Labeled Boron Compounds

The course of chemical reactions in boron chemistry can be readily followed using B-labeled compounds. For instance, using isotopically labeled boron compoimds will show whether the exchange of substituents between two boron compounds is accompanied by boron transfer or not. Only a few such studies 

Boron-10 isotopic labeling of boron compounds is more useful than B labeling since the latter isotope is more abundant in nature (80.39%). Commercially available starting materials for °B labeling are °B-enriched elemental boron or boric acid. The °B content may be higher than 90%, and it is convenient for mechanistic studies to use a material containing 93.7% B and 6.3% B. 

The compound [ B](OH)3t proved a convenient starting material for the preparation of more reactive boron compounds. The procedures follow classical reactions, though some modifications were introduced in order to achieve high yields of the B-labeled species. 

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DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE A very corrosive material. When heated to decomposition it emits very toxic fumes of F , B oxides. See BORON COMPOUNDS, ACETIC ACID, and FLUORIDES. 

DOT CLASSIFICATION 4.1 Label Flammable Solid, Poison SAFETY PROFILE Poison by inhalation, ingestion, skin contact, and intraperitoneal routes. Ignites in O2 at 100°C. Forms impact-sensitive explosive mixtures with ethers (e.g., dioxane) and halocarbons (e.g., carbon tetrachloride). Incompatible with dimethyl sulfoxide. When heated to decomposition it emits toxic fumes of boron oxides. See also BORON COMPOUNDS and BORANES. 

Hafnium-like boron is known to be a neutron absorber or neutron moderator element, and, therefore, composites of boron carbide, B4C, and hafnium diboride, HfB2, can be considered as nuclear materials. These boron compounds after sintering and °B/"B isotopic ratio adapting are found to be heterogeneous polyphone cermets useful for nuclear applications (Beauvy et al. 1999). Boron acid obtained from the °B enriched boron trifluoride also was used in nuclear reactors (Shalamberidze et al. 2005). Amorphous boron powders enriched both in °B and "B, boron carbide, and zirconium diboride (ZrB2) powders and pallets labeled with °B isotope And applications in nuclear engineering too. The °B enriched Fe-B and Ni-B alloys are useful for the production of casks for spent nuclear fuel transfer and storage. 

Hawthorne, M. R, R. J. Wiersema, and M. Takasugi. 1972. Preparation of tumor-specific boron compounds. 1. In vitro studies using boron-labeled antibodies and elemental boron as neutron targets. J. Med. Chem. 15 449 52. 

Joly [21] reported the preparation of boron carbide in 1883, labeling the product as B3C, whilst in 1899 Moisson [22] labeled the compound as BeC. Yet, another 50 years passed until Ridgeway [23] suggested the stoichiometry to be 4 to 1. Today, it is well established that the composition of boron carbide has no exact stoichiometric composition but ranges from B4 3C to B10.4C. The composition of commercially produced boron carbide, using the carbothermal reduction of boron oxide in arc furnaces, is usually close to B4C, which corresponds to the stoichiometric limit on the high-carbon side. 

Alternatively, radiohalogen-labeled compounds may be prepared by way of isotopic labeling from the unlabeled bromo or iodo derivatives by various two-step reaction sequences. Examples include the use of trialkylsilyl synthons as described in References 10—13, and the use of boronic acid synthons as described in References 14 and 15. 

Shinkai et al. described the synthesis of dendritic saccharide sensors based on a PAMAM dendrimer labeled with eight boronic acid residues [183]. The dendritic compound showed enhanced binding affinity for D-galactose and d-fructose. The fact that the dendritic boronic acid functions as a saccharide sponge is ascribed primarily to the cooperative action of two boronic acids to form an intramolecular 2 1 complex. When one boronic acid binds a saccharide, its counterpart cannot participate in dimer formation and seeks a guest. 

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