Biomedical subjects

Andrew S Ichimura

Publications and source records attributed to Andrew S Ichimura.

4 recordsLinked to original sources

PubMed2006

One-dimensional zigzag chains of Cs-: the structures and properties of Li+ (cryptand[2.1.1])Cs- and Cs+ (cryptand[2.2.2])Cs-.

The crystal structure and properties of lithium (cryptand[2.1.1]) ceside, Li+ (C211)Cs-, are reported. Li+ (C211)Cs- is the second ceside and third alkalide with a one-dimensional (1D) zigzag chain of alkali metal anions. The distance between adjacent Cs- anions, 6 A, is shorter than the sum of the van der Waals radii, 7 A. Optical, magic angle spinning NMR, two-probe alternating and direct current conductivity, and electron paramagnetic resonance measurements reveal unique physical properties that result from the overlap of adjacent Cs- wave functions in the chain structure. The properties of cesium (cryptand[2.2.2]) ceside, Cs+ (C222)Cs-, were also studied to compare the effects of the subtle geometric changes between the two 1D zigzag chain structures. Li+ (C211)Cs- and Cs+ (C222)Cs- are both low-band-gap semiconductors with anisotropic reflectivities and large paramagnetic 133Cs NMR chemical shifts relative to Cs- (g). An electronic structure model consistent with the experimental data has sp2-hybridized Cs- within the chain and sp-hybridized chain ends. Ab initio multiconfiguration self-consistent field calculations on the ceside trimer, Cs3(3-), support this model and indicate a net bonding interaction between nearest neighbors. The buildup of electron density between adjacent Cs- anions is visualized through an electron density difference map constructed by subtracting the density of three cesium atoms from the short Cs3(3-) fragment.

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PubMed2006

Intramolecular pi-dimerization in a 1,1'-bis(verdazyl)ferrocene diradical.

The solid state structure of 1,1'-bis(verdazyl)ferrocene reveals the two radical moieties associated intramolecularly to give the first example of a pi-dimer of a stable verdazyl radical. The pi-dimer structure is not maintained in solution. Magnetic characterization indicates that the radicals are sufficiently strongly antiferromagnetically coupled so as to render the molecule diamagnetic at room temperature.

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PubMed2003

Structural and magnetic properties of vanadyl dichloride solvates: from molecular units to extended hydrogen-bonded solids.

The preparation, structural characterization and magnetic properties of three solvent adducts of VOCl(2), trans-VOCl(2)(THF)(2)(H(2)O) (1), trans-VOCl(2)(H(2)O)(2).2Et(2)O (2) and cis-VOCl(2)(MeOH)(3) (3) are described. In these solids, hydrogen bonding among the inorganic complexes is the critical determinant of the formation of extended magnetic networks. Compound forms one-dimensional double chains where alternating monomers from the two branches of the chain are hydrogen bonded via the V-Cl ... H-O-V network (with an axial water molecule and equatorial chloride ions). Magnetic studies indicate no interaction among the vanadyl centers. The paramagnetism of 1 is consistent with the extension of the network from the hydrogen donor site of the axial water, which is orthogonal to the d(xy) magnetic orbital. Compound 2 forms one-dimensional chains with water molecules of adjacent monomers held together by hydrogen bonds to ether molecules (V-O-H ... O(ether) ... H -O-V). The chain network radiates only through the equatorial plane of the complex where the water molecules are located. The presence of the intervening solvent molecule between hydrogen bonds of the primary coordination sphere magnetically insulates metal centers and compound is also a simple paramagnet. Removal of the solvent turns on the magnetic interaction and neighboring spin centers couple antiferromagnetically. Compound 3 forms a layered structure via V-Cl ... H-O-V hydrogen bonding, where all the hydrogen donor sites participate in the formation of the network. The vanadyl spin centers, at distances of 5.5 and 6.5 A from each other, couple antiferromagnetically (J/k=-0.7 K). Thus, magnetic coupling among metal centers is achieved when the hydrogen bond network directly radiates from the coordination plane containing the magnetic orbital. These results further support the utility of hydrogen bond as a viable design element in the construction of low dimensional, magnetic solids.

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PubMed2002

Toward inorganic electrides.

Electrides are materials in which alkali metals (Li through Cs) ionize to form bound alkali cations and "excess" electrons. The electrons reside in large cavities or channels or both in the host lattice. We report here the first synthesis of thermally stable inorganic electrides with cation-to-electron ratios of 1:1 as in organic electrides. Although alkali metal adducts to alumino-silicate zeolites are well known, the cation-to-electron ratio is generally 3:1 or greater because these zeolites contain alkali cations prior to incorporation of the alkali metal. In this work, two pure silica zeolites, ITQ-4and ITQ-7, with pore diameters of approximately 7 A, absorb up to 40 wt % cesium from the vapor phase (even at room temperature). The other alkali metals (except Li) can also be introduced at elevated temperatures. The optical and magnetic properties of the cesium-loaded samples suggest ionization to form Cs+ and e- with substantial electron-spin pairing. The metal-loaded samples are stable to at least 100 degrees C and are able to reduce small aromatic molecules such as benzene and naphthalene to the radical anions within the pores of the zeolite.

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