One-dimensional silver(I) chain of lacunary alpha-Keggin anions

A novel chain-like silver polyoxotungstophosphate is formed when Ag(I) metal centres, exhibiting an unusual eight-coordination fashion, bridge a monolacunary [PW11O39]7- anion to four bridging mu2-oxygen atoms of a neighbouring lacunary alpha-Keggin anion.     

Self-assembly of a lacunary alpha-Keggin undecatungstophosphate into a three-dimensional network linked by s-block cations

The crystal structure of [(CH3)4N]4Na2H[alpha-PW11O39].8H2O has been determined by using the Weissenberg camera at the BL04B2 beamline of SPring-8, revealing that it contains a disorder-free lacunary [alpha-PW11O39]7- anion with one sodium cation embedded into its lacuna that links the oxometalate building blocks into a one-dimensional chain, which is then woven into a three dimensional latticework by another Na+.     

Li+-templated complexation of cylindrical macrotricyclic host with naphthalene diimide: Cation-controlled switchable complexation processes

Anthracene-based cylindrical macrotricyclic polyether (1) containing two dibenzo-30-crown-10 cavities has been proved to be an efficient host for the templated complexation with N,N’-dipropyl-1,4,5,8-naphthalenetetracarboxylic diimide in the presence of lithium ions in both solution and solid state. Host 1 could also form 1:1 complex with the bispyridinium salt with two β-hydroxyethyl groups in solution and in the solid state. Moreover, it was also found that the switchable complexation processes between the macrotricyclic host and two different kinds of guests could be chemically controlled by the addition and removal of lithium ions.     

Cation-controlled self-assembly of a hexameric europium wheel

The simple asymmetric tetradentate ligand 2,2':6',2' '-terpyridine-6-carboxylic acid leads to the self-assembly of the first europium nanowheel containing europium ions in two different coordination environments. Moreover the self-assembly of bis(terpyridinecarboxylate) europium species to form a hexameric wheel capable of strongly binding LnIII cations is controlled by the ligand/cation ratio.     

Molecular dynamics simulations of dendrimer-encapsulated alpha-Keggin ions in trichloromethane solution

We report on molecular dynamics simulations of dendrimer-encapsulated alpha-Keggin ions in trichloromethane solution. The simulations were done within the NVE ensemble at temperatures around T = 300 K. The eight examined systems are model compounds for dendrizymes, a hybrid material where a polyoxometalate ion (the core) is surrounded by amphiphilic cationic dendrimers (the shell) such that the complete system may exhibit enzyme-like regioselectivity and substrate selectivity, e.g., in olefin oxidation. The influence of dendrimer type, dendrimer generation, and number of dendritic cations bound by electrostatic interaction to the polyoxometalate core on the structure and dynamics of the shell has been studied. It is shown that the resulting distribution of trichloromethane molecules within the shell may serve as an indicator for the shell's permeability for small molecules. The dendritic shell causes a size exclusion effect that influences the access of small molecules to the central polyoxometalate ion, i.e., to that part where the enzyme-like reaction of a dendrizyme is supposed to take place.     

Kinetics of Na+-dependent D-glucose transport

The kinetic parameters of the Na+-dependent glucose transport system have been determined in isolated membrane vesicles for D-glucose, Na+, and phlorhizin. The D-glucose flux measurements were carried out by the equilibrium exchange procedure at constant external and internal Na+ concentrations and zero potential. Equations were developed to extract information about Km and Vmax from uptake measurements into a vesicle population that is heterogeneous with respect to size (surface to volume ratio). The Km for D-glucose was 14 mM and independent of the Na+-concentration, while the Vmax was strongly Na+-dependent and increased 15-fold between 1 and 100 mM Na+. The Km of Na+ for activation of the Vmax was 18 mM. The calculated KI values for phlorhizin were 2.7 and 1.9 micrometer when determined under active and equilibrating D-glucose flux conditions, respectively.     

Solvation of Na+ in argon clusters

The structures and stabilities of Ar(n)Na+ clusters (n < or = 54) are investigated using atomistic potentials fitted to reproduce ab initio calculations performed at the coupled-cluster level on the smaller clusters. Polarization effects are described using either the interaction between dipoles induced by the sodium ion, or a small charge transfer in the framework of a fluctuating charges model. In both models, extra three-body contributions of the Axilrod-Teller type are also included between the sodium ion and all pairs of argon atoms. The two models predict essentially similar growth patterns, and a transition in the metal ion coordination from 8 (square antiprism) to 12 (icosahedron) is seen to occur near n = 50, in response to the intrasolvent constraints.     

