Enhanced Antioxidant Activity and Reduced Cytotoxicity of Silver Nanoparticles Stabilized by Different Humic Materials.

The current article describes the biological activity of new biomaterials combining the "green" properties of humic substances (HSs) and silver nanoparticles. The aim is to investigate the antioxidant activity (AOA) of HS matrices (macroligands) and AgNPs stabilized with humic macroligands (HS-AgNPs). The unique chemical feature of HSs makes them very promising ligands (matrices) for AgNP stabilization. HSs have previously been shown to exert many pharmacological effects mediated by their AOA. AgNPs stabilized with HS showed a pronounced ability to bind to reactive oxygen species (ROS) in the test with ABTS. Also, higher AOA was observed for HS-AgNPs as compared to the HS matrices. In vitro cytotoxicity studies have shown that the stabilization of AgNPs with the HS matrices reduces the cytotoxicity of AgNPs. As a result of in vitro experiments with the use of 2,7-dichlorodihydrofluorescein diacetate (DCFDA), it was found that all HS materials tested and the HS-AgNPs did not exhibit prooxidant effects. Moreover, more pronounced AOA was shown for HS-AgNP samples as compared to the original HS matrices. Two putative mechanisms of the pronounced AOA of the tested compositions are proposed: firstly, the pronounced ability of HSs to inactivate ROS and, secondly, the large surface area and surface-to-volume ratio of HS-AgNPs, which facilitate electron transfer and mitigate kinetic barriers to the reduction reaction. As a result, the antioxidant properties of the tested HS-AgNPs might be of particular interest for biomedical applications aimed at inhibiting the growth of bacteria and viruses and the healing of purulent wounds.

Yedoma Permafrost Releases Organic Matter with Lesser Affinity for Cu2+ and Ni2+ as Compared to Peat from the Non-Permafrost Area: Risk of Rising Toxicity of Potentially Toxic Elements in the Arctic Ocean.

Pollution of the Arctic Ocean by potentially toxic elements (PTEs) is a current environmental problem. Humic acids (HAs) play an important role in the regulation of PTE mobility in soil and water. The permafrost thaw releases ancient organic matter (OM) with a specific molecular composition into the Arctic watersheds. This could affect the mobility of PTEs in the region. In our study, we isolated HAs from two types of permafrost deposits: the Yedoma ice complex, which contains pristine buried OM, and the alas formed in the course of multiple thaw-refreezing cycles with the most altered OM. We also used peat from the non-permafrost region as the recent environmental endmember for the evolution of Arctic OM. The HAs were characterized using 13C NMR and elemental analysis. Adsorption experiments were conducted to assess the affinity of HAs for binding Cu2+ and Ni2+. It was found that Yedoma HAs were enriched with aliphatic and N-containing structures as compared to the much more aromatic and oxidized alas and peat HAs. The adsorption experiments have revealed that the peat and alas HAs have a higher affinity for binding both ions as compared to the Yedoma HAs. The obtained data suggest that a substantial release of the OM from the Yedoma deposits due to a rapid thaw of the permafrost might increase the mobility of PTEs and their toxicity in the Arctic Ocean because of much lesser "neutralization potential".

Nature-like solution for removal of direct brown 1 azo dye from aqueous phase using humics-modified silica gel.

The objective was to estimate suitability of humics-modified silica gels for adsorptive removal of the Direct Brown 1 trisazo dye from aqueous phase. The major advantage of the proposed adsorbents is that of an ecologically sound procedure of immobilizing silanized humic derivatives onto silica gel in aquatic solutions. The silanized humic derivatives, in turn, are obtained without a use of organic solvent by reacting natural humic materials from peat and coal with 3-aminopropyltriethoxyorganosilane in water. These silanized derivatives are surface active and are capable of self assembling into humic adlayers at the water solid interface. A use of this approach allows for immobilization of up to 220 mg of humic materials per 1 g of SiO2. The adsorption capacity of humics-modified silica gels with respect to the Direct Brown 1 trisazo dye varied from 3.5 up to 8.8 mg per 1 g of SiO2. The maximum sorption obtained for the silanized derivative with 50% modification degree was comparable to adsorption capacity of activated coal to this dye (7.5 mg g(-1)). The results of this adsorption study, warrant further studies of azo dye removal from aqueous environments.