Aqueous Anions Research Articles

Selective Aqueous Anion Recognition in an Anionic Host

Selective Aqueous Anion Recognition in an Anionic Host

Aqueous anion binder for phenolate and nitro substituted phenolates through second-sphere coordination network

A series of four cobalt(III) complexes, [Co(Hbig)3]1.5Cl3.5(Ph).2H2O (1), [Co(Hbig)3] (PNP)3.H2O (2), [Co(Hbig)3](DNP)3.H2O (3) and [Co(Hbig)3](TNP)3·4H2O (4) have been synthesized by reacting [Co(Hbig)3]Cl3.H2O (Hbig: biguanide) with sodium phenolates (Ph: pheonlate, PNP: 4-nitrophenolate, DNP: 2,4-dinitrophenolate or TNP: 2,4,6-trinitrophenolate) in 1:3 molar ratio in aqueous medium. All the complexes were initially characterized by physiochemical and spectroscopic (UV–Visible, IR and NMR) studies. Anion binding affinity of complex cation for anions has been studies in aqueous medium using UV–Visible spectroscopic titrations and found log β values for anions. The single crystal X-ray structures of complex 3 and 4 were also determined and stacking of layers has been observed in both the structures. These stacking layers contains layers of [Co(Hbig)3]3+, nitro-phenolate (DNP or TNP) and water molecules along b-axis. These layers connected with one another by numerous intermolecular N-H…O hydrogen bonds leads to formation of second-sphere coordination network. Further, all the complexes and their respective reactants have been tested for antimicrobial activities against strain of Gram negative (P. aeruginosa, E. coli, K. pneumoniae, S. typhi), strain of Gram positive bacteria (B. subtilis, S. epidermidis) and antifungal against C. herbarum, A. alternata and F. oxysporum.

Supramolecular methods: utilising ChemFETs to evaluate aqueous anion affinity of hydrophobic receptors

ABSTRACT The host–guest interaction and affinity of hydrophobic receptors towards aqueous anions can be evaluated by incorporating a receptor into a polymeric membrane and applying these membranes to FET-based sensing devices. A series of anions screened using these ChemFET (chemically sensitive field effect transistor) sensors based on different receptors can also provide a Hofmeister-like ordering of anions based on their respective detection limits. Although the general trends of selectivity coefficients often follow the Hofmeister Series, the specific anion affinity profiles are generally unique to each receptor and provide insight into receptor selectivity. In this methodspaper, we provide a detailed example of how our lab uses ChemFETs to evaluate host–guest interactions of hydrophobic host receptors with aqueous anions, and a detailed procedure for fabricating ChemFET sensor devices is presented along with selected case studies for readers interested in applying related ion recognition strategies in sensors of this type.

Phenolate-thiazole based reversible “turn-on” chemosensor for the selective detection of carbonate anion: X-ray crystallography, DFT/TDFT, and cell study

A new phenolate-thiazole derivative (L) has been synthesized and structurally characterized.The chemo-sensing activity of L is detected by the naked eye for the aqueous carbonate anion in the pH range of 4 to 8. The selective ‘turn-on’ fluorescence occurs through the formation of a stable intermediate L∙CO32–(1) following the PET mechanism. The limit of detection (LOD) is found 0.18 µM based on the absorbance-based assay.The quinonoid form of bromophenol unit binds strongly with CO32– through thiazole nitrogen and hydrazinic nitrogen. Further, the selective holding of CO32– anion over other planar tetranuclear anions (e.g., SO32–, NO3–) happens with several intra and intermolecular hydrogen bonds as envisaged by the DFT/TDFT study. The formation mechanism of L∙CO32– is proposed based on experimental and theoretical studies. The biological experiments (MTT and cell imaging)reveal the non-cytotoxicity nature of L and the biocompatible uptake of L mostly in the cytoplasm at physiological pH.

