bungenberg de jong 's sequences of cation binding to polymer-bound anionic sites established , over 40 years ago , that the most common cations , na+ , k+ , mg+ ( + ) and ca+ ( + ) , in biological materials behaved differently in the presence of the three most common polyanionic charges , carboxylate , diester phosphate and ester sulphate .
C0003075
anionic
C0038720
sulphate