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  • 1
    Electronic Resource
    Electronic Resource
    X-ray structural study of a zinc(II) inclusion complex of a phenolate-pendant cyclam (1992)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 12 (1992), S. 377-387 
    Details
    ISSN: 1573-1111
    Keywords: Charles Pedersen ; crown ethers ; phenol-pendant cyclam-zinc(II) complex ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The molecular structure of phenol-pendant cyclam-zinc(II) complex,4a, has been determined by X-ray structure analysis. Crystals of4a · ClO4 · CH3OH (C16H27N4OZn · ClO4 · CH3OH) are monoclinic, space groupP21/nn, with four molecules in the unit cell of dimensionsa=31.198(2) Å,b=8.426(1) Å,c=8.214(1) Å, andβ=93.96(1)°. The structure was solved by the heavy atom method and refined anisotropically toR=0.044,R w=0.062 for 1551 independent reflections. The complex assumes a five-coordinate, square pyramidal geometry, where zinc(II) is surrounded by the cyclam moiety in a planar fashion with the pendant phenolate anion occupying an axial position. An extremely short Zn-O(phenolate) bond distance of 1.983(5) Å, in conjunction with the 0.288 Å displacement of Zn(II) above the cyclam N4 plane toward the phenolate, accounts for the extremely low pK a value of 5.8 for the pendant phenol. These facts about4a, in comparison with the previous findings for the Ni(II) (4b) and Cu(II) complexes (4c) with the same ligand, illustrate well the characteristics of zinc(II) ion coordination properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01053875
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  • 2
    Electronic Resource
    Electronic Resource
    Bis(ZnII-cyclen) complex as a novel receptor of barbiturates in aqueous solution (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 617-623 
    Details
    ISSN: 0947-6539
    Keywords: barbiturates ; macrocycles ; molecular recognition ; receptors ; zinc complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new bis-zinc(II) receptor (Zn2L), which has two macrocyclic 12-membered tetraamine (cyclen) ZnII complexes connected through a p-xylene bridge, has been synthesized as a novel host molecule to recognize barbiturates (such as barbital (bar)) in aqueous solution. Each of the zinc(II) ions in the biszinc(II) receptor was originally intended to match the dianionic barbital anion (bar2-) with supplementary hydrogen bonds between the cyclen NH's and the three carbonyl oxygens in complementary positions to yield a 1:1 complex, Zn2L-bar2-. From an aqueous solution of equimolar Zn2L and barbital at pH 8, however, a cyclic 2:2 complex, (Zn2L-bar2-)2, was isolated and characterized by X-ray crystal analysis. The NMR study in 10% (v/v) D2O/H2O has revealed dissociation of (Zn2L-bar2-)2 solely into the original target 1:1 complex Zn2L-bar2- and established the dimerization constant for 2Zn2L-bar2- → (Zn2L-bar2-)2, Kd ( = [(Zn2L-bar2-)2]/[Zn2L-bar2-]2) to be 103.4 M-1. The thermodynamic parameters were evaluated from the NMR measurements at 25, 35, 45, and 55°C: ΔG = -1.9 × 104 J mol-1, ΔH = - 3.3 × 104 J mol-1, ΔS = - 49 J mol-1 K-1 at 25°C. Potentiometric pH titration of Zn2L (1 mM) and barbital (1 mM) disclosed extremely facile deprotonation of the two imido groups of barbital at pH less than 7 to form the dianionic barbital-bound ZnII complexes Zn2L-bar2- and (Zn2L-bar2-)2, where-by the barbital binding affinity for Zn2L was estimated to be Kbar ( = [Zn2L-bar2-]/[uncomplexed Zn2L][uncomplexed barbital]) = 105.8 M-1 at pH 8 and 25°C with I = 0.10 (NaNO3). The significance of the bis-zinc(II) receptor in stabilizing the dianionic barbital is evident by comparison with the interaction of ZnII-cyclen complex (ZnL) with barbital, which yields only a 1:1 monoanionic barbital complex, ZnL-bar- (Kbar = [ZnL-bar-]/[uncomplexed ZnL][uncomplexed barbital] = 104.2M-1 at pH 8 and 25°C with I = 0.10 (NaNO3)).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020602
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  • 3
    Electronic Resource
    Electronic Resource
