Reversible self-assembly of dendrimer based on polyhedral oligomeric silsesquioxanes (POSS)

Synthesis of (Hyper)Branched Monohydroxyl Alkoxysilane Oligomers toward Silanized Urethane Prepolymers

The aim of this work was the synthesis of (hyper)branched oligomers based on trialkoxysilane in various conditions and further application of them in order to modify the urethane prepolymers. Hydroxyl-terminated trialkoxysilane was used as a monomer for homo-condensation. It was obtained by reaction of 3-aminopropyl trialkoxysilane (APTES) with ethylene carbonate (EC). The reaction was based on the attack of amine at the carbonyl carbon atom followed by ring opening of the carbonate to give a urethane (carbamate) product. The next step was the condensation via substitution of ethoxy groups on silicon atom with the terminal hydroxyalkyl groups present in the primary product with the evolution of ethanol. Accordingly, the impact of temperature and type of catalyst on process efficiency was investigated. A quantitative analysis of reaction progress and products of the conversion of EC together with ethanol evolution was conducted by means of gas chromatography, which allowed us to determine the formation of monomeric product and, indirectly, of oligomeric products. It was found that at room temperature after 24 h, the majority of the monomeric product was isolated, whereas at elevated temperature in the presence of Ti-based catalyst, further condensation of the monomer into branched oligomers was preferred, and, moreover, the application of vacuum intensified that process. The obtained products were structurally characterized by ¹H and ²⁹Si NMR, MALDI-ToF and Gel Permeation Chromatography. Finally, two different alkoxysilane products, monomeric and oligomeric, were applied for modification of urethane prepolymer, forming silanized one (SPUR). The influence of the silanizing agent on the mechanical and thermal properties of the moisture-cured products was shown before and after additional conditioning in water.

Synthesis of Silsesquioxanes with Substituted Triazole Ring Functionalities and Their Coordination Ability

A synthesis of a series of mono-T8 and difunctionalized double-decker silsesquioxanes bearing substituted triazole ring(s) has been reported within this work. The catalytic protocol for their formation is based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) process. Diverse alkynes were in the scope of our interest-i.e., aryl, hetaryl, alkyl, silyl, or germyl-and the latter was shown to be the first example of terminal germane alkyne which is reactive in the applied process' conditions. From the pallet of 15 compounds, three of them with pyridine-triazole and thiophenyl-triazole moiety attached to T8 or DDSQ core were verified in terms of their coordinating properties towards selected transition metals, i.e., Pd(II), Pt(II), and Rh(I). The studies resulted in the formation of four SQs based coordination compounds that were obtained in high yields up to 93% and their thorough spectroscopic characterization is presented. To our knowledge, this is the first example of the DDSQ-based molecular complex possessing bidentate pyridine-triazole ligand binding two Pd(II) ions.

Towards a Real Knotaxane

Two classes of mechanically interlocked molecules, [3]rotaxanes and knotted [1]rotaxanes, were the subject of this investigation. The necessary building blocks, alkyne-terminated axles containing two ammonium ions and azide-terminated stoppers, and azide-containing substituted macrocycles, have been synthesized and characterized. Different [3]rotaxanes were synthesized by copper-catalyzed “click” reactions between the azide stoppers and [3]pseudorotaxanes formed from the dialkyne axles and crown ethers (DB24C8). Methylation of the triazoles formed by the “click” reaction introduced a second binding site, and switching via deprotonation/protonation was investigated. In preliminary tests for the synthesis of a knotted [1]rotaxane, pseudorotaxanes were formed from azide-containing substituted macrocycles and dialkyne substituted diammonium axles, and copper-catalyzed “click” reactions were carried out. Mass spectral analyses showed successful double “click” reactions between two modified macrocycles and one axle. Whether a knotted [1]rotaxane was formed could not be determined.

The crown ether size and stereochemistry affect the self-assembly, hydrogelation, and cellular interactions of crown ether/peptide conjugates

Crown ether ring size affects nanofiber morphology of hydrogels upon conjugation with D- and L-phenylalanine dipeptides. Random nanofibers showed enhanced cell adhesion and proliferation whereas twisted nanofibers displayed weak cell attachments.

Postpolymerization modification based on dynamic imine chemistry for the synthesis of functional polyacetylenes

This study established a postpolymerization modification method for the preparation of functional polyacetylenes based on dynamic imine chemistry.

[60]Fullerene–porphyrin [n]pseudorotaxanes: self-assembly, photophysics and third-order NLO response

Herein we report a series of porphyrin and methano[60]fullerene that undergo self-assembly.

Synthesis of aromatic functionalized cage-rearranged silsesquioxanes (T8, T10, and T12) via nucleophilic substitution reactions

Organic-inorganic hybrid nano-building blocks of aromatic nitro-, aldehyde-, and bromo-functionalized polyhedral oligomeric silsesquioxanes were easily prepared through nucleophilic substitutions, starting from the reactions between octakis(3-chloropropyl)octasilsesquioxane and phenoxide derivatives. These phenoxide anions not only supply the substitution functions to a silsesquioxane cage, but can also induce a cage-rearrangement leading to the formation of octa-, deca-, and dodecahedral silsesquioxane cages.

