Phylogenetic analysis of hyperaccumulator plant species for heavy metals and polycyclic aromatic hydrocarbons

Increasing concentration of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in the soil may impose a serious threat to living organisms due to their toxicity and the ability to accumulate in plant tissues. The present review focuses on the phylogenetic relationships, sources, biotransformation and accumulation potential of hyperaccumulators for the priority HMs and PAHs. This review provides an opportunity to reveal the role of hyperaccumulators in removal of HMs and PAHs from soils, to understand the relationships between pollutants and their influence on the environment and to find potential plant species for soil remediation. The phylogenetic analysis results showed that the hyperaccumulators of some chemicals (Co, Cu, Mn, Ni, Zn, Cd) are clustered on the evolutionary tree and that the ability to hyperaccumulate different pollutants can be correlated either positively (Cd–Zn, Pb–Zn, Co–Cu, Cd–Pb) or negatively (Cu–PAHs, Co–Cd, Co–PAHs, Ni–PAHs, Cu–Ni, Mn–PAHs). Further research needs to be extended on the focus of commercializing the techniques including the native hyperaccumulators to remediate the highly contaminated soils.

     

Ion-Radical Conversions in Main or Side Chains of Nitrogen-Containing Polymers in Nitrogen Dioxide Atmosphere

Mechanism of nitrogen dioxide interaction with polymers containing amide and imide groups in the main or side chains of macromolecules (polycaproamide, polyvinylpyrrolidone, poly-m-phenylene isophthalamide and polypyromellitimide) is considered. The initiators of conversions of polymers of the given classes are not monoradicals of nitrogen dioxide rather than its equilibrium dimers in the form of nitrosyl nitrate. In primary oxidizing reaction of an electron transfer from donor groups of macromolecules to nitrosyl nitrate, radical cations, nitric oxide and nitrate anion are formed, which in the subsequent reactions give products of nitration and nitrosation. These products are precursors of stable acylalkylaminoxyl, acylarylaminoxyl, iminoxyl macroradicals. The specific interactions of nitrogen dioxide dimers with functional groups of macromolecules determine features of the mechanism of ion-radical conversions of the polymers and the composition of radical and molecular products. The direct detection of radical cations has been realized by ESR method for confirmation of the ion-radical initiation concept using model reaction of nitrogen dioxide with triphenylamine.