和N-CNC均可以稳定存在.在此基础上分别研究了Na原子在CNC、B-CNC和N-CNC上的吸附行为.结果表明：1) Na原子在CNC五元碳环中心顶部位置的吸附最强,吸附能为-2.52 eV. CNC的能隙(Eg)为1.96 eV. 2) B和N掺杂CNC后,B-CNC和N-CNC的导电性均显著增强. 3)与CNC相比,Na原子在B-CNC上的吸附增强,而在N-CNC上的吸附则显著减弱.这表明B-CNC有望作为Na离子电池的负极材料.本文的研究结果对以CNC为负极材料的Na离子电池的研究提供了理论指导.     

硼掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的B掺杂石墨烯(BBLG)表面的吸附性质进行了研究.确定了不同B掺杂浓度时BBLG的最稳定B分布结构,计算了Na在PBLG和不同掺杂浓度的BBLG表面的吸附能.计算结果表明,B原子掺杂倾向于占据上层中对位或次临近位置,并与下层中六边形碳环中心相对,B_4C_(32)的形成能最小;B掺杂浓度的增加使BBLG中上层石墨烯片层结构起伏增大,而对下层影响较小;Na在BBLG表面吸附高度和平均层间距受上层结构起伏影响显著;Na倾向于吸附在B_9C_(27)表面B原子的上方,使原始平面结构产生起伏,Na与B_9C_(27)表面的结合最稳定.     

Conformational changes of Na,K-ATPase probed with eosin Y

Time-resolved fluorescence and binding studies have been carried out on Na,K-ATPase in the presence of the fluorescent dye eosin Y to obtain thermodynamic and kinetic parameters for the interaction of the enzyme with different cations. Eosin Y binding is indicated by a 3 ns fluorescence decay process and is observed only in the presence of mono- and divalent cations. This type of cation binding is interpreted as a nonselective electrostatic interaction, with negatively charged groups of the enzyme providing a high-affinity eosin Y binding site. Eosin Y binding is observed only under conditions where the enzyme exists in the conformational state F₁. The kinetic parameters of eosin Y binding have been determined employing stopped-flow fluorometry.     

ICP-MS/ICP-AES测定小麦穗离体培养籽粒营养元素及重金属含量

环境中重金属污染会导致谷物营养缺乏、代谢紊乱.借助ICP-MS/ICP-AES系统和离体穗培养方法,准确测定灌浆期不同浓度铜、镉(0,5,15,45 mg·L-1)处理对籽粒营养元素及重金属元素含量的影响.结果显示,不司浓度铜、镉处理显著降低小麦粒重;外源铜促进了籽粒P,K,Mg,Ca,Na,Mn和Zn含量的增加,抑制了 Fe和B的吸收.镉的加入对小麦籽粒P,K,Ca,Mg和Mn的吸收起促进作用,然而对Na,Fe,Zn和B的吸收起拮抗作用.外源铜、镉抑制小麦籽粒对Hg的积累,但籽粒Cu和Cd含量最高分别超过国家食品卫生标准的55和62倍,存在极大安全隐患.     

氮掺杂的石墨烯作为钠离子电池负极材料的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯、氮掺杂的石墨烯和叽咯石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,三种石墨烯中,钠原子的最佳吸附位置为H位.与本征石墨烯相比,氮掺杂的石墨烯对钠原子的吸附能提高,叽咯石墨烯对钠原子的吸附能是-3.274 eV,约为本征石墨烯对钠原子吸附能的1.7倍.钠原子与叽咯石墨烯中的氮原子发生轨道杂化,而与本征石墨烯和氮掺杂的石墨烯没有发生轨道杂化现象.叽咯石墨烯能够吸附10个钠原子,与本征石墨烯相比显著提高,氮掺杂的石墨烯只能吸附4个钠原子.因此,叽咯石墨烯有望成为一种潜在的储钠材料.     

肉苁蓉不同生育阶段矿质元素含量

应用ICP -AES技术测定了肉苁蓉不同生育阶段矿质元素含量.结果显示:(1)肉苁蓉药材的最佳采收期(肉质茎生长期),常量矿质元素中K含量高达9.45 mg·g-1,五种常量矿质元素的含量比例为K∶Na∶P∶Ca∶Mg=12∶ 3.4∶1.6∶ 1.4∶1,微量矿质元素中Fe含量最高为97.31 μg· g-1,五种微...