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Potentiometric and Thermodynamic Studies of Some Metal–Cysteine Complexes
Author(s) -
Ghiamati Ebrahim,
Sheikhani Faezeh,
Farrokhi Alireza
Publication year - 2018
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.201700022
Subject(s) - chemistry , potentiometric titration , stability constants of complexes , metal , electroanalytical method , inorganic chemistry , metal ions in aqueous solution , cysteine , chemical stability , ion , organic chemistry , enzyme
A new and simple potentiometric method is developed to determine the stability constants of cysteine complexes with Mn(II), Cu(II), Zn(II), Cd(II), and Ce(III) metal ions using a modified Bjerrum method. Potentiometric titrations were performed in water and water/dioxane mixtures at five different temperatures. The least and highest stable complexes were those of Cu(II) and Zn(II), respectively. Furthermore, by conducting the experiments at temperatures of 15, 20, 25, 35, and 45 °C, the thermodynamic parameters Δ H °, Δ S °, and Δ G ° for the pertinent complexes were calculated. The results show that the Δ H ° values of the complexes are positive except for Zn(II). Negative values of Δ G ° are evidence for the spontaneity of the reactions.