Small Anions Research Articles

Prokaryotic Community Structure and Metabolisms in Shallow Subsurface of Atacama Desert Playas and Alluvial Fans After Heavy Rains: Repairing and Preparing for Next Dry Period.

The Atacama Desert, the oldest and driest desert on Earth, displays significant rains only once per decade. To investigate how microbial communities take advantage of these sporadic wet events, we carried out a geomicrobiological study a few days after a heavy rain event in 2015. Different physicochemical and microbial community analyses were conducted on samples collected from playas and an alluvial fan from surface, 10, 20, 50, and 80 cm depth. Gravimetric moisture content peaks were measured in 10 and 20 cm depth samples (from 1.65 to 4.1% w/w maximum values) while, in general, main anions such as chloride, nitrate, and sulfate concentrations increased with depth, with maximum values of 13–1,125; 168–10,109; and 9,904–30,952 ppm, respectively. Small organic anions such as formate and acetate had maximum concentrations from 2.61 to 3.44 ppm and 6.73 to 28.75 ppm, respectively. Microbial diversity inferred from DNA analysis showed Actinobacteria and Alphaproteobacteria as the most abundant and widespread bacterial taxa among the samples, followed by Chloroflexi and Firmicutes at specific sites. Archaea were mainly dominated by Nitrososphaerales, Methanobacteria, with the detection of other groups such as Halobacteria. Metaproteomics showed a high and even distribution of proteins involved in primary metabolic processes such as energy production and biosynthetic pathways, and a limited but remarkable presence of proteins related to resistance to environmental stressors such as radiation, oxidation, or desiccation. The results indicated that extra humidity in the system allows the microbial community to repair, and prepare for the upcoming hyperarid period. Additionally, it supplies biomarkers to the medium whose preservation potential could be high under strong desiccation conditions and relevant for planetary exploration.

Ion Association in Lanthanide Chloride Solutions.

A better understanding of the solution chemistry of the lanthanide (Ln) salts in water would have wide ranging implications in materials processing, waste management, element tracing, medicine and many more fields. This is particularly true for minerals processing, given governmental concerns about lanthanide security of supply and the drive to identify environmentally sustainable processing routes. Despite much effort, even in simple systems, the mechanisms and thermodynamics of LnIII association with small anions remain unclear. In the present study, molecular dynamics (MD), using a newly developed force field, provide new insights into LnCl3(aq) solutions. The force field accurately reproduces the structure and dynamics of Nd3+, Gd3+ and Er3+ in water when compared to calculations using density functional theory (DFT). Adaptive‐bias MD simulations show that the mechanisms for ion pairing change from dissociative to associative exchange depending upon cation size. Thermodynamics of association reveal that whereas ion pairing is favourable, the equilibrium distribution of species at low concentration is dominated by weakly bound solvent‐shared and solvent‐separated ion pairs, rather than contact ion pairs, reconciling a number of contrasting observations of LnIII–Cl association in the literature. In addition, we show that the thermodynamic stabilities of a range of inner sphere and outer sphere LnClx(3-x)+ coordination complexes are comparable and that the kinetics of anion binding to cations may control solution speciation distributions beyond ion pairs. The techniques adopted in this work provide a framework with which to investigate more complex solution chemistries of cations in water.

Structural Evolution of Iridium Oxide Cluster Anions IrnOm– (n = 5–8) with Sequential Oxidation: Binding Mode of O Atoms and Ir Framework

Geometric structures of small cluster anions of iridium oxide IrnOm– (n = 5–8, m = 0–14) were investigated by ion mobility mass spectrometry (IMMS) and theoretical calculation to clarify the evolut...

Macrofluidic Device for Preparative Concentration Based on Epitachophoresis.

