Single-ion anisotropy in a four-spin system: mixing of S-states

A four-spin system with s=1 and the single-ion anisotropy, D∑ _j [s _jz ] ² , is considered. When D≠0 the Hamiltonian of the system does not commute with S ² and, therefore, S cannot be used as an additional label of energy levels. In this work we concentrate on the problem of mixing states with different total spins S. The Hamiltonian matrix is transformed to the symmetry-adapted basis (with subspaces labeled by the irreducible representations of the symmetry group) and next, after solving the eigenproblem for S ², to the basis with vectors labeled by S. Each eigenproblem is solved exactly (at least numerically) and the eigenstates are expressed as ∑ _S a _S |S〉. The coefficients a_S are analyzed, especially for their D-dependence. Even in such a small system different schemes of level mixing can be observed.      

Single-ion recycling reactions

A single ion is enough: Ion reaction rates and reaction product branching ratios could be determined through repeated regeneration of the original target ion by photodissociation after each reaction. The product molecule was identified through nondestructive mass spectrometry. Finally, the target ion was regenerated through photodissociation of the molecular ion.     

Single-ion conducting polymer electrolytes as a key jigsaw piece for next-generation battery applications

As lithium-ion batteries have been the state-of-the-art electrochemical energy storage technology, the overwhelming demand for energy storage on a larger scale has triggered the development of next-generation battery technologies possessing high energy density, longer cycle lives, and enhanced safety. However, commercial liquid electrolytes have been plagued by safety issues due to their flammability and instability in contact with electrodes. Efforts have focused on developing such electrolytes by covalently immobilizing anionic groups onto a polymer backbone, which only allows Li⁺ cations to be mobile through the polymer matrix. Such ion-selective polymers provide many advantages over binary ionic conductors in battery operation, such as minimization of cell polarization and dendrite growth. In this review, the design, synthesis, fabrication, and class are reviewed to give insight into the physicochemical properties of single-ion conducting polymer electrolytes. The standard characterization method and remarkable electrochemical properties are further highlighted, and perspectives on current challenges and future directions are also discussed.

A review of the physicochemical properties of single-ion conducting polymer electrolytes is presented. The standard characterization method, remarkable electrochemical properties and perspectives are further highlighted.     

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy

Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L_2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine Fe^I dopant ions to be linearly coordinated, occupying a D_6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L_2,3-edge XAS from which the energy reduction of 3d_z² due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L₃-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm⁻¹), that corresponds with Orbach relaxation via the first excited, M_J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.

Taking advantage of synchrotron light source methods, we present the geometric and electronic structure of iron doped in lithium nitride.     

Single-ion versus dipolar origin of the magnetic anisotropy in iron(III)-oxo clusters: a case study

A multitechnique approach has allowed the first experimental determination of single-ion anisotropies in a large iron(III)-oxo cluster, namely [NaFe6(OCH3)12(pmdbm)6ClO4 (1) in which Hpmdbm = 1,3-bis(4-methoxyphenyl)-1,3-propanedione. High-frequency EPR (HF-EPR). bulk susceptibility measurements, and high-field cantilever torque magnetometry (HF-CTM) have been applied to iron-doped samples of an isomorphous hexagallium(III) cluster [NaGa6(OCH3)12-(pmdbm)6]ClO4, whose synthesis and X-ray structure are also presented. HF-EPR at 240 GHz and susceptibility data have shown that the iron(III) ions have a hard-axis type anisotropy with DFe = 0.43(1) cm(-1) and EFe = 0.066(3) cm(-1) in the zero-field splitting (ZFS) Hamiltonian H = DFe[S2(z) - S(S + 1)/3] + Fe[S2(x) - S2(y)]. HF-CTM at 0.4 K has then been used to establish the orientation of the ZFS tensors with respect to the unique molecular axis of the cluster, Z. The hard magnetic axes of the iron(III) ions are found to be almost perpendicular to Z, so that the anisotropic components projected onto Z are negative, DFe(ZZ)= -0.164(4) cm(-1). Due to the dominant antiferromagnetic coupling, a negative DFe(ZZ) value determines a hard-axis molecular anisotropy in 1, as experimentally observed. By adding point-dipolar interactions between iron(III) spins, the calculated ZFS parameter of the triplet state, D1 = 4.70(9) cm(-1), is in excellent agreement with that determined by inelastic neutron scattering experiments at 2 K, D1 = 4.57(2) cm(-1). Iron-doped samples of a structurally related compound, the dimer [Ga2(OCH3)2(dbm)4] (Hdbm = dibenzoylmethane), have also been investigated by HF-EPR at 525 GHz. The single-ion anisotropy is of the hard-axis type as well, but the DFe parameter is significantly larger [DFe = 0.770(3) cm(-1). EFe = 0.090(3) cm(-1)]. We conclude that, although the ZFS tensors depend very unpredictably on the coordination environment of the metal ions, single-ion terms can contribute significantly to the magnetic anisotropy of iron(III)-oxo clusters, which are currently investigated as single-molecule magnets.     

