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  • 1
    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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  • 2
    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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    Paper (German National Licenses)
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