Publications by authors named "Inaki Guardado"
Background: Previous studies showed that phosphate can be complexed by humic acids (HA) through stable metal (M) bridges (PMHA). We studied the thermodynamic properties of PMHA and their relationships with the ability of PMHA to both decrease soil P fixation and increase P availability for plants. With this aim, we studied the theoretical stability of PFeHA, PAlHA and PCaHA by molecular modelling methods in relation to the degree and intensity of P absorption in soils and the ability of plants to take up complexed P.
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- Previous research has shown that while stable phosphate-metal-humic complexes can form, only a small amount of the metal in these complexes actually interacts with phosphate.
- The study explored the structural and electronic characteristics of these complexes involving metals like Fe(III), Al(III), and Zn(II) using infrared spectroscopy (FTIR), fluorescence, and molecular modeling techniques.
- Results indicated that phosphate binding strengthens the metal-carboxylate bond in Fe and Zn complexes, while the effect is less pronounced with Al, and the modeling suggested that greater stability in metal-humic interactions leads to lower phosphate fixation.
Size distribution, maximum complexing ability, and stability constants for phosphate-metal-humic (PO43--M-HA) complexes involving two trivalent (Fe and Al) and five divalent metal (M) bridges (Zn, Cu, Mn, Ca, and Mg) were investigated at the pH values 4, 6, and 8. Results highlighted the existing competition between metal-humic acid (M-HA) aggregation and the formation of PO43--M-HA complexes. However, the fact that only a very low fraction of complexed metal is involved in PO43- fixation seems to be related to the existence of specific electronic and/or steric requirements in the binding site in the metal-humic complex.
View Article and Find Full Text PDFThe aim of this work is to study the suitability of the complementary use of ultrafiltration (UF) and the interaction with an anion-exchange resin (AR) to characterize of phosphate-metal-humic complexes in solution. The results indicate that a methodological approach consisting of the validation and calibration of the AR method by the UF method and the further use of the AR method is suitable for characterizing phosphate-metal complexes. Such an approach has proven to be useful for calculating the phosphate maximum binding capacity of iron-humic complexes and stability constants.
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