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  • 1
    ISSN: 1572-8854
    Keywords: 3-Amino-1,2,4-triazole ; hydrogen bonding ; x-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 3-Amino-1,2,4-triazolium (3-AT) 5-nitrofuran-2-carboxylate has been prepared and its x-ray crystal structure reported (a = 12.363(3) Å, b = 12.5720(10) Å, c = 12.8550(10) Å, Pbca, orthorhombic, Z = 8, and D c = 1.604 mg m−3). The solid-state packing of this organic acid-base salt consists of a three-dimensional hydrogen-bonded network which exhibits a cage-like repeat unit involving both the N(2)–H and N(4)–H sites of 3-AT. A review of five such structures reveals that in all cases the carboxylate groups interact with either of these sites [and the N(31)H2] and form a R 2 2(8) graph set interaction. Analysis of all 3-AT complexes which form this interaction reveals that the hydrogen-bonding distances between the non-hydrogen atoms are not equal [av. 2.712(5) Å and 2.897(5) Å], with the shorter distance being the interaction between the heterocyclic nitrogen and the corresponding carboxylate oxygen. Furthermore, a review of the interactive modes of all 3-AT adducts has been undertaken.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2234
    Keywords: Key words: K+ channel ; Glycoporin ; LamB ; ScrY ; Conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The Poisson-Boltzmann equation was solved numerically for models of the pore regions of the Shaker K+ channel and of two glycoporins (LamB and ScrY) to yield electrostatic potential profiles along the pore axes. From these potential profiles, single-channel current-voltage (I–V) relations were calculated. The importance of a proper treatment of the ionisation state of two rings of aspartate sidechains at the mouth of the K+ channel pore emerged from such calculations. The calculated most likely state, in which only two of the eight aspartate sidechains were deprotonated, yielded better agreement with experimental conductance data. An approximate calculation of single-channel conductances based simply on pore geometry yielded very similar conductance values for the two glycoporins. This differed from an␣experimentally determined conductance ratio of ScrY:LamB=10:1. Preliminary electrostatics calculations appeared to reproduce the observed difference in conductance between the two glycoporins, confirming that single-channel conductance is determined by electrostatic as well as geometric considerations.
    Type of Medium: Electronic Resource
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