 About the affinities of Bases).Another outcome of his work was that Bredig introduced the idea of a Zwitterion, a dipolar ion with at least one positive and one negative functional group, and a net charge of zero.Bredig spent the next year and a half doing postdoctoral work at the laboratories of J. H. van't Hoff in Amsterdam, M. Berthelot in Paris and S. Arrhenius in Stockholm.