Interaction of L-tartaric acid with alkaline metals and open chain polyammonium cations in aqueous solution

The interaction of L-tartrate with alkaline metal ions was studied by potentiometry and ultraviolet circular dichroism (UV/CD), and the formation of L-tartrate–polyammonium cation species was also studied by calorimetry. The ultraviolet circular dichroism technique was also used in order to clarify some aspects of the ion pair formation process between L-tartrate anion and alkaline (various ionic strength values were employed) or polyammonium cations. As in potentiometry, tetraethylammonium chloride has been considered as a reference ionic medium (that is, used as a non-interactive salt) for each comparison of the CD spectra recorded in different solutions. The spectropolarimetric technique was shown to be an efficient means of establishing the capacity of the ions considered for mutual conformational adaptability. Some differences clearly appear between the ion pairs formed by L-malate, studied in a previous paper, and L-tartrate anions. In the systems L-tartrate–polyammonium cations the species ALHr are formed [L = tartrate, A = amine, r = 1, 2, ... , (n + 1), n = maximum protonation degree of amine] with stability depending on the charges involved in the formation reaction. Comparisons are made with other carboxylic ligands previously investigated.