Valinomycin, an antibiotic ionophore (ion carrier), is a functional analog of the cyclic hexaether [18] crown-6 (18C6). Both valinomycin and 18C6 molecules form lipophilic complexes with alkali metal ions. Hence, upon addition of valinomycin or 18C6, alkali metal salts become soluble in non-polar organic solvents. The ability to complex cations allows valinomycin molecules to transport these ions across cell membranes. Since 18C6 molecules bind alkali metal cations in a similar way, by wrapping them in a “greasy coat”, cell transport processes by valinomycin can be imitated using the more cost-efficient and less hazardous 18C6. In a simple test tube experiment, cell conditions are mimicked by means of a triphasic system consisting of an aqueous magnesium sulfate (MgSO4) solution (bottom phase) and an aqueous potassium permanganate (KMnO4) solution (top phase) which are separated by a methyl benzoate phase serving as a liquid membrane. If a solution of 18C6 is injected into the methyl benzoate phase of this “vertical Pressman cell”, a salt transfer from the upper aqueous phase to the bottom phase can be observed, modelling the effect of valinomycin in living cells. Appropriate simplifications for use in schools are discussed and animations are provided to illustrate the ionophore-facilitated cell transport.
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