Anion storing, oxygen vacancy incorporated perovskite oxide composites for high-performance aqueous dual ion hybrid supercapacitors

Dual ion storage hybrid supercapacitors (HSCs) are considered as a promising device to overcome the limited energy density of existing supercapacitors while preserving high power and long cyclability. However, the development of high-capacity anion-storing materials, which can be paired with fast charging capacitive electrodes, lags behind cation-storing counterparts. Herein, we demonstrate the surface faradaic OH− storage mechanism of anion storing perovskite oxide composites and their application in high-performance dual ion HSCs. The oxygen vacancy and nanoparticle size of the reduced LaMnO3 (r-LaMnO3) were controlled, while r-LaMnO3 was chemically coupled with ozonated carbon nanotubes (oCNTs) for the improved anion storing capacity and cycle performance. As taken by in-situ and ex-situ spectroscopic and computational analyses, OH− ions are inserted into the oxygen vacancies coordinating with octahedral Mn with the increase in the oxidation state of Mn during the charging process or vice versa. Configuring OH− storing r-LaMnO3/oCNT composite with Na+ storing MXene, the as-fabricated aqueous dual ion HSCs achieved the cycle performance of 73.3% over 10,000 cycles, delivering the maximum energy and power densities of 47.5 W h kg−1 and 8 kW kg−1, respectively, far exceeding those of previously reported aqueous anion and dual ion storage cells. This research establishes a foundation for the unique anion storage mechanism of the defect engineered perovskite oxides and the advancement of dual ion hybrid energy storage devices with high energy and power densities.

Aqueous pyruvate partly dissociates under deep ultraviolet irradiation but is resilient to near ultraviolet excitation

The deep ultraviolet photochemistry of aqueous pyruvate is believed to have been essential to the origin of life, and near ultraviolet excitation of pyruvate in aqueous aerosols is assumed to contribute significantly to the photochemistry of the Earth’s atmosphere. However, the primary photochemistry of aqueous pyruvate is unknown. Here we study the susceptibility of aqueous pyruvate to photodissociation by deep ultraviolet and near ultraviolet irradiation with femtosecond spectroscopy supported by density functional theory calculations. The primary photo-dynamics of the aqueous pyruvate show that upon deep-UV excitation at 200 nm, about one in five excited pyruvate anions have dissociated by decarboxylation 100 ps after the excitation, while the rest of the pyruvate anions return to the ground state. Upon near-UV photoexcitation at a wavelength of 340 nm, the dissociation yield of aqueous pyruvate 200 ps after the excitation is insignificant and no products are observed. The experimental results are explained by our calculations, which show that aqueous pyruvate anions excited at 200 nm have sufficient excess energy for decarboxylation, whereas excitation at 340 nm provides the aqueous pyruvate anions with insufficient energy to overcome the decarboxylation barrier.

Functionalization of reduced montmorillonite as an adsorbent toward aqueous anion: role of layer charge density

Montmorillonite (Mt) is widely used in various fields due to its abundant resources and excellent adsorption performance, while the hydration and adsorption properties of raw or functionalized Mt are affected by its intrinsic property, layer charge density (LCD). Herein, a series of reduced-charge montmorillonites (RC-Mt) with high, medium, and low layer charges were prepared by the method of lithiation and microwaving Ca-Mt. Meanwhile, the effects of artificially regulated layer charge density on Mt’s structure, hydration properties, and the removal ability of aqueous anions by the poly (diallyl dimethylammonium chloride) functionalized Mt (PDDA-Mt) were also investigated. Results showed that the LCD of Mt decreased with the increasing microwave time or power. In addition, the physicochemical properties of RC-Mt which included cation exchange capacity (CEC), colloidal index, and swelling properties decreased as the LCD decreased. Furthermore, the adsorption capacity of Mt for NO3- was significantly improved following the PDDA functionalization. The kinetic modeling suggests that the Pseudo-first-order model better characterized the adsorption of Ca-Mt and Li-Mt than the Pseudo-second-order model. On the other hand, the good fit of the Pseudo-second-order model implied that the adsorption process of nitrate on RC-Mt and PDDA-Mt is mainly driven by chemisorption control. The adsorption thermodynamics indicated that the adsorption process was spontaneous. Furthermore, the FTIR and XPS results suggested that in addition to diffusion and electrostatic interactions, the adsorption mechanism of PDDA-Mt was mainly attributed to the ion exchange between chloride and nitrate on the quaternary ammonium group of PDDA.

