Non-covalent (iso)guanosine-based ionophores for alkali(ne earth) cations

Different (iso)guanosine-based self-assembled ionophores give distinctly different results in extraction experiments with alkali(ne earth) cations. A lipophilic guanosine derivative gives good extraction results for K+, Rb+, Ca2+, Sr2+, and Ba2+ and in competition experiments it clearly favors the divalent Sr2+ (and Ba2+) cations. 1,3-Alternate calix[4]arene tetraguanosine hardly shows any improvement in the extraction percentages compared to its reference compound 1,3-alternate calix[4]arene tetraamide. This indicates that one G-quartet does not provide efficient cation complexation under these conditions. In the case of the lipophilic isoguanosine derivative there is a cation size dependent affinity for the monovalent cations (Cs+ ≫ Rb+ ≫ K+), but not for the divalent cations (Ca2+ > Ba2+ > Sr2+ > Mg2+). In competition experiments the isoguanosine derivative, unlike guanosine, does not discriminate between monovalent and divalent cations, giving an almost equal extraction of Cs+ and Ba2+.