We have developed a new separation device to concentrate and collect ions from several milliliter sample volumes to microliter fractions. Unlike most conventional platforms, this device has circular architecture. The electrophoretic migration operates from the outer perimeter toward the center. Separations can be performed both in continuous (zone electrophoresis) and discontinuous (moving boundary) electrolyte systems. We use a discontinuous electrolyte system comprising a leading and a terminating electrolyte to concentrate samples containing small organic anions and DNA fragment. The agarose gel stabilizes the boundary between the leading and terminating electrolytes. The milliliter volume sample is mixed with the terminating electrolyte and migrates through the gel toward the center. The concentrated total sample is collected in microliter fraction at the center. The potential for preparative concentration of DNA is demonstrated using a DNA ladder. Because zone migration accelerates as it moves toward the center, we named this method Epitachophoresis from the Greek word "επιταχυνω (epitachýnο)", meaning "acceleration". To the best of our knowledge, this unique circular architecture has not been previously described.

Small molecule-facilitated anion transporters in cells for a novel therapeutic approach to cystic fibrosis.

Cystic fibrosis (CF) is a lethal autosomal recessive genetic disease that originates from the defective function of the CF transmembrane conductance regulator (CFTR) protein, a cAMP-dependent anion channel involved in fluid transport across epithelium. Because small synthetic transmembrane anion transporters (anionophores) can replace the biological anion transport mechanisms, independent of genetic mutations in the CFTR, such anionophores are candidates as new potential treatments for CF. In order to assess their effects on cell physiology, we have analysed the transport properties of five anionophore compounds, three prodigiosines and two tambjamines. Chloride efflux was measured in large uni-lamellar vesicles and in HEK293 cells with chloride-sensitive electrodes. Iodide influx was evaluated in FRT cells transfected with iodide-sensitive YFP. Transport of bicarbonate was assessed by changes of pH after a NH4 + pre-pulse using the BCECF fluorescent probe. Assays were also carried out in FRT cells permanently transfected with wild type and mutant human CFTR. All studied compounds are capable of transporting halides and bicarbonate across the cell membrane, with a higher transport capacity at acidic pH. Interestingly, the presence of these anionophores did not interfere with the activation of CFTR and did not modify the action of lumacaftor (a CFTR corrector) or ivacaftor (a CFTR potentiator). These anionophores, at low concentrations, transported chloride and bicarbonate across cell membranes, without affecting CFTR function. They therefore provide promising starting points for the development of novel treatments for CF.

Resonance-Mediated Below-Threshold Delayed Photoemission and Non-Franck-Condon Photodissociation of Cold Oxyallyl Anions.

The photoexcitation of cold oxyallyl anions was studied below the adiabatic detachment threshold at a photon energy of 1.60 eV. Photodetachment was observed through two product channels, delayed electron emission from a long-lived anionic state and dissociative photodetachment via absorption of a second photon. The former produced stable neutral C3 H4 O, while the latter resulted in the concerted elimination of CO+C2 H4 products. The neutral oxyallyl singlet state has a barrier-free route to cyclopropanone as well as zwitterionic character with a large charge separation and dipole moment. The role of long-lived dipole-bound resonances built on the singlet state below the detachment threshold is discussed. These results provide one of the first observations of delayed photoemission in a small cold molecular radical anion, a consequence of the complex electronic structure of the neutral diradical, and provide an example of resonance-mediated control of the photodissociation processes.

Resonance‐Mediated Below‐Threshold Delayed Photoemission and Non‐Franck–Condon Photodissociation of Cold Oxyallyl Anions

AbstractThe photoexcitation of cold oxyallyl anions was studied below the adiabatic detachment threshold at a photon energy of 1.60 eV. Photodetachment was observed through two product channels, delayed electron emission from a long‐lived anionic state and dissociative photodetachment via absorption of a second photon. The former produced stable neutral C3H4O, while the latter resulted in the concerted elimination of CO+C2H4 products. The neutral oxyallyl singlet state has a barrier‐free route to cyclopropanone as well as zwitterionic character with a large charge separation and dipole moment. The role of long‐lived dipole‐bound resonances built on the singlet state below the detachment threshold is discussed. These results provide one of the first observations of delayed photoemission in a small cold molecular radical anion, a consequence of the complex electronic structure of the neutral diradical, and provide an example of resonance‐mediated control of the photodissociation processes.

Slc26 Family of Anion Transporters in the Gastrointestinal Tract: Expression, Function, Regulation, and Role in Disease.

