Chains Of Ions Research Articles

Structural Defects in Ion Chains by Quenching the External Potential: The Inhomogeneous Kibble-Zurek Mechanism

The nonequilibrium dynamics of an ion chain in a highly anisotropic trap is studied when the transverse trap frequency is quenched across the value at which the chain undergoes a continuous phase transition from a linear to a zigzag structure. Within Landau theory, an equation for the order parameter, corresponding to the transverse size of the zigzag structure, is determined when the vibrational motion is damped via laser cooling. The number of structural defects produced during a linear quench of the transverse trapping frequency is predicted and verified numerically. It is shown to obey the scaling predicted by the Kibble-Zurek mechanism, when extended to take into account the spatial inhomogeneities of the ion chain in a linear Paul trap.

Studies on outer sphere electron transfer reactions of some surfactant-cobalt(III) complexes with ferrocyanide anion

The kinetics and mechanism of reduction of the surfactant-cobalt(III) complex ions, cis-[Co(bpy)2(C12H25NH2)2]3+ and cis-[Co(phen)2(C12H25NH2)2]3+ (bpy = bipyridyl, phen = 1,10-phenan-throline, C12H25NH2 = dodecylamine) by Fe(CN6)4− in self-micelles were studied at different temperatures. Experimentally the reaction was found to be second order and the electron transfer postulated as outersphere. The rate constant for the electron transfer reaction for both the complexes was found to increase with increase in the initial concentration of the surfactant-cobalt(III) complex. This peculiar behaviour of dependence of second-order rate constant on the initial concentration of one of the reactants has been attributed to the presence of various concentration of micelles under different initial concentration of the surfactantcobalt(III) complexes in the reaction medium. The effect of inclusion of the long aliphatic chain of the surfactant complex ions into β-cyclodextrin on these reactions has also been studied.

Syntheses, Structures and Electrochemistry Properties of Two Dicyanamide Manganese(III) Complexes [Mn(5‐Brsalen)(dca)]·CH3OH and [Mn(3‐Meosalphen)(dca)(H2O)

AbstractTwo manganese(III)‐dicyanamide compounds, [Mn(5‐Brsalen)(dca)]·CH3OH (1) and [Mn(3‐Meosalphen)(dca)(H2O)] (2) (dca = dicyanamide anion, [N(CN)2]–), were synthesized and characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray structure analysis, and cyclic voltammetry. The structure of complex 1 is an infinite zigzag chain of hexacoordinate MnIII ions, in which the adjacent manganese atoms are connected by dca in μ1,5‐bridging mode. The molecular structure of complex 2 consists of a hexacoordinate MnIII atom, which generates a slightly distorted octahedral arrangement, and a dimer structure is formed by intermolecular hydrogen bonding interactions. The electrochemical properties of the two complexes were measured by cyclic voltammetry.

Morphology, structure, optical, and electrical properties of AgSbO3

The morphology of defect pyrochlore-type, AgSbO3 microparticle/nanoparticles obtained via solid state reaction evolve from irregular to Fullerene-like polyhedra before finally decomposing into metal-organic framework-5 like particles with increase in sintering temperature. The defect pyrochlore-type AgSbO3 particles are slightly Ag deficient while the valence of the antimony ion is shown to be +5 giving rise to a probable stoichiometry of Ag1−xSbVO3−x/2, with x∼0.01–0.04. A highly structured diffuse intensity distribution observed via electron diffraction is interpreted in terms of correlated displacements of one-dimensional (1D) silver ion chains along ⟨110⟩ directions. A redshifting in the absorption edges in UV-visible absorption spectra is observed for samples prepared at sintering temperatures higher than 1000 °C and attributed to the surface plasma resonance effect associated with small amounts of excess metallic Ag on the Ag1−xSbVO3−x/2 particles. An electrical properties investigation of the silver antimonate samples via dielectric, conductivity, and electric modulus spectroscopy shows a prominent dielectric relaxation associated with grain boundaries. The silver ion conductivity is associated with correlated displacements of 1D silver ion chains along ⟨110⟩ directions.

