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1
Yamuna, Thammarse S., Jerry P. Jasinski, Manpreet Kaur, Brian J. Anderson e H. S. Yathirajan. "5-(4-Fluorophenyl)-2H-pyrazol-1-ium 2,2,2-trifluoroacetate". Acta Crystallographica Section E Structure Reports Online 70, n. 4 (15 marzo 2014): o429—o430. http://dx.doi.org/10.1107/s1600536814005200.
Testo completoAbstract (sommario):
The title salt, C9H8FN2+·C2F3O2−, crystallizes with two independent cations (AandB) and two independent anions (CandD) in the asymmetric unit. In the cations, the dihedral angles between the benzene and pyrazolium rings are 23.7 (3)° in cationAand 1.8 (8)° in cationB. In the crystal, each anion links to the two cationsviaN—H...O hydrogen bonds, forming a U-shaped unit with anR44(14) ring motif. These U-shaped units stack along theaaxis and are linkedviaC—H...O and C—H...F hydrogen bonds, forming slabs lying parallel to (100). Within the slabs there are π–π interactions between the pyrazolium rings [inter-centroid distance = 3.6326 (15) Å] and between the benzene rings [inter-centroid distance = 3.7244 (16) Å]. In the anions, the F atoms of the trifluoromethyl groups are disordered over two sets of sites, with refined occupancy ratios of 0.58 (3):0.42, 0.540 (14):0.46 (14), and 0.55 (2):0.45 (2) for anionC, and 0.73 (5):0.27 (5), 0.63 (5):0.37 (5), and 0.57 (8):0.43 (8) for anionD.
2
Schefe, C. R., M. Watt, W. J. Slattery e P. M. Mele. "Organic anions in the rhizosphere of Al-tolerant and Al-sensitive wheat lines grown in an acid soil in controlled and field environments". Soil Research 46, n. 3 (2008): 257. http://dx.doi.org/10.1071/sr07139.
Testo completoAbstract (sommario):
Several sampling methods were investigated for the quantification of organic anions in the rhizosphere of Al-tolerant (ET8) and Al-sensitive (ES8) wheat plants in soil systems. Controlled environment studies used anion exchange membranes to collect rhizosphere organic anions (from root tips and mature regions of nodal roots) from ET8 and ES8 plants at the 6-leaf stage in a glasshouse environment. Using the anion exchange membranes, a selection of organic anions were detected on the tips and mature regions of roots, with ET8 and ES8 having similar rhizosphere organic anion profiles. The field experiment used 2 established methods of organic anion collection: rhizosphere soil and root washings. The ET8 and ES8 wheat lines had similar levels of organic anions, including malate, in the rhizosphere (using soil shaken from roots and root washings) at 3 sampling times (4 and 6 leaves, and flowering). The rhizosphere organic anions differed significantly from the bulk soil, with the concentration and range of organic anions in the rhizosphere decreasing towards flowering, presumably due to physiological changes in plant and root growth. This study used several techniques to investigate organic anion exudation by roots, with organic anions detected using all techniques. However, technical limitations of these techniques were recognised: (i) the lack of simultaneous exposure of root tips to both the anion exchange membrane and the chemical stimulant, e.g. Al3+; and (ii) the inability to derive the origin of organic anions measured in rhizosphere soil and root washings. The challenge for future soil-based organic anion research is to identify the dominant stress that has triggered an exudation response (i.e. Al toxicity, P deficiency), and to clearly differentiate between plant- and microbial-derived contributions to exudation.
3
Parthé, Erwin. "Crystal chemical information to be obtained from the bond-number equality concept". Acta Crystallographica Section B Structural Science 62, n. 2 (15 marzo 2006): 335–37. http://dx.doi.org/10.1107/s0108768106003065.
Testo completoAbstract (sommario):
Based on the bond-number equality concept an equation is derived for anion complexes of normal valence compounds with triangularly and/or tetrahedrally coordinated central atoms and anions having one, two, three and four bonds to central atoms: %Δ = 4 − (n/m′) × [2 − %A [1] + %A [3] + 2 × %A [4]]. %Δ is the ratio of the number of central atoms with triangular anion coordination to the sum of all central atoms in the anion complex. n/m′ is the ratio of the number of all A anions to the number of all central atoms C′ in the anion complex. %A [1] is the ratio of the number of anions with one bond to a central atom to the sum of all anions in the anion complex. %A [3] and %A [4] are defined accordingly. The equation can be used to formulate the possible crystal chemical formulae, which are characterized by partitions of central atoms and anions according to their bond numbers. Nitridosilicates and selected oxoborates are treated as examples of applications of the equation.