SLC26 family members are multifunctional transporters of small anions, including Cl- , HCO3 - , sulfate, oxalate, and formate. Most SLC26 isoforms act as secondary (coupled) anion transporters, while others mediate uncoupled electrogenic transport resembling Cl- channels. Of the 11 described SLC26 isoforms, the SLC26A1,2,3,6,7,9,11 are expressed in the gastrointestinal tract, where they participate in salt and water transport, surface pH-microclimate regulation, affect the microbiome composition, the absorption, and secretion of oxalate and sulfate, and other functions that require further study. Several intestinal or extra-intestinal diseases are related to SLC26A mutations. Patients with congenital chloride diarrhea (CLD) suffer from Cl- -rich acidic diarrhea and systemic alkalosis due to SLC26A3 mutations. Patients with osteochondrodysplastic syndromes experience skeletal defects due to SLC26A2 mutations, resulting in defective sulfate absorption in enterocytes and sulfate uptake in chondrocytes. Because of functional interactions between SLC26 and other proteins, such as the Cl- channel CFTR, some of the intestinal cystic fibrosis manifestations may be attributed to impaired SLC26 isoform localization and function. The altered expression of SLC26 members due to inflammation or operative procedures have important consequences on intestinal transport and barrier function in common diseases as inflammatory bowel disease or bariatric surgery. The present review gives an overview on the current state of knowledge of the intestinally expressed SLC26A isoforms (SLC26A1,2,3,6,7,9,11) from the history of their functional identification, cloning and expression, the insights into their function, interaction partners and regulation gained in heterologous expression systems and Slc26a-deficient mice, to information about their transcriptional regulation and roles in gastrointestinal disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:839-872, 2019.

Functional Role of Basolateral ClC-2 Channels in the Regulation of Duodenal Anion Secretion in Mice.

Although ClC-2 channels are important in colonic Cl- secretion, it is unclear about their roles in small intestinal anion secretion. Therefore, we sought to examine whether ClC-2 channels play important roles in anion secretion, particularly duodenal bicarbonate secretion (DBS). Duodenal mucosae from mice were stripped of seromuscular layers and mounted in Ussing chambers. Both duodenal short-circuit current (Isc) and HCO3- secretion in vitro were simultaneously recorded. DBS in vivo was measured by a CO2-sensitive electrode. Lubiprostone, a selective ClC-2 activator, concentration-dependently increased both duodenal Isc and DBS only when applied basolaterally, but not when applied apically. Removal of extracellular Cl- abolished lubiprostone-induced duodenal Isc, but did not alter HCO3- secretion even in the presence of DIDS, a Cl-/HCO3- exchanger inhibitor. However, further addition of glibenclamide, a CFTR channel blocker, abolished lubiprostone-evoked HCO3- secretion. Moreover, lubiprostone-induced HCO3- secretion was impaired in CFTR-/- mice compared to wild-type littermates. Luminal perfusion of duodenal lumen with lubiprostone did not alter basal DBS in vivo, but lubiprostone (i.p.) was able to induce DBS, which was also significantly inhibited by Cd2+, a ClC-2 channel blocker. [Ca2+]cyt level, Ca2+-activated K+ channel- and cAMP-mediated duodenal Isc, and HCO3- secretion were unchanged by lubiprostone. We have provided the first evidence for the novel functional role of basolateral ClC-2 channels in the regulation of duodenal anion secretion.

Screening of Suitable Ionic Liquids as Green Solvents for Extraction of Eicosapentaenoic Acid (EPA) from Microalgae Biomass Using COSMO-RS Model.

Omega-3 poly unsaturated fatty acids (PUFA) particularly eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have many health benefits including reducing the risk of cancer and cardiovascular disease. Recently, the use of ionic liquids (ILs) in lipid extraction from microalgae provides the potential to overcome common drawbacks, offers several other benefits. To date, very limited researches are available to focus on extracting microalgae lipid and PUFA in particular by using ILs. The objective of current work is to screen the potential ILs that can be applied in EPA extraction. In this study, fast ILs screening was performed with the help of a conductor like screening model for real solvents (COSMO-RS) and the ILs with higher capacity values for use in extraction of EPA were compared. According to the results, the highest capacity for EPA extraction among 352 screened cation/anion combinations belongs to [TMAm][SO4]. It is expected to achieve a higher yield of EPA once applying this combination as the solvent in the process of extraction. ILs with small anions were observed to have higher capacities, as well possessing higher charge density compared to larger ones, and therefore, they are more preferable for extraction purposes. Moreover, shorter alkyl chain cations are preferred when using imidazolium-based IL, which agrees with experimental data.

