Abstract: The pKa's of saxitoxin and a number of its derivatives have been determined. In most cases, the determinations were made by both potentiometric titration and observation of the change in I3C NMR chemical shift with pH. From these measurements it is clear that both dissociations of saxitoxin result from guanidinium groups. Thus the previous hypothesis that the first dissociation involved the ketone hydrate must be abandoned, and the more ...
