Species In Aqueous Environment Research Articles

Differences in the Reaction Mechanisms of Chlorine Atom and Hydroxyl Radical with Organic Compounds: From Thermodynamics to Kinetics.

Hydroxyl radical (HO•) and chlorine atom (Cl•) are common reactive species in aqueous environments. However, the intrinsic difference in their reactions with organic compounds has not been revealed. This study compared the reaction mechanisms of HO• and Cl• with 13 aromatic and 11 aliphatic compounds by quantum chemical calculation and laser flash photolysis. Both HO• and Cl• can spontaneously react with aromatic compounds via radical adduct formation (RAF), hydrogen atom transfer (HAT), and single electron transfer (SET) pathways. The SET reactions of Cl• were more thermodynamically favorable than HO•, but contrary results were obtained for HAT reactions. According to the free energy of activation (ΔGaq‡), the dominant oxidation mechanisms of aromatic compounds were RAF and SET by HO• and SET by Cl•. The important role of SET in the HO• reactions with aromatic compounds was further verified by accurately calculating the solvation free energy of HO•/HO- and experimentally tracking the radical cations, which were generally neglected in previous studies. Meanwhile, the ΔGaq‡ value of each reaction pathway of Cl• was lower than that of HO•, resulting in higher rate constants of Cl• with aromatic compounds than HO•. For saturated aliphatic compounds, HAT was found to be the only mechanism accounting for their transformation by HO• and Cl•. This study proposed general rules for the reaction mechanisms of HO• and Cl• and unraveled their differences in the aspects of thermodynamics and kinetics, providing fundamental information for understanding contaminant transformation in processes involving HO• and Cl•.

An investigation on the structural stability of ZIF-8 in water versus water-derived oxidative species in aqueous environment

The zeolitic-imidazolate-framework-8 (ZIF-8) is one of the extensively studied metal-organic frameworks (MOF) materials because of its unique structure. For its potential applicability in numerous fields, it becomes crucial to have detailed studies on the structural stability of ZIF-8, especially in aqueous environments. A number of studies have been conducted to investigate the breakdown process of the ZIF-8 structure in water; which is known as the hydrolysis of ZIF-8. However, those studies reported different opposing experimental observations on the role of water on the structural stability of ZIF-8, which created obscurity in understanding this phenomenon. This study explored the effects of different water-derived species on the structural stability of ZIF-8; specifically, examined the effects of only water and water with different oxidative species that may be generated by water molecules' dissociation under external energy or catalyst presence. To this effort, we experimentally probed the physical and chemical structural changes of ZIF-8 in DI water and three different solutions of hydrogen peroxides (H2O2); taking H2O2 as the source of oxidative species. To assess the changes in elemental compositions, chemical bonds, functional groups, crystal structure, and morphology, all the samples were analyzed by X-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray (EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscope, X-ray diffractometer (XRD), and scanning electron microscope (SEM). Significant structural changes in ZIF-8 occurred mainly in the presence of oxidative species in water. Notably, oxidative species’ concentration exceeding 1 M heightened the deformation of the ZIF-8 structure.

A General Design Strategy Enabling the Synthesis of Hydrolysis-Resistant, Water-Stable Titanium(IV) Complexes.

Despite its prevalence in the environment, the chemistry of the Ti4+ ion has long been relegated to organic solutions or hydrolyzed TiO2 polymorphs. A knowledge gap in stabilizing molecular Ti4+ species in aqueous environments has prevented the use of this ion for various applications such as radioimaging, design of water-compatible metal-organic frameworks (MOFs), and aqueous-phase catalysis applications. Herein, we show a thorough thermodynamic screening of bidentate chelators with Ti4+ in aqueous solution, as well as computational and structural analyses of key compounds. In addition, the hexadentate analogues of catechol (benzene-1,2-diol) and deferiprone (3-hydroxy-1,2-dimethyl-4(1H)-pyridone), TREN-CAM and THPMe respectively, were assessed for chelation of the 45 Ti isotope (t1/2 =3.08 h, β+ =85 %, Eβ+ =439 keV) towards positron emission tomography (PET) imaging applications. Both were found to have excellent capacity for kit-formulation, and [45 Ti]Ti-TREN-CAM was found to have remarkable stability in vivo.

