NMR-controlled titrations: characterizing aminophosphonates and related structures

Abstract

Aminophosphonic acids, aminophosphinic acids, and aminophosphonous acids give rise to interesting protonation and metal complex formation equilibria, which can be monitored by potentiometric and NMR spectroscopic methods. A hyphenated technique referred to as NMR-controlled titrations or titration-dependent NMR spectroscopy has been introduced. Vicinal and geminal bisphosphonic acids have also been characterized by this method. Gradients (titration shifts) in chemical shifts and coupling constants were used to elucidate the structures of the protolytic species. Microscopic dissociation equilibria have also been studied by NMR-controlled titrations for glufosinate and 4-aminophenylphosphonic acid. Some comments are made on the UV-vis-controlled titration of the latter compound. Novel, advanced algorithms were used to estimate the error of analytical and NMR parameters, such as pK values, molar fractions, and ion-specific chemical shifts, describing the aminophosphonate ligands in each protonation form. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:562–582, 2000