A three-dimensional microporous metal-organic framework with large hydrogen sorption hysteresis

A three-dimensional microporous metal-organic framework [Cd(2)(Tzc)(2)](n), which is dehydrated from [Cd(2)(Tzc)(2)(H(2)O)(2)](n), exhibits selective gas adsorption and large hydrogen sorption hysteresis.     

Brownian motion of a drop with hysteresis dissipation

Small water drops placed on a low-energy substrate with a slight tilt were vibrated parallel to the support with bands of Gaussian white noise of different powers. The drops drifted downward on the inclined support accompanied with random forward and backward movements. For a hysteresis free surface, the drift velocity should only be the product of the component of the gravitational acceleration and the Langevin relaxation time, being independent of the power of noise. On the other hand, in the presence of hysteresis, as is the case here, the drift velocity depends strongly on the power of the noise. This result illustrates the role of hysteresis in the drifted motion of drops on a surface subjected to vibration, which has important bearings on various forms of work fluctuation relations.     

Dynamics of the NH4+ ion in ABX3 perovskites

The Raman and ir spectra of NH₄MnF₃, NH₄ZnF₃ and NH₄MnCl₃ have been measured in order to study the internal vibration modes of NH₄⁺ in different surrounding conditions. The internal force constants have been determined and compared to their values in ammonium halides and in the free ion, Their trends have been discussed in terms of the hydrogen bonding and volume effects. The intraionic polarizability parameters have also been obtained and compared to those of CH₄.     

Analytical theory of hysteresis in ion channels: two-state model

Channel-forming proteins in a lipid bilayer of a biological membrane usually respond to variation of external voltage by changing their conformations. Periodic voltages with frequency comparable with the inverse relaxation time of the protein produce hysteresis in the occupancies of the protein conformations. If the channel conductance changes when the protein jumps between these conformations, hysteresis in occupancies is observed as hysteresis in ion current through the channel. We develop an analytical theory of this phenomenon assuming that the channel conformational dynamics can be described in terms of a two-state model. The theory describes transient behavior of the channel after the periodic voltage is switched on as well as the shape and area of the hysteretic loop as functions of the frequency and amplitude of the applied voltage. The area vanishes as the voltage period T tends to zero and infinity. Asymptotic behaviors of the loop area A in the high- and low-frequency regimes, respectively, are A approximately T and A approximately T(-1).     

Collisionally damped ion motion in ICR spectrometry

A Schrödinger equation equivalent to the Langevin equation of ion motion in ICR cells is presented. A wave function for the scattering states has been found as the solution to the equation of ion motion under the influence of electric and magnetic fields perturbed by a scattering potential. Applying the minimized wave packet as a wave function describing coherent states, the scattering amplitudes are determined explicitly. The connection between the collision cross section and the scattering amplitudes is found by making use of the incoming and outgoing particle flux density. The collision cross section found in this way is converted from quantum theory to classical physics. The collision cross section, which plays an essential role in the determination of rate constants can be determined by the aid of ICR experimental data if the contribution of an alternating electric field is taken into account.     

Probing shapes of bichromophoric metal-organic complexes using ion mobility mass spectrometry

Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexes carrying pendant chromophores. The three complexes investigated were the copper(II) complex Cu(DAC)2+ (DAC = 1,8-bis(9-methylanthracyl)cyclam, cyclam = 1,4,8,11-tetraazacyclotetradecane), the N-nitrosylated ligand DAC-NO, and the Roussin's red salt ester (mu-S,mu-S')-protoporphyrin-IX-bis(2-thioethyl ester)tetranitrosyldiiron (PPIX-RSE). From the IM-MS data coupled with theoretical calculations, it was found that [Cu(II)(DAC - H)]+ exists as a single conformer, with one anthracenyl group above the cyclam and the other below, similar to the crystal structure of Cu(II)(DAC)2+. The metal-free N-nitrosylated ligand (DAC-NO + H)+ has two conformations: one family of structures has one anthracenyl group above the cyclam and one below, while the other has both anthracenyl groups on the same side of the cyclam. These observations are consistent with 1H NMR data for the neutral DAC-NO complex that indicate the presence of two geometric isomers in solution. The third species, PPIX-RSE, has a porphyrin chromophore covalently linked to an Fe2S2(NO)4 cluster for use as a precursor for the photochemical delivery of nitric oxide in single- and two-photon excitation processes. Ion mobility indicates the presence of two (PPIX-RSE + H)+ conformations, consistent with the previous interpretation of the bimodal fluorescence lifetime decay seen for PPIX-RSE. DFT structures, in good agreement with the IM-MS cross sections, indicate two "bent" conformations with the planes of the porphyrin and Fe2S2 rings at different angles with respect to each other.     

