ustract -Ionophores as components for analytically relevant ion selective electrodes have to exhibit a specified lipophilicity and a free energy of activation of < 45-65 kJ mol-l for the ligand exchange reaction. The selectivity of membranes may be tuned by membrane-technological interventions (dielectric constant of membrane phase, ionophore concentration, concentration of ionic sites confined to membrane phase). Molecular modelling techniques can guide the design of ionophores of a given

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... ent selectivity and reduce the number of ionophore candidates to be synthesized. The selectivity enhancement expected for a covalent link of ionophore subunits is analyzed. Significant effects are predicted only if suitable ligand preorganization is realized.