A General Design Strategy Enabling the Synthesis of Hydrolysis‐Resistant, Water‐Stable Titanium(IV) Complexes

AbstractDespite its prevalence in the environment, the chemistry of the Ti4+ion has long been relegated to organic solutions or hydrolyzed TiO2polymorphs. A knowledge gap in stabilizing molecular Ti4+species in aqueous environments has prevented the use of this ion for various applications such as radioimaging, design of water‐compatible metal–organic frameworks (MOFs), and aqueous‐phase catalysis applications. Herein, we show a thorough thermodynamic screening of bidentate chelators with Ti4+in aqueous solution, as well as computational and structural analyses of key compounds. In addition, the hexadentate analogues of catechol (benzene‐1,2‐diol) and deferiprone (3‐hydroxy‐1,2‐dimethyl‐4(1H)‐pyridone), TREN‐CAM and THPMerespectively, were assessed for chelation of the45Ti isotope (t1/2=3.08 h, β+=85 %, Eβ+=439 keV) towards positron emission tomography (PET) imaging applications. Both were found to have excellent capacity for kit‐formulation, and [45Ti]Ti‐TREN‐CAM was found to have remarkable stability in vivo.

Filter design for arsenic species in aqueous environments: An ab initio optimization of the absorbing capacity of magnetite-based arsenic filters

Polluted water sources are a public health issue causing concerns in regions with a low-quality water treatment system. Gastrointestinal diseases, skin associated illness, and even skin cancer development commonly link to prolonged intakes of arsenic compounds. Thus, we propose the design of a low-cost, eco-friendly arsenic filter using a magnetite-based adsorbent. Density functional theory calculations warrant the optimal adsorbing capacity in the filter design with magnetite nanoparticles (Mag-NPs) capturing up to 5 arsenic species diluted in aqueous environments. A lineal and a geometric model describe the collective adsorbing mechanism of the Mag-NPs for determining the filter’s dimensions. Finally, our filter design framework is applied using the water source conditions of the Toacaso community in Ecuador.

Optimization of Antimony Removal by Coagulation-Flocculation-Sedimentation Process Using Response Surface Methodology

Coprecipitation-adsorption plays a significant role during coagulation-flocculation-sedimentation (C/F/S) of antimony (Sb) in water. This work uses a Box–Behnken statistical experiment design (BBD) and response surface methodology (RSM) to investigate the effects of major operating variables such as initial Sb(III, V) concentration (100–1000 µg/L), ferric chloride (FC) dose (5–50 mg/L), and pH (4–10) on redox Sb species. Experimental data of Sb(III, V) removal were used to determine response function coefficients. The model response value (Sb removal) showed good agreement with the experimental results. FC showed promising coagulation behavior of both Sb species under optimum pH (6.5–7.5) due to its high affinity towards Sb species and low residual Fe concentration. However, a high dose of 50 mg/L of FC is required for the maximum (88–93%) removal of Sb(V), but also for the highest (92–98%) removal of low initial concentrations of Sb(III). Furthermore, BBD and RSM were found to be reliable and feasible for determining the optimum conditions for Sb removal from environmental water samples by a C/F/S process. This work may contribute to a better understanding and prediction of the C/F/S behavior of Sb(III, V) species in aqueous environments, to reduce potential risks to humans.

Hydration structure of As–III aqueous solutions from ab initio molecular dynamics simulations

A comprehensive study of aqueous arsenic acid (H3AsO3) and its deprotonated derivatives, namely H2AsO3− and HAsO32−, is carried out employing Car-Parrinello Molecular Dynamics (CPMD). Calculations are carried out with and without the incorporation of the dispersion correction, and critical comparison of its role on various structural and dynamical properties of the solute-solvent system are discussed. Aqueous H3AsO3 and H2AsO3− species solvated by 60 water molecules (which closely emulates normal pH conditions) are found to be stable, that is, without undergoing proton transfer with the solvent over the 50 ps of MD simulations performed. However, HAsO32− is found to be stable only in the basic media, emulated through the introduction of a hydroxyl ion (OH−) in lieu of one water molecule. The AsO33− species is not stable, and protonates quickly to HAsO32−, even under the basic environment of a hydroxyl ion (OH−) among 59 other water molecules simulated. Detailed analysis of the hydrogen bonding and vibrational spectra provide fresh microscopic insights on the hydration structure and dynamical characteristics of these species in aqueous environment. The spectroscopic insights derived, through comparison with their parent gas-phase species (H3AsO3), would be useful in the detection as well as quantification these species in various aqueous environments, for developing water remediation strategies of these environmentally hazardous species.

