Boron essential function

Boron apparently has an essential function that somehow regulates parathormone action, and therefore indirectly influences the metabolism of Ca, P, Mg, and cholecalci-ferol. Boron is needed by the parathyroid and has been shown to prevent loss of Ca and bone demineralization in postmenopausal women (Nielsen et al. 1988). 

Nielsen FH (2002a) Does boron have an essential function similar to an omega-3 fatty add function Mengen- und Spurenelemente 21 1238—1250. 

After 70 years of effort, a biochemical function for boron in plants was identified. In primary cell walls, boric acid cross-links two chains of pectic polysaccharide at the rhamnogalacturonan-II region through borate-diester bonding between two side-chain apiosyl residues, thus forming a network of pectic polysaccharides (O Neill et al. 1996, Matoh 1997). Boron is suspected to have additional essential functions... 

Until 1950, 13 mineral elements were classified as essential these comprised the major elements (calcium, phosphorus, potassium, sodium, chlorine, sulphur, magnesium) and the micro or trace elements (iron, iodine, copper, manganese, zinc and cobalt). By 1970, molybdenum, selenium, chromium and fluorine had been added to the list subsequently, arsenic, boron, lead, lithium, nickel, silicon, tin, vanadium, rubidium and aluminium have also been included, the list varying slightly according to the different authorities. Plant and animal tissues contain a further 30 mineral elements, in small quantities, for which no essential function has been found. They may be acquired from the environment, but it has been suggested that as many as 40 or more elements may have metabolic roles in mammalian tissues. Fortunately, many of these trace elements, especially those of more recent discovery, are required in such minute quantities, or are so widely distributed in foods for animals, that deficiencies are likely to be extremely rare under normal practical conditions. 

The boron requirement and wall pectin content of many plants are correlated [54-56]. There is increasing evidence that a function of boron essential for normal plant growth and development is to covalently cross-link wall pectins (see Figure 5A). The structural organization of a boron cross-linked pectin network is likely to be a factor that contributes to the physical and biochemical properties of the wall because boron deficiency results in abnormal walls. For example, the results of recent studies provide evidence that the pore size of pectin-rich cell walls is determined in large part by borate ester cross-linking of RG-II [57]. 

The quality of the experimental evidence for nutritional essentiality varies widely for the ultratrace elements. The evidence for the essentiality of three elements, iodine, molybdenum and selenium, is substantial and noncontroversial specific biochemical functions have been defined for these elements. The nutritional importance of iodine and selenium are such that they have separate entries in this encyclopedia. Molybdenum, however, is given very little nutritional attention, apparently because a deficiency of this element has not been unequivocally identified in humans other than individuals nourished by total parenteral nutrition or with genetic defects causing disturbances in metabolic pathways involving this element. Specific biochemical functions have not been defined for the other 15 ultratrace elements listed above. Thus, their essentiality is based on circumstantial evidence, which most often is that a dietary deprivation in an animal model results in a suboptimal biological function that is preventable or reversible by an intake of physiological amounts of the element in question. Often the circumstantial evidence includes an identified essential function in a lower form of life, and biochemical actions consistent with a biological role or beneficial action in humans. The circumstantial evidence for essentiality is substantial for arsenic, boron, chromium, nickel, silicon, and vanadium. The evidence for essentiality for the... 

Boronic esters have been used in a wide range of transformations. These useful reagents have been transformed into numerous functional groups and are essential reagents for several C-C bond-forming reactions. Transition metal-catalyzed hydroboration of olefins often leads to mixtures of branched and linear products. Several groups have reported asymmetric reductions of vinyl boronic esters [50-52] with chiral rhodium P,P complexes however, the first iridium-catalyzed reduction was reported by Paptchikhine et al (Scheme 10) [53]. 

Boron is one of the essential materials for obtaining high specific impulse of a ducted rocket However, the combustion efficiency of boron-containing gas-generating pyrolants is low due to incomplete combustion of the boron particles in the ramburner.[i3-i l Fig. 15.20 shows the combustion temperature ofa boron-containing pyrolant with and without boron combustion as a function of air-to-fuel ratio, 8. A typical boron-containing pyrolant is composed of mass fractions of boron particles b(0-30), ammonium perchlorate ap(0.40), and carboxy-terminated polybutadiene ctpb(0-30). If the boron particles burn completely in the ramburner, the maximum combustion temperature reaches 2310 K at 8 = 6.5 and v = Mach 2 p =... 

Boron may be an essential nutrient in several species of aquatic vertebrates. Insufficient boron (<3 pg B/L 62 pg B/kg ration) interfered with the normal development of the South Afiican clawed frog (Xenopus laevis) during organogenesis, and substantially impaired normal reproductive function in adult frogs (Fort et al. 1998). Impaired growth of rainbow trout (Oncorhynchus mykiss) embryos was documented at <90 pg B/L, and death of zehrafish (Brachydanio rerio) embryos at <2 pg B/L (Rowe et al. 1998). 

No requirement for boron in mammals is proven, although evidence is accumulating suggesting that boron may be an essential nutrient. Boron is related to normal energy utilization, immune function, and metabolism of bone, minerals, and lipids (Penland 1998). Boron deficiency (<0.04... 

Iron-catalyzed Suzuki-Miyaura coupling reactions were also reported by Nakamura and colleagues (entry 27) [67]. Alkyl halides 1 and mixed pinacol aryl(butyl)borates, generated in situ from arylboronates and butyllithium, were used as the reagents and 10 mol% of the iron complexes 16a or 16b as the catalysts. The addition of 20 mol% of MgBr2 was essential for the success of the reaction. Products 3 were isolated in 65-99% yield. The methodology tolerates ester and nitrile functions. The reaction starts probably by initial boron-iron transmetalation to generate a diaryliron(II) complex. 

When considering the suitability of a bead production technique for imprinting, it is essential to evaluate the compatibility of the conditions used for polymerisation with those required for complex formation between functional monomers and templates. Where covalent imprinting methods are used, the covalent adducts are often highly stable and need quite harsh conditions to disrupt them. Such adducts could be used in most of the procedures described below with reasonable expectation of success. The same can be said for many metal-chelate complexes, which have stabilities approaching covalently bonded structures. The use of cyclic boronate esters is an exception. This adduct is unstable in water and hence cannot be combined efficiently with aqueous suspension polymerisation. 

Boron is an essential trace element for plants and is beneficial for animals and humans. Dietary boron obviously plays a role in immune functions. Among the best-known natural boron-containing compounds are polyketide antibiotics such as boromycin, aplasmomycins, borophycin and tatrolons. Attempts are underway to incorporate boron into different biologically active molecules, particularly for medicinal application, e.g. for boron neutron capture therapy of brain tumors. Some boron-containing biomolecules may apparently act as signaling molecules that interact with cell surfaces. 

Boron (B) may be the next element to be recognized as essential in human nutrition. The evidence is largely circumstantial because there is no clear biological function for boron in humans. 

Efforts to discover whether other elements might be essential intensified during the 1970s. Although it is believed that arsenic, nickel, silicon, and boron are probably essential to humans, it has been difficult to determine whether other minerals have specific biological functions in humans or other animals. 

Bones are actually living protein networks to which minerals attach themselves. Not aU of the minerals deposited on bones are essential to bone building. There are at least two dozen elements in bones that have no known function in the human body, as well as a handful of nonessential elements, such as boron, strontium, silicon, barium, bismuth, and arsenic (yes, arsenic), that are believed to do some good. Five toxic elements—lead, cadmium, mercury, polonium, and radium—are often found in human bones. As long as they are stabilized in the bones, they do no apparent harm. 

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