Ions In Shells Research Articles

Transport Mechanism of Hydroxide Ions Focused on the Vehicle Mechanism Near the Cation Sites in Anion Exchange Membranes

We investigated the transport factors of hydroxide ions in anion exchange membrane (AEM). We used partially fluorinated quaternized QPAF-4 polymer with trimethylammonium groups as the AEM material and analyzed it using classical molecular dynamics (MD) simulations. Analysis of the dependence of density on water content (λ) suggested that the voids in the QPAF-4 polymer are fully filled with water molecules under high λ conditions (λ = 15), and as the polymer absorbs additional water molecules, it expands, resulting in a decrease in density. Furthermore, radial distribution function analysis and existence ratio analysis of hydroxide ions in the solvation shells of trimethylammonium groups indicated that increasing λ reduces the overlap of the first solvation shells and causes hydroxide ions to migrate from the first to the second solvation shell. This result indicates that these structural factors contribute to the enhanced diffusivity of hydroxide ions under high λ conditions.

Manifestation of the thermal motion of ions in the conductivity spectrum of liquid water

The nonresonant component of the dynamic conductivity spectrum of liquid water in the frequency range of 104–1014 Hz is described by a model of free charged particles participating in thermal motion. The background of IR spectrum is represented by the diffusion response of elementary charges in the form of protons, holes, and H3O+ and OH– ions; terahertz loss (1010 Hz) is a response of the same ions in hydrate shells; microwave absorption at frequencies below 107 Hz is represented by the response of the same ions surrounded by the hydrate shell and additionally by the ionic atmosphere.

Hidden charge states in soft-x-ray laser-produced nanoplasmas revealed by fluorescence spectroscopy.

Highly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least 11+.

Mixed-salt effects on the conformation of a short salt-bridge-formingαhelix: A simulation study

The structure of a single alanine-based ACE-AEAAAKEAAAKA-NH2 peptide in explicit aqueous solutions with mixed inorganic salts (NaCl and KCl) is investigated by using molecular simulations. The concentration of Na(+), c(Na(+)), varies from 0.0M to 1.0M, whereas the concentration of K(+) is 1-c(Na(+)). The simulated peptide is very sensitive to the change of concentration ratio between Na(+) and K(+). When the concentration ratio between Na^{+} and K^{+} is changed from 0.5/0.5, the structure of the peptide becomes loose or disordered. This specific phenomenon is confirmed via checking the changes of helix parameters and mapping the free energy along different coordinates. The higher normalized probability of forming direct and indirect salt bridges between residues Glu7(+) and Lys11(+) and the smallest probability of forming ringlike structures should be responsible for the stabilized helix structure in the 0.5 Na(+)/0.5 K(+) solution. Furthermore, a noticeable conformational transition from an extended helix to an α helix is found in the 0.5 Na(+)/0.5 K(+) solution, where a local ion cloud shows that some Na(+) ions in the inner shells are still directly binding with the peptide, while K(+) in the outer shells are moving into the inner shells, keeping the peptide in the collapsed state.

Luminescent SiO<SUB>2</SUB> Particles: Porous Structure of Matrix and Stability of Quantum Dots

Luminescent CdSe/Cd0.5Zn0.5S quantum dots (QDs) with narrow size distribution and high photoluminescence (PL) efficiency were fabricated via a two-step organic synthesis. The QDs were coated with a SiO2 shell by a reverse micelle route. The thickness of SiO2 shell on the QDs was adjusted for investigating the effect of the porous structure of SiO2 matrix on the stability of the QDs. When the shell thickness of SiO2 shells is less than 5 nm, the pores of SiO2 shell are type II (cylindrical pores). In contrast, the pores of SiO2 shell are type IV (one-neck-flask-shaped pores) while the shell thickness is 10 nm. The stability of SiO2-coated QDs was investigated in phosphate-buffered saline (PBS, pH - 7.4) buffer solutions using various phosphate concentrations. The QDs coated with a SiO2 shell with type IV pores revealed high stability compared with those with type II pores. This is ascribed that cylindrical pores (type II) accelerated the transfer of ions in SiO2 shells compared with type IV pores.

