Search results for " Metal ions"
showing 10 items of 24 documents
Anisotropic double exchange in orbitally degenerate mixed valence systems
2000
Abstract The problem of the double exchange is considered for the mixed valence dimers in which one or both transition metal ions possess orbitally degenerate ground states. In the pseudo-angular momentum representation, the general formula is deduced for the matrix elements of double exchange involving the transfer integrals and all spin and orbital quantum numbers. The pairs 3 T 1 t 2 2 – 2 T 2 t 2 1 and 3 T 1 t 2 2 – 4 A 2 t 2 3 are considered in three high-symmetric topologies: edge-shared D2h, corner-shared D4h, and face-shared D3h bioctahedra. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of an orbital nature. The character of the a…
Aging and Memory Effects in PLZT 8/65/35 Ceramics Modified with 3d Transition-Metal Ions
2015
The temperature and frequency dependencies of the dielectric susceptibility in relaxor electro-optical PLZT 8/65/35 modified with 3d transition-metal ions (Mn, Fe, Co, Ni) measured to study the aging and memory effects are reported. The studies of aging at room temperature show that 3d admixtures (Me) in PLZT 8/65/35 ceramics at small to medium concentration range (Me < 1.0 wt.%) change the depth of dispersion, the aging amplitude and the temperature range of the memory effect. At admixture concentrations Me →1.0 wt% the aging and memory effect are significantly reduced (or eliminated).The obtained results suggest that aging effects are determined by two substantial acceptor effects of the …
A novel approach for obtaining α,β-diaminophosphonates bearing structurally diverse side chains and their interactions with transition metal ions stu…
2020
Aminophosphonates are an important group of building blocks in medicinal and pharmaceutical chemistry. Novel representatives of this class of compounds containing nontypical side chains are still needed. The aza-Michael-type addition of amines to phosphonodehydroalanine derivatives provides a simple and effective approach for synthesizing N′-substituted α,β-diaminoethylphosphonates and thus affords general access to aminophosphonates bearing structurally diverse side chains. Thermodynamic analysis of the chosen aminophosphonates at physiological pH proves that they serve as potent chelators for copper(II) ions and moderate chelators for nickel(II) ions.
Divalent metal ion buffers with low pH-sensitivity
1973
Es werden Puffersysteme fur divalente Metallionen beschrieben, die im Bereich von etwa pH 6–10 gegenuber den herkommlichen Metallpuffern eine bemerkenswert niedrige pH-Abhangigkeit der Metallionenkonzentration und der Pufferkapazitat zeigen. Die Puffersysteme bestehen aus einem starken Komplexbildner (vorzugsweise einer Polyaminocarbonsaure) und zwei verschiedenen, divalenten Metallionen, die bezuglich der Bindung durch den Komplexbildner in Konkurrenz stehen. Dasjenige Metallion, dessen Konzentration gepuffert werden soll, wird als Primarion bezeichnet. Das zweite Ion, das Sekundarion genannt wird, soll vom Komplexbildner mindestens um den Faktor 10–100 schwacher gebunden werden. Die Gesam…
Double Exchange in Orbitally Degenerate Mixed Valence Clusters: Magnetic Anisotropy, Vibronic Effects
2001
In this paper we consider the vibronic problem of the double exchange in mixed-valence dimers containing transition metal ions in orbitally degenerate ground states. The vibronic model includes interaction with the breathing local modes (Piepho-Krausz-Schatz-PKS) as well as the modulation of metal-metal distances as suggested by Piepho. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of orbital nature. PKS interaction is expected to suppress the magnetic anisotropy of the system, while the intercenter vibrations tend to enhance it. The roles of spin-orbit coupling and temperature are revealed for the systems with different geometries.
Magnetic Exchange between Orbitally Degenerate Ions: A New Development for the Effective Hamiltonian
1998
A new approach to the problem of the kinetic exchange for orbitally degenerate ions is developed. The constituent multielectron metal ions are assumed to be octahedrally coordinated, and strong crystal field scheme is employed, making it possible to take full advantage from the symmetry properties of the fermionic operators and collective electronic states. In the framework of the microscopic approach, the highly anisotropic effective Hamiltonian of the kinetic exchange is constructed in terms of spin operators and standard orbital operators (matrices of the unit cubic irreducible tensors). As distinguished from previous considerations, the effective Hamiltonian is derived for a most genera…
Kinetic evidence for the solubilization of pyridine-2-azo-p-dimethylaniline in alkanediyl-α,ω-bis(dimethylcetylammonium nitrate) surfactants. Role of…
2004
The incorporation of the bidentate ligand pyridine-2-azo-p-dimethylaniline (PADA) into micellar aggregates of the dimeric cationic surfactants propanediyl-, hexanediyl- and dodecanediyl-alpha,omega-bis(dimethylcetylammonium nitrate) (16-3-16,2NO(3)(-), 16-6-16,2NO(3)(-) and 16-12-16,2NO(3)(-), respectively) has been studied at 25 degreesC by examining the kinetics of the complexation reaction of the Ni(II) ion with this ligand. For comparison, cetyltrimethylammonium nitrate ( CTAN), which can be considered as the "monomeric'' surfactant of 16-3-16,2NO(3)(-), has also been used. The kinetic data have shown that, for 16-3-16,2NO(3)(-) and CTAN, at a surfactant concentration below the critical…
Development of a biosensor for copper detection in aqueous solutions using an Anemonia sulcata recombinant GFP.
2014
Fluorescent proteins from marine organisms represent potential candidates for biosensor development. In this paper, we described the isolation of a native green fluorescent protein from Anemonia sulcata and the cloning and purification of its equivalent as a recombinant protein in Escherichia coli. Furthermore, the spectroscopic behaviours of the native and recombinant GFPs were investigated as a function of Cu2+, Cd2+, Pb 2+ and Ni2+ concentration. Our results suggest the high selectivity of both proteins at copper than the other metals and, for the recombinant protein, a great sensitivity at a very low concentration (0.1-1 μM). Moreover, starting from these data, using the combination of …
Sequestering ability of landfill leachate towards toxic metal ions
2017
The great part of municipal solid wastes is worldwide stored in sanitary landfills. The interaction of organic and inorganic wastes with rainwater produces in the landfill a leachate of extremely variable composition. It depends on several variables such as the type of wastes, the age of landfill, the pH, the redox potential, etc [1-2]. Four are the recognized categories of pollutants in landfill leachate: inorganic macrocomponents, dissolved organic matter (DOM), heavy metals and xenobiotic organic compounds [3]. In particular, heavy metals (arsenic, cadmium, copper, lead, mercury, etc.) are usually present at concentration of few ppb and up to some ppm. A variable but consistent fraction …
Pseudopeptidic ligands: exploring the self-assembly of isophthaloylbisglycine (H2IBG) and divalent metal ions.
2012
We present a systematic study of the complexation of the new pseudopeptidic ligand isophthaloylbisglycine (H(2)IBG) with divalent metal ions of varying ionic radius. This work represents the initial employment of H(2)IBG in the coordination chemistry of alkaline earth, 3d transition, Zn(II) and Cd(II) metal elements. Infrared, NMR, thermal, magnetic, adsorption and theoretical studies of these compounds are also discussed.