Add time:09/09/2019         Source:sciencedirect.com

The interaction between the aluminum ion (Al3+) and Inogashira fulvic acid (IFA) at pH 3 was investigated using the calibration curve method for 27Al NMR spectra. The average conditional stability constant (log K) can be calculated to be 2.00–2.04 (M−1) (bidentate–monodentate) from the results of 27Al NMR measurements. In addition, because IFA has various coordination sites, including COOH, phenolic and/or alcoholic OH groups, we attempted to synthesize 2,3-dihydroxyterephthalic acid (cas 19829-72-2) (DHTPA) as a model compound with the functional groups of IFA for the investigation of the microscopic coordination mechanism between Al3+ and IFA by potentiometric titration and 27Al NMR measurements. The pKai values of DHTPA could be determined successfully (pKa1 = 2.3, pKa2 = 3.4 and pKa3 = 7.2; pKa4 was not determined), and these values indicate that DHTPA can act as a powerful chelating ligand, even at pH 3. DHTPA can interact with Al3+, and it predominantly forms 1:1 and 2:1 Al–DHTPA complexes. The calculated average conditional formation constant (log K1 and K2) of each complex can be determined as 1.09 (1:1) and 4.81 (M−1) (2:1). The results obtained showed that both the 1:1 and 2:1 Al–DHTPA complexes are formed and Al3+ interacts with IFA at pH3.

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