Detailed Potentiometric Study of Al³⁺ and Cr³⁺ with Malic Acid in Aqueous Solutions
Pages 213-218
Yahia Z. Hamada, Marcus Harris, Kiva Burt, Jasmine Greene and Khalid Rosli

DOI: http://dx.doi.org/10.6000/1929-6037.2013.02.04.2

Published: 30 November 2013

Abstract: It appeared that malic acid solubilized both Al³⁺ and Cr³⁺ in aqueous solutions at all pH-values in 0.1 M NaNO₃ at 25 ^oC. The detailed potentiometric measurements indicated that these free tri-valent metal ions released a net of three protons (3H⁺’s) into the solution. Free malic acid released a net of (2H⁺’s) into the solution from the two carboxylates. However, in the presence of metal ions malic acid effectively releases a net of three protons (3H⁺’s) into the solution; two from the two carboxylates and the third from the alcoholic group. The reaction mixture of Al³⁺:malic acid indicated the formation of a dimeric species. The proposed structure of this dimeric species is in good agreement with what has been shown in the literature. We are presenting a dimeric species that may play an important role in malate transportation across cell membrane. Formation of the Al³⁺-malic acid complexes cover the span of a total of 400 mV; from +250 mV to -150 mV. The Cr³⁺-malic acid reaction mixture indicated the formation of a dimeric species as well.