Speciation of uranyl ions in fulvic acid and humic acid: a DFT exploration

Abstract

The speciation of uranyl ions in fulvic acid (FA) and humic acid (HA), based on models of larger sizes, is systematically studied using density functional theory (DFT). Four uranyl binding sites are suggested for FA and based on their energetics, the preferential binding sites are proposed. The computed binding sites include two chelating types, one through the carboxylate group and one via the hydroxo group. A systematic way to attain the possible structure for Stevenson's HA model is carried out using a combined molecular dynamics (MD) and quantum chemical approach. Calculated structures and energetics reveal many interesting features such as conformational flexibility of HA and binding of hydrophobic molecules in agreement with the experimental suggestions. Five potential binding sites are proposed for uranyl binding to HA and the calculated geometries correlate nicely with the experimental observations. Our binding energy calculations reveal that apart from uranyl binding at the carboxylate functional group, binding at other functional groups such as those involving quinone and hydroxo sites are also possible. Finally, based on our cluster calculations the strength of uranyl binding to HAs and FAs is largely influenced by neighbouring groups via hydrogen bonding interactions.

Molecular dynamic simulation of asphaltene co-aggregation with humic acid during oil spill

“…humic acids) and the petroleum-based systems (e.g. asphaltenes, resins and polycyclic aromatic hydrocarbons) (Kuznicki et al, 2008(Kuznicki et al, , 2009Bandela et al, 2011;Sundararajan et al, 2011;Bhattacharya et al, 2012;Jian et al, 2013).…”

Binding characteristics of Cd2+, Zn2+, Cu2+, and Li+ with humic substances: Implication to trace element enrichment in low-rank coals

“…The strongest combination of mixed functional groups to chelate metal ions is hydroxyl and carboxyl (supported by Sundararajan et al, 2011), followed by two hydroxyls, hydroxyl and carbonyl, carboxyl and carbonyl, two carboxyls in the decreasing order ( Figure 5). As to this sequence, the latter three are largely influenced by electron-withdrawing groups, i.e.…”

“…Due to the fact that ortho hydroxyl forms hydrogen bond with benzoic acid and develops steric hindrance, the destruction of conjugation between the aryl and the carboxylate changes benzene ring of the salicylic acid from week electron-donating group to electron-withdrawing group. It also deviates In specific, the atom in purple is Li, while grey is C, red is O, and white is H. The ligand in 1a is deprotonated acetic acid, while 1b deprotonated 2-methyl-propionic acid, 2a deprotonated benzoic acid, 2b-e deprotonated salicylic acid, 2f-h deprotonated gallic acid, 3a-c deprotonated benzoquinonetetracarboxylic acid, 3d deprotonated 2,5-dihydroxy-benzoquinone, 4a-e deprotonated fulvic acid (rebuilt from Sundararajan et al, 2011). the electroneutrality, then decreases the BE value of organolithium complex, although the extent is lower than that corresponding to deprotonated benzoquinonetetracarboxylic acid.…”

“…Although the concrete molecular structure of HSs has yet not been determined due to its large molecular size and complexity, the main functional groups able to form complex with metals include carboxyl, hydroxyl, and phenol of local configuration. Sundararajan et al (2011) showed that the predominant of adsorptive site for uranyl ion was the carboxyl and the functional groups nearby might aid the chelation. For other metal ions with smaller size, whether identical adsorption behaviors can be observed has yet not been intensively investigated.…”

Environmental modeling of uranium interstitial compositions of non-stoichiometric oxides: experimental and theoretical analysis

“…The environmental protection strategies for monitoring the migration processes of radionuclides in the geosphere and long storage of nuclear waste have involved complex models of environmental processes and experimental chemical, geochemical, physical and biological factors (Stoliker et al 2011;Ilton et al 2012;Jung et al 2012;Malaviya and Singh 2012;Chandrasekaran et al 2011;Sundararajan et al 2011;Mayer et al 2013;Walton and Mitchell 2013;Qiu and Burns 2013;Hocking et al 2013;Knope and Soderholm 2013). This complexity of the theoretical modeling and the experimental design of radionuclide migration in surface and groundwater; its speciation in wastewater, sorption onto soils, sediments and manure has been further complicated by the dual physical nature uranium between rare element and semiconductor as a result of the characteristics of 5f-electrons at an intermediate localization regime.…”