- Quaternary ammonium ions can externally block voltage-gated K+ channels. Establishing a theoretical and experimental model that predicts KDS and the selectivity of K+ over Na+ ions
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The physicochemical basis for the high ion selectivity of potassium channels is poorly understood. In the present studies, external blockade of cloned voltage-gated potassium channels with alkyl quaternary ammonium ions are analyzed from a model derived from theory and experimental data. Atomic mass units, electrostatic potential residing on the nitrogen atom, the COSMO van der Waals solvent accessible surface, the Onsager solvation model, and the isodensity PCM solvation model are computed at the semi-empirical and the ab initio levels of theory. A structure-activity relationship (SAR) exists between the calculated values and the experimentally obtained KD (mM). The SAR model gives us KD predictions and when K+ and Na+ are incorporated into the model, it dramatically predicts the selectivity of K+ over Na+ ions.
- Wempe
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- Silver (I) activated quaternization of tertiary amines by alkyl iodides: Overall analysis coupling homogeneous and heterogeneous processes
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Kinetic data for the silver (I) activated homogeneous and heterogeneous quaternization of tributylamine by alkyl iodides in toluene is presented. Silver iodide was used as a solid catalyst. Solution and surface parameters were obtained applying the multistep kinetic model, previously proposed by Santos and Barbosa. A scrutiny of the derived quantities evidences competing structural and electronic effects. The solution reaction is dominated by structural factors while electronic effects govern the surface process. An overall analysis considering data from triethylamine systems, earlier investigated, allowed the establishment of a parallelism between the homogeneous and heterogeneous processes. A molecular level study involving size, shape and orientation of the chemical species on the surface, lead to estimates of interfacial layer thicknesses. A combination of surface parameters superficial reacting monolayer thicknesses and, the parallelism between homogeneous and heterogeneous catalysis consented the evaluation of "volumetric surface rate constants" which are directly comparable with their solution counterparts.
- Santos, M. Soledade C.S.,Barbosa, Ester F.G.
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