Inversion of selective binding of transition metal ions by Langmuir monolayers of amphiphilic cyclen

Selective binding of Cu(II), Ni(II), and Zn(II) from aqueous solutions of transition metal salts and their mixtures by Langmuir monolayers of dicetyl cyclen (DCC) was investigated. A direct relationship between the subphase pH and the selectivity of macrocyclic molecules with respect to particular metal ions was deduced from analysis of the π-A isotherms of DCC monolayers and the X-ray fluorescent spectra of the corresponding Langmuir-Blodgett (LB) films. Unusual inversion of the macrocycle selectivity from preferential binding of Cu2+ to complex formation with Ni2+ upon a decrease in subphase pH was revealed for a DCC monolayer.