Reduction of Na+ within a {Mg2Na2} Assembly

Ionic compounds containing sodium cations are notable for their stability and resistance to redox reactivity unless highly reducing electrical potentials are applied. Here we report that treatment of a low oxidation state {Mg₂Na₂} species with non-reducible organic bases induces the spontaneous and completely selective extrusion of sodium metal and oxidation of the Mg^I centers to the more conventional Mg^II state. Although these processes are also characterized by a structural reorganisation of the initially chelated diamide spectator ligand, computational quantum chemical studies indicate that intramolecular electron transfer is abetted by the frontier molecular orbitals (HOMO/LUMO) of the {Mg₂Na₂} ensemble, which arise exclusively from the 3s valence atomic orbitals of the constituent sodium and magnesium atoms.     

Flavonoid inhibitors of Na+,K+-ATPase

Summary A comparative investigation of the inhibiting influence on transport Na⁺,K⁺-ATPase of four flavone aglycones and eight of their glycosides has been performed on the microsomal fraction of the cells of the cerebral cortex.It has been shown that in concentrations of 1·10^–4 to 5·10^–6 M M myricetin, quercetin, luteolin, and myricetin 3-glucoside possess an appreciable inhibiting effect. For kaempferol and its glycosides, as for the glycosides of quercetin and luteolin, the inhibiting effect is extremely feeble.Institute of Biochemistry, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–46, January–February, 1977.     

Organophilization of Na+-montmorillonite with polyfluorinated alcohols

Modification of Na⁺-montmorillonite with polyfluorinated alcohols was performed. The structure of the modified Na⁺-montmorillonite was studied by derivatography and Fourier IR spectroscopy. The effect of calcite as clay component on the capability for physical and chemical binding of polyfluorinated alcohols was revealed.     

Active transport of Na + and K + through animal cell membranes

The transport of Na⁺ out of the cell and K⁺ into the cell against a concentration gradient is catalyzed by a (Na⁺ + K⁺)-activated ATPase. The way in which the cations pass through the cell membrane has not yet been elucidated. Studies on the ATP hydrolysis revealed a Na⁺-dependent phosphorylation of the enzyme protein; the conformation of the enzyme also appears to change. The energy required for transport of the cations against their concentration gradients is probably provided by K⁺-dependent hydrolysis of the enzyme-bound phosphate. The enzyme can synthesize ATP from inorganic phosphate and ADP on reversal of the cation concentration gradient. By keeping the enzyme in a particular conformation, the cardiac glycoside ouabain specifically inhibits the Na⁺ pump.     

Structural and dynamic investigations of aqueous clusters of Na+ and K+

Using computer modeling, we have studied Na⁺–24H₂O and K⁺–24H₂O clusters. We propose ion-water interaction potentials. We obtain structural, energy, and dynamic characteristics of the studied clusters. We show different mechanisms for exchange of water molecules surrounding the Na⁺ and K⁺ ions: single-particle in the case of Na⁺, and close to K⁺, along with single-particle exchange, a large percentage of multiparticle cooperative exchange of water molecules. This difference is explained by the different degrees of orientation of the water molecules surrounding these ions, by the presence of a unified deformed network of H bonds in the K⁺ cluster and its absence in the Na⁺ cluster. We propose a negative hydration mechanism for the K⁺ ion.Institute of General and Inorganic Chemistry, Russian Academy of Sciences. Institute of Physical Chemistry, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 96–104, March–April, 1993.     

Isolation of a stable lacunary Dawson-type polyoxomolybdate cluster

A polyoxotetradecamolybdate cluster [Mo(14)O(38)(OAc)(6)](2-), which has a lacunary core of the Wells-Dawson structure, is isolated by the reduction of [Mo(6)O(19)](2-). The Mo(14) core is comprised of a mixed valence of [Mo(V)(4)Mo(VI)(10)], exhibiting multi-step reversible redox processes that experience both oxidation and reduction.     

The clustering reactions of Na+ and Pb+ with several important ligands

Enthalpy, Entropy, and Gibb's free energy changes for the clustering reactions of Na⁺ and Pb⁺ with several important atmospheric molecules and organic solvents have been measured by using high pressure mass spectrometry (HPMS). The unusually strong bonding has been found in Na⁺ ion complexes where ligands have large high moments and polarizabilities as well as in Pb⁺ ion complexes. The enhancement of the bonding by ion-high moment, ion-induced dipole, and dispersion interactions may account for the strong bonding in some of Na⁺ ion complex systems, while the strong bonding in Pb⁺ ion complexes may results from the hybridization of 6s and 6p orbitals of Pb⁺ ion.     

Metal-mediated self-assembly of tetrapyridyl porphyrins by Na+ ions

In the presence of the sodium salt of a bulky anion, which allows the solubility of Na(+) in low polarity solvents, various tetra(4-pyridyl)porphyrin derivatives can spontaneously self-assemble from CH(2)Cl(2) into supramolecular nanostructures exhibiting a long-range order, through the coordination of Na(+) ions by the pyridyl moieties at the macrocycle periphery.