Resolution of carboxylate protonation microequilibria of NTA, EDTA and related complexones.
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 1.83-2.02logk units, which are reduced by 0.05-0.12logk units upon a nearby carboxylate protonation.
Szakács
Zoltán
Z
Laboratory for Speciation, Drug and Trace Analysis, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/a, H-1117 Budapest, Hungary.
Béni
Szabolcs
S
Noszál
Béla
B
D002264:Carboxylic Acids / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011522:Protons
D002264:Carboxylic Acids; D011522:Protons; D004492:Edetic Acid