Iron Oxidation in Mops Buffer. Effect of Phosphorus Containing Compounds

Fe2+ autoxidation in Mops buffer both in absence and presence of substoichiometric concentrations of EDTA, H2O2 and of Fe3+ is greatly affected by phosphorus containing compounds. They increase the lag phase, characteristic of Fe2+ oxidation in this buffer, and decrease the rate of the reaction. This effect is due to the phosphates of the molecule. The ability of the different compounds tested to affect Fe2+ oxidation, however, appears to be influenced also by the rest of the molecule. The concentration of the different phosphorus containing compounds that inhibits 50% of Fe2+ oxidation is rather different. The effect exerted appears to be the result of an equilibrium between an inhibitory effect on the pathway of Fe2+ oxidation that occurs in Mops buffer and the onset of a different oxidation pathway of Fe2+ similar to that occurring in Na phosphate buffer. A hypothesis is proposed that the phosphorus containing compounds inhibit Fe2+ oxidation by binding Fe3+ and decreasing its ability to accelerate Fe2+ autoxidation. It is suggested that the presence in vitro and in vivo of phosphorus containing compounds may modify Fe2+ autoxidation and thus the production of oxygen active species.