Strength of Flocs Formed by the Complexation of Lysozyme with Leonardite Humic Acid

Aggregation and aggregates properties of natural organic and nanosized macromolecules such as humic substances and proteins are crucial to explore so-called colloid-mediated transport and the fate of substances in soil and water environments. Therefore, the aggregation and dispersion, charging, and floc strength of lysozyme (LSZ)–leonardite humic acid (LHA) flocs were experimentally investigated. The experiments were performed in different salt concentrations and LSZ to LHA mass ratios as a function of pH. We obtained the stronger flocs at pH 4.4, where the isoelectric point (IEP) of the complex with the mass ratio 2.5 was confirmed. Thus, the aggregation of LSZ–LHA flocs is mainly caused by charge neutralization. We obtained the floc strength of 4.7 nN around IEP at low salt concentration of 3 mM, which was stronger than 2.8 nN in high salt concentration of 50 mM. The effect of salt concentration can be rationalized by charge-patch attraction at low salt concentration. With increasing mass ratio, the IEP shifted to higher pH. This is due to the increase in positive charge from LSZ in the mixture. The effect of the LSZ to LHA mass ratio on the maximum strength was weak in the range studied.

Hg-Pb binary heavy metals interaction study with Humic Acid: monitoring by FTIR spectroscopy

<p>This work shows that infrared spectroscopy is an easy and fast analytical technique for monitoring the behavior of the humic acids Fluka and Leonardite in contact with binary solutions of mercury and lead. Given the complexity of the structure of humic acid, the experiments were carried out on simple model molecules.<strong></strong></p><p>The spectra showed a shift (30 cm^-1) of the antisymmetric stretching vibration band from the carboxylate function -COO^- from 1590 to 1560 cm^-1 for the humic acids Fluka-binary solution interaction. In the case of mercury alone, the shift was of 40 cm^-1, it can be seen that this shift has dropped by 10cm^-1, which proves that the cationic exchange becomes more difficult.<strong></strong></p><p>We have confirmed that the affinity is due to the ionic radius, the reduction potential and the ionic potential. We reinforced this by a fourth parameter which is the frequency separations between the-COO^- antisymmetric and symmetric stretches (Dn_as-s). We have found thatDn_as-sis strongly related to the type of fixed metal. The spectra also showed the variation of the intensity of the C=O elongation vibration band of the carboxylic function -COOH up to 1610 cm^-1 for the Leonardite humic acid-binary interaction. The high concentration of the binary solution did not result in the total disappearance of the C=O band as in the Leonardite humic acid-mercury alone interaction study. This proves that some carboxylic sites are not accessible to Hg²⁺ ions.</p>

Rare earth elements as tracers of active colloidal organic matter composition

Environmental contextThe origin of organic matter at Earth’s continental surface can be either terrestrial or microbial, and its precise composition can influence its reactivity towards metals. We investigated the potential of rare earth elements to fingerprint the origin of various organic matters through their reactivity and composition. The rare earth element patterns can be useful tools to determine the reactivity and also pristine source of natural organic matter. AbstractRare earth elements (REEs) have been shown to be efficient tracers of the functional sites and/or complexes formed on humic molecules. In the present study, we test the potential of REEs to be used as tracers of the sources of humic substances (HSs). Three types of organic matter (OM) of terrestrial and microbiological origin were tested. The experiments of REEs binding to the HSs were combined with size-fractionation experiments. The REE patterns were the most fractionated in the &lt;10kDa fraction. For Leonardite humic acid (LHA) and Aldrich humic acid (AHA), the REE patterns were consistent with the REEs binding to strong but low density sites for a low REE/C loading. By contrast, for Pony Lake fulvic acid (PLFA), the REE pattern was similar to the REE pattern developed onto a bacteria cell surface and was attributed to the REEs binding to phosphate surface sites. Fluorescence and elemental analysis of PLFA showed that the &lt;10kDa fraction was the fraction with the stronger microbiological character, which suggested the REEs were probably bound to PLFA through REE-phosphate complexes. Such results therefore provide a new possibility for the use of REEs to assess an OM source without the need to perform numerous or complex analytical methodologies.

Aggregation and stabilization of multiwalled carbon nanotubes in aqueous suspensions: influences of carboxymethyl cellulose, starch and humic acid

Aggregation and stability of multiwalled carbon nanotubes in aqueous solutions were investigated with two polysaccharide stabilizers (carboxymethyl cellulose and a water soluble starch) and a natural organic matter (leonardite humic acid).