Nitrogen‐Doped Bifunctional Carbon Dots: Photoluminescence Investigation, and Fluorescent Recognition Applications

AbstractIn this work, three kinds of bifunctional carbon dots fluorescent sensor a‐CDs, b‐CDs and c‐CDs were prepared using 2,2‐di(prop‐2‐yn‐1‐yl)malonic acid as substrate, which are rich in carboxylic acid and conjugated structure. The morphology, chemical composition and optical properties of the prepared carbon quantum dots were characterized by transmission electron microscopy (TEM), X‐ray Photoelectron spectroscopy (XPS), FTIR, X‐ray diffraction (XRD), UV‐vis spectroscopy and fluorescence (FL). They display excellent water solubility, thermal stability and salt resistance, and overcomes the loss of optical activity in the dry state, which have been applied to the detection of aqueous metal ions and anions. Among them, the fluorescence quenching of Hg2+ and Cu2+ by a‐CDs and b‐CDs is obvious, which can be used as a highly sensitive dual ion sensor. At the same time, it has a good recognition and detection effect on 0–12 ppm ClO− or MnO4−, and the detection limits are as low as 0.1209 ppm and 0.0574 ppm, respectively. In addition, chiral c‐CDs can specifically recognize Hg2+, and the synergistic effect of c‐CDs and Hg2+ can improve the recognition of chiral enantiomers.

Ultrafast Vibrational Wave Packet Dynamics of the Aqueous Guanine Radical Anion Induced by Photodetachment.

Studying the ultrafast dynamics of ionized aqueous biomolecules is important for gaining an understanding of the interaction of ionizing radiation with biological matter. Guanine plays an essential role in biological systems as one of the four nucleobases that form the building blocks of deoxyribonucleic acid (DNA). Guanine radicals can induce oxidative damage to DNA, particularly due to the lower ionization potential of guanine compared to the other nucleobases, sugars, and phosphate groups that are constituents of DNA. This study utilizes femtosecond optical pump-probe spectroscopy to observe the ultrafast vibrational wave packet dynamics of the guanine radical anion launched by photodetachment of the aqueous guanine dianion. The vibrational wave packet motion is resolved into 11 vibrational modes along which structural reorganization occurs upon photodetachment. These vibrational modes are assigned with the aid of density functional theory (DFT) calculations. Our work sheds light on the ultrafast vibrational dynamics following the ionization of nucleobases in an aqueous medium.

Removal of aqueous selenite anions from wastewater by electrodeposition and recycling used for catalyst of effective water splitting

Transforming toxic selenium in industrial wastewater into selenium resources is a significant challenge to realize the upgrading of valuable element resources and the removal of pollutants. Here, we chose copper, cobalt, and nickel foam as the electrode materials and used electrodeposition to capture selenite from selenium-containing wastewater. The effects of operating voltage, initial concentration, stirring rate and time on the removal efficiency of selenium were investigated. Among them, the removal efficiency of copper foam for 100 mg L−1 selenite could reach 91.2 % at −1.5 V operating voltage. The composition, morphology and structure of the products after electrodeposition were characterized by XPS, FESEM and TEM. The OER and HER properties of the electrodeposited products Cu2Se, CoSe2 and NiSe were evaluated by density functional theory calculations. It was proved that selenium could improve the electron transfer rate, and CoSe2 also had better HER performance than NiSe. The products formed after electrodeposition could be combined for overall water splitting to achieve efficient hydrogen production. This study proved the mechanism and resource utilization process of selenite removal through electrodeposition.

Evaluating impacts of bambusuril pocket size and sterics on anion binding trends using ChemFET sensors.

Chemically-sensitive Field Effect Transistors (ChemFETs) are a useful tool to evaluate aqueous anion affinity of hydrophobic supramolecular scaffolds. More specifically, ChemFETs can be used to probe impacts of receptor modification to aqueous anion affinity. In this study, ChemFETs are used to evaluate the anion affinity of both dodeca-n-butyl bambus[6]uril and dodecabenzyl bambus[6]uril to assess steric effects in the chemical selectivity of the sensor membrane. The ChemFETs were evaluated through a series of common anions in the Hofmeister series in order to ascertain the difference in detection limit imparted by the specific functionalization of the bambus[6]uril macrocycles, which are quite sensitive to modest steric effects. Significant improvements to perchlorate and nitrate detection limits were observed via n-butyl bambusuril-containing sensor membranes over detection limits recorded with benzyl bambusuril sensors.

