Aqueous solvation of As(OH)3: A Monte Carlo study with flexible polarizable classical interaction potentials

Ultrasensitive Reagent for Ratiometric Detection and Detoxification of III in Water and Mitochondria

Toxicity induced by inorganic arsenic as AsO₃^3- (iAs^III) is of global concern. Reliable detection of the maximum allowed contaminant level for arsenic in drinking water and in the cellular system remains a challenge for the water quality management and assessment of toxicity in the cellular milieu, respectively. A new Ir(III)-based phosphorescent molecule (AS-1; λ_Ext = 415 nm and λ_Ems = 600 nm, Φ = 0.3) is synthesized for the selective detection of iAs^III in an aqueous solution with a ratiometric luminescence response even in the presence of iAs^V and all other common inorganic cations and anions. The relatively higher affinity of the thioimidazole ligand (HPBT) toward iAs^III led to the formation of a fluorescent molecule iAs^V-HPBT (λ_Ext = 415 nm and λ_Ems = 466 nm, Φ = 0.28) for the reaction of iAs^III and AS-1. An improved limit of quantitation (LOQ) down to 0.2 ppb is achieved when AS-1 is used in the CTAB micellar system. Presumably, the cationic surfactants favor the localization of AS-1@CTAB^Micelle in mitochondria of MCF7 cells, and this is confirmed from the images of the confocal laser fluorescence scanning microscopic studies. Importantly, cell viability assay studies confirm that AS-1@CTAB^Micelle induces dose-dependent detoxification of iAs^III in live cells. Further, luminescence responses at 466 nm could be utilized for developing a hand-held device for the in-field application. Such a reagent that allows for ratiometric detection of iAs^III with LOQ of 2.6 nM (0.5 ppb) in water, as well as helps in visualizing its distribution in mitochondria with a detoxifying effect, is rather unique in contemporary literature.

The intrinsic mechanism of catalytic oxidation of arsenite by hydroxyl-radicals in the H3AsO3-CO32-/HCO3--H2O system: A quantum-chemical examination

Arsenite is a highly toxic compound present in many water sources around the world. The removal of arsenite from water requires its oxidation to arsenate which is much more amenable to treatment using well attested technologies. Prior research has shown that the oxidation of arsenite by hydroxyl radicals is significantly accelerated in the presence of carbonate ions but the intrinsic mechanisms of the acceleration have not yet been established. The main goal of the present work was to examine the oxidation of arsenite in the framework of the density functional theory, to establish a detailed microscopic level mechanism of interactions between arsenite and hydroxyl radicals and to elucidate the nature of the catalytic effect of carbonate ions. Results of this study demonstrate that the [As(OH)₂CO₃]^- complex is the thermodynamically most stable species formed in the system H₃AsO₃-CO₃^2-/HCO₃^--H₂O. Interactions of the hydroxyl radical with the [As(OH)₂CO₃]^- complex yield the pre-reaction complex [As(OH)₃CO₃]^-∗ in the reaction of subsequent oxidation of arsenite. The structures of the reactants, products and transition states, as well as pre- and post-reaction complexes corresponding to several possible mechanisms of the first stage of As(III) oxidation to As(IV) intermediate using hydroxyl radicals in the absence and in the presence of [As(OH)₂CO₃]^-, were determined in this study. The data demonstrate that the arsenite-carbonate complexes [As(OH)₂CO₃]^- are characterized by a significantly lower activation energy of the first oxidation stage under the action of a hydroxyl radical (2.8 kcal/mol) compared to that for the free arsenite H₃AsO₃ (13.6 kcal/mol).

Aqueous Solvation of SmI3: A Born-Oppenheimer Molecular Dynamics Density Functional Theory Cluster Approach

We report the results of Born-Oppenheimer molecular dynamics (BOMD) simulations on the aqueous solvation of the SmI₃ molecule and of the bare Sm³⁺ cation at room temperature using the cluster microsolvation approach including 37 and 29 water molecules, respectively. The electronic structure calculations were done using the M062X hybrid exchange-correlation functional in conjunction with the 6-31G** basis sets for oxygen and hydrogen. For the iodine and samarium atoms, the Stuttgart-Köln relativistic effective-core potentials were utilized with their associated valence basis sets. When SmI₃ is embedded in the microsolvation environment, we find that substitution of the iodine ions by water molecules around Sm(III) cannot be achieved due to an insufficient number of explicit water molecules to fully solvate the four separate metal and halogen ions. Therefore, we studied the solvation dynamics of the bare Sm³⁺ cation with a 29-water molecule model cluster. Through the Sm-O radial distribution function and the evolution of the Sm-O distances, the present study yields a very tightly bound first rigid Sm(III) solvation shell from 2.3 to 2.9 Å whose integration leads to a coordination number of 9 water molecules and a second softer solvation sphere from 3.9 to 5 Å with 12 water molecules. No water exchange processes were found. The theoretical EXAFS spectrum is in excellent agreement with the experimental spectrum for Sm(III) in liquid water. The strong differences between the solvation patterns of Sm(III) vs Sm(II) are discussed in detail.