The Flexible Polyelectrolyte Hypothesis of Protein−Biomineral Interaction

Biomineralization is characterized by a high degree of control over the location, nature, size, shape, and orientation of the crystals formed. For many years, it has been widely believed that the exquisitely precise nature of crystal formation in biological tissues is the result of stereochemically specific interactions between growing crystals and extracellular matrix proteins. That is, the ability of many mineralized tissue proteins to adsorb to particular faces of biominerals has been attributed to a steric and electrical complementarity between periodic regions of the polypeptide chain and arrays of ions on the crystal face. In recent years, however, evidence has accumulated that many mineral-associated proteins lack periodic structure even when adsorbed to crystals. It also appears that protein-crystal interactions involve a general electrostatic attraction rather than arrays of complementary charges. In the present work, we review these studies and present some relevant new findings involving the mineral-modulating phosphoprotein osteopontin. Using molecular dynamics simulations, we show that the adsorption of osteopontin peptides to hydroxyapatite crystals does not involve a unique conformation of the peptide molecule, and that the adsorbed peptides are not aligned with rows of Ca(2+) ions on the crystal face. Further, we show that the interface between osteopontin peptides and calcium oxalate monohydrate crystals consists of peptide regions of high electronegativity and crystal faces of high electropositivity. Collectively, the above-mentioned studies suggest that interactions between mineral-modulating proteins and biologically relevant crystals are primarily electrostatic in nature, and that molecular disorder assists these proteins in forming multiple bonds with cations of the crystal face.

New Vanadium Oxide Nanostructures: Controlled Synthesis and Their Smart Electrical Switching Properties

Control over the different polymorphs of vanadium oxide that possess electrical switching properties is advancing rapidly as a result of the need to address energy-efficiency issues; an example of which is the intelligent regulation of infrared light demonstrated by these polymorphs. Recent advances in the development of new vanadium oxide structures as well as their promising electrical switching properties are summarized here. Theoretical analysis and experimental results suggest that the presence of infinite vanadium ion chains in the crystal structure plays a decisive role in determining the electrical properties of vanadium oxides. The successful synthesis of new vanadium oxide materials and their nanostructures not only promotes a mechanistic understanding of the temperature-driven electrical switching properties but also provides the right materials for constructing smart devices that can selectively filter out infrared light.

Analytic approximations to the phase diagram of the Jaynes-Cummings-Hubbard model

We discuss analytic approximations to the ground-state phase diagram of the homogeneous Jaynes-Cummings-Hubbard (JCH) Hamiltonian with general short-range hopping. The JCH model describes, e.g., radial phonon excitations of a linear chain of ions coupled to an external laser field tuned to the red motional sideband with Coulomb-mediated hopping or an array of high-$Q$ coupled cavities containing a two-level atom and photons. Specifically, we consider the cases of a linear array of coupled cavities and a linear ion chain. We derive approximate analytic expressions for the boundaries between Mott-insulating and superfluid phases and give explicit expressions for the critical value of the hopping amplitude within the different approximation schemes. In the case of an array of cavities, which is represented by the standard JCH model, we compare both approximations to numerical data from density-matrix renormalization-group calculations.

Preparation of Dicke states in an ion chain

We have investigated theoretically and experimentally a method for preparing Dicke states in trapped atomic ions. We consider a linear chain of $N$ ion qubits that is prepared in a particular Fock state of motion $|m⟩$. The $m$ phonons are removed by applying a laser pulse globally to the $N$ qubits and converting the motional excitation to $m$ flipped spins. The global nature of this pulse ensures that the $m$ flipped spins are shared by all the target ions in a state that is a close approximation to the Dicke state $|{D}_{N}^{(m)}⟩$. We calculate numerically the fidelity limits of the protocol and find small deviations from the ideal state for $m=1$ and $m=2$. We have demonstrated the basic features of this protocol by preparing the Bell state $|{D}_{2}^{(1)}⟩$ in two ${^{25}\text{M}\text{g}}^{+}$ target ions trapped simultaneously with an ${^{27}\text{A}\text{l}}^{+}$ ancillary ion.

Hysteretic Gas Sorption in a Microporous Metal–Organic Framework with Nonintersecting 3D Channels

AbstractA permanently porous metal–organic framework (MOF) based on infinite chains of metal ions and angular dicarboxylate ligands was synthesized, and its unusual gas sorption properties were characterized. Zn2+ ions react with 2,7‐ndcH2 (2,7‐naphthalenedicarboxylic acid) to produce a double‐walled framework, [Zn(2,7‐ndc)]. The porous MOF possesses narrow channels in three perpendicular directions. Gas sorption studies using Ar, CO2, H2, N2, and O2 at various temperatures reveal that saturation isotherms show a stepwise adsorption and hysteresis loops that are highly unusual features for microporous materials. The unexpected gas sorption behavior of the microporous MOF is due to the unique arrangement of the pore channels and their narrow passages comparable to the critical dimensions of adsorptive gases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2010)