Two- and one-photon absorption spectra of aqueous thiocyanate anion highlight the role of symmetry in the condensed phase.

We present the two-photon absorption (2PA) spectrum of aqueous thiocyanate calculated using high-level quantum-chemistry methods. The 2PA spectrum is compared to the one-photon absorption (1PA) spectrum computed using the same computational protocol. Although the two spectra probe the same set of electronic states, the intensity patterns are different, leading to an apparent red-shift of the 2PA spectrum relative to the 1PA spectrum. The presented analysis explains the intensity patterns and attributes the differences between the 1PA and 2PA spectra to the native symmetry of isolated SCN , which influences the spectra in the low-symmetry solvated environment. The native symmetry also manifests itself in variations of the polarization ratio (e.g., parallel vs. perpendicular cross sections) across the spectrum. The presented results highlight the potential of 2PA spectroscopy and high-level quantum-chemistry methods in studies of condensed-phase phenomena.

Phosphate adsorption by amino acids intercalated calcium aluminum hydrotalcites: Kinetic, isothermal and mechanistic studies

Phosphorus is widely used in agriculture and industry. However, excessive phosphorus can cause eutrophication in aquatic environment. Therefore, the development of an simple, efficient and economical method for phosphate removal from wastewater is urgently needed. In this study, calcium aluminum layered double hydroxides (CaAl-LDHs) and six amino acid intercalated calcium aluminum layered double hydroxides (CaAl-amino acid-LDHs) was prepared by a facile method. In order to identify optimal amino acid, the adsorption performance of phosphate for six CaAl-amino acid-LDHs were comparatively studied. A high phosphate adsorption capacity were observed for l-Aspartic acid intercalated calcium aluminum layered double hydroxides (CaAl-Asp-LDHs). Experimental results showed that CaAl-Asp-LDHs can achieve phosphate anion adsorption capacity of 569.95 mg/g, which is significantly higher than that of CaAl-LDHs (236.86 mg/g) at pH 6.0 and favorable selectivity was observed when compared with other common anions. CaAl-Asp-LDHs exhibited a faster phosphate removal than that of CaAl-LDHs. The adsorption data of aqueous phosphate anion using CaAl-LDHs and CaAl-Asp-LDHs could be well described by the Langmuir isotherm model and pseudo-second order kinetics. Furthermore, based on the structural and morphological features, as well as fourier transform infrared spectrometer (FT-IR), diffraction of x-rays (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscope with energy dispersive x-ray spectroscopy (SEM-EDS) and element mapping, the phosphate adsorption mechanism on CaAl-Asp-LDHs involved the electrostatic attraction, hydrogen bonds, complexation and ion exchange. Compared with the performance of other phosphate sorbents in other reported, CaAl-Asp-LDHs has the highest adsorption value. The synthesized CaAl-Asp-LDHs, therefore, would be a promising environmentally friendly material for the efficient removal of phosphate from aquatic environments.

Removal and recycling of aqueous selenite anions using cobalt-based metal–organic-framework coated on multi-walled carbon nanotubes composite membrane

The utilization of selenium as a novel functional material is rapidly expanding, and the retrieval of selenium from waste containing selenium is gaining recognition in the industry. This study prepared a novel composite membrane coated with the cobalt-based metal–organic framework coated on multi-walled carbon nanotubes (Co-MOF@MWCNTs). The MWCNTs served as the skeleton to support the active components of Co-MOF, which enabled efficient removal and resource utilization of liquid selenite (SeO32−). The morphology, structure, and composition of the prepared membrane were characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), etc.. Applying a permeate flux of 67.08 L m−2 h−1, the SeO32− removal efficiency of the composite membrane reached up to 92.2%. The composite membrane containing CoSeO4 can be used as an electrocatalytic oxygen evolution catalyst. Density functional theory calculations and electrochemical analysis showed that the conversion from O* to OOH* was a rate-determining step. Under 1.0 M KOH conditions, the lowest overpotential for Co-MOF@MWCNTs-40 at 10 mA cm−2 was 360 mV. In this study, the process of selenium resource utilization and the mechanism of SeO32− removal by Co-MOF@MWCNTs are revealed. It demonstrates that membrane-based sequestration of SeO32− can provide a viable approach for SeO32− removal and utilization in wastewater.

