2-Phosphonobutane-1,2,4,-Tricarboxylic Acid (PBTC): pH-Dependent Behavior Studied by Means of Multinuclear NMR Spectroscopy |
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| Authors: | Jerome Kretzschmar Anne Wollenberg Satoru Tsushima Katja Schmeide Margret Acker |
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| Affiliation: | 1.Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, 01328 Dresden, Germany; (S.T.); (K.S.);2.Radiochemistry and Radioecology, Technical University Dresden, 01062 Dresden, Germany;3.Central Radionuclide Laboratory and Radiation Protection, Technical University Dresden, 01062 Dresden, Germany;4.International Research Frontiers Initiative, Institute of Innovative Research, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan |
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| Abstract: | Although 2-phosphonobutane-1,2,4,-tricarboxylic acid, PBTC, has manifold industrial applications, relevant and reliable data on the protonation of PBTC are poor. However, these data are critical parameters for ascertaining PBTC speciation, especially with regard to a sound structural and thermodynamic characterization of its metal ion complexes. A rigorous evaluation of pH-dependent 1H, 13C, and 31P chemical shifts along with accessible scalar spin–spin coupling constants (J) was performed in order to determine the pKa values of PBTC in 0.5 molal NaCl aqueous solution by means of nuclear magnetic resonance (NMR) spectroscopy. The phosphonate group revealed pKa values of 0.90 ± 0.02 and 9.79 ± 0.02, and the pKa values associated with the carboxylic groups are 3.92 ± 0.02, 4.76 ± 0.03, and 6.13 ± 0.03. Supported by DFT-calculated structures revealing strong intramolecular hydrogen bonding, the sequence of deprotonation could be unambiguously determined. |
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| Keywords: | PBTC NMR DFT protolysis speciation thermodynamic constant |
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