Oxalic acid has two adjoining carboxylic groups and the values for its dissocation constants are greater than for dicarboxylic acids with longer carbon chains. It is a chelating agent and easily forms oxalates with metal ions. In water, oxalates with Na and K are very soluble, with Mg poorly soluble, and Ca practically insoluble. The toxicity can be a result of a combination with Ca to form insoluble oxalate and create a deficiency of Ca in the body, and an accumulation of oxalic acid itself in the body. Amino acids also from stable coordination complexes with bentonites in the presense of chelating cations Cu, Co, or Zn. Ionophores or ion bearers are naturally occurring compounds which carry or transport small cations selectively across the lipid barriers of the cell membrane. Ionophores may be either channel-forming proteins which span the membrane through which cations can pass, or of carrier type.