Trace metal-citric acid complexes as inhibitors of calcification and crystal growth. I. Effects of Fe(III), Cr(III) and Al(III) complexes on calcium phosphate crystal growth.

The crystal growth of calcium phosphate has been shown to be inhibited by a low molecular weight Fe(III)-citric acid complex formed when there are high ratios of citrate:iron at neutral pH in aqueous solution. Synergism with citric acid was also observed in systems containing Al(III) or Cr(III) ion, but different unknown complexes seemed to be involved. These results are in qualitative agreement with a preceding study involving calcification of an organic matrix. Since chelating agents like citric acid can compete with the storage proteins for iron, we suggest that the Fe(III)-citrate complexes studied here may be formed in vivo and participate in regulating biologic calcification.