Calorimetrically measurable enthalpic isotope effect

Calorimetric techniques have revealed that the enthalpy of reaction with water is more exothermic by about 2.2 kcal/mol, for the perdeuteriated naphthalene anion radical (K+C10D8*-(s) + H2O(liq) --> 1/2C10D8H2(s) + 1/2C10D8(s) + KOH(aq)) than it is for the perprotiated system. These results, when coupled with the known enthalpy of electron transfer between naphthalene and its perdeuteriated analogue imply that the heat of hydrogenation of naphthalene decreases by about 1.8 kcal/mol upon perdeuteriation of the naphthalene.     

Single-ion and molar conductances. Application to transference number data analysis

Several of the present molar conductance equations have been examined in detail in order to obtain equations for the concentration dependence of the single-ion conductances which, when combined with existing conductance and transference data, permit three independent evaluations of the conductance parameters, in particular the association constant and the distance of closest approach of two ions of opposite charge. In order to make use of existing transference data it was necessary to develop a suitable extrapolation equation. It is shown that the procedures outlined constitute a useful test of the concentration dependence of transference numbers found experimentally.Equipe de recherche associée au C.N.R.S., ERA 310.     

聚阴离子单离子导体凝胶电解质的制备及其在锂离子电池中的应用

以2-丙烯酰胺-2-甲基丙磺酸(AMPS)与Li₂CO₃反应制得AMPSLi单体,以(聚偏氟乙烯-六氟丙烯)共聚物(PVDF-HFP)为基膜条件进行原位聚合,加入乙二醇二甲醚(DME),1,3-二氧戊烷(DOL)作为增塑剂,制备了一种聚阴离子单离子导体凝胶电解质。采用电化学工作站进行电化学稳定窗口与迁移数表征。结果表明：单离子导体凝胶电解质具有2~4.5 V的宽电化学稳定窗口以及高达0.74的锂离子迁移数。采用磷酸铁锂（LFP）作正极,金属锂作负极,PVDF-HFP-PAMPSLi单离子导体作为电解质组装电池。在不加入锂盐时,电池在2C电流密度下具有125 mAh·g^-1的高比容量和超过500次的循环次数;在5 C的高电流密度下具有100 mAh·g^-1的比容量与超过300次的稳定循环能力,并保持接近100%的稳定库伦效率。      

Single-ion heat capacities, C(p)(298)ion, of solids: with a novel route to heat-capacity estimation of complex anions

Single-ion heat capacities, C(p)(298)(ion), are additive values for the estimation of room-temperature (298 K) heat capacities of ionic solids. They may be used for inferring the heat capacities of ionic solids for which values are unavailable and for checking reported values, thus complementing our independent method of estimation from formula unit volumes (termed volume-based thermodynamics, VBT). Analysis of the reported heat-capacity data presented here provides a new self-consistent set of heat capacities for both cations and anions that is compatible (and thus may be combined) with an extensive set developed by Spencer. The addition of a large range of silicate species permits the estimation of the heat capacities of many silicate minerals. The single-ion heat capacities of individual silicate anions are observed to be strictly proportional to the total number of atoms (Si plus O), n, contained within the silicate anion complex itself (e.g., for the anion Si(2)O(7)(2-), n = 9, for SiO(4)(2-), n = 5), C(p)(silicate anion)/J K(-1) mol(-1) = 13.8n, in a new rule that is an extension of the Neumann-Kopp relationship. The same linear relationship applies to other homologous anion series (for example, oxygenated heavy-metal anion complexes such as niobates, bismuthates, and tantalates), although with a different proportionality constant. A similar proportionality, C(p)(complex anion)/J K(-1) mol(-1) ≈ 17.5n, which may be regarded as a convenient "rule of thumb", also applies, although less strictly, to complex anions in general. The proportionality constants reflect the rigidity of the complex anion, being always less than the Dulong-Petit value of 25 J K(-1) mol(-1). An emergent feature of our VBT and single-ion approaches to an estimation of the thermodynamic properties is the identification of anomalies in measured values, as is illustrated in this paper.     