4
Li, Lei, Yu-Jian Hong, Dong-Yang Chen, Wang-Chuan Xiao e Mei-Jin Lin. "Anion–π interactions in lithium–organic redox flow batteries". Chemical Communications 55, n. 16 (2019): 2364–67. http://dx.doi.org/10.1039/c8cc09834d.
Testo completoAbstract (sommario):
The interactions between the electrolyte anions and electron-deficient redox-active organic molecules (anion–π interactions) have strong influences on the battery properties due to the anion–π-induced formation of radical anions or sandwich-like aggregates.
5
Wilkinson, Hazel S., e William T. A. Harrison. "Hexane-1,6-diammonium bis(dihydrogenarsenate): infinite anionic layers containing R 6 6(24) loops". Acta Crystallographica Section E Structure Reports Online 63, n. 3 (28 febbraio 2007): m902—m904. http://dx.doi.org/10.1107/s1600536807007672.
Testo completoAbstract (sommario):
The title compound, C6H18N2 2+·2H2AsO4 −, contains a network of doubly protonated centrosymmetric hexane-1,6-diammonium cations and dihydrogenarsenate anions. These species interact by way of cation-to-anion N—H...O and anion-to-anion O—H...O hydrogen bonds, the latter leading to infinite sheets of the H2AsO4 − anions.
6
Salhany, James M. "Anion binding characteristics of the band 3 / 4,4'-dibenzamidostilbene-2,2'-disulfonate binary complex: Evidence for both steric and allosteric interactions". Biochemistry and Cell Biology 77, n. 6 (1 dicembre 1999): 543–49. http://dx.doi.org/10.1139/o99-061.
Testo completoAbstract (sommario):
A novel kinetic approach was used to measure monovalent anion binding to better define the mechanistic basis for competition between stilbenedisulfonates and transportable anions on band 3. An anion-induced acceleration in the release of 4,4prime-dibenzamidostilbene-2,2prime-disulfonate (DBDS) from its complex with band 3 was measured using monovalent anions of various size and relative affinity for the transport site. The K1/2 values for anion binding were determined and correlated with transport site affinity constants obtained from the literature and the dehydrated radius of each anion. The results show that anions with ionic radii of 120-200 pm fall on a well-defined correlation line where the ranking of the K1/2 values matched the ranking of the transport site affinity constants (thiocyanate < nitrate equivalent to bromide < chloride < fluoride). The K1/2 values for the anions on this line were about 4-fold larger than expected for anion binding to inhibitor-free band 3. Such a lowered affinity can be explained in terms of allosteric site-site interactions, since the K1/2 values decreased with increasing anionic size. In contrast, iodide, with an ionic radius of about 212 pm, had a 10-fold lower affinity than predicted by the correlation line established by the smaller monovalent anions. These results indicate that smaller monovalent anions have unobstructed access to the transport site within the band 3 / DBDS binary complex, while iodide experiences significant steric hindrance when binding. The observation of steric hindrance in iodide binding to the band 3 / DBDS binary complex, but not in the binding of smaller monovalent anions, suggests that the stilbenedisulfonate binding site is located at the outer surface of an access channel leading to the transport site.Key words: band 3, anion transport, membrane protein structure, red cell membrane.
7
Attiogbe, Francis K., Samar K. Bose, Wei Wang, Alastair McNeillie e Raymond C. Francis. "The peroxymonocarbonate anions as pulp bleaching agents. Part 1. Results with lignin model compounds and chemical pulps". BioResources 5, n. 4 (18 agosto 2010): 2208–20. http://dx.doi.org/10.15376/biores.5.4.2208-2220.