    Potentiometric discrimination between planar and octahedral anionic metal cyano complexes by liquid membrane electrodes based on lipophilic macrocyclic dioxopolyaminesDedicated to the memory of Prof. Dr. Wilhelm Simon, who has made major contributions to the field of analytical chemistry, particularly by introducing the use of antibiotics as well as of synthetic compounds as sensory elements for ion-selective electrodes. (1993)
    Weinheim : Wiley-Blackwell
    Electroanalysis 5 (1993), S. 731-738 
    Details
    ISSN: 1040-0397
    Keywords: Macrocyclic polyamines ; Ion-selective electrodes ; Metal cyano complexes ; Recognition of coordination structure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel type of poly(vinyl chloride) matrix liquid membrane electrodes that are capable of discriminating between planar and octahedral anionic metal cyano complexes has been developed by exploiting as the sensory elements lipophilic derivatives of macrocyclic dioxopolyamines (13-hexadecyl-1,4,8,11-tetraaza-12,14-dioxocyclotetradecane, 15-hexadecyl-1,4,7,10,13-pentaaza-14,16-dioxocyclohexadecane). Potentiometric response behaviors of these electrodes for a series of anionic metal cyano complexes were compared with those of the electrodes based on the corresponding nondioxo macrocyclic pentaamine (15-hexadecyl-1,4,7,10,13-pentaazacyclohexadecane) as well as a conventional anion exchanger (Capriquat®). The electrodes based on the dioxopolyamines displayed strong potentiometric responses at pH 4.0 to the metal cyano complexes having a planar structure ([Ni(CN)4]2-, [Pt(CN)4]2-). In contrast, the responses to the metal cyano complexes having an octahedral structure ([Fe(CN)6]3-, [Fe(CN)6]4-) were only negligible. On the other hand, for all of the guests tested, the electrodes based on the nondioxo macrocyclic pentaamine or the anion exchanger showed strong linear responses to both planar and octahedral complexes. These results represent a new mode of potentiometric discrimination displayed by dioxo-type macrocyclic polyamines having both amine and amide moieties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140050905
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  • 4
    Electronic Resource
    Electronic Resource
    CF3Br—H2 reaction in shock waves (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 25 (1993), S. 983-993 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CF3Br—H2 mixtures highly diluted with Ar were studied by using a time-resolved IR-emission of HBr and a gas-chromatography for reaction products. The temperature range covered was 1000-1600 K and the total pressure behind the reflected shock waves used was 1.2-2.6 atm. CF3H, C2F6, and C2F4 were produced and the yields of these products were determined as a function of temperature. The main product under our experimental conditions was CF3H. The mechanism and the rate constants of CF3Br—H2 reaction at high temperatures were discussed. The experimental data was satisfactorily modeled using a 14-reaction mechanism. Reaction (5) played an important role in the formation of CF3H together with reaction (4). The rate constant expression k5 = 2.2 × 1013 exp(-12 kcal/RT) cm3 mol-1 s-1 gave the best agreement between the calculated and observed results. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550251202
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  • 5
    Electronic Resource
    Electronic Resource
    High temperature pyrolysis of 1,5-cyclooctadiene and 4-vinylcyclohexene in shock waves (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 25 (1993), S. 1037-1042 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,5-cyclooctadiene or 4-vinylcyclohexene mixture diluted with argon was heated to temperatures in the range 880-1230 K behind reflected shock waves. Profiles of IR-laser absorption were measured at 3.39 μm. From these profiles, rate constants k1 and k2 for the decyclization reactions 1,5-cyclooctadiene → biradical and 4-vinylcyclohexene → biradical were evaluated as k1 = 5.2 × 1014 exp(-48.3 kcal/RT) s-1 and k2 = 3.5 × 1014 exp(-55.3 kcal/RT) s-1, respectively. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550251208
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