Dendritic nanoglobules with polyhedral oligomeric silsesquioxane core and their biomedical applications

Dendrimers have been recognized as promising materials for biomedical applications due to their unique properties, such as well-defined unimolecular structures, precise molecular weights and high degrees of branching and surface functionality. The dendrimers with a polyhedral oligomeric silsesquioxane core – nanoglobules – have many advantageous features over traditional dendrimers, including more functional groups at the same generation of dendrimers, well-defined 3D structures and relatively compact morphologies. Various nanoglobules of polyhedral oligomeric silsesquioxane-core dendrimers have been synthesized and investigated for biomedical applications. Nanoglobules have been used as carriers for developing drug-delivery systems, gene-delivery systems and imaging contrast agents with precisely defined structures and sizes. This article summarizes the recent developments in nanoglobules for biomedical applications.

From trigonal bipyramidal to platonic solids: self-assembly and self-sorting study of terpyridine-based 3D architectures

Using a series of tritopic 2,2':6',2″-terpyridine (tpy) ligands constructed on adamantane, three discrete 3D metallo-supramolecular architectures were assembled, i.e., trigonal bipyramidal, tetrahedron, and cube. The self-assembly used tritopic ligands as corner directing units and metal ions as glue units at the edge. The angles of the linkers between adamantane and tpy head play a critical role in guiding the assembled structures, which have the general formula of M3nL2n, where M denotes metal ion and L denotes ligand. All complexes were fully characterized by (1)H, (13)C NMR, diffusion-ordered NMR spectroscopy, ESI-MS, and traveling-wave ion mobility-mass spectrometry. The binary mixtures of LA and LC or LB and LC underwent a self-sorting process that led to the self-assembly of discrete 3D structures. The self-sorting behavior is solely based on the angles precoded within the arm of tritopic ligands. Moreover, kinetic study of preassembled cube and tetrahedron demonstrated a slow ligand exchange process toward a statistical mixture of hetero tetrahedrons with LA and LB.

Water soluble octa-functionalized POSS: all-click chemistry synthesis and efficient host-guest encapsulation

A series of water soluble octa-functionalized POSSs were facilely synthesized via thiol-ene and Menschutkin click chemistry. Among them, octa-alkynyl POSS further reacted with azide-terminal alkyl long chains, resulting in a well-defined, amphiphilic octopus-like POSS. For the first time it was used for host-guest encapsulation and it exhibited an ultrahigh loading capability.

Synthesis and isolation of methacrylate- and acrylate-functionalized polyhedral oligomeric silsesquioxanes (T8, T10, and T12) and characterization of the relationship between their chemical structures and physical properties

Novel organic-inorganic hybrid nanobuilding blocks of methacrylate- and acrylate-functionalized polyhedral oligomeric silsesquioxanes were easily prepared via nucleophilic substitution on octakis(3-chloropropyl)octasilsesquioxane, using sodium methacrylate and sodium acrylate, respectively. From a practical standpoint, these cage-rearranged silsesquioxanes (T8, T10, and T12) could be readily isolated in their pure form with conventional silica gel column chromatography. Octakis(3-propyl methacrylate)octasilsesquioxane (T8) is a colorless, crystalline solid with a melting point of 66.7-67.2 °C, while other cage products are colorless viscous liquids at room temperature. Moreover, we report that the chemical structure/physical property relationship of silsesquioxane cages not only is dependent on the symmetry of the inorganic silsesquioxane core at a given temperature but also is dictated by the organic substituent mobility. Structures of the products were confirmed by (1)H, (13)C, and (29)Si NMR spectroscopy and high resolution electrospray ionization mass spectrometry analysis.

Synthesis and reactivity of nitrogen nucleophiles-induced cage-rearrangement silsesquioxanes

Novel phthalimide and o-sulfobenzimide-functionalized silsesquioxanes were successfully synthesized via nucleophilic substitution reactions from octakis(3-chloropropyl)octasilsesquioxane. Surprisingly, the formation of deca- and dodecasilsesquioxanes cages was discovered during substitution with phthalimide, but only octasilsesquioxane maintained a cage in the o-sulfobenzimide substitution reaction. Moreover, we report the electronic effect of nitrogen nucleophiles to promote cage-rearrangement of inorganic silsesquioxane core for the first time. Structures of products were confirmed by (1)H, (13)C, and (29)Si NMR spectroscopy, ESI-MS analysis, and single-crystal X-ray diffraction.

Breaking symmetry toward nonspherical Janus particles based on polyhedral oligomeric silsesquioxanes: molecular design, "click" synthesis, and hierarchical structure

The design, synthesis, and self-assembly of a series of precisely defined, nonspherical, polyhedral oligomeric silsesquioxane (POSS)-based molecular Janus particles are reported. The synthesis aims to fulfill the "click" philosophy by using thiol-ene chemistry to efficiently install versatile functionalities on one of the POSS cages. In such a way, both the geometrical and chemical symmetries were broken to create the Janus feature. These particles self-organize into hierarchically ordered supramolecular structures in the bulk. For example, the Janus particle with isobutyl groups on one POSS and carboxylic groups on the other self-assembles into a bilayered structure with head-to-head, tail-to-tail arrangements of each particle, which further organize into a three-dimensional orthorhombic lattice. While the ordered structure in the layers was lost upon heating via a first-order transition, the bilayered structure persisted throughout. This study provides a model system of well-defined molecular Janus particles for the general understanding of their self-assembly and hierarchical structure formation in the condensed state.