Two new amphiphilic p-tert-butylcalix[4]arene derivatives were investigated in order to understand two important features of ionophores, namely ion complexation and the possibility of incorporation or translocation across biological membranes [1, 2]. The derivatives used have one or two nalidixic acid moieties grafted at the calixarene lower rim.

In this study Langmuir films of two calixarene derivatives were formed on pure water and on aqueous solutions of mono- and divalent metal chlorides: LiCl, NaCl, KCl, MgCl₂, CaCl₂, BaCl₂, CuCl₂, and ZnCl₂. The complexation properties were studied using surface pressure and surface potential measurements, as well as Brewster angle microscopy and polarization modulation infrared reflection-absorption spectrometry. The compression isotherms were determined as a function of salt concentration using aqueous solutions in the range 5·10^-6 to 5·10^-2 M. On the other hand, the compression experiments were performed at different temperatures: 20, 25, 30, 37, and 40 ^oC giving access to a thermodynamic analysis.

The compression isotherms of the monolayers formed on different subphases show differentiation between the monovalent and divalent cations with both calixarene derivatives. This differentiation was interpreted in terms of conformational changes occurring in the ligands upon complexation. The differences of the conformations of the mono- and divalent cation complexes may be important from the point of view of the interactions with lipid membranes and the biological activity of these potential ionophores.

[1] Korchowiec, B.; Ben Salem, A.; Corvis, Y.; Regnouf-de-Vains, J.-B.; Korchowiec, J.; Rogalska, E. J. Phys. Chem. B 2007, 111, 13231-13242.

[2] Corvis, Y., Korchowiec, B., Korchowiec, J., Badis, M., Mironiuk-Puchalska, E., Fokt, I., Priebe, W., Rogalska, E. J. Phys. Chem. B 2008, 112, 10953-10963.

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1. Influence of three oxicam drugs on the properties and enzymatic lipolysis of model membranes
2. Calixarene - lipid monolayers: towards enzymatic engineering of lipid membranes.