title: XAFS studies of cobalt(II) binding by solid peat and soil-derived humic acids and plant-derived humic acid-like substances.
abstract: This work has examined cobalt(II) binding by a variety of solid humic acids (HAs) isolated from peat, plant and soil sources at temperatures down to 60K. The results confirm that X-ray absorption near-edge spectroscopy (XANES) measurements cannot distinguish between aquo and carboxylato ligands in the inner coordination sphere of Co(II). However, between 1 and 2 inner-sphere carboxylato ligands can be detected in all the peat, plant and soil-derived HA samples by extended X-ray absorption fine structure (EXAFS) measurements, indicating inner-sphere coordination of HA-bound Co(II). The precision of C(carboxylate) detection is limited by the extent and quality of the data and the contribution from inner-sphere O to the Fourier transformed peaks used to detect carbon. Putative chelate ring formation is consistent with a relatively negative entropy change in step A, the stronger Co(II) binding step by HA functional groups, and could relate to 'non-exchangeable' metal binding by HSs.
authors.affiliation: Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, USA. e.ghabbour@neu.edu
authors.forename: Elham A
authors.initials: EA
authors.lastname: Ghabbour
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Davies
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D005583:Fourier Analysis; D006812:Humic Substances / Q000032:analysis*; D012987:Soil / Q000032:analysis*; D013057:Spectrum Analysis; D013816:Thermodynamics; D014965:X-Rays
chemical_list: D006812:Humic Substances; D012987:Soil; D003035:Cobalt