Boric acid adsorption on humic acids: Ab initio calculation of structures, stabilities, B NMR and B,B isotopic fractionations of surface complexes |
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| Authors: | JA Tossell |
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| Institution: | Department of Chemistry and Biochemistry, University of Maryland College Park, MD 20742, USA |
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| Abstract: | Boric acid, B(OH)3, forms complexes in aqueous solution with a number of bidentate O-containing ligands, HL−, where H2L is C2O4H2 (oxalic acid), C3O4H4 (malonic acid), C2H6O2 (ethylene glycol), C6H6O2 (catechol), C10H8O2 (dioxynaphthalene) and C2O3H4 (glycolic acid). McElligott and Byrne McElligott, S., Byrne, R.H., 1998. Interaction of  and  in seawater: Formation of  . Aquat. Geochem.3, 345-356.] have also found B(OH)3 to form an aqueous complex with  . Recently Lemarchand et al. Lemarchand, E., Schott, J., Gaillardeet, J., 2005. Boron isotopic fractionation related to boron sorption on humic acid and the structure of surface complexes formed. Geochim. Cosmochim. Acta69, 3519-3533] have studied the formation of surface complexes of B(OH)3 on humic acid, determining 11B NMR shifts and fitted values of formation constants, and 11B, 10B isotope fractionations for a number of surface complexation models. Their work helps to clarify both the nature of the interaction of boric acid with the functional groups in humic acid and the nature of some of these coordinating sites on the humic acid. The determination of isotope fractionations may be seen as a form of vibrational spectroscopy, using the fractionating element as a local probe of the vibrational spectrum. We have calculated quantum mechanically the structures, stabilities, vibrational spectra, 11B NMR spectra and 11B,10B isotope fractionations of a number of complexes B(OH)2L− formed by reactions of the type: |
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