Synthesis of first- and second-generation imidazole-terminated POSS-core dendrimers and their pH responsive and coordination properties

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.

POSS ionic liquid crystals

“…A wide variety of polyhedral oligomeric silsesquioxane (POSS)-based functional materials have been developed using ionic species. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] We recently reported the synthesis of POSS-based ILs, and we investigated their thermal properties. 25,26 By tethering multiple ion pairs composed of imidazolium cations and carboxylates to the vertices of POSS cores or by simply adding POSS molecules with acid groups, the melting temperatures of the ion pairs decreased and their thermal stabilities increased.…”

Silsesquioxane organofunctionalized with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole: Preparation and subsequent reaction with silver and potassium hexacyanoferrate(III) for detection of l-cysteine

“…POSSs are known as hybrid organic-inorganic nanocomposites -the inorganic core provides stability to the molecule and organic arms can establish its specific properties [7][8][9][10][11]. In particular, due to the highly symmetrical three-dimensional nature of their nucleus, POSSs are good precursors for the production of hybrid organic-inorganic materials [6,12] and these nanomaterials have recently shown great or advantageous functional properties for a wide range of technological applications, such as dendritic precursors [13][14][15][16], polymer precursors [17,18], as precursors for developing liquid crystals [19,20], homogeneous and heterogeneous catalysis [21,22], electroactive films [23], additives [24,25], antibacterial [26], and also used in thin films and coatings for various applications, including nanocomposites [10,11,27]. Thus, silsesquioxanes containing the chlorine element at their ends, such as octakis(3-chloropropyl)octasilsesquioxane, can be easily modified by the organic/inorganic process.…”

Syntheses of biphenyl‐terminated polyhedral oligomeric octasilicate‐core dendrimers and their single‐component optical transparent free‐standing thermoplastic films

“…The use of POSS‐ or OS‐cores for dendrimer synthesis is particularly attractive because of their minimal numbers of synthetic steps when compared with using conventional cores. They have relatively globular conformations and few entanglements of their branches, with a high proportion of terminal functional groups positioned on the external surface of the dendrimers, even in earlier generations of the dendrimers . The terminal function groups in the first‐generation POSS‐core dendrimer are isolated and inhibit interaction with neighboring branches.…”