Abstract
Alkali-metal ions from weak complexes with various low-molecular-weight organic ligands [1]. Most of these ligands are of biological interest and are present both in biofluids an in natural waters. Since a large amount of alkali-metal ions is present in all natural fluids ( e.g. sodium and potassium are the main ionic constituents of all intra- and extracellular liquids and play a fundamental role in electrical communication through membranes), the knowledge of the formation constants of their complexes is quite important. Furthermore, the comparison of the stability constants concerning complexes of other metal ions, determined in different ionic media (in particular K + and Na +), can give rise to some uncertainties if the formation constants of the alkali-metal complexes are unknown. For the above reasons we thought it useful to study systematically the complexes of alkali-metal ions with carboxylic and hydroxycarboxylic acids. The formation constants have been determined potentiometrically by alkalimetric titrations of the acid using KNO 3, NaNO 3, NaClO 4, LiNO 3, CsNO 3 and tetrathylammonium bromide as background in the concentration range 0.03–1.0 mol dm −3 at 25° and 37 °C. Citrate, tartrate, malate, oxalate, malonate, phthalate and succinate ligands were investigated. The potentiometric data have been analyzed by using modified versions of ACBA [2] and MINIQUAD [3] least squares computer programs. All the ligands considered form complexes with alkali-metal ions and the stability constants show the trends citrate > tartrate > malate > and oxalate > malonate ∼ phthalate > succinate for hydroxycarboxylic and carboxylic acids respectively. As regards the metal ion the trend is Li>Na>K>Cs. The hydroxycarboxylic acids form protonated species too.
Published Version
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