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  • 1
    Electronic Resource
    Electronic Resource
    The pH-Partition Profile of the Anti-Ischemic Drug Trimetazidine May Explain Its Reduction of Intracellular Acidosis (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 616-624 
    Details
    ISSN: 1573-904X
    Keywords: trimetazidine ; lipophilicity ; proton transfer ; ionic partition diagram ; ITIES
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The anti-ischemic drug trimetazidine (TMZ) acts by a combination of molecular mechanisms which begin to be understood. Thus, it acts in the micromolar range to significantly reduce intracellular acidification during ischemia. To search for a possible physicochemical explanation of this phenomenon, we investigated the transfer mechanisms of the various electrical forms of this dibasic drug. Methods. The transfer characteristics of TMZ were studied by electrochemistry at the water/1,2-dichloroethane interface. Cyclic voltammetry was used to measure the formal transfer potentials of singly and doubly protonated forms of TMZ (noted TH+ and TH2 2+, respectively ) as a function of aqueous pH, and the partition coefficient of neutral TMZ (log P T) was measured by two-phase titration. Results. log P T was measured to be 1.04 ± 0.06, and the acid-base dissociation constants in water were deduced to be pK w a1 = 4.54 ± .02 and pK w a2 = 9.14 ± 0.02. The partition coefficients of TH+ and TH2 2+ were found to be respectively log P 0′ TH+ = −3.78 ± 0.16 and log P 0′ TH 2 2+= −9.84 ± 0.30, which agrees well with the charge being delocalized on two nitrogen atoms in TH+. The pH-partition profile of TMZ was then established in the form of its ionic partition diagram, which showed that the affinity of the ions for the organic phase is pH-dependent and strongly increased by the interfacial potential. Conclusions. This behavior suggests a physiochemical mechanism whereby efflux of protonated TMZ out of an acidified cell is facilitated, in effect exporting protons to extracellular space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018899802836
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  • 2
    Electronic Resource
    Electronic Resource
    The micro water/1,2-dichloroethane interface as a transducer for creatinine assay (1995)
    Springer
    Microchimica acta 117 (1995), S. 175-185 
    Details
    ISSN: 1436-5073
    Keywords: biosensor ; micro-ITIES ; creatinine ; amperometric-ISE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Facilitated ammonium ion transfer reactions, using the crown ether dibenzo-18-crown-6, at a single microhole supported water/1,2-dichloroethane interface were used as the transducer to detect the biomolecule creatinine. The ammonium ion was produced during the enzymatic action of creatinine deiminase on creatinine. A prototype sensing device incorporating a Teflon gas permeable membrane, to exclude possible interferents, yielded a linear amperometric response to added creatinine from 20 μM to 1 mM. This range is sufficient for that required for the determination of creatinine in serum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01244888
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  • 3
    Electronic Resource
    Electronic Resource
    Amperometric detection of the ammonium ion by facilitated ion transfer across the interface between two immiscible electrolyte solutions (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 425-434 
    Details
    ISSN: 1040-0397
    Keywords: Liquid-liquid interface ; Ammonium ion ; Nonactin ; Ionophores ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Facilitated ion transfer reactions of the ammonium, potassium, and sodium ions with the ionophores dibenzo-18-crown-6, nonactin, and valinomycin were investigated at the water/ 1, 2-dichloroethane interface. Association constants for the various reactions studied were calculated to determine the selectivity imparted by the ionophores on the transferring ions. Of the ionophores studied, nonactin was found to be the most selective towards the ammonium ion, with a calculated association constant of 14.1.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070505
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  • 4
    Electronic Resource
    Electronic Resource
    The liquid-liquid micro-interface for the amperometric detection of urea (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 714-721 
    Details
    ISSN: 1040-0397
    Keywords: Urea ; Liquid-liquid interface ; Enzymatic assay ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The detection of the ammonium ion produced by the enzymatic action of urease on urea is investigated electrochemically by means of Facilitated ion transfer reactions at liquid-liquid micro-interfaces. The urease was used either in a dissolved form (free in aqueous solution) or immobilized onto the surface of an ammonia gas permeable membrane. The sensing structure utilizing the ammonia gas permeable membrane allowed the detection of urea from 200μM to 4mM. Thick film technology was utilized in conjunction with UV excimer laser photoablation techniques to fabricate a inicroelectrode strip sensor for the ammonium ion.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070804
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanism of Transfer of a Basic Drug across the Water/1,2-Dichloroethane Interface: The case of quinidine (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 101-117 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical transfer of quinidine across the H2O/1,2-dichloroethane interface was investigated by cyclic voltammetry, so as to determine its lipophilicity. The formal transfer potential was measured as a function of the pH of the aqueous phase. Both singly and doubly protonated quinidine cations can transfer across the interface, and their formal Gibbs free energies of transfer were observed to be 7.7 and 31.2 kJ mol-1, respectively. Between pH 0 and 3, only the doubly charged quinidine was present in the aqueous phase and was observed to transfer. Between pH 3 and 6, the transfer of both cations occurred. The proportion of doubly charged quinidine decreased progressively in this pH range and disappeared completely above pH 6. The overall process was analyzed using a thermodynamic model. The relationship between the various forms of quinidine in both phases and pH was established and found to be in good agreement with the experimental results. With this model, the acid-base equilibrium constants in the organic phase could be calculated as pKa1o = 9.66 ± 0.21 and pKa2o = 14.20 ± 0.16 (the subscripts a1o and a2o refer to the first and second dissociation constants). This study illustrates how the partition of ionic species can be taken into account in the determination of lipophilicity and in the description of the passive transfer of organic drugs.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790111
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  • 6
    Electronic Resource
    Electronic Resource
    Electrochemical Study of Phase-Transfer Catalysis Reactions: The Williamson ether synthesis (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 231-242 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer properties of the ionic species involved in the Williamson ether synthesis by phase-transfer catalysis were investigated using electrochemical techniques developed for the study of polarised liquid/liquid interfaces. This approach allows the measurement of the apparent partition coefficients of the transferring species. From these data, it is proposed that the role of the phase-transfer catalyst salt in the reaction mechanism is to establish a Galvani distribution potential difference between the two phases which in turn acts as the driving force for transferring the reactive aqueous ions to the organic phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770125
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