The incorporation and controlled release of dopamine from a sulfonated β–cyclodextrin–doped conducting polymer

Pyrrole was electropolymerised in the presence of sulfonated β–cyclodextrin to give a conducting polypyrrole film doped with the anionic cyclodextrin, PPy–sβ–CD. On reduction of the polymer film at −0.80 V vs SCE, high concentrations of dopamine (DA) were incorporated and the DA was subsequently released at a potential of 0.10 V vs SCE. Much higher levels of DA were incorporated and released at PPy–sβ–CD compared to polypyrrole films doped with smaller anions and doped with the larger para–toluene sulfonic acid. In addition to releasing higher concentrations of DA, the DA was less prone to oxidation and degradation in the presence of the sulfonated β–cyclodextrin. This was attributed to the formation of an inclusion complex between the protonated DA molecule and the anionic CD. The higher release rates were explained in terms of the immobile nature of the large CD and the high charge density with approximately 9 sulfonated groups attached to the rim of the CD cavity, which facilitated the uptake of high levels of DA. Approximately 6.0 μmol cm−2 of DA was released at 0.10 V vs SCE over 60 min on reducing the PPy–sβ–CD film for 30 min at −0.80 V vs SCE. Higher levels of 9.6 μmol cm−2 were obtained on increasing the reduction period to 60 min, while levels of 14.0 μmol cm−2 were achieved with thicker polymer films.

An Electrostatic Switch for Gating the Electromechanical Activity of SLC26A5 (prestin)

SLC26 comprises a family of multifunctional anion transporters that mediate passive or coupled transport of small anions. SLC26A5 (prestin) stands out by functioning as a voltage-driven mechanical actuator in sensory outer hair cells. The quasi-piezoelectric function of prestin depends on binding of intracellular anions, suggesting that the underlying dynamics may be derived from an ancestral anion transport mechanism. We previously identified the structural architecture of prestin as a 7 transmembrane domain inverted repeat architecture, a layout shared with SLC4 (e.g., AE1) and SLC23 transporters. To address the molecular mode of action of anions in electromechanical function, we conducted a glutamate scan of the putative anion binding site. While introduction of glutamate at most positions probed was disruptive for protein function, glutamate at a central position (S396E) was tolerated. Moreover, S396E rendered prestin anion-independent and insensitive to competitive anionic blockers. We conclude that S396E reveals location and coordination of substrate anions. Anion binding may enable the voltage-dependent conformational transition by perturbing a local hydrogen or electrostatic network. To gain insights into the conformational dynamics underlying electromechanical activity we performed cysteine accessibility scanning mutagenesis of transmembrane segments 3 and 10, which mainly form the binding site as defined by glutamate substitution. Accessibility was essentially restricted to intracellular reagents. However, a position within TM3 near the substrate binding site was accessible both from the inside and from the outside - contrary to the crystal structure of the bacterial homolog SLC26Dg predicting inaccessibility to extracellular solutes in the inside-open conformation. Two-sided accessibility thus indicates movement of the rigid TM bundle comprising TMs 3 and 10 towards the extracellular side, possibly in an elevator-like movement. We speculate that this partial movement constitutes the conformational transition underlying prestin's electromechanical activity.

A novel reversed-phase and weak anion-exchange mixed-mode stationary phase based on horizontal polar-copolymerized approach for separation of small organic molecules and inorganic anions

