Boron-Oxygen Species

The presence of metal salts, particularly those containing alkaline-earth cations and/or haUdes, cause some shifts in the polyborate equiUbria. This may result from direct interaction with the boron—oxygen species, or from changes in the activity of the solvent water (63). 

The conversion of borazine precursors to a-BN proceeds under smoother conditions than the reduction conversion processes originating from boron-oxygen species. The borazine derivatives are prepared by known procedures (for example, from Na[BH4] and [NH4]Cl BCI3 and [NH4]CI [46, 47]), and the B-Cl borazines formed may be cross-linked, for example, by reaction with [(CH3)3Si]2NH [48, 49] to give oligomeric gel precursors for a-BN. Resultant a-BN... 

There is an extensive and complex structural chemistry of boron-oxygen anionic species (polyborates), in aqueous or nonaqueous solution and in the melt or solid state, Six-membered ring formation dominates, but the structural chemistry of the species is complicated since boron exists in either 3- or 4-coordinate environments, or various combinations of these. Thus most polymeric species consist of (6—0)3 rings joined by boron atoms linked to an intervening oxygen atom, or y rings sharing a common boron atom. 

Boron suboxides have boron oxygen mole ratios equal to or greater than one. These compounds range from molecular species to refractory solid-state materials. Monomeric vapor-phase BO and B2O2 have been studied by spectroscopic techniques. In addition to these rather unstable high-temperature species, several forms of solid noncrystalline boron suboxides have been reported. A water-soluble low-temperature form is obtained by the vacuum dehydration of tetrahydroxydiborane at 220°C (equation 5). At 500 °C, this form converts to a light brown modification that has also been obtained by reactions of boric oxide with elemental boron, boron carbide, or carbon at high temperatures (>1250 °C). 

Sensing systems using boronic acids are of particular interest to the editors of this book, " who have established a track record in the area over a number of years. The editors, often in collaboration with authors of chapters in this book, have reported on boron-containing anion sensors, carbohydrate sensors, " glycation recognition, reactive oxygen species detection and enantiodiscrimination sensors and mechanisms of sensing... 

Boron-Oxygen Compounds. Work on the kinetics of complexation between phenyl-boronic acid and oxalic acid or malonic acid shows the existence of parallel pathways involving conjugate acid-base species of the ligand. Studies have also been published on the kinetics of complex formation between boric acid and benzoyl-acetone or a substituted benzophenone. ... 

Another role for active filler is to increase the anti-oxidation behavior of CMC composites. The lifetime of CMCs which are partly made of carbon is strongly depended on the efficiency of the anti-oxidation systems used to reduce the oxygen permeability. Extensive studies have been undertaken to improve the oxidation resistance of carbon fiber reinforced CMCs, and most are related to the application of boron-bearing species. 

The closest organic specie to the inorganic boric acid are the boronic acids generally described as R-B(OH)2. Boronic acids have been shown to act as inhibitors of the subtilisins. X-ray crystallographic studies of phenylboronic acid and phenyl-ethyl-boronic acid adducts with Subtilisin Novo have shown that they contain a covalent bond between the oxygen atom of the catalytic serine of the enzyme and the inhibitor boron atom (Matthews et al, 1975 and Lindquist Terry, 1974). The boron atom is co-ordinated tetrahedrally in the enzyme inhibitor complex. It is likely that boric acid itself interacts with the active site of the subtilisins in the same manner. 

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