Hydronium ion motion in nanometer 3-methyl-pentane films

An ion soft-landing approach was applied to study the motion of hydronium (D(3)O(+)) and cesium (Cs(+)) ions from 84 to 104 K in glassy 3-methyl-pentane (3MP) films vapor deposited on Pt(111). Both ions were found to have very similar mobilities in 3MP. The span of ion mobilities probed is from approximately 10(-18) to approximately 10(-13) m(2) V(-1) s(-1). Ion transport in these films was studied as a function of film thickness and electric field strength. The drift velocity was found to be linear with applied field below about 2 x 10(8) Vm and deviated from linearity above this. To a large extent, D(3)O(+) and Cs(+) motion in 3MP was well predicted by a simple continuum-based ion mobility model in films from 25 to 20,000 ML thick (including pronounced perturbations 7 ML from both the vacuum and Pt interfaces). The mobility varied with temperature more slowly than predicted by Stokes' law, which may be due to extended inhomogeneous structures in the 3MP near its glass transition at 77 K.     

The carbenium ion - oxonium ion exchange processes related to vinyl and ring-opening polymerization

It has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species. Equilibria between carbenium ions (CH₃OCH₂⁺A⁻ has been used as a model) and their onium counterparts ((CH₃)₂O taken as a model base) as well as between covalent species (CH₃OCH₂OSO₂CF₃) and the corresponding oxonium ion (with a (CH₃)₂O ligand) have been studied by dynamic ¹H and ¹⁹F NMR. Total ionization of methoxymethyl triflate (CH₃OCH₂OSO₂CF₃) has been shown to increase indeed from 10⁴ (-10°C) to 10⁶ (-70°C) times when 1,0 mol·L⁻¹ of (CH₃)₂O is added. Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers.     

Study of the correlated motion of ion mixtures in an rf ion trap

We observed variations of the signal position versus the filament temperature, and thus the relative amounts of Ba⁺ and BaO⁺ ions stored simultaneously in an rf trap. The tendency of variations is explained by a generalized model of two coupled ion clouds, in which the coupling condition and the frequencies of correlated motions depend on the ion masses, the force constants of the applied trapping field and the Coulomb interaction between the ions as well as the relative ion numbers of the two ion clouds.     

Characteristics of electrical field and ion motion in surface‐electrode ion traps

In this article, we calculated the potential function of the surface‐electrode ion trap (SEIT) by using Green's function method, optimized trap size, obtained the coefficients of the multipoles and analyzed ion trajectories in the RF potential. The optimized SEIT not only increases its trapping well depth by a factor of about 15, but also has relatively good linearity of the field (or large quadrupole component). The current design of SEIT can work well either as the ion guide for ion transmission or as the ion trap for ion confinement. Our research can be used to calculate the potential function in the SEIT with different device parameters, understand ion motions in the traps and optimize instrument performance. The method for calculating potential function can be expanded to planar and halo ion traps. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of ion structures in structurally related compounds using precursor ion fingerprinting

Structurally-related alkaloids were analyzed by electrospray ionization/multiple stage mass spectrometry (ESI/MS ⁿ ) at varying collision energies to demonstrate a conceptual algorithm, precursor ion fingerprinting (PIF). PIF is a new approach for interpreting and library-searching ESI mass spectra predicated on the precursor ions of structurally-related compounds and their matching product ion spectra. Multiple-stage mass spectra were compiled and constructed into “spectral trees” that illustrated the compounds’ product ion spectra in their respective mass spectral stages. The precursor ions of these alkaloids were characterized and their spectral trees incorporated into an MS ⁿ library. These data will be used to construct a universal, searchable, and transferable library of MS ⁿ spectra. In addition, PIF will generate a proposed structural arrangement utilizing previously characterized ion structures, which will assist in the identification of unknown compounds.     

Employ ionic liquid to stabilize black-phase formamidinium perovskites

正The certified power conversion efficiency (PCE) of perovskite solar cells which have emerged as the most promising candidates for next-generation thin-film photovoltaics has exceeded 25%.Among all available compositions,formamidinium lead iodide perovskite(FAPbI_3) has a theoretically higher efficiency than the other perovskite analogues due to its narrower bandgap [1,2] and hence has attracted widespread attention.However,due to the large size of the formamidinium cation,the black-phase of FAPbI_3 is metastable at room temperature and tends to transform to non-photoactiveδ-phase [3],which greatly limits its applications.Therefore,stabilizing the black-phase of FAPbI_3 at room temperature has become a great challenge in the community,which urgently needs a remedy.     

Analytical approach for description of ion motion in quadrupole mass spectrometer

Implementation of the analytical method of the solution of the Mathieu equation in conjunction with the algebraic presentation of Mathieu functions is discussed in this work. This approach is used for the analytical expression of fundamental properties of the quadrupole field such as ion trajectory stability and transmission. Extensive comparison with the matrix method is presented with demonstration of the fundamental advantages of the analytical method. However, contrary to the matrix method, the analytical method is limited to the cos trapping waveforms.     