Selective Chemical Enhancement via Graphene Oxide in Infrared Attenuated Total Reflection Spectroscopy

Graphene oxide (GO) as a readily prepared graphene derivative comprises negatively charged oxygenated functional groups, and a mixture of sp2 and sp3 carbon domains. In comparison with hydrophobic graphene, GO is characterized by superior water dispersibility, and may noncovalently interact with a significantly wider range of molecules. Taking advantage of GO and infrared attenuated total reflection spectroscopy (IR-ATR), an efficient strategy enabling unprecedented absorption signal amplification via chemical enhancement of various molecular species in aqueous environment was demonstrated in this study. The evolution of selectively enhanced molecular fingerprints across the entire mid-infrared spectral range was in situ monitored in real time, while retaining the characteristic molecular IR absorptions, and confirms the utility of GO as a suitable and versatile material in surface-enhanced infrared absorption spectroscopy (SEIRA) scenarios.

Molecular dynamics characterization of silver colloidal interfaces for SERS applications. Gallic acid test

AbstractOne of the most useful applications of silver colloidal solutions is in surface‐enhanced Raman spectroscopy (SERS), because the amplification factor of about 106 allows the vibrational study and detection of highly diluted species in aqueous environment, and more recently in early diagnosis of cancer and imaging. A useful colloid for SERS is that reported by Leopold and Lendl (Colloid 1). However, SERS response from anions or rich electron density molecules has been difficult to obtain in this colloid. Recently, a minor modification of the surface charge density (Colloid 2) allowed to observe reproducible SERS spectrum from gallate anion (GA−). In this work, the structure of both solid and solution interfaces were characterized using molecular dynamics. Experimental values of ζ‐potentials were reproduced by simulations, and the chemical potential of GA− approaching both interfaces was calculated using “umbrella sampling” and the weighted histograms analisys methodology (WHAM). The calculated barrier to approach the interface of Colloid 1 is 2.8 kJmol−1 greater than in Colloid 2, and the stability of GA− with Colloid 2 at the minimum is 3.5 kJmol−1 more stable than with Colloid 1. Finally, the calculated average orientation of GA− adsorbed onto the colloidal surface is in excellent agreement with the experimental SERS observations.

When alcohol is the answer: Trapping, identifying and quantifying simple alkylating species in aqueous environments

Alkylating agents are a significant class of environmental carcinogens as well as commonly used anticancer therapeutics. Traditional alkylating activity assays have utilized the colorimetric reagent 4-(4-nitrobenzyl)pyridine (4NBP). However, 4NBP based assays have a relatively low sensitivity towards harder, more oxophilic alkylating species and are not well suited for the identification of the trapped alkyl moiety due to adduct instability. Herein we describe a method using water as the trapping agent which permits the trapping of simple alkylating electrophiles with a comparatively wide range of softness/hardness and permits the identification of donated simple alkyl moieties.

Electroanalytical methods in characterization of sulfur species in aqueous environment

Electroanalytical (voltammetric, polarographic, chronoamperometric) methods on an Hg electrode were applied for studying of different sulfur compounds in model and natural water systems (anoxic lakes, waste water, rain precipitation, sea-aerosols). In all investigated samples typical HgS reduction voltammetric peak, characteristic for many different reduced sulfur species (RSS: sulfide, elemental sulfur, polysulfide, labile metal sulfide and organosulfur species) was recorded at about -0.6 V vs. Ag/AgCl reference electrode. In addition, in anoxic waters which are enriched with sulfide and iron species, voltammetric peaks characteristic for the presence of free Fe(II) and FeS nanoparticles (NPs) were recorded at -1.4 V and around -0.45 V, respectively. Depending on the used electroanalytical method and experimental conditions (varying deposition potential, varying time of oxidative and/or reductive accumulation, sample pretreatment i.e. acidification followed by purging) it is possible to distinguish between different sulfur species. This work clearly shows a large potential of the electrochemistry as a powerful analytical technique for screening water quality regarding presence of different reduced sulfur species and their speciation between dissolved and colloidal/nanoparticle phases.

Elimination of Pb2+ through electrocoagulation: Applicability of adsorptive stripping voltammetry for monitoring the lead concentration during its elimination

The aim of this manuscript is to develop a combined method for the detection and remediation of Pb2+ species in aqueous environment. The electrocoagulation (EC) process of Pb2+ has been studied, using an electrolytic flow cell equipped with Al sacrificial electrodes and by working under galvanostatic conditions (by applying currents of 0.25, 0.5 and 0.75A). The concentration of Pb2+ during EC was monitored by Adsorptive Stripping Voltammetry (AdSV) and data were also confirmed by Atomic Absorption Spectroscopy (AAS). The experimental results of EC showed that the performances of the process slightly depend on the applied current; a complete removal of the pollutant is obtained in all cases, however with different treatment times (90, 75 and 45min for 0.25, 0.5 and 0.75A, respectively). Furthermore, the AdSV, when compared with the AAS, has shown that the electroanalytical approach represents a fast and quite reliable alternative for monitoring heavy metal remediation applications.

