Boron accumulation

Boron accumulated in blood, brain, and liver, reaching 30-67 mg B/kg DW in 2-15 days. Boron was eliminated rapidly, with few detectable residues after 1 day on a boron-free diet (12)... 

The regional arid soils have a relatively high B content and the mosaic spots of these soils are characterized by very high boron accumulation (Table 13). 

In plants that have restricted boron mobility, boron accumulates in old leaves. Eventually the boron becomes toxic and the leaves die and drop this results in the elimination of boron from the plant. 

Boron accumulates in both aquatic and terrestrial plants but it does not seem to biomagnify in the food chain. Boron does not biomagnify in aquatic food chains and has low potential to accumulate in aquatic organisms, as judged by studies in the San Joaquin River, California,... 

Yanagie, H., H. Kumada, T. Nakamura, S. Higashi, I. Ikushima, Y. Morishita, A. Shinohara, M. Eijihara, M. Suzuki, Y. Sakurai, H. Sugiyama, T. Kajiyama, R. Nishimura, K. Ono, J. Nakajima, M. Ono, M. Eriguchi, and H. Takahashi. 2011a. Feasibility evaluation of neutron capture therapy for hepatocellular carcinoma using selective enhancement of boron accumulation in tumor with intra-arterial administration of boron-entrapped water-in-oil-in-water emulsion. A /. Radial hot. 69 1854-1857. 

The recommended daily intake of boron is <20 mg. Actual amounts are dependent on food composition and local conditions. It is estimated that people ingest about 2-10 mg of boron a day, but boron deficiency in humans has not yet been recorded. Boron contained in foods is easily absorbed in the gastrointestinal tract, but 30-92% of boron ingested is excreted in the urine. At higher doses of boric acid, boron accumulates in the nervous system. 

The mechanism of initiation in cationic polymerization using Friedel-Crafts acids appeared to be clarified by the discovery that most Friedel-Crafts acids, particularly haUdes of boron, titanium, and tin, require an additional cation source to initiate polymerization. Evidence has been accumulating, however, that in many systems Friedel-Crafts acids alone are able to initiate cationic polymerization. The polymerization of isobutylene for instance can be initiated, reportedly even in the absence of an added initiator, by AlBr or AlCl (19), TiCl ( )- Three fundamentally different... 

As can be seen in Fig. 3.67, the corrosion resistance of amorphous alloys changes with the addition of metalloids, and the beneficial effect of a metaU loid in enhancing corrosion resistance based on passivation decreases in the order phosphorus, carbon, silicon, boron (Fig. 3.72). This is attributed partly to the difference in the speed of accumulation of passivating elements due to active dissolution prior to passivation... 

Several dendrimeric borane and carborane systems have been developed for use as boron-delivery agents.147 In vitro tests with a boronated dendrimer-epidermal growth factor bioconjugates indicated that they are endocytosed, resulting in the accumulation of boron in lysosomes. 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Pendleton, G.W., M.R. Whitworth, and G.H. Olsen. 1995. Accumulation and loss of arsenic and boron, alone and in combination, in mallard ducks. Environ. Toxicol. Chem. 14 1357-1364. 

B excess Aral-Caspian low plain, Kazakhstan Brunozems, Solonetses, and Solonchaks are enriched in B, up to 280 ppm. The increased content of B in forage species, up to 0.15% by dry weight Accumulation of B in animal organisms leads to the disturbance of B excretion function of liver, reducing activity of amilase and, partly, of proteinase of the intestine tract in human and sheep. Endemic boron ententes sometimes accomplished by pneumonia. Human, sheep and camel morbidity... 

For compounds to be useful in BNCT, they must allow administration to a patient (usually through the blood stream), accumulate or be retained in the tumor, be of low toxicity, and on the basis of the required accumulation, carry as many boron atoms as possible. To achieve the latter, boron clusters are of great value. In this chapter, the chemistry of some clusters is described that have found application in BNCT (see Scheme 2.2-1). The focus is on the o-carborane system dicarba-doso-dodecaborane, C2B1oH12, and its degradation product nido-carborate,... 

