Water-soluble anionic POSS-Core dendrimer: Synthesis and copper(II) complexes in aqueous solution

A carboxylic acid-terminated polyhedral oligosilsesquioxane (POSS)-coredendrimer(POSS-CO2H) was synthesized from octa(3-ammoniumpropyl)octasilsesquioxane octachloride (POSS-NH3+) via a t-butyl ester-terminated POSS-core dendrimer that was prepared from neutralized POSS-NH3+ and t-butyl acrylate. Complexing properties of the sodium salts Of POSS-CO2H (POSS-CO2Na) with Cu2+ were studied in comparison with those of the G1.5 poly(amidoamine) (PAMAM) dendrimer (G1.5-CO2Na) by spectroscopic approach and isothermal titration calorimetry. In the case of G1.5-CO2Na, Cu2+-N-4 and Cu2+-N2O2 complexes are possible coordination modes, and only a Cu2+-N2O2 complex can be formed for POSS-CO2Na. In the case of POSS-CO2Na, upon increasing the concentration of Cu2+. the values of the binding constants decreased. However, the values of binding constants in the regions of the Cu2+-N2O2 coordination mode for G1.5-CO2Na increased with increasing concentration of Cu2+. This observation suggests that the uptake of Cu2+ is inhibited by increasing binding numbers of Cu2+ due to the rigid structure of the POSS-core dendrimer.