Resolution of carboxylate protonation microequilibria of NTA, EDTA and related complexones

Szakács, Zoltán and Béni, Szabolcs and Noszál, Béla (2008) Resolution of carboxylate protonation microequilibria of NTA, EDTA and related complexones. TALANTA, 74 (4). pp. 666-674. ISSN 0039-9140

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Abstract

Potentiometric and NMR–pH titrations were carried out on four classical complexones to elucidate their overall and site-specific basicities. NMR–pH profiles and Bjerrum's functions were adjusted to compound-specific symmetries and appropriate evaluation methods were developed. Symmetry-modulated relationships between the macro- and microconstants were deduced and self-consistent sets of microconstants were determined. The inherent basicity of carboxylates surrounded by adjacent, intramolecular ammonium and carboxylate sites have been found to be in the range of 1.83–2.02 log k units, which are reduced by 0.05–0.12 log k units upon a nearby carboxylate protonation.

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