Extension of measurable range of film dosimetry by a low energy X-ray absorption method

The availability of an X-ray absorption technique employing a very low power X-ray tube was examined to extend measurable range for photographic film dosimetry. The X-ray tube having titanium target was operated at 8 kV and 0.2 microA to emit Ti KX-rays of moderate intensity. The degree of the Ti KX-ray absorption, defined as similar to photographic density, was measured for the two kinds of badge film, Fuji gamma-ray badge film and Kodak personal monitoring film, type 2 exposed for 60Co or 137Cs gamma-rays and developed by the respective standard procedures. The experimental results show that the dosimetric range of 0.01-100 R for the Fuji film and 0.03-1,000 R for the Kodak film may be easily measured by 1 minute counting with the relative statistical error (sigma) of 10%.     

On identifiability for chemical systems from measurable variables

The dynamics of the composition of chemical species in reacting systems can be characterized by a set of autonomous differential equations derived from mass conservation principles and some elementary hypothesis related to chemical reactivity. These sets of ordinary differential equations (ODEs) are basically non-linear, their complexity grows as much increases the number of substances present in the reacting media and can be characterized by a set of phenomenological constants (kinetic rate constants) which contains all the relevant information about the physical system. The determination of these kinetic constants is critical for the design or control of chemical systems from a technological point of view but the non-linear nature of the ODEs implies that there are hidden correlations between the parameters which maybe can be revealed with a identifiability analysis.     

Circuit resonance energy: a key quantity that links energetic and magnetic criteria of aromaticity

Energetic and magnetic criteria of aromaticity are different in nature and sometimes make different predictions as to the aromaticity of a polycyclic pi-system. Thus, some charged polycyclic pi-systems are aromatic but paratropic. We derived the individual circuit contributions to aromaticity from the magnetic response of a polycyclic pi-system and named them circuit resonance energies (CREs). Each CRE has the same sign and essentially the same magnitude as the corresponding cyclic conjugation energy (CCE) defined by Bosanac and Gutman. Such CREs were found to play a crucial role in associating the energetic criteria for determining the degree of aromaticity with the magnetic ones. We can now interpret both energetic and magnetic criteria of aromaticity consistently in terms of CREs. Ring-current diamagnetism proved to be the tendency of a cyclic pi-system to retain aromatic stabilization energy (ASE) at the level of individual circuits.     

Single-ion solvation free energies and the normal hydrogen electrode potential in methanol, acetonitrile, and dimethyl sulfoxide

The division of thermodynamic solvation free energies of electrolytes into contributions from individual ionic constituents is conventionally accomplished by using the single-ion solvation free energy of one reference ion, conventionally the proton, to set the single-ion scales. Thus, the determination of the free energy of solvation of the proton in various solvents is a fundamental issue of central importance in solution chemistry. In the present article, relative solvation free energies of ions and ion-solvent clusters in methanol, acetonitrile, and dimethyl sulfoxide (DMSO) have been determined using a combination of experimental and theoretical gas-phase free energies of formation, solution-phase reduction potentials and acid dissociation constants, and gas-phase clustering free energies. Applying the cluster pair approximation to differences between these relative solvation free energies leads to values of -263.5, -260.2, and -273.3 kcal/mol for the absolute solvation free energy of the proton in methanol, acetonitrile, and DMSO, respectively. The final absolute proton solvation free energies are used to assign absolute values for the normal hydrogen electrode potential and the solvation free energies of other single ions in the solvents mentioned above.     

