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Effects of Solution Chemistry on the Fluorescence and Electrophoretic Behaviours of Humic Acid

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In the soil, the metal-organic interactions, including complexation reactions, that occur between Humic Acid (HA) and various cations (Ba2+, Ca2+, Cu2+, and Zn2+) play a key role in the speciation of divalent ions, and therefore in controlling their biological availability, accumulation and mobility. In order to elucidate the mechanism of such reactions, the effect of various divalent salts (BaCl2, CaCl2, CuCl2, and ZnCl2) on the fluorescence and surface charge properties of a commercial HA, were investigated in the present work. The data indicate that in the presence of increasing added salt amount of BaCl2, CaCl2, and ZnCl2, the HA fluorescence intensities decrease linearly and zeta-potential magnitude diminished and reached plateau value. However, non-linear marked decrease of the HA fluorescence intensities, and enhanced zeta-potential decrease, were observed in the presence of increasing CuCl2 added salt amount. Further, by decreasing the aqueous phase pH, in the range pH = 10-4, similar decreases of the HA fluorescence intensities and zeta-potential magnitudes, were also observed. It is shown that Cu2+ divalent cations, as compared to Zn2+, Ba2+, and Ca2+ ions, exhibit greater fluorescence quenching ability and complexing capacity of HA macromolecules. The observed fluorescence and surface charge decrease of HA macromolecules, in the presence of divalent cations, result from cation exchange process, and lead to conformational changes of the macromolecule. The fluorescence and zeta potential data indicate that HA macromolecule has different capacities to interact with various metal ions, and the order of divalent cation complexing capacity with HA is found as follows: Cu > Ba > Ca∼Zn.
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Keywords: COMPLEXATION; DIVALENT CATION; FLUORESCENCE; HUMIC ACID; QUENCHING; ZETA-POTENTIAL

Document Type: Research Article

Publication date: March 1, 2013

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  • Journal of Colloid Science and Biotechnology is an international multidisciplinary peer- reviewed journal covering all aspects of colloid science including colloids preparation, characterization, structure-property relationships, spectroscopy, chemical and physical properties and applications of colloids in biotechnology, medicine and pharmaceuticals. This journal deals with interdisciplinary research areas of chemistry, physics, biology, materials science, polymer science, nanotechnology covering all topics related to colloids such as latexes, emulsions, suspensions, micellar systems, gels, composites, hybrids, surfactants, aerosols, foams, minerals, soft matter, microfluidics, encapsulation processes of active molecules, biomolecules, surfacial and interfacial processes, catalysis, electrochemistry, theoretical aspects, computer simulations and colloids in biotechnology and medicine.
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