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PubMed2005

New metal iodates: syntheses, structures, and characterizations of noncentrosymmetric La(IO3)3 and NaYI4O12 and Centrosymmetric beta-Cs2I4O11 and Rb2I6O15(OH)2.H2O.

Four new metal iodates, beta-Cs2I4O11, Rb2I6O15(OH)2.H2O, La(IO3)3, and NaYI4O12, have been synthesized hydrothermally, and the structures were determined by single-crystal X-ray diffraction techniques. All of the reported materials contain I5+ cations that are in asymmetric coordination environments attributable to their stereoactive lone pair. Second-order nonlinear optical measurements on noncentrosymmetric La(IO3)3 and NaYI4O12, using 1064-nm radiation, indicate that both materials have second-harmonic-generating properties with efficiencies of approximately 400xSiO2. Converse piezoelectric measurements revealed d33 values of 5 and 138 pm V-1 for La(IO3)3 and NaYI4O12, respectively. Infrared and Raman spectroscopy and thermogravimetric analyses are also presented for all of the reported materials. Crystal data: beta-Cs2I4O11, monoclinic, space group P2(1)/n (No. 14), with a=12.7662(14) A, b=7.4598(8) A, c=14.4044(16) A, beta=106.993(2) degrees, V=1311.9(2) A3, and Z=4; Rb2I6O15(OH)2.H2O, triclinic, space group P (No. 2), with a=7.0652(17) A, b=7.5066(18) A, c=18.262(4) A, alpha=79.679(4) degrees, beta=85.185(4) degrees, gamma=70.684(4) degrees, V=898.9(4) A3, and Z=2; La(IO3)3, monoclinic, space group Cc (No. 9), with a=12.526(2) A, b=7.0939(9) A, c=27.823(4) A, beta=101.975(4) degrees, V=2418.4(6) A3, and Z=4; NaYI4O12, monoclinic, space group Cc (No. 9), with a=31.235(3) A, b=5.5679(5) A, c=12.5451(12) A, beta=91.120(3) degrees, V=2181.3(4) A3, and Z=4.

Journal Article↗
PubMed2005

Gallium tris(iodate), Ga(IO3)3.

Ga(IO(3))(3) crystallizes in the space group P6(3), with the Ga atom at a site with imposed threefold symmetry. The crystal structure consists of slightly distorted GaO(6) octahedra that are bridged by I atoms of IO(3)(-) groups, giving rise to a three-dimensional polar network. The framework contains unoccupied hexagonal channels running parallel to the hexagonal [001] direction. The iodate groups have their stereochemically active non-bonded electron pairs pointing in the same direction along [001], which creates the polarity in the structure. The I-O bond distances and O-I-O angles are normal, being in the ranges 1.783 (3)-1.847 (2) A and 94.68 (11)-99.61 (12) degrees , respectively.

Journal Article↗
PubMed1980

Modification of sodium inactivation in myelinated nerve by Anemonia toxin II and iodate. Analysis of current fluctuations and current relaxations.

(1) Na+ currents and Na+ current fluctuations were measured in single myelinated nerve fibres of Rana esculenta under voltage-clamp conditions. The process of Na+ inactivation was modified by external treatment with 7 microM Anemonia Toxin II or by internal application of 20 or 40 mM IO3(-). (2) At depolarization of 24 and 32 mV the spectral density of Na+ current fluctuations could be described as the sum of two contributions, Sh(f) and Sm(f), representing the spectrum from fluctuations of the inactivation (h) and activation (m) gates, respectively. At higher depolarizations of 40 and 48 mV the low frequency (h) fluctuations could be better fitted by the sum, Sh1(f)+Sh2(f), of two separate Lorentzian functions. (3) The Na+ current and the variance of Na+ current fluctuations between 150 and 450 ms after depolarization are increased by one order of magnitude after application of Anemonia Toxin II or IO3(-). (4) The kinetics of Na+ current inactivation were described as A1 x exp(-t/tau h1) + A2 x exp(-t/tau h2) + B. The constant, tau h1, of fast Na+ inactivation was the same in normal and modified nerve fibres. The slow inactivation time constant, tau h2, increased with increasing depolarizations in modified fibres but decreased under control conditions. In all cases tau h2 showed a similar voltage dependence as the time constant found by fitting the low frequency fluctuations of Na+ current with one Lorentzian function, Sh(f). (5) It is concluded that Anemonia Toxin II and IO3(-) modify a fraction of Na+ channels in an all-or-none manner. A lower limit of the number of modified Na+ channels is estimated from the Na+ current and the variance Na+ current fluctuations. 7 microM external Anemonia Toxin II modifies more than 17% and 20 or 40 mM internal IO3(-) more than 8% of all Na+ channels. The inactivation gates in modified channels experience an electric field different from that in normal fibres.

Animals↗