Ultra-Traces Detection by Gold-Based Electrodes in As(III) Novel Photoremediation

The aim of this manuscript is to develop a combined method for the detection and remediation of As(III) species in aqueous environment. Linear sweep adsorptive stripping voltammetric technique, based on the use of commercially available gold nanoparticle-modified screen-printed electrodes is proposed to detect ultra traces of As(III) in solution. The choice of inexpensive and disposable electrodes permits to eliminate undesirable fouling processes, usually occurring in this kind of electroanalytical methods. The achieved limit of detection, one order of magnitude lower than the World Health Organization tolerance level (10 ppb), allows to monitor the trend of the photocatalytic oxidation of arsenite to less noxious arsenate, especially in the range of As(III) ultra traces. The UV-assisted photooxidation of As(III) is performed by using titania layers, prepared by electrophoretic deposition of both commercial- and laboratory-made TiO2 nanopowders. This novel photocatalytic approach, based on immobilized particles, avoids the expensive filtration step, usually required in slurry systems.

Revision of the Biodistribution of Uranyl in Serum: Is Fetuin-A the Major Protein Target?

Uranium is a natural actinide present as uranyl U(VI) species in aqueous environments. Its toxicity is considered to be chemical rather than radiotoxicological. Whatever the route of entry, uranyl reaches the blood, is partly eliminated via the kidneys, and accumulated in the bones. In serum, its speciation mainly involves carbonate and proteins. Direct identification of labile uranyl-protein complexes is extremely difficult because of the complexity of this matrix. Thus, until now the biodistribution of the metal in serum has not been described, and therefore, little is known about the metal transport mechanisms leading to bone accumulation. A rapid screening method based on a surface plasmon resonance (SPR) technique was used to determine the apparent affinities for U(VI) of the major serum proteins. A first biodistribution of uranyl was obtained by ranking the proteins according to the criteria of both their serum concentrations and affinities for this metal. Despite its moderate concentration in serum, fetuin-A (FETUA) was shown to exhibit an apparent affinity within the 30 nM range and to carry more than 80% of the metal. This protein involved in bone mineralization aroused interest in characterizing the U(VI) and FETUA interaction. Using complementary chromatographic and spectroscopic approaches, we demonstrated that the protein can bind 3 U(VI) at different binding sites exhibiting Kd from ∼30 nM to 10 μM. Some structural modifications and functional properties of FETUA upon uranyl complexation were also controlled. To our knowledge, this article presents the first identification of a uranyl carrier involved in bone metabolism along with the characterization of its metal binding sites.

What sharks can tell us about the evolution of MHC genes.

Similarity in structural features would argue that sharks possess class I, class IIA and class IIB genes, coding for classical peptide-presenting molecules, as well as non-classical class I genes. Some aspects of shark major histocompatibility complex genes are similar to teleost genes and others are similar to tetrapod genes. Shark class I genes form a monophyletic group, as also seen for tetrapods, but the classical and nonclassical genes form two orthologous clades, as seen for teleosts. Teleost class I genes arose independently at least four different times with the nonclassical genes of ray-finned fishes and all the shark and lobe-finned fish class I genes forming 1 clade. The ray-finned fish classical class I genes arose separately. In phylogenetic trees of class II alpha 2 and beta 2 domains, the shark and tetrapod genes cluster more closely than the teleost genes and, unlike the teleost sequences, the class II alpha 1 domains of sharks and tetrapods lack cysteines. On the other hand, both shark and teleost genes display sequence motifs in the antigen-binding cleft that have persisted over very long time periods. The similarities may reflect common selective pressures on species in aqueous environments while differences may be due to different evolutionary rates.

Triplet states of protoporphyrin IX and protoporphyrin IX dimethyl ester

Laser and conventional flash photolysis have been used to obtain the triplet—triplet absorption spectra, triplet lifetimes, rates of oxygen quenching and quantum efficiencies of triplet formation of protoporphyrin IX as the dication, monocation and free base in several solvent systems. The results are rationalised in terms of protoporphyrin IX existing as a monomer in organic or detergent solvents and as an aggregated species in aqueous environments.