Ultraviolet spectrum of domoic acid

Abstract

The ultraviolet spectrum of aqueous domoic acid solutions has an intense absorption band, whose λ max shifts from 240.0 ± 0.3 nm at pH 1.3 to 244.7 ± 0.3 nm at pH 12.3. At the same time, its ε max increases from 24250 to 26700 L mol −1 cm −1 . At pH 7 λ max is 242.8 ± 0.3 nm and ε max is 26035 ± 200 L mol −1 cm −1 Analysis of the variation of λ max and ε max with pH allowed us to estimate the values of these quantities for each of the five stages of protonation of domoic acid and to verify the pK values reported by Takemoto and Daigo. Keywords: ultraviolet spectrum, pK values, protonation, domoic acid.