When specific compounds for BNCT are to be prepared, the cluster compounds must be covalently attached to organic moieties. The chemistry of such reactions will be the focus of this chapter. It should be borne in mind, however, that the boron spedes might in themselves already constitute suitable candidates for selective accumulation or retention in tumors, and perhaps also possess other pharmacological properties. Thus, Na2Bi2HnSH (BSH) (see Section 2.2.5.1), which is clinically used for BNCT of glioblastoma [2], and its thiocyanate derivative Na2Bi2HnSCN [12], are both taken up in tumor tissue without additional targeting units. 

It is of interest to note that the anomeric effect directs the boron substituent into the a-configuration in the case of mannose, despite the considerable steric demand. NMR studies in solution indicate that the usual 4Q conformation of the pyranose is retained, with the boron substituent in the axial position. Depending on the sugar moiety, tumor uptake is observed when the compounds are given to tumor-bearing animals. Accumulation is, however, only transient, and within a fairly short time, the boron is lost from the tumor, and from other tissues. Even at... 

In the interim period, results have accumulated steadily, in endeavors to address and extend the chemistry beyond the initial perceived limitations. These limitations include the following (a) the effective catalytic syntheses are confined to the reactions utilizing catecholborane (b) the scope of alkenes for which efficient rate, regio- and enantio-selectivity can be achieved is limited, and (c) the standard transformation mandates the oxidation of the initially formed (secondary) boronate ester to a secondary alcohol, albeit with complete retention of configuration [8]. Nonetheless, for noncatalytic hydroboration reactions that lead to the formation of a trialkylborane, a wide range of stereo-specific transformations may be carried out directly from the initial product, and thereby facilitate direct C-N and C-C bond formation [9]. 

It has long been recognized that boron is required by higher plants [61, 62], and recent research indicates the involvement of boron in three main aspects of plant physiology cell wall structure, membrane function, and reproduction. In vascular plants, boron in solution moves in the transpiration stream from the roots and accumulates in the stems and leaves. Once in the leaves, the translocation of boron is limited and requires a phloem transport mechanism. The nature of this mechanism was only recently elucidated with the isolation of a number of borate polyol compounds from various plants [63-65]. These include sorbitol-borate ester complexes isolated from the floral nectar of peaches and mannitol-borate ester complexes from the phloem sap of celery. The implication is that the movement of boron in plants depends on borate-polyol ester formation with the particular sugar polyol compounds used as transport molecules in specific plants. 

Available data for aquatic invertebrates and boron suggest that the no-observable-effect levels were 13.6 mg B/L for freshwater organisms and 37 mg B/L for marine biota (Table 29.7). Juvenile Pacific oysters Crassostrea gigas) accumulated boron in relation to availability, but showed no prolonged retention following cessation of exposure (Thompson et al. 1976). At industrial discharge levels of about 1.0 mg B/L, no hazard is apparent to oysters and aquatic vertebrates (Thompson et al. 1976). 

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... 

Eaton, RM. 1944. Deficiency, toxicity, and accumulation of boron in plants. Jour. Agric. Res. 69 221 -211. 

Frick, H. 1985. Boron tolerance and accumulation in the duckweed, Lemna minor. Jour. Plant Nutr. 8 1123-1129. 

Graham, R.D., R.M. Welch, D.L. Grunes, E.E. Cary, and W.A. NorveU. 1987. Effect of zinc deficiency on the accumulation of boron and other mineral nutrients in barley. Soil Sci. Soc. Amer. Jour. 51 652-657. 

Maeso, E.S., E.E Valiente, I. Bonilla, and P Mateo. 1985. Accumulation of proteins in giant cells, induced by high boron concentrations in Chlorella pyrenoidosa. Jour. Plant Physiol. 121 301-311. 

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