A23187 Ionophore—ca2+ interfacial complex: a monolayer approach

This paper presents a new approach to study A23187 ionophore in an aqueous environment. The ionophore was spread at the air—water interface. Surface pressure and tritium—hydrogen surface exchange measurements demonstrated the conformational stability of A23187 in the free and complexed forms at the interface. Exchange measurements suggested that the A23187 ionophore adopts an interfacial conformation in which hydrogen bonds are not accessible to the aqueous solvent. Surface potential measurements allowed the calculation of the intrinsic dissociation constant of the ionophore carboxylic group in an aqueous environment (pKi = 5). The ionophore activity sequence for bivalent ions was Ca2+>Mg2+⇓Ba2+ This sequence is comparable to those obtained by other authors inorganic solution. Surface radioactivity measurements performed with 45Ca2+ in the subphase demonstrated the formation of a neutral complex between two negatively charged ionophore molecules and one Ca2+ ion. This reaction was only observed at pH higher than 5. The association constant of the interfacial ionophore-Ca2+ complex was calculated