Thermodynamic and Kinetic Stability Constants of Selected Carboxylic Acids and Iron

Thermodynamic stability constants for complexes of lactic, malic, succinic and citric acids with both ferrous and ferric iron were determined. The rate of transfer of iron to apotransferrin, which has been defined as the kinetic stability constant, was also determined for both these and ascorbic acid complexes. The thermodynamic stability constants for malate and succinate were similar to ascorbate while that for lactate was somewhat lower. The kinetic stability constants in ascending order were as follows: lactate, ascorbate and malate, succinate and citrate. However, data from this study indicated that the slope of the Initial portion of the iron exchange curves might be a better measure of potential bioavailability. In descending order the slopes were: ascorbate, lactate, malate, citrate, and succinate.