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Boronic polyol complexes

When halogen atoms are present in the epoxide such as in epichlorohydrin, 3,3,3-trichloropropylene oxide (TCPO) or 4,4,4-trichloro-l,2-butylene oxide (TCBO), or in the initiator, acid catalysts, e.g. boron trifluor-ide etherate, may be used (13-18). Vogt cind Davis (16) found that, if the concentration of catalyst/ini-tiator (polyol) complex is decreased with respect to TCPO in order to obtain higher molecular weight products, side reactions such as cyclization reactions become increasingly important. Boron trifluoride also promotes dimerization of alkylene oxides to dioxane or alkyl derivatives of dioxane as described by Fife and Roberts ( ). The use of acid catalysts, e.g. Lewis acids, promotes formation of a greater amount of terminal primary alcohol groups when compared to base catalysis of epoxides. [Pg.242]

FRET donor and acceptor can also be incorporated into the self-assembled nanofibers of supramolecular hydrogels. In this way Ikeda et developed a gel-based fluorocolorimetric sensor for polyols. The acceptor is boronic acid-appended. In the presence of polyols, it forms boronate ester complexes with the polyols, becomes negatively charged and more hydrophilic, and therefore migrates from the hydrophobic site. The increased distance between the donor and acceptor results in the fluorescence color change, from which the presence of polyols can be detected. [Pg.282]

It is known that boronic acids can bind with hydroxyl compounds, including polyols such as PVA, through the complex formation of a reversible covalent bonding [56, 57]. [Pg.148]

A recent example of diasteromeric amplification with achiral guests and a racemic library can be seen in the work of Iwasawa and coworkers. The library members consisted of a racemic polyol and l,4-benzenedi(boronic acid) [2], When these components were mixed in an equimolar ratio in methanol, a precipitate formed, which was insoluble in other organic solvents and thought to be a polymeric boronate. However, when the library members were mixed in the presence of toluene or benzene, a precipitate again formed, but it was soluble in several (nonprotic) organic solvents where boronic ester exchange is slow. With toluene a [2 2] complex of the polyol and diboronic acid formed, as evidenced by NMR and FAB-MS data. X-ray crystallography confirmed that a cyclic structure formed with... [Pg.157]

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. [Pg.21]

The chirality of carbohydrates were sensitively delected by complexation with porphyrin 83 and by observing the induced CD spectra.One carbohydrate molecule can bind two boronic-acid-appended porphyrins 83 using four hydroxy groups. The exciton coupling between two porphyrins in the CD spectra was used to detect the absolute configuration of the polyols. [Pg.303]

Similar to borate-polyol gels, the interpolymer complex gels based on boronate-diol interactions also show pH- and temperature-dependent behaviors. Kiser et synthesized interpolymer complex gels using a pair... [Pg.274]

The reversible formation of boronic esters by the interaction of boronic acids and polyols in water was first examined in the seminal study of Lorand and Edwards [49]. This work followed an equally important study on the elucidation of the structure of the borate ion [124]. By measuring the complexation equilibrium between phenylboronic acid and several model diols and monosaccharides using the method of pH depression, ester formation was shown to be more favorable in solutions of high pH where the boronate ion exists in high concentrations (Equation 19, Figure 1.12). This study also confirmed the Lewis acid behavior of boronic acids and the tetracoordinate structure of their conjugate base, i.e., the hydroxyboronate anion (Section 1.2.2.4). Another conclusion is that free boronic adds have lower Lewis add strengths than their neutral complexes with 1,2-diols. For example, the pJC, of PhB(OH)2 decreases... [Pg.21]

The reaction of polyhydroxy compounds with boric acid or boronic acids has been used for derivatization and separation of carbohydrates and other compounds containing vicinal diols using different chromatographic and electrophoretic techniques (1,9,69). The mechanism of reaction is a complex between cis diol moieties and borate or boronate groups. It has been demonstrated that it is the borate ion, rather than boric acid, which is complexed by the polyol (70,71). The reaction is pH dependent and the optimum conditions are usually at pH > 8.0. In a pH ranging from 8 to 12, aqueous borate solutions contain tetrahydroxyborate ions and also more highly condensed polyanions such as triborate and tetraborate. Equilibrium between the different species depends on the pH and the total borate concentration. [Pg.495]

Geffen, N., R. Semiat, M. S. Eisen, Y. Balazs, 1. Katz, and C. G. Dosoretz. 2006. Boron removal from water by complexation to polyol componnds. J. Memb. Sci. 286 45—51. [Pg.154]


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See also in sourсe #XX -- [ Pg.9 , Pg.21 ]




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