Abstract
A potentiometric study showed that aldoses of the lyxo-series: d-lyxose, d-mannose and l-rhamnose, form dinuclear anionic complexes with tungstate or molybdate ions in acidic solutions. 95Mo NMR confirmed this result by revealing the presence of two non-equivalent metal atoms in the molybdate complexes. The corresponding formation constants were determined. The d-lyxose complexes had the higher stabilities, and the W VI complexes were more stable than their Mo VI homologues. The 13C NMR spectra were reassigned by means of a 2-D experiment and showed that all three carbohydrates were complexed in pyranose form. The chelating hydroxyl groups were strongly deshielded and displayed increased direct coupling constants 1 J CH. It can be concluded that the prevailing species in aqueous acidic solution cannot be furanose complexes similar to that characterized in solid state from molybdate— d-lyxose mixtures.
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