Solubility of domoic acid in water and in non-aqueous solvents

Abstract

The solubility of domoic acid (DA) in H2O and D2O, in aqueous NaCl solution and in several non-aqueous solvents was measured by NMR and UV spectroscopies. The solubility in water is comparable with that of aminoacids such as glutamic acid and aspartic acid. It is markedly pH-dependent, passing through a minimum at the isoelectric point, the increase towards both higher and lower pH values indicating that the anionic and cationic forms are more soluble than the neutral form. The effect of NaCl on the solubility of DA in water is negligible. The solubility of DA in alcohols is lower than in water but it is much higher than the solubility of glutamic acid or aspartic acid. The octanol–water partition coefficient for DA at pH 5.32, Kow = 0.0037, was obtained by a direct UV measurement. The low value of Kow indicates that aquatic organisms cannot take up DA directly from the water and bioaccumulation may proceed only through dietary intake. Key words: solubility of domoic acid, NMR of domoic acid, UV spectra of domoic acid, octanol–water partition coefficient of domoic acid.