A novel silica-based reversed-phase/weak anion-exchange mixed-mode chromatography (MMC) stationary phase referred to as OTAS was synthesized based on the horizontal polar-copolymerized approach using trichlorooctadecylsilane (ODS) and (3-glycidyloxypropyl)trimethoxysilane (GPS) as ligands, and then followed by the reaction of epoxy group with diethylamine to introduce the tertiary ammonium functional group. The new stationary phase was characterized by instrumental analysis, and evaluated by separating the mixture of alkylbenzene homologues in reversed-phase mode and acidic organic compounds in ion-exchange chromatography mode, respectively. The results indicate that not only the baseline separation of 11 kinds of neutral and acidic organic compounds can be achieved successfully, but also 5 kinds of inorganic anions can be separated completely. The chromatographic property of OTAS column can be controlled by adjusting the molar ratio of ODS to GPS. Moreover, the OTAS column was used successfully to analyze the inorganic anions in the actual water samples. The good separation and selectivity of OTAS column suggests that the new MMC stationary phase can be used for the analysis of complex samples containing of neutral and acidic organic compounds or inorganic anions.

Ionic aggregation-induced emission dye with bulky counterions for preparation of bright near-infrared polymeric nanoparticles.

Dyes exhibiting aggregation-induced emission (AIE) are attractive building blocks for the preparation of bright fluorescent nanomaterials. AIEgens are especially efficient in pure dye aggregates, whereas they are much less explored as dopants in NPs built of hydrophobic polymers. Here, we describe an approach that combines cationic AIEgens with bulky hydrophobic counterions (fluorinated tetraphenylborates) that enables preparation of small and bright AIEgen-loaded polymeric NPs. To this end, we synthesised a cationic tetraphenylethylene (TPE) derivative and studied its salts with counterions of different sizes and hydrophobicities. In organic solvent/water mixtures, all these salts exhibited typical AIE behaviour, whereas only salts with bulky hydrophobic counterions exhibited strongly red-shifted emission in the near-infrared (NIR) region. Encapsulation of these salts into poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) NPs revealed that bulky counterions ensure (i) formation of small (∼50 nm) AIEgen-loaded polymeric NPs; (ii) good fluorescence quantum yield (up to 30%); and (iii) NIR emission reaching 700 nm. By contrast, AIEgens with small inorganic anions (perchlorate and hexafluorophosphate) blended with PMMA-MA produced large aggregates with emission in the far-red region. Single-particle microscopy revealed that our 50 nm AIEgen-loaded PMMA-MA NPs were 6-fold brighter than the NIR emitting quantum dots (QD705). These NPs feature low cytotoxicity and compatibility with live cell imaging, in contrast to large aggregates of AIEgens with small inorganic counterions that failed to internalize into the cells. The present work shows that combination of cationic AIEgens with bulky counterions opens new routes for the preparation of bright polymer-based nanomaterials.

Small molecule anion transporters display in vitro antimicrobial activity against clinically relevant bacterial strains.

Highly active transmembrane anion transporters have demonstrated their activity against antibiotic-resistant and clinically relevant bacterial strains. This type of compound offers promise as a strategy to develop novel antibacterial agents.

Small triiminopyrrolic molecular cage with high affinity and selectivity for fluoride.

A small molecular cage (4) with high affinity and complete selectivity for fluoride to the limit of detection over other competing small anions was synthesized. Cage 4 was also found to retain the encapsulated fluoride anion within its cavity even after one or two pyrrolic NH protons were subject to deprotonation.

Surface tension of binary mixtures of (ionic liquid + tributyl phosphate)

In this work, surface tension was determined for binary mixtures of imidazolium based ionic liquids (ILs) and tributyl phosphate (TBP) over the whole composition range at temperatures from (293.15 to 323.15) K and atmospheric pressure. The ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6) and 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([Bmim]Tf2N) were used in this work. According to the experimental data, surface tension deviations (δγ) and thermodynamic properties, including surface enthalpy (Hγ), surface entropy (Sγ), enthalpy of vaporisation △lgHmo and Hildebrand solubility parameter (SH), were also calculated. The results show that γ values of ILs are significantly higher than that of TBP. And the contribution of the anion size to the surface tension of ILs follows the order of BF4− > PF6− > Tf2N−, which indicates the low negative charge delocalization of small anion can lead to high γ values. Moreover, the strong electrostatic interactions between cation and anion in ILs result in the higher concentration of TBP at surface. As a result, δγ values for all the studied systems are all negative over the entire range of composition. Additionally, due to the high surface organization of ILs, surface entropies for ILs are much lower than that of TBP.

