Polydiacetylene vesicles functionalized with N-heterocyclic ligands for metal cation binding.

Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA with metal chelating sites have been prepared and characterized. Their response to the presence of metal cations in buffered aqueous solution has been investigated by monitoring changes of colour, UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the addition of other metal salts, containing ions like Li(+), Na(+), K(+), Mg(2+), Ca(2+), Cr(2+), Ni(2+), Fe(2+), Co(2+), Cu(2+) or Pb(2+), failed to show any changes. The metal ion coordination selectivity of the ligands is slightly different for the vesicle surface immobilized ligands compared to the reported metal cation binding of the corresponding ligands in solution, which may be due to the special environment at the lipid-solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain their response to the presence of aqueous solutions of metal ions if immobilized in transparent polyvinyl alcohol films or on paper.