Materials with Boronate Affinity

Although the first report on boronic acids was published in 1862, boronate affinity materials have not been extensively investigated until recently. In recent years, various boronate-functionalized materials, such as macroporous monoliths, nanoparticles, and mesoporous materials, have been developed into important tools for the facile selective extraction of cis-diol-containing compounds. With these matrices, several important materials with teamed boronate affinity and boronate avidity as well as boronate affinity-based molecularly imprinted polymers have been prepared. 

In 1970, Weith and co-workers first prepared boronic acid-functionalized chromatographic media via immobilizing APBA to cellulose for the separation of nucleic acid components and carbohydrates. Since then, various boronate affinity chromatographic media such as cellulose, sephacryl, sepharose, polyacrylamide and silica beads have been developed because of the merits of boronate affinity for capturing cis-diol-containing biomolecules. Various matrices and boronic acid derivatives are listed in Table 11.3. It can 

Sulfhydryl cellulose Catechol [2-(diethylamino)carbonyl-4-b ro mome thy 1] p he ny Iboronate 92 

To reduce the binding pH, Scouten and co-workers first synthesized a novel boronate affinity ligand, catechol [2-(diethylamino)carbonyl-4-bromomethyljphenylboronate, which contains intramolecular B-O coordination. Then, this ligand was coupled to sulfhydryl cellulose. The novel boronate affinity gel bound the glycoprotein horseradish peroxidase (HRP) at neutral condition (pH 7.0), at which the immobilized enzyme retain 90.12% of its original activity. 

In addition to the conventional boronate affinity materials for pH-con-trolled captu re-release of c/s-diol-containing compounds, thermally responsive boronate affinity materials have recently attracted attention for their applications in separation science and biomedicine. For example, Deng and 

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Regarding the quantity of boron adsorbed, adsorption maxima calculated with the Langmuir adsorption equation 16,17, 25-27) vary from approximately 10 up to 100 figrams of B/gram of soil. Soils derived from volcanic ash deposits adsorb unusually large amounts of boron 16, 18) because of their enriched contents of amorphous materials with affinity for anions. 

Boron nitride is a wide band gap semiconductor. For BN a negative electron affinity (NEA) can be expected [84]. Materials with this property can be used, for example, in cold cathode emitters. NEA occurs if the vacuum energy level lies below the minimum of the conduction band. Beside the electronic structure of the bulk material the surface conditions of the considered material are quite important [85]. 

Ion exchange processes function by replacing undesirable ions of a liquid with ions such as H+ or OH from a solid material in which the ions are sufficiently mobile, usually some synthetic resin. Eventually the resin becomes exhausted and may be regenerated by contact with a small amount of solution with a high content of the desired ion. Resins can be tailored to have selective affinities for particular kinds of ions, for instance, mercury, boron, ferrous iron, or copper in the presence of iron. Physical properties of some commercial ion exchange resins are listed in Table 15.4 together with their ion exchange capacities. The most commonly used sizes are -20 + 50 mesh (0.8-0.3 mm) and -40 -h 80 mesh (0.4-0.18 mm). 

The boron is injected into the patient usually as a carborane (e.g. the ring-compound C2H12B10) which is furnished with two mercapto-groups to give affinity for protein. Although there is 19% of B in natural boric acid (the rest is mainly B), the therapeutic material is further enriched. One hour after the injection, a neutron beam from a thermonuclear reactor is lined up with an appropriately localized hole made in the patient s skull. The pioneer clinical work was done in Tokyo (Hatanaka and Sano, 1973 cf Wong, Tolpin and Lipscomb, 1974). 

Although an Ni/Mo alloy melt does not wet a-BN, slow interface reactions are observed [20]. On the other hand, mutual wettability of materials sometimes is a first indication for chemical affinity. Thus, the wettability of a-BN by aluminium and aluminium alloys increased with increasing temperature a content of rare earth metals in the aluminium melt leads to a decrease of the wettability [21]. Reaction-bonded a-BN is completely eroded by liquid steel at 1650°C in an Ar atmosphere [22]. The contact angles formed on graphite substrates by molten lead di-chloride/alkali metal chloride mixtures do not change when the Ar atmosphere is replaced by CI2. However, when air is introduced complete wetting is observed after about five minutes. This is not the case with a boron nitride substrate [23]. 

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