Valinomycin in ion-selective electrodes enhances the selectivity for which ion?

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Multiple Choice

Valinomycin in ion-selective electrodes enhances the selectivity for which ion?

Explanation:
Valinomycin acts as a highly selective ion carrier (ionophore) for potassium in ion-selective electrodes. Its cyclic peptide cavity is the perfect size and coordination environment for K+, coordinating with carbonyl groups to form a stable K+ complex and shuttling it across the membrane. This makes the electrode’s potential respond primarily to potassium activity while greatly reducing interference from other ions. Sodium, calcium, and chloride don’t fit the binding site as well (Na+ is smaller, Ca2+ is divalent and less compatible with the pocket, and Cl− is an anion), so valinomycin enhances selectivity specifically for potassium.

Valinomycin acts as a highly selective ion carrier (ionophore) for potassium in ion-selective electrodes. Its cyclic peptide cavity is the perfect size and coordination environment for K+, coordinating with carbonyl groups to form a stable K+ complex and shuttling it across the membrane. This makes the electrode’s potential respond primarily to potassium activity while greatly reducing interference from other ions. Sodium, calcium, and chloride don’t fit the binding site as well (Na+ is smaller, Ca2+ is divalent and less compatible with the pocket, and Cl− is an anion), so valinomycin enhances selectivity specifically for potassium.

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