Probing the interactions of GlcNH2 with boric acid via NMR spectroscopy

Abstract

The essential role of boronic esters in controlling both the direction and selectivity of chemical reactions as well as their significant function in catalytic activity have been demonstrated for industrially important processes. The specific interaction analyses of the monosaccharide GlcNH₂ with boric acid are of interest since monosaccharides serve as model systems for the more sophisticated carbohydrate molecules. The interaction of GlcNH₂ with boric acid was systematically investigated by numerous NMR techniques. A 1 : 1 chelate boron complex coordinated at the cis-1,2 position of GlcNH₂ was identified as the major species in DMSO-d₆ solution via¹H and ¹³C INEPT DOSY NMR spectroscopy. This specific boron nitrogen coordination mechanism was further supported by the ¹H–¹⁵N HSQC spectra. Variations in the spin–lattice relaxation times (T₁) of the ¹³C₁ nucleus also provided quantitative data regarding this non-covalent interactions. This is an application of ¹H, ¹³C INEPT DOSY, ¹H–¹⁵N HSQC, and relaxation methods to study such aggregations in solutions. These methods have potential applications in the characterization of reactive intermediates in biomass conversions.