Synthesis and White Light Emission of Rare Earth‐Doped HfO2 Nanotubes

Luminescent nanotubes based on rare earth (RE) (Eu, Tb)‐doped hafnia (HfO2) were prepared by radio frequency (RF) sputtering with electrospun polyvinylpyrolidone (PVP) nanofibers as templates. The nanotubes annealed at 500°C have a uniform structure with desired tubular morphologies. Various colors of photoluminescence (PL) could be easily obtained by tuning the concentrations of the RE ions in the HfO2 host. The Eu‐ and Tb‐codoped HfO2 (HfO2:Eu&Tb) nanotubes exhibited white light emissions under a 325 nm excitation. Good Commission International de I'Eclairage (CIE) coordinates (0.333, 0.323) and color temperature (Tc) (5465 K) were achieved in the HfO2:Eu&Tb nanotubes. Experimental evidence showed that the presence of blue emission originates from the defect states in HfO2 nanotubes, the green and the red emissions can be attributed to the inner 4f shell transitions of corresponding Tb3+ ions and Eu3+ ions in HfO2 shells, respectively. Compared with RE‐doped HfO2 films, the nanotube samples showed intense white light emissions, revealing that the HfO2:Eu&Tb nanotubes are an efficient white light‐emission material.

Interface electronic structures ofBaTiO3@Xnanoparticles (X=γ-Fe2O3,Fe3O4,α-Fe2O3, and Fe) investigated by XAS and XMCD

The electronic structures of ${\text{BaTiO}}_{3}@X$ (core@shell) nanoparticles ($X=\ensuremath{\gamma}{\text{-Fe}}_{2}{\text{O}}_{3}$, ${\text{Fe}}_{3}{\text{O}}_{4}$, and Fe) have been investigated by employing soft x-ray-absorption spectroscopy and x-ray magnetic circular dichroism (XMCD). It is found that the valence states of Ti ions near interfaces are formally tetravalent $({\text{Ti}}^{4+}:3{d}^{0})$ and that the valence states of Fe ions in shells are essentially the same as those of the corresponding bulk materials, with some disorder in the site occupations for $X=\ensuremath{\gamma}{\text{-Fe}}_{2}{\text{O}}_{3}$ and ${\text{Fe}}_{3}{\text{O}}_{4}$. The negligible $\text{Ti}\text{ }2p$ XMCD signals were observed, indicating that the induced spin polarization of the interface $\text{Ti}\text{ }3d$ electrons is negligible in ${\text{BaTiO}}_{3}@X$ nanoparticles.

Planar Coulomb bicrystals

We numerically studied two-component planar Coulomb crystals (planar bicrystals) in rf traps. The number of ions in the inner shell was found to be limited by the mass difference between the two components and we calculated the maximum possible number of ions in the inner shells for various mass ratios. When large axial potentials are applied the spatial separation between components depends on the trapping parameters as well as on the ion masses and charges. We derived the spatial separation both theoretically and numerically and discussed its effect on the efficiency of sympathetic cooling and on rf heating. We suggest using planar bicrystals for implementing quantum simulation and computation.

Theoretical Investigation of Electron Paramagnetic Resonance Spectra and Local Structure Distortion for Mn2+ Ions in CaCO3:Mn2+ System: A Simple Model for Mn2+ Ions in a Trigonal Ligand Field

This paper reports on a novel application of a ligand field model for the detection of the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand field and the spin-orbit coupling for the d5 configuration ion in a trigonal ligand field, the local distortion structure of the (MnO6)10- coordination complex for Mn2+ ions doped into CaCO3, have been investigated. Both the second-order zero-field splitting parameter b(0)2 and the fourth-order zero-field splitting parameter b(0)4 are taken simultaneously in the structural investigation. From the electron paramagnetic resonance (EPR) calculations, the local structure distortion, DeltaR=-0.169 A to -0.156 A, Deltatheta=0.996 degrees to 1.035 degrees for Mn2+ ions in calcite single crystal, DeltaR=-0.185 A to -0.171 A, Deltatheta=3.139 degrees to 3.184 degrees for Mn2+ ions in travertines, and DeltaR=-0.149 A to -0.102 A, Deltatheta=0.791 degrees to 3.927 degrees for Mn2+ ions in shells are determined, respectively. These results elucidate a microscopic origin of various ligand field parameters which are usually used empirically for the interpretation of EPR and optical absorption experiments. It is found that the theoretical results of the EPR and optical absorption spectra for Mn2+ ions in CaCO3 are in good agreement with the experimental findings. Moreover, to understand the detailed physical and chemical properties of the doped CaCO3, the theoretical values of the fourth-order zero-field splitting parameters b(0)4 for Mn2+ ions in travertines and shells are reported first.