On the aqueous solvation of AsO(OH)3vs. As(OH)3. Born–Oppenheimer molecular dynamics density functional theory cluster studies

BOMD simulations were used to reveal the hydration features of As(OH)₃ and (for the first time) AsO(OH)₃ in aqueous solution.

Partitioning of Alkali Metal Salts and Boric Acid from Aqueous Phase into the Polyamide Active Layers of Reverse Osmosis Membranes

The partition coefficient of solutes into the polyamide active layer of reverse osmosis (RO) membranes is one of the three membrane properties (together with solute diffusion coefficient and active layer thickness) that determine solute permeation. However, no well-established method exists to measure solute partition coefficients into polyamide active layers. Further, the few studies that measured partition coefficients for inorganic salts report values significantly higher than one (∼3-8), which is contrary to expectations from Donnan theory and the observed high rejection of salts. As such, we developed a benchtop method to determine solute partition coefficients into the polyamide active layers of RO membranes. The method uses a quartz crystal microbalance (QCM) to measure the change in the mass of the active layer caused by the uptake of the partitioned solutes. The method was evaluated using several inorganic salts (alkali metal salts of chloride) and a weak acid of common concern in water desalination (boric acid). All partition coefficients were found to be lower than 1, in general agreement with expectations from Donnan theory. Results reported in this study advance the fundamental understanding of contaminant transport through RO membranes, and can be used in future studies to decouple the contributions of contaminant partitioning and diffusion to contaminant permeation.

Aqueous solvation of HgClOH. Stepwise DFT solvation and Born–Oppenheimer molecular dynamics studies of the HgClOH–(H2O)24 complex

We address the aqueous solvation of HgClOH through a systematic study of stepwise hydration considering the HgClOH–(H₂O)_n structures with n = 1–24.

Theoretical study of the aqueous solvation of HgCl2: Monte Carlo simulations using second-order Moller-Plesset-derived flexible polarizable interaction potentials

A study of the solvation of HgCl(2) including ab initio aggregates of up to 24 water molecules and the results of extensive Monte Carlo simulations for the liquid phase using MP2-derived interaction potentials is presented. The interaction potentials are flexible, polarizable, and include non-additive effects. We conclude that a cluster description of the solvation mechanism is limited when compared to the condensed phase. The molecular image derived from the MC simulations is peculiar. It resembles that of a hydrophobic solute, which explains the rather easy passage of this neutral molecule through the cell membrane; however, it also shows an intermittent binding of one, two, or three water molecules to HgCl(2) in the fashion of a hydrophilic solute.

Theoretical study of the solvation of HgCl2, HgClOH, Hg(OH)2 and HgCl3(-): a density functional theory cluster approach

The determination of the solvation shell of Hg(II)-containing molecules and especially the interaction between Hg(II) and water molecules is the first requirement to understand the transmembrane passage of Hg into the cell. We report a systematic DFT study by stepwise solvation of HgCl(2) including up to 24 water molecules. In order to include pH and salinity effects, the solvation patterns of HgClOH, Hg(OH)(2) and HgCl(3)(-) were also studied using 24 water molecules. In all cases the hydrogen bond network is crucial to allow orbital-driven interactions between Hg(II) and the water molecules. DFT Born-Oppenheimer molecular dynamics simulations starting from the stable HgCl(2)-(H(2)O)(24) structure revealed that an HgCl(2)-(H(2)O)(3) trigonal bipyramid effective solute appears and then the remaining 21 water molecules build a complete first solvation shell, in the form of a water-clathrate. In the HgCl(2), HgClOH, Hg(OH)(2)-(H(2)O)(24) optimized structures Hg also directly interacts with 3 water molecules from an orbital point of view (three Hg-O donor-acceptor type bonds). All the other interactions are through hydrogen bonding. The cluster-derived solvation energies of HgCl(2), HgClOH and Hg(OH)(2) are estimated to be -34.4, -40.1 and -47.2 kcal mol(-1), respectively.

A refined potential for hydroxylamine clusters and the liquid phase

A detailed study including ab initio calculations and classic Monte-Carlo simulations of hydroxylamine in the gas and liquid phases is presented. A classical interaction potential for hydroxylamine, which includes polarizability, many-body effects, and intramolecular relaxation, was constructed. The results of the simulation were compared to the available experimental data in order to validate the model. We conclude that liquid hydroxylamine has a multitude of hydrogen bonds leading to a large density where the existence of cis conformers and clusters of these conformers is possible. This explains the occurrence of the classical [R. Nast and I. Z. Foppl, Z. Anorg. Allg. Chem. 263, 310 (1950)] scheme for the molecule's decomposition at room temperature and its large exothermicity and instability.