Boron-polysaccharide complexs

Under alkaline conditions, boric acid (or at this pH, boron tetrahydrate) forms complexes with diols 11) The formation of such a complex between two polysaccharide molecules can lead to crosslinking. The use of borax can, therefore, be expected to increase the stability of the bonds between the hemicellulose and between the hemicellulose and cellulose fibers in the paper. 

From the known, differential complexing between boronic acids and polyhydroxy compounds, it follows that carbohydrate mixtures may be separated by column-chromatographic methods that exploit the differences. Nucleoside and nucleotide boronates have been separated on columns of anion-exchange resins,90 and sugars and alditols have been shown to be differentially retained on such resins in the sulfonated phenylboronic acid form,64 but perhaps the best uses of column chromatography in this connection have incorporated the resolving powers of insoluble polymers to which boronic acid groups have been covalently bonded. Such insoluble forms of boronates have been synthesized either by substitution of polysaccharide derivatives, or by polymerization of suitable arylboronic acids. 

J. Zhang, C. D. Geddes, and J. R. Lakowicz, Complexation of polysaccharide and monosaccharide with thiolate boronic acid capped on silver nanoparticle. Anal Biochem., 332 (2004) 253-260. 

A characteristic chemical feature of boronic acids is the formation of reversible covalent complexes with 1,2- or 1,3-diols such as ethylene glycoL sugars, and polysaccharides. In aqueous solutions, boronic adds exist in equilibrium between an undissociated neutral trigonal form and a dissociated anionic tetrahedral form. In the presence of diols, neutral boronic acids barely form cyclic boronale esters by reaction with diols because these esters are generally hydrolytically unstable, but boronate anions form stable anionic boronate esters. Thus, the formation of complexes depends on the pH of the solution and pK of the boronic acid. 

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