Authors:István Hullár, András Valentin Vucskits, Erzsébet Berta, Emese Andrásofszky, András Bersényi, and József Szabó
, L. E. , Nelson , D. W. and West , D. X. ( 1981 ): The mechanism of copper (II) binding by humicacid: an electron spin resonance study of a copper (II)-humicacid complex and some adducts with nitrogen donors . Soil Sci. Soc. Am. J. 45 , 745
Authors:József Szabó, András Valentin Vucskits, Erzsébet Berta, Emese Andrásofszky, András Bersényi, and István Hullár
. X. ( 1981 ): The mechanism of copper (II) binding by humicacid: an electron spin resonance study of a copper (II)-humicacid complex and some adducts with nitrogen donors . Soil Sci. Soc. Am. J. 45 , 745 – 749
Commercial humic acid (HA) was anchored onto silica gel (SiAPTS) previously modified with 3-aminopropyltrimethoxysilane (APTS).
HA was anchored onto SiAPTS through two routes: adsorption and covalent chemical immobilization onto the surface. The adsorption
occurred by adding SiAPTS to HA in an aqueous solution, producing SiHA1, while chemical immobilization was performed by reacting
HA suspended in N,N-dimethylformamide with SiAPTS, to yield SiHA2. The infrared spectra confirm HA immobilization using both
procedures and the termogravimetric results showed that the anchored compounds have significantly thermal stability increased.
While natural HA presents a thermal stability up to 200C, the anchored compound presents a thermal stability near to 750C.
Authors:C. Kaya, N.A. Akram, M. Ashraf, and O. Sonmez
Application of salt stress (100 mM) through root growing medium caused a considerable decrease in plant fresh and dry biomass, maximum quantum yield (Fv/Fm), chlorophyll contents, leaf water potential, and leaf Ca, K, P and N concentrations of two maize cultivars (Apex 836 and DK 5783). However, salt-induced increase was observed in leaf osmolality (LO), proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), Na+ concentration and activities of enzymatic antioxidants, such as catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD). Of five humic acid (HA) levels used under non-stress and stress conditions in an initial experiment, 100 mg L−1 was chosen for subsequent studies. Exogenous application of humic acid (HA) at the rate of 100 mM as a foliar or pre-sowing seed treatment significantly increased the plant biomass, Fv/Fm, chlorophyll pigments and proline contents, while it considerably reduced the leaf water potential, H2O2 and MDA contents as well as the activities of all the afore-mentioned enzymatic antioxidants. Of both modes of exogenous treatment, foliar spray was better in improving plant biomass, chlorophyll contents, LO, leaf Na+ as well as the accumulation of all nutrients measured, however, in contrast, seed pre-treatment was more effective in altering leaf proline, H2O2 and MDA contents. Of both maize cultivars, cv. DK 5783 excelled in plant biomass, chlorophyll contents and leaf N, Ca and K concentrations as well as in the activities of all three antioxidant enzymes, whereas cv. Apex 836 was superior in leaf Na+ and P concentrations, H2O2 and MDA contents. Cv. DK 5783 was comparatively better in salt tolerance as compared to cv. Apex 836. Overall, exogenous application of HA was effective in improving salinity tolerance of maize plants which can be attributed to HA-induced increase in plant biomass, chlorophyll contents, mineral nutrients and activities of key antioxidant enzymes.
Fluoride (F–) binding to humic acid has been measured as a function of pH (5–6.6). The pH dependent binding is attributed to the anion being trapped within the large structure (territorial bound) but is not bound to a particular functional group (site bound). Studying fluoride binding provides insight to cation, anion and neutral species interactions with humic acid.
The stability constants of the complex of Pu/III/ with a humic acid at pH 2.9 and 5.0 were measured using solvent-extraction technique. The organic extractant was dinonyl naphthalene sulphonic acid in sodium form /NaD/ in benzene while the humate aqueous phase had a constant ionic strength of 0.5M /NaClO4/. The total carboxylate capacity of the humic acid was determined by direct potentiometric titration to be 6.201 Meq g–1. The apparent pKa increased as the degree of ionization // increased. The 1g
1 values of the complex of Pu/III/ with humic acid have been determined to be 2.8 and 3.11 at pH 2.9 and 5.0, respectively.
Authors:A. Paulenová, P. Rajec, M. Žemberyová, G. Sasköiová, and V. Višacký
The binding of strontium by humic acid was studied in systems designed to model soil leaching conditions. Ultrafiltration experiments were conducted for a wide range of CaCl and NaCl concentrations and for the pH range 4 to 7. It was found that the recovery of humic acid slowly decreased with increasing pH. This occurred because at neutral and basic solutions the increasing degree of ionization of the carboxylate groups leads to the full repulsion state of the humic acid and to increasing of the strontium binding (strontium recovery 60% at pH 7) with this natural polyelectrolyte. The strontium complexation in the presence of calcium was studied in different series of metal concentrations at pH 5 and the ionic strength 0.1M NaCl. The results were explained on the base of the metal ion charge neutralization model of humic complexation (CNM). Loading capacity (cca 40%) and complexation constants and Sr (3.51±0.27) and Ca (3.10±0.29) with Aldrich humic acid were found.
Authors:N. Kamei-Ishikawa, K. Tagami, and S. Uchida
This study investigated selenium sorption kinetics on humic acid (HA) as a function of initial Se concentration (10–300 μg·1−1) and solid/liquid ratio (0.01–0.1). From the result, it was clear that the Se sorption kinetics on HA could be expressed
by a pseudo-second order equation. This was possible because the sorption mechanism on HA is a multiple sorption process including
specific and non specific mechanisms. Additionally, the 3-D empirical equation for the amount of sorbed Se could be determined
as a function of the initial Se concentration and solid/liquid ratio.