Extended X-ray Absorption Fine Structure Revealed the Mechanism of Arsenate Removal by the Fe/Mn Oxide-Based Composite under Conditions of Fully Saturated Sorption Sites.

Molecular mechanism of arsenate removal by a promising inorganic composite based on Fe/Mn oxides and MnCO3 was studied under the rarely investigated conditions of fully saturated sorption sites (characteristic of dynamic sorption, such as water treatment plants) at the pH of 4/6/7/8 using As K-edge extended X-ray absorption fine structure (EXAFS)/X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). Comparison of arsenic speciation in the initial adsorbate solution (calculated by Visual MINTEQ) and after sorption (determined by As 3d XPS) allowed the interpretation of the initializing forces of the interfacial processes. Contribution of various solid phases of this composite anion exchanger to the removal of arsenate was disclosed by examining the Fe 2p3/2 and Mn 2p3/2 XPS spectra supported by FTIR. As K-edge EXAFS simulation not only proved the chemisorptive binding of aqueous As(V) anions to the Fe/Mn oxide-based adsorbent but also demonstrated the presence of a variety of sorption sites in this complex structured porous material, which became available step-wise upon an increasing pressure on the interface with high arsenate loading during the long-term sorption process. The type of inner-sphere complexation of As(V) on the saturated surface discovered by As K-edge EXAFS modeling was a function of pH. Analysis of EXAFS fitting data resulted in suggestion of a methodological idea on how the EXAFS-derived coordination numbers can be used to distinguish the localization of adsorbed ions (surface versus structure emptiness). This work also provides more insights into the superiority of composite adsorbents (compared to the materials based on individual compounds) in terms of their capability to adapt/change the molecular sorption mechanism in order to inactivate (remove) more toxic aqueous anions.

A molecular switch-type receptor recognizes aqueous acetate by facilitating proton transfer through hydrogen bonding

Aqueous anion recognition using artificial receptors is of great interest but full of challenges. Typically, anion-selective receptors are designed by selecting scaffolds that have either hydrogen bonding sites or positively charged moieties. Herein, we constructed an acetate-responsive chromogenic molecular switch with a phenolphthalein backbone and achieved the visual recognition of acetate in pure water. UV–Vis and 1H NMR titration data reveal that the molecular switch receptor has good selectivity and binding towards acetate. Mechanistic studies have shown that this molecular switch-type anion receptor recognizes acetate through hydrogen bonding to facilitate proton transfer. Our findings are expected to pave the way for a new class of aqueous anion receptors and the development of new molecular recognition mechanisms.

Vesicular glutamate transporters are H+-anion exchangers that operate at variable stoichiometry

Vesicular glutamate transporters accumulate glutamate in synaptic vesicles, where they also function as a major Cl- efflux pathway. Here we combine heterologous expression and cellular electrophysiology with mathematical modeling to understand the mechanisms underlying this dual function of rat VGLUT1. When glutamate is the main cytoplasmic anion, VGLUT1 functions as H+-glutamate exchanger, with a transport rate of around 600 s−1 at −160 mV. Transport of other large anions, including aspartate, is not stoichiometrically coupled to H+ transport, and Cl- permeates VGLUT1 through an aqueous anion channel with unitary transport rates of 1.5 × 105 s−1 at −160 mV. Mathematical modeling reveals that H+ coupling is sufficient for selective glutamate accumulation in model vesicles and that VGLUT Cl- channel function increases the transport efficiency by accelerating glutamate accumulation and reducing ATP-driven H+ transport. In summary, we provide evidence that VGLUT1 functions as H+-glutamate exchanger that is partially or fully uncoupled by other anions.

