Complexes with mannitol, borate

Complex D-mannitol borates are used in electrolytic condensers. Molybdic and arsenic acids also form association complexes with hexitols which increase the acidity of the inorganic acids. Rotational exaltation is obtained with the salts of these acids. 

In studies with amino acids and similar compounds, the ligand is nearly always monomeric. This situation changes greatly in those cases where the ligand can form dimers and higher condensation n-mers, such as phosphate (20), borate (21, 22, 23), and where polynuclear species are possible, such as with the copper (II) ion (24) and the Fe(III)ion (25). To extend these studies and to consider the analyses of other types of systems that reversibly form complexes, the mannitol-borate system which has previously been studied (26, 27), but without taking all forms of the borate ligands into account was examined. 

The complexes with boric acid and borates have been of more interest. The ability of D-mannitol to render boric acid more acidic is well known and forms the basis of an anal3rtical method allowing boric acid to be titrated as a monobasic acid. The boric acid complexes have been... 

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. 

The hydroxy a-amino acids l-serine and l-threonine, used as models for the 2-amino-2-deoxy glyconic acids, have been complexed with Ni(II) at 37 °C in aqueous solutions of 0.15M potassium nitrate. Values for the stability constants were obtained from iso-pH titration data which were collected by alternate, small, incremental additions of metal ion and potassium hydroxide being made such that the pH of the solution remained nearly constant. The data were consistent with the predominance of MLn species, along with additional protonated and hydrolyzed complexes. There was no evidence for the involvement of the hydroxyl group in chelation. By the same iterative computations the complexes formed between borate and mannitol have been analyzed, and the stability constants have been calculated. Complexes with mannitohborate stoichiometries of I.T, 1 2, 1 3, and 2 1 were proposed. 

Figure 4. Reactions of borate with mannitol with the log formation constants of the complexes at 25°C and 0.15M in potassium nitrate...

An example of some recent data which was interpreted to support this assumption is the work of Knoeck and Taylor (12). Using PMR spectra of mannitol-boric acid solutions, they observed that a decrease in pH resulted in a decrease in the mannitol-boric acid complex concentration. These results are supported by nB nuclear magnetic resonance (NMR) spectroscopy (16) which showed that the complex between mannitol and boric acid increased with increasing pH. However, Knoeck and Taylor (12) reasoned that since an increase in pH resulted in an increase in the borate anion concentration, as well as an increase in the complex concentration, the diol reacts only with the borate ion to produce the complex. 

Boron (B, at. mass 10.81) is a metalloid with properties somewhat similar to those of silicon. In chemical analysis, only boron(III) compounds are of importance. Boron forms complexes with fluoride and polyalcohols (e.g., mannitol and glycerol). In an anhydrous medium, boric acid reacts with methanol to form the volatile trimethyl borate. 

A potentiometric study of complexes formed by boric acid or potassium borate with mannitol in water or aqueous KCl solution has been carried out.2 The formation constant -Kcn of the mono-mannitoboric complex was determined (pAcn = 0.20 in HgO as solvent). 

A review has appeared on the synthetic, analytical, and biological uses of borate complexes of carbohydrates. The interaction of molybdate and tungstate with mannitol and glucitol have been further studied in dilute solution by potentiometric methods. ... 

Recently Isbell and coworkers have published the results of an extensive study of the behavior of solutions of sorbitol and D-mannitol in the presence of tetraborates. They found that sorbitol appears to form three complex borate compounds, whereas D-mannitol forms only two. Since the specific rotation in the tetraborate-D-mannitol system is a function of the ratio of the components and is independent of concentration at constant tetraborate-D-mannitol ratios, D-mannitol can be determined quantitatively by this method. However, sorbitol cannot be determined this way because the change in observed rotation at constant tetraborate concentration shows a reversal with increasing amounts of sorbitol. 

Borate complexes have been utilized by Brigl and Griiner47 to effect partial esterification. Anhydrous D-glucose and metaboric acid dissolved in acetone give a complex which exhibits the analysis of a diborate. Reaction of the latter with an excess of benzoyl chloride gives 2,6-di-O-benzoyl-D-glucose (XL). D-Mannitol likewise forms a diborate, which produces the 1,6-di-O-benzoyl derivative (XLI) upon benzoylation. In the presence of boric acid, D-glucose diethyl thioacetal yields the 6-benzoate (XLII). In the non-aqueous medium the formation of complexes... 

Arsenious acid, As(OH)s, behaves as a weak acid with a dissociation constant of about 8X10 at 25°. As is the case with boric acid, the addition of n-mannitol to aqueous solutions of arsenious acid increases the acidity of the solution. The formation constants for complexes between polyhydroxy compounds and the arsenite ion have been found to be considerably smaller than those for the corresponding borate complexes. This is also reflected in the absolute mobilities of such compounds during electrophoresis in arsenite solution. 

Raman spectra of aqueous solutions of borate anion in the presence of ethylene glycol and mannitol have been reported. They are consistent with the formation of 1 1 and 2 1 polyol borate complexes. It was suggested that the 2 1 complex had Cg symmetry, i.e. the five-membered ring is non-planar. 

For sensitive borate detection, a large excess of mannitol is added to a meth-anesulfonic acid eluent to increase the borate conductance via complexation. A special concentrator column (trace bomte concentrator, TBC-1) was developed for the ultratrace analysis of borate. The stationary phase of this concentrator is functionalized with a cis-diol, on which borate is selectively retained. Minimum detection limits in the lower nanogram/Liter range are obtained when large sample volumes are preconcentrated, so that this method is suitable for the trace analysis of borate in deionized water. As an example. Figure 5.10 shows the chromatogram of a 500 ng/L borate standard, which was obtained upon pneumatic preconcentration of 160 mL of the respective standard solution. An lonPac... 

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