Misphasing of ion motion in quadratic potential induced by space-periodic disturbance

An ideally quadratic potential used in different types of ion mass analyzer such as Paul trap, Kingdon trap and quadratic field reflectron may be space-periodically disturbed due to inaccuracy of fabrication and design features. If ion motion in such devices is computer-simulated, disturbances of potential may be caused by the peculiarity of the computation method. The problem investigated in this work is the effect that weak space-periodic disturbance of a quadratic potential takes on the ion motion in such a potential. The effect of the disturbance we considered is the misphasing of an ion cloud oscillating in a disturbed quadratic potential. A method to evaluate the characteristic misphasing time is presented. For the case of disturbance amplitude being constant along ion trajectories, the designated problem may be considered analytically. If the disturbance amplitude depends on oscillation co-ordinate, the result can be obtained by use of numerical integration. An example of numerical calculation is presented.     

Lithium ion pathways in LiFePO4 and related olivines

Determining ion transport pathways as regions of low bond valence mismatch represents a simple, reliable way of characterizing ion transport pathways in local structure models, provided that the local structure model captures the essential structural features. The examples of LiFePO₄ and other olivine-type mixed conductors discussed here demonstrate the impact of structural disorder on the ion transport pathway and mechanism. The effect of Li′_Fe antisite defects on the transition from one- to two-dimensional conduction pathway dimensionality as well the possibility of heterogeneous doping of LiFePO₄ by a lithium phosphate glass surface layer are discussed in detail.     

毛细管离子色谱及相关新技术

与离子色谱（IC）成功的商业发展形成对比的是IC技术多年来一直鲜有新意,使人们对IC的认识多停留在作为一项无机离子特别是阴离子分析的工具上。而事实上,IC不仅可以解决常规无机阴、阳离子的有效分析,同时还可以解决有机酸、有机胺、糖类、氨基酸等大量用HPLC无法或难以解决的药物分析。另外,需要进一步指出的是相对于HPLC的有机相体系和GC的气相体系,IC所使用的水相淋洗液与生物样品水溶液体系更兼容。近期有关市场的调查（Chromatography Market Profile Ion Chromatography）也说明IC有关通用和环境分析应用的比例已经不断减少,而包括药物、农业、食品及化工的应用却在不断增加（LC GC North America, 29(2011)214）。而在理论上,著名分析化学家Paul R. Haddad教授2008年在其综述文章（J. Chromatogr. A, 1184 (2008) 456–473）,讨论了IC的最新发展,除了对IC固定相、微型化、色谱峰容量的扩展及联用技术讨论之外,特别加上一个章节“Ion chromatography and bioanalysis—two different worlds?”,对目前特别关注的生物标志物如多肽、蛋白质、糖蛋白、寡糖、多糖,及核酸等样品的分离与传统IC分离小分子样品没有实质的差异,而作为上述生物样品最大的检测问题是它们均缺乏有效的特征紫外吸收,无法用常规紫外检测器进行检测。可否采用毛细管离子色谱（CIC）来解决这些问题？CIC是目前IC技术的前沿研究领域,可以视为nano-LC的对等IC系统,具有样品和淋洗液消耗少、质量灵敏度高、易于和MS、ICP联用等优势。具有分析技术风向标之称的、目前世界上最大的国际分析仪器展－美国匹兹堡展销会在2011年3月14-17日期间首次安排了半天的CIC专场讨论会。CIC通常是指分离柱内径在0.1-0.5 mm的IC系统。分离柱尺寸的降低要求其它关键部件作相应的改动,而这些改动不是简单的降低机械尺寸,它需要结构性和整体性的改动,属于再创造。下文就近期CIC几大关键部件技术的新进展作一介绍。     

Photocurrent generation from semiconducting manganese oxide nanosheets in response to visible light

Unilamellar nanosheet crystallites of manganese oxide generated the anodic photocurrent under visible light irradiation (lambda < 500 nm), while the nanosheets themselves were stable as revealed by in-plane XRD and UV-visible absorption spectra. The band gap energy was estimated to be 2.23 eV on the basis of the photocurrent action spectrum. The molecular thickness of approximately 0.5 nm may facilitate the charge separation of excited electrons and holes, which is generally very difficult for strongly localized d-d transitions. The monolayer film of MnO2 nanosheets exhibited the incident photon-to-electron conversion efficiency of 0.16% in response to the monochromatic light irradiation (lambda = 400 nm), which is comparable to those for sensitization of monolayer dyes adsorbed on a flat single-crystal surface. The efficiency declined with increasing the layer number of MnO2 nanosheets, although the optical absorption was enhanced. The recombination of the excited electron-hole pairs may become dominant when the carriers need to migrate a longer distance than 1 layer through multilayered nanosheets.