Ion-Sensitive Monolayers and Langmuir–Blodgett Films of Amphiphilic Cyclen: Selectivity and Regeneration

Complexation of dicetyl cyclen with transition metal ions in the monolayers on the surface of aqueous solutions of Cu(II), Ni(II), Zn(II), Ag(I) and their mixtures was studied. It was established that the selectivity of the interaction of the monolayer composed of this ligand with transition metal ions is determined by the subphase pH value. It is disclosed that, in the acidic region of subphase pH values, dicetyl cyclen in the monolayer bounds predominantly the Ni(II) ions from solutions containing Cu²⁺ and Ni²⁺ ions, although its complexes with Ni(II) in the bulk under these conditions are less stable than similar complexes with Cu(II). The effect of conformational and charge states of the ligand on the protonation of macrocycle and the stability of its complexes is discussed. The possibility of the reversible regeneration of the monolayers and the Langmuir–Blodgett films of the complexes of dicetyl cyclen and copper(II) ions is shown to occur with no changes in the structure and properties of this planar system. It is shown that the Langmuir–Blodgett films based on dicetyl cyclen can be used as a sensor element for the quantitative analysis of the content of Cu(II) ions in dilute solutions.