Analytical Sciences

pH-Independent Recognition of Polyhydroxy Compounds by Niobium(V) Porphyrin Complex with Unique Sugar Selectivity

Takuya DOI, Norihide KACHIKAWA, Takashi YASUI, and Akio YUCHI

Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan

The niobium(V) complex with tetraphenylporphin having OH⁻ as an auxilliay ligand exists as a dimeric complex, [Nb₂(tpp)₂O₃] at a total concentration >10^−4.5 mol dm⁻³, and reacts with an aliphatic or aromatic polyhydroxy compound to form a monomeric complex containing chelate rings by coordination of the deprotonated species, and to cause an appreciable UV-Vis spectral change. In contrast to phenylboronic acid (PBA), the reactivity of [Nb₂(tpp)₂O₃] is independent of pH at least between 4 and 8. Aliphatic comounds are more reactive than aromatic compounds in dioxane–water, while the reactivity order is reversed in the two-phase reaction. The sugar selectivity order of [Nb₂(tpp)₂O₃] in dioxane–water (10:1) (sorbose > fructose >> mannose > arabinose, galactose > glucose) is appreciably different from that of PBA (fructose > sorbose >> arabinose > galactose > mannose > glucose). This may be related to the difference in size of the Lewis acidic center.

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