Fluorescent conjugated polyfluorene with pendant lactopyranosyl ligands for studies of Ca²⁺-mediated carbohydrate-carbohydrate interaction

A well-defined fluorescent conjugated polyfluorene with pendant lactopyranosyl ligands was easily prepared through Cu(I)-catalyzed azide/alkyne "click" ligation and Suzuki coupling polymerization. As a fluorescent multivalent modelsystemof glycoconjugates, thepolymerwasfirstusedfor studies ofmetalion-mediatedcarbohydrate-carbohydrate interaction based on fluorescence spectroscopy. A significant fluorescence quenching of the lactosyl-bearing polyfluorene was observed upon addition of calcium ion, which is attributed to the polymer aggregation derived from Ca²⁺-mediated complex formation. Dynamic light scattering can also prove Ca²⁺-induced aggregation of the polymer based on determination of the corresponding hydrodynamic diameters. The calcium-mediated lactose-lactose interaction was reversible when treated with EDTA. In control studies, Ca²⁺-induced fluorescence quenching can not be observed for cellobiosyl- or galactosyl-functionalized polymer analogues, which show that specific sugar structures are critical for carbohydrate-metal complex formation.