XPS determined mechanism of selenite (HSeO3−) sorption in absence/presence of sulfate (SO42−) on Mg-Al-CO3 Layered double hydroxides (LDHs): Solid phase speciation focus

Success in adsorptive removal depends on solid phase speciation, which predetermines the extraction mechanism. This work investigates the mechanism of selenite (HSeO3−) sorption on Mg-Al Layered double hydroxides (LDHs), prepared by the original alkoxide-free sol-gel method, which already demonstrated outstanding removal of aqueous selenium species. Using X-ray Photoelectron Spectroscopy (XPS) as most relevant technique allowed to reveal the phase speciation in solid state as a function of two variables, competing sulfate and pH (8.5; 7.0; 4.5), and to detect the phases responsible for selenite uptake. Despite the leading initializing role of Mg-containing phases, selenite ended up to be chemically bound to one aluminium-based phase. The involvement of the second sorption mechanism via anion exchange of the interlayer carbonate with aqueous selenite depended on absence/presence of competing sulfate and pH. Comparison with the analogues results on selenate (SeO42−) sorption on the same material (published) resulted in discovery of the differences in XPS feature changes upon either physisorption or chemisorption. This is the first report, which discloses that physisorption of aqueous anion to a particular solid phase shifts the respective envelopment binding energies, whist chemisorptive binding causes considerable alterations (decreases/shifts) of XPS features of the specific binding solid species, such as Al(OH)3, however, it preserves nearly the same XPS characteristics of the envelopment peaks. Based on these discoveries, here we suggest a methodological idea on using the results of XPS analysis for interpretation of molecular mechanism of ion sorption on inorganic ion exchangers and to reliably distinguish the chemisorption from physisorption.

Environmental Factors Controlling the Electronic Properties and Oxidative Activities of Birnessite Minerals

Recent studies of birnessite-type lattices show that they have an unusually low-lying band structure with an electron affinity value of 6.0 eV, which is the highest among all common oxides and sulfides in an aqueous solution. This study reports on the underlying mechanism through which environmental factors, such as organic and inorganic ligands, exert a strong influence on the band structure and oxidative reactivity of various synthetic and natural birnessite phases. Specifically, the study evaluated the effect of (i) disorder/crystallinity, (ii) common aqueous cations, and (iii) Mn(II) and Mn(III) complexing anionic ligands on Cr(III) to Cr(VI) oxidation activity, Mn dissolution, and the band structure of birnessite mineral with the aim of finding correlations between them. The results show that the high oxidative activity of various birnessites is coupled with their high electron affinity, which, in turn, is modulated by various aqueous anions and cations through their dynamic influence on the dissolution-controlled structural Mn(III)/Mn(II) content. Inorganic cations of different ionic radii and hydration strengths control the interlayer spacing of the basal sheets, while inorganic and organic aqueous anions control the extent of Mn(II) and Mn(III) complexation. Their combined effects are seen to govern the efficiency of Mn dissolution from the crystal, which modulates the birnessite activity and band structure.

Excess-electron capture and energy transfer to bulk water for aqueous DNA nucleotide.

We performed QM/MM simulations to investigate excess-electron attachment to four aqueous DNA nucleotide anions (dRT-). The negative QM/MM vertical electron affinities (-0.86 to -0.59 eV) reveal that aqueous dRT- anions improbably capture the excess electron near 0 eV. Comparing with the calculations in the gas phase and without the background charges, it can be found that first-shell water molecules have a larger contribution to the promotion of the ability of the excess-electron capture and the bulk-water polarization has a small effect on vertical electron affinities. The phosphate group hampers the attachment of the very low-energy excess electron to aqueous dRT-. The large adiabatic electron affinities (1.45-1.96 eV) and vertical detachment energies (1.92-2.44 eV) reveal that stable dRT2- dianions could be formed after dRT- anions catch the higher-energy excess electron (>0.59 eV). We computed the energy changes in the dRT2- structural relaxations. The QM-region conformational changes cause small energy alterations (-0.28 to 0.35 eV). The QM/MM energy decreases are 2.31-2.73 eV which mainly come from QM computations (3.49-4.00 eV) embedded in the background charges. The analysis of excess-electron distributions indicates that the polarization of bulk water and structural relaxations of dianions induce the excess-electron redistributions in the QM region and produce large QM-energy decreases. The MM energy changes are -1.27 to -1.11 eV for four aqueous dianions. The negative values demonstrate that the energy of the MM region would increase in dRT2- structural relaxations. In contrast with the values of the polarized QM computations, about 30% of the energy released by the QM region is transferred to bulk water in the MM region. The large energy dissipation probably suppresses DNA damage by the low-energy electron.