Analytical Sciences

¹³C and ²⁷Al NMR and Potentiometric Study on the Interaction between Aluminium Ions and Quinolic Acid in Acidic Aqueous Solutions

Takushi YOKOYAMA* * , Hikaru ABE**, Tsutomu KURISAKI** and Hisanobu WAKITA**

*Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
**Department of Chemistry, Faculty of Science, Fukuoka University, Jonan, Nanakuma, 814-0180, Japan

The interaction between aluminium ion (Al) and quinolic acid (L) in acidic aqueous solution was investigated by potentiometry and ¹³C and ²⁷Al NMR spectroscopy. In the ²⁷Al NMR spectra, two peaks were observed at 8 and 15.6 ppm, which were assigned to AlL and AlL₂ complexes, respectively. The ¹³C NMR spectra provide clear evidence that the L acts as a bidentate ligand and that the L coordinates with a nitrogen atom and an oxygen atom of the adjacent carboxylic group to form a chelate complex with a five-membered ring. From a potentiometric study, the formation constants (log beta₁ and log beta₂) for the AlL and AlL₂ complexes were estimated to be 4.52±0.02 and 7.99±0.05, respectively. (Keywords: Aluminium ion, phytotoxicity, quinolic acid, functional group, natural organic compound, NMR)

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