Structure of caesium disulfate at 120 and 273 K

The crystal structures of Cs2S2O7 at 120 and 273 K have been determined from X-ray single-crystal data. Caesium disulfate represents a new structure type with a uniquely high number of independent formula units at 120 K: In one part caesium ions form a tube surrounding the disulfate ions, [Cs8(S2O7)6+]n; in the other part a disulfate double-sheet sandwiches a zigzagging caesium ion chain, [Cs2(S2O7)6-]n. Caesium disulfate shows an isostructural order-disorder transition between 230 and 250 K, where two disulfate groups become partially disordered above 250 K. The Cs+-ion arrangement shows a remarkable similarity to the high-pressure Rb(IV) metal structure.

2-photon ionization for efficient seeding and trapping of strontium ions

We describe an efficient way to photoionize strontium atoms in a linear radio-frequency trap. We use a 2-photon second order process to excite the autoionization resonance (4d2+5p2) 1D2 in neutral strontium (Sr). A doubled Ti:sapphire laser system is used at 431 nm to provide 100 fs pulses at 82 MHz. The fabrication of the laser systems for addressing the Sr+ transitions necessary for laser cooling and excitation of quantum jumps, vacuum system and ion trap structure are also described. With the current setup a easy and repeatable trapping of linear ion chains is readily achieved at very low Sr vapor pressures.

Small polaron mass with a long range density–displacement type interaction

Abstract In this work renormalization of the effective mass of an electron due to a small polaron formation is studied within the framework of the extended Holstein model. It is assumed that an electron moves along the one-dimensional chain of ions and interacts with ions vibrations of a neighboring chain via a long-range density–displacement type force. By means of the exact calculations a renormalized mass of a nonadiabatic small polaron is obtained at strong coupling limit. The obtained results compared with the mass of small polaron of ordinary Holstein model. The effect of ions vibrations polarization on the small polaron mass is addressed.

Two-qubit cells made of boron nitride nanotubes for a quantum computer

The electronic structure of boron nitride nanotubes (8, 0) with intercalated alkali metal atoms and alkaline-earth metal ions is studied. It is shown by calculation that the spin density is localized on individual atoms or ions. The antiferromagnetic state of a linear chain of atoms and ions turns out to be energetically more favorable. Exchange interaction between spins is fairly weak. Such systems are suggested to be used as two-qubit cells for a quantum computer.

Quantum search in a nonclassical database of trapped ions

We propose an implementation of the Grover's search algorithm in a nonclassical database using a linear chain of trapped ions. The database comprises all collective states with two ionic excitations; hence the number of database entries scales quadratically with the number of ions $N$. The system is initialized in an even superposition of all register states, i.e., in the symmetric Dicke state with $N$ ions sharing two excitations. The reflection-about-the-mean operator is produced merely by global addressing of the ion string by an off-resonant pulse with a suitable area, whereas the oracle operator is a control-phase gate. This simplification should allow a demonstration of quantum search in a database of hundreds of elements without needing to synthesize multiqubit quantum gates. The technique does not rely on coherent addition or subtraction of phonons, and hence the ion chain can be sympathetically cooled throughout the process.

Further investigation of the biodegradability of imidazolium ionic liquids

In continuation of our earlier investigations, this report presents a rationale behind the design of a series of imidazolium based ionic liquids and their biodegradation using the CO2 headspace test (ISO 14593 method, OECD 310). The effect on biodegradability of these salts through variation of the N-substituted side chains of imidazolium ions was examined further through incorporation of various functional groups and increased alkyl chain lengths. A series of anions containing moieties known to be biodegradable were also incorporated into a number of imidazolium based salts and examined in a similar fashion.

Magnetic structure and phase diagram of Sr5Rh4O12 frustrated Ising magnet

The magnetic structure of Sr5Rh4O12 is based on Ising chains of rhodium ions with a variable valence, Rh3+-Rh4+. The ordering in the chains is assumed to be ferromagnetic. It has been shown that the magnetic structure and phase diagram of Sr5Rh4O12 are well described in a model taking into account weak antiferromagnetic interactions between the nearest and next-nearest neighbors on the triangular lattice of ferromagnetic Ising chains. The ground state at low temperatures is the two-sublattice stripe phase; this phase in the magnetic field is transformed to the ferrimagnetic phase and, then, to the ferromagnetic phase. Small plateaus can be observed in the region of the transition from the ferrimagnetic phase to the ferromagnetic one.

