Amino-acid-based zwitterionic polymer and its Cu(II)-induced aggregation into nanostructures: a template for CuS and...

A convenient and water-based approach is described for the synthesis of an l-lysine-based zwitterionic polymer, poly(ε-l-lysinyl acrylamide) (PLAM), without using protecting group chemistry, chromatographic purifications, and organic solvents as the reaction media. PLAM contains both amine and carboxylic acid groups in each repeating unit, which can either be protonated or deprotonated just by altering the pH of the solution to obtain overall positive or negative charge. PLAM is tested for its applicability as a zwitterionic polymeric buffer in water. Cu(II) ion-induced aggregation of PLAM as a function of solution pH is studied. Spherical nanogel aggregates are formed at pH 9.5 due to aggregation of PLAM through its complexation with Cu(II) ion. Spherical aggregates appear to dissociate via breaking of the complexation at a pH < 5.5 resulting in molecular dissolution of PLAM. This aggregation process is pH reversible. The Cu(II)-PLAM aggregates are used as a template for fabrication of CuO and CuS nanoparticles.