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 pH>7.2, 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 Cu2+ ions indicated that coordination modes of POSS-Im16 changed from the Cu2+–N2O2 complex to the Cu2+–N4 complex as the concentration of the dendrimers increased; however, only one complexation mode (Cu2+–N4) existed between Cu2+ ions and POSS-Im32.
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Acknowledgements
This study is a part of the Kyoto City Collaboration of Regional Entities for the Advancement of Technology Excellence of JST. We thank Professor Tsuyoshi Kawai of the Nara Institute of Science and Technology for making MALDI-TOF-MS measurements, which are supported by the Kyoto-Advance Nanotechnology Network.
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Naka, K., Masuoka, S., Shinke, R. et al. Synthesis of first- and second-generation imidazole-terminated POSS-core dendrimers and their pH responsive and coordination properties. Polym J 44, 353–359 (2012). https://doi.org/10.1038/pj.2011.145
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DOI: https://doi.org/10.1038/pj.2011.145
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