FUNDAMENTALS OF THE ZWITTERIONIC HYDROPHILIC GROUP

Zwitterionic functional groups possess the greatest polarity found within the nonionic class of hydrophilic groups. Their nomenclature, common misconceptions as to their classification and properties, and their ion exchange and acid-base reactions are discussed. The hydrophilicity of zwitterionic compounds is strongly influenced by the structure and basicity of the anionic substituent group, and to a lesser degree by the length of the ion bridge that binds together these oppositely charged substituent groups. Methylene groups within the ion bridge contribute to the lipophilicity of the molecules, but to a lesser degree than do methylene groups within the long chain.