Cyclic peptides-assisted transport of metal ions across liquid-organic membrane

The formation of alkali and alkaline-earth metal picrate complexes with cyc lo(Pro-Gly)(n) ionophores (1, n = 3; 2, n = 4) can facilitate the migration of metal ions across a bulk liquid CH2Cl2 membrane. The migration behavior was studied by measuring the solution absorption at 356 nm, using a UV/Vis spectrophotometer, and the rates can be determined by comparing the initia l absorption of donor solutions with the absorption of the corresponding re ceiver solutions as the function of time. It was found that cyclic peptide 1 shows higher transport activity for the studied alkali and alkaline-earth metal ions than compound 2, which is related to the backbone flexibility o f the cyclic peptides. The findings In this work suggest that the rate of i onophore-facilitated ion transport depends not only on the ability of compl ex formation in aqueous phase, but also on the ability of complex dissociat ion in organic phase.