Studies on outer-sphere electron transfer between iron(II) and some surfactant–cobalt(III) complexes in micelles as well as in β-cyclodextrin

The kinetics and mechanism of iron(II) reduction of the surfactant–cobalt(III) complex ions, cis-[Co(bpy) 2(C 12H 25NH 2) 2] 3+, cis-[Co(phen) 2(C 12H 25NH 2) 2] 3+ (bpy = 2,2′ bipyridine, phen = 1,10 phenanthroline, C 12H 25NH 2 = dodecylamine) in self-micelles were studied at different temperatures. Experimentally the reaction was found to be second order and the electron transfer postulated as outer-sphere. The second order rate constant for this electron transfer reaction for both the complex ions was found to increase with increase in the initial concentration of these surfactant–cobalt(III) complex ions. The effect of inclusion of the long aliphatic chain of the surfactant complex ions into β-cyclodextrin on these reactions has also been studied.

Binding Modes of a trans-Vinylbipyridinium Surfactant Bearing a Hexadecyl Chain to Cucurbit[n]uril (n = 6-8) in Aqueous Solution

Alkyl chains of naturally occurring fatty acids usually adopt the strain-free extended conformation in solution or gas phase. However, the conformations of alkyl chains are highly environment-dependent. Sometimes they adopt unusual, seemingly high-energy conformations. For example, alkyl chains confined in synthetic hosts adopt helical conformations. Another example is U-shaped conformations. Fatty acid binding proteins (FABPs) offer special environments for fatty acids such as palmitic acid and oleic acid to adopt a “U-shaped” conformation. The back-folding phenomenon of aliphatic chains found in Nature was scarcely observed in synthetic systems until recently. An alkyl chain bound to the cavity of γ-cyclodextrin (γ-CD) was suggested to adopt a U-shaped conformation based on fluorescence life-time measurements, which has never been confirmed, however. Recently, we reported an unequivocal example of the back-folding of aliphatic chains bound to a synthetic host. The alkyl chains of alkyltrimethylammonium ions bound to a hydrophobic cavity of cucurbit[8]uril (CB[8]), a member of host family cucurbit[n]uril (CB[n], n = 5-10), adopt a U-shaped conformation, which has been unequivocally characterized by various methods. However, the same alkyl chains of alkyltrimethylammonium ions were found to have an extended conformation when bound to CB[6] or CB[7]. Extending this work, we investigated the host-guest complex formation of CB[n] with other types of amphiphilic molecules containing a long alkyl chain. Herein, we report different binding modes of an amphiphilic molecule comprising a vinylbipyridinium unit as a polar head and a hexadecyl chain as a hydrophobic tail to CB[n] (n = 6, 7, and 8) in aqueous solution, and discuss the different conformations adopted by the alkyl chain.

Synthesis and characterization of vanadium(III) and vanadium(IV) polymers containing 3,5-pyrazoledicarboxylato

Three vanadium polymers [V2(µ-OH)2(H2O)2(Hpdc)2] n (1), {[Na2(µ-H2O)2][V2O2(pdc)2]} n (2) and {[K2(µ-H2O)][V2O2(pdc)2]} n (3) (H3pdc = 3,5-pyrazoledicarboxylate acid) have been hydrothermally synthesized and characterized by spectroscopic methods, magnetic susceptibility measurements and X-ray crystallography. The structure of 1 consists of infinite double-stranded chains. Both 2 and 3 are 3D coordination polymers, featuring ladder-like moieties, made up of [V2O2(pdc)2] subunits, interconnected by pairs of alkali ion chains. Variable-temperature magnetic behavior reveals the existence of antiferromagnetic interactions in 1 and dominant ferromagnetic interactions in 2 and 3.

In-situ Observation of the Behavior of Liquid Oxides during the Application of an Electric Potential: Bubble Formation and Dissolution in Liquid Silicates

When a potential is applied to a liquid silicate slag, bubbles of oxygen can be produced. Under certain conditions, these bubbles can be observed to redissolve in the liquid slag. This occurs under isothermal conditions when the potential is eliminated and under a thermal gradient during the application of a potential. There are two potential reasons for this observation: molecular solubility or the depolymerization of chains of silicate ions. Both hypotheses are discussed with the suggestion that depolymerization of chains of silicate ions may be responsible for the observed bubble dissolution behavior.