Single-ion activities and Mn(Hg)/Mn(II) reactions in aqueous solutions of alkaline-earth chlorides

Combined thermodynamic and kinetic studies have yielded convenient single-ion activity coefficients for manganese(II), alkaline-earth, and chloride ions and standard exchange currents for the two steps of the Mn(Hg)/Mn(II) electrode in 0.005 M MnCl₂+0.495 M MeCl₂ (for Me=Mg, Ca, Sr, Ba, and Mn) at 25°C. The results indicate that the fall in mean ionic activity coefficient for the alkaline-earth chlorides along the sequence from magnesium to barium is carried to a larger extent by the cation than by the anion, that also the activity coefficient for the minority cation Mn(II) falls along this sequence, and that other than activity-coefficient effects on the Mn(Hg)/Mn(II) reactions appear only with barium ions, which retard the reactions additionally. The results are discussed with emphasis on ionic interactions and double-layer effects.     

Uncertainty in repeated measurement of a small non-negative quantity: explanation and discussion of Bayesian methodology

This article considers the problem of uncertainty evaluation when there are repeated measurements of a small quantity known to be non-negative. A solution to this problem has recently been put forward by the Analytical Methods Committee of the Royal Society of Chemistry (Accred Qual Assur 13:29–32). The Bayesian statistical basis of this solution is explained and discussed. It is shown that the performance of this procedure can be poor in an important subset of measurement situations.     

Quality and quantity within medicine

The concept of quality is placed both within a historical as well as philosophical light. It is argued that nowadays general and laboratory medicine is a logical extension of economical and social concepts which stem from the beginning of the twentieth century. However, it seems that medicine cannot be explained based entirely upon these concepts. The medical field has a variety of definitions of quality: all depending on the person and/or institution posing the questions. The quality concept sometimes concerns an individual and sometimes a group of individuals. The quality definition and indicator scores are then different. This quantified quality can also be looked upon from an eastern (i.e. Japanese, Chinese, ancient Greece) perspective. The ideal world, framed within a cyclic evaluation between well-defined static situations, does not relate easily with the individualized (quantified quality) western medical world. Nevertheless, we are in search of a quality concept that balances the western industrial model of medicine and the eastern, philosophical approach. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. Apart from exceptional circumstances, they are not submitted to the usual referee procedure and go essentially unaltered. Presented at the European Conference on Quality in the Spotlight in Medical Laboratories, 7–9 October 2001, Antwerp, Belgium     

Elements very rapidly measurable by INAA in biological and environmental materials

In connection with the increasing usage of reference materials in INAA work, and with the continuing interest in this laboratory in rapid analyses via very short-lived induced activities, 13 biological and 8 environmental reference materials have been processed, under rapid analysis conditions, by the reactor-flux INAA Advance Prediction Computer Program. The results described show that a total of 33 induced (n, ) activities of 26 elements are detectable in these 21 reference materials, in total analysis times ranging from 1.5 to 192 seconds.     

Nobiletin: efficient and large quantity isolation from orange peel extract

It is known that nobiletin possesses anticancer, antiviral and anti-inflammatory activities. Recently, the demand for nobiletin in large quantities and high purity has increased. However, conventional normal-phase silica gel chromatography and C(18)-reverse-phase separation methods cannot satisfy the requirement of pure and gram scale nobiletin in a timely manner. In exploring the composition and the biological activities of polymethoxyflavones from sweet orange (Citrus sinensis) peel, we developed an efficient isolation method for nobiletin. By employing this methodology, pure nobiletin, in gram quantities, was obtained in only one purification cycle. The orange peel extract was loaded onto a silica gel flash column and eluted by a mixed solvent system of ethyl acetate and hexanes, and the fractions collected. Upon combination of the eluted fractions, mainly containing nobiletin and 5,6,7,4'-tetramethoxyflavone, and concentration under reduced pressure, the resultant residue was loaded onto a Regis chiral column. Gram amounts of nobiletin and 5,6,7,4'-tetramethoxyflavone were then eluted with ethanol and hexanes, respectively.