Interaction of Malate and Lactate with Chromium(III) and Iron(III) in Aqueous Solutions

Abstract

Malate is generated from the hydration of fumarate by the action of fumarase in the citric acid cycle. Lactate is one of the most important products of glucose catabolism. From our ongoing efforts to study and understand the interaction and behavior of many hydroxycarboxylates with variety of metal ions (Hamada et al., 2003a; 2003b), we are reporting the interaction and behavior of malate and lactate with the Cr³⁺ and the Fe³⁺ ions using the potentiometric method in aqueous solutions at 25 °C. It appeared that the potentiometric titration graphs are different for the different titration systems; these differences are discussed. It also appeared that the malate as a chelating ligand solubilized both Cr³⁺ and Fe³⁺ at the physiological pH. In contrast to malate, the lactate ligand did not solubilize either Cr³⁺ or Fe³⁺ at the physiological pH. The Cr³⁺ and the Fe³⁺ lactate systems form the simple one‐to‐one metal chelates because only one proton was observed in all metal to lactate molar ratios with both the Cr³⁺ and the Fe³⁺ metal ions, even when we increased the lactate to metal ratio to 5 fold excess, i.e., in the 1∶5 titration systems.

Keywords:

• malate
• lactate
• chromium
• iron
• ternary complexes

Acknowledgments

The authors would like to thank the Nebraska Academy of Science for the research grants awarded to Y. Z. Hamada over the last four years to purchase most of the chemicals and equipment used in this study. YZH also would like to thank the new initiative grant from WSC, and WSC foundation annual grant. We would like to give special thanks to Professor Mark Hammer of WSC for reading the manuscript and his useful suggestions.