Abstraction of the I Atom from CH3I by Gas-Phase Au n - (n = 1-4) via Reductive Activation of the C-I Bond.

Gas-phase reactions of atomic gold anions and small gold cluster anions, Aun– (n = 1–4), with CH3I were investigated to clarify the effect of the cluster size on C–I bond activation and to elucidate the key properties of Au clusters that govern the reactivity. AunI– identified by mass spectrometry was observed as a common reaction product. Photoelectron spectroscopy and density functional theory calculations revealed that Au2I– has a linear structure in which the I atom is bonded to Au2, and Au3I– and Au4I– take a two-dimensional structure in which the I atom is bonded to triangular Au3 moieties. Pseudo-first-order kinetic analyses of the reaction revealed the inverse correlation of the reactivity of Aun– toward CH3I and the electron affinity of Aun, indicating the reductive activation of the C–I bond. Especially, Au2– showed the highest reactivity to form Au2I– as the main product, whereas the adduct compound Au2CH3I– was hardly formed, in sharp contrast to the reaction of Au– reported previously. On the basis of theoretical calculations, we propose that the reaction proceeded dominantly via the I atom abstraction pathway (attack of Au2– from the I atom side), which is highly preferential from the viewpoint of both the energetics and a steric factor. This study demonstrates that not only the reactivity but also the reaction mechanisms and products are governed by the cluster size in C–I bond activation by Au clusters at the smallest size region.

Submerging a Biomimetic Metallo-Receptor in Water for Molecular Recognition: Micellar Incorporation or Water Solubilization? A Case Study.

Molecular recognition in water is an important topic, but a challenging task due to the very competitive nature of the medium. The focus of this study is the comparison of two different strategies for the water solubilization of a biomimetic metallo-receptor based on a poly(imidazole) resorcinarene core. The first relies on a new synthetic path for the introduction of hydrophilic substituents on the receptor, at a remote distance from the coordination site. The second involves the incorporation of the organosoluble metallo-receptor into dodecylphosphocholine (DPC) micelles, which mimic the proteic surrounding of the active site of metallo-enzymes. The resorcinarene ligand can be transferred into water through both strategies, in which it binds ZnII over a wide pH window. Quite surprisingly, very similar metal ion affinities, pH responses, and recognition properties were observed with both strategies. The systems behave as remarkable receptors for small organic anions in water at near-physiological pH. These results show that, provided the biomimetic site is well structured and presents a recognition pocket, the micellar environment has very little impact on either metal ion binding or guest hosting. Hence, micellar incorporation represents an easy alternative to difficult synthetic work, even for the binding of charged species (metal cations or anions), which opens new perspectives for molecular recognition in water, whether for sensing, transport, or catalysis.

Allosteric Control of Photofoldamers for Selecting between Anion Regulation and Double-to-Single Helix Switching.

Allosteric regulation of protein structure and function is a hallmark of biology. The structures of protein-like abiological foldamers have been subject to allosteric control, however, regulation of their function is rare. We report this behavior using a photoactive foldamer following the discovery that small and large anions select between single and double helical structures, respectively. Correspondingly, these anions activate different functions in the photofoldamer; small anions turn on photoregulation of anion concentrations while large anions turn on chiroptical switching of quaternary structure. For this demonstration, we used an aryl-triazole based photofoldamer in which the light-driven trans-cis isomerization of azobenzenes alters intrastrand π-π contacts while the triazoles define the allosteric anion-binding site. Binding to 11 anions of increasing size was quantified (Cl-, Br-, NO2-, I-, NO3-, SCN-, BF4-, ClO4-, ReO4-, PF6-, SbF6-). Contrary to expectations that single helices will expand to accommodate larger and larger guests, this behavior only occurs for smaller anions (Cl- to NO3-; <45 Å3) beyond which the larger anions form double helices (SCN- to SbF6-; >45 Å3). With small anions, the single helix regulates anion concentrations when the azobenzenes are photoswitched. The binding of large anions favors a chiral double helix and activates light-driven switching into racemic single helices thereby modulating the quaternary structure and chiroptical activity. This work shows how complex multifunctional outcomes emerge when allosteric changes in structure are expressed in intrinsically functional foldamers.