Amino Acid Side Chain Interactions in the Presence of Salts

The effects of salt on the intermolecular interactions between polar/charged amino acids are investigated through molecular dynamics simulations. The mean forces and associated potentials are calculated for NaCl salt in the 0-2 M concentration range at 298 K. It is found that the addition of salt may stabilize or destabilize the interactions, depending on the nature of the interacting molecules. The degree of (de)stabilization is quantified, and the origin of the salt-dependent modulation is discussed based upon an analysis of solvent density profiles. To gain insight into the molecular origin of the salt modulation, spatial distribution functions (sdf's) are calculated, revealing a high degree of solvent structuredness in all cases. The peaks in the sdf's are consistent with long-range hydrogen-bonding networks connecting the solute hydrophilic groups, and that contribute to their intermolecular solvent-induced forces. The restructuring of water around the solutes as they dissociate from close contact is analyzed. This analysis offers clues on how the solvent structure modulates the effective intermolecular interactions in complex solutes. This modulation results from a critical balance between bulk electrostatic forces and those exerted by (i) the water molecules in the structured region between the monomers, which is disrupted by ions that transiently enter the hydration shells, and (ii) the ions in the hydration shells in direct interactions with the solutes. The implications of these findings in protein/ligand (noncovalent) association/dissociation mechanisms are briefly discussed.

The mineralization of CO 3−2 ions in crab shells, and their mimetic composite materials

The fixation of CO 3 −2 ions dissolving in the water-sphere on the surface of chitin, chitosan, and their derivatives and composite materials was examined as a mimetic model for the mineralization of CO 2 in crab shells. 1) An SEM detection of crystalline CaCO 3 on the surface of chitin-protein fibrils in the cuticles of crab shells, 2) the preparation of novel composite materials which are mimetic of crab shells, 3) a method for the detection of CO 3 −2 ions by an attenuated total reflectance (ATR) apparatus attached to a FT-IR spectrometer, and 4) a non-enzymatic mineralization of CO 3 −2 ions on the surface of these materials.

Secondary processes during tantalum electrodeposition in molten salts

A comparative study of cathodic and anodic processes during the electrolysis of tantalum containing chloride and chloride-fluoride melts is presented. The substitution of chloride ions by fluoride ions in the ligand shells of Ta(IV) and Ta(V) species is proposed as the basis for a mechanism for the formation of sludge and the outgrowth of films from the electrode over the surface of the electrolyte during tantalum electrodeposition employing a soluble anode configuration.

Hyperfine Interaction Constants of theF-Center Electron with the Lattice in Alkali Halides (with NaCl Structure)

On the basis of the de Boer model for the $F$ center, one can obtain expressions for the coupling constants in the hyperfine interaction of the $F$ electron with a nucleus of the lattice. These constants can be determined experimently by means of "electron nuclear double resonance." The comparison of the theoretical expressions and the empirical values permits an estimate of the importance of the several factors determining these coupling constants. The formal similarity between the magnetic dipole-dipole constants and the contribution of the $F$ electron to the electric quadrupole coupling constants is exploited. The measured magnetic constants are used in the discussion of the quadrupole constants. It is shown that the polarization of the lattice, as a result of the displacement of the ions in the first few shells around the negative-ion vacancy, is important in determining the electric quadrupole coupling constant. This conclusion is in qualitative agreement with Kojima's calculations in LiF. It also explains the fact that while the magnetic interaction shows negligible deviation for "axial" symmetry at sites of lower symmetry, this is not true for the electric quadrupole interaction.