Abstract
The complex-formation equilibria between aluminum(III) ion and l-(+)-ascorbic acid (AA) in 0.1 M KCl ionic medium at 25 °C and 0.15 M NaCl ionic medium at 37 °C were studied by glass electrode pH-metric measurements. The obtained experimental results were explained by the formation of the following complexation species: a weak mononuclear 1:1 species AlL 2+ together with two trinuclear mixed-hydroxo species Al 3H −5L 4 and Al 3H −5L 3+ in acidic aqueous solutions. Meanwhile, the formation of the complexes and structures of Al with AA were proved by multinuclear ( 1H, 13C, 27Al) NMR spectra in the pH range 2.0–5.0. It is supposed that Al directly coordinates with AA at O-3 moiety; also, Al can coordinate with the O-1 and O-2 moieties of ascorbate ion through the weakly binding and the intramolecular hydrogen bonding in acidic aqueous solutions.
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