No abstract

Imidazole-terminated first-and second-generation poly(amidoamine)-type oligomeric silsesquioxanes (POSS)-core dendrimers (denoted as POSS-Im16 and POSS-Im32, respectively) were synthesized by the ester-amide exchange reaction from first-and second-generation methyl ester-terminated POSS-core dendrimers, respectively. Transmittances of the aqueous POSS-Im32 solution drastically decreased at pH47.2, but the change was reversible without hysteresis. The results of pH titrations for POSS-Im16 and POSS-Im32 showed well-defined one-step titration curves identical to those of monomeric imidazole compounds, such as 1-methylimidazole. Such simple acid-base behavior caused phase transition in the aqueous dendrimer solution to be highly sensitive to pH changes. The pKa values of 1-methylimidazole, POSS-Im16 and POSS-Im32 were 7.3, 7.0 and 6.7, respectively. Spectrophotometric titrations of the aqueous dendrimer solutions with Cu 2+ ions indicated that coordination modes of POSS-Im16 changed from the Cu 2+ -N 2 O 2 complex to the Cu 2+ -N 4 complex as the concentration of the dendrimers increased; however, only one complexation mode (Cu 2+ -N 4 ) existed between Cu 2+ ions and POSS-Im32.