Boronic supramolecular assemblies

The rapid development of carborane chemistry is mainly due to their practical applications. For instance, the potential utility of carborane polymers as gaskets, O-rings, and electrical connector inserts has been reported. Their functionality for solvent extraction of radionuchdes as well as the potential medicinal value of the isoelectronic and isostructural boron analogues of biologically important molecules has been the subject of many review articles. For example, a number of boron compounds have been found to possess anti-inflammatory and antiarthritic activity in animal model studies. Boron compounds have also been implicated in studies designed to probe the importance of the so-called anionic subsite of acetylcholine esterase and Ach receptors. But, by far the most interesting practical apphcations of carboranes are in areas of boron neutron capture therapy (BNCT) and supramolecular assembly. 

The same research group has also exploited the sugar-boronic acid interactions as shown with 7, to create oriented supramolecular assemblies [67-75]. 

In comparison to abundant examples of noncovalent supramolecular assemblies,relatively few structures have been built with strong covalent bonds. This is due to the fact that normal covalent bonds are not easily broken and reformed. One can manipulate the temperature and conditions so that the formation of stable imines, esters, disulfides, hydrazones, and boronate esters is reversible. Some examples of these covalent self-assembled systems include disulfide hosts and covalent organic frameworks. ... 

In conclusion, covalent interactions have proven to be very valuable in the constrnction of supramolecular assemblies and sensors. Especially important are the reversible ones including (i) boronic acid interactions with diols... 

There is abundant information available on supramolecular assemblies that incorporate boronic acids. The vast majority of these ensembles have been observed primarily in the solid state, though several are stable in solution. This section begins with a brief discussion of hydrogen bonded assemblies, followed... 

B. Novel Phenyl-Boron-Phenyl Sandwich Supramolecular Assembly... 

FIGURE 4. Electron-deficient boron atoms (yellow) in aromatic boronate esters tend to stack in supramolecular assemblies between electron-rich re-clouds, forming a phenyl-boron-phenyl sandwich. 

As demonstrated by examples, these relatively novel assemblies hold promise in a number of different venues. The simple phenyl-boron-phenyl binding motif provides a unique supramolecular assembly strategy for researchers to take advantage of. Macrocyclic assemblies have been shown to serve as host molecules for molecular recognition events. Linear polymers have shown self-repair capabihties as well as serving as wide band-gap semiconductors. And porous COFs provide stable network geometries for the inclusion of guests. 

Membranes and Molecular Assemblies The Synkinetic Approach 6 Calixarenes Revisited 7 Self-assembly in Supramolecular Systems 8 Anion Receptor Chemistry 9 Boronic Acids in Saccharide Recognition 10 Calixarenes An Introduction, 2nd Edition 11 Polymeric and Self Assembled Hydrogels From Fundamental Understanding to Applications 12 Molecular Logic-based Computation 13 Supramolecular Systems in Biomedical Fields 14 Synthetic Receptors for Biomolecules Design Principles and Applications... 

Boron Sensing, Synthesis and Supramolecular Self-Assembly 17 Porous Polymers Design, Synthesis and Applications... 

For the community of supramolecular chemists, however, the sensor-analyte assemblies that display defined complex stoichiometry are more important. An excellent example of important electroneutral guests successfully addressed by fluorescence-based PET sensors are sugars, and saccharide sensing by boronic acids is a major success story of supramolecular chemists. Figure 17 shows two examples of PET-based saccharide sensors. 

Recent studies have started to broaden the choice of substrates to include surfaces that possess intriguing properties that could be used to interface with the adsorbed supramolecular structure or to influence the self-assembly process via substrate-adsorbate interactions. Examples of such surfaces include two surfaces that exhibit a moire superstructure, graphene, and boron-nitride monolayers. ... 

Boron Sensings Synthesis and Supramolecular Self-Assembly... 

FRET donor and acceptor can also be incorporated into the self-assembled nanofibers of supramolecular hydrogels. In this way Ikeda et developed a gel-based fluorocolorimetric sensor for polyols. The acceptor is boronic acid-appended. In the presence of polyols, it forms boronate ester complexes with the polyols, becomes negatively charged and more hydrophilic, and therefore migrates from the hydrophobic site. The increased distance between the donor and acceptor results in the fluorescence color change, from which the presence of polyols can be detected. 

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