Testo completoAbstract (sommario):
The peroxymonocarbonate mono-anion (HCO4─) is generated when the bicarbonate anion is added to a H2O2 solution. The mono-anion is believed to have a pKa value of ca. 10 and as such would start dissociating to the di-anion (CO42─) at pH ca. 8. The mono-anion should demonstrate electrophilic properties, while the di-anion should be a nucleophile. In an alkaline, non-sulfur pulping process such as soda/AQ, Na2CO3 could be obtained from the chemical recovery system and carbonated with CO2 from a flue gas stream to produce NaHCO3. In such a case only H2O2 would need to be purchased to generate the peroxymonocarbonate (PMC) anions. Bicarbonate anions could also be produced from the carbonation of solutions containing NaOH, Mg(OH)2 or mined Na2CO3. One or both of the PMC anions was found to be effective in oxidizing two lignin model compounds as well as lowering the lignin content of kraft and soda/AQ hardwood pulps. The PMC anions were generated in-situ by NaHCO3 or Na2CO3 + CO2 addition to dilute H2O2 solutions.
8
Kovanda, František, Eva Kovácsová e David Koloušek. "Removal of Anions from Solution by Calcined Hydrotalcite and Regeneration of Used Sorbent in Repeated Calcination-Rehydration-Anion Exchange Processes". Collection of Czechoslovak Chemical Communications 64, n. 9 (1999): 1517–28. http://dx.doi.org/10.1135/cccc19991517.
Testo completoAbstract (sommario):
Synthetic hydrotalcite calcined at 350-550 °C was used for the removal of arsenate, chromate, and vanadate ions from water solutions. The initial anion concentrations were 0.002 mol l-1. The sorption isotherms were measured at 20 °C and at neutral pH. The Langmuir adsorption isotherm was used for the sorption capacity evaluation. The ability of the calcined hydrotalcite to remove the anions from solution decreased in the order of vanadate - arsenate - chromate. The hydrotalcite calcined at 450 °C exhibited the best sorption ability for all the anions. The sorbed anions were released by anion exchange in a carbonate-containing solution and the hydrotalcite after subsequent calcination was used again for the removal of anions. The repeating cycles calcination-rehydration-anion exchange gradually reduced the adsorption capacity of the hydrotalcite. The sorption capacity decreased by 50% after the first two cycles but it did not change significantly in the subsequent cycles. When chromate anions were adsorbed, the decrease in sorption capacity was not observed during repeated calcination-rehydration-anion exchange cycles. The change in the sorption capacity was influenced by the ability of calcined hydrotalcite to regenerate the layered crystal structure during the rehydration process.
9
Yuan, Dan, e Yuan Fang Li. "Carboxyphenyl-terpyridine-based series of gels for procedural visual recognition of multi-anions". Analytical Methods 10, n. 41 (2018): 5032–37. http://dx.doi.org/10.1039/c8ay01679h.
Testo completoAbstract (sommario):
The gelation of 4-[2,2′:6′,2′′-terpyridine]-4′-ylbenzoic acid (Hcptpy) occurred with various metal ions and specific anions. With the gel formation, corresponding metal ions and anions were recognized. Also, the metal–organic gels (MOGs) possess stimuli response property to anions. A step-by-step anion recognition progress was established based on one Hcptpy ligand and realized the selective identification 12 kinds of anions.
10
McCarty, Nael A., e Zhi-Ren Zhang. "Identification of a region of strong discrimination in the pore of CFTR". American Journal of Physiology-Lung Cellular and Molecular Physiology 281, n. 4 (1 ottobre 2001): L852—L867. http://dx.doi.org/10.1152/ajplung.2001.281.4.l852.
Testo completoAbstract (sommario):
The variety of methods used to identify the structural determinants of anion selectivity in the cystic fibrosis transmembrane conductance regulator Cl− channel has made it difficult to assemble the data into a coherent framework that describes the three-dimensional structure of the pore. Here, we compare the relative importance of sites previously studied and identify new sites that contribute strongly to anion selectivity. We studied Cl−and substitute anions in oocytes expressing wild-type cystic fibrosis transmembrane conductance regulator or 12-pore-domain mutants to determine relative permeability and relative conductance for 9 monovalent anions and 1 divalent anion. The data indicate that the region of strong discrimination resides between T338 and S341 in transmembrane 6, where mutations affected selectivity between Cl− and both large and small anions. Mutations further toward the extracellular end of the pore only strongly affected selectivity between Cl− and larger anions. Only mutations at S341 affected selectivity between monovalent and divalent anions. The data are consistent with a narrowing of the pore between the extracellular end and a constriction near the middle of the pore.
11
Xie, Huifang, e Ming Wah Wong. "Computational Design of Thiourea-based Cyclophane Sensors for Small Anions". Australian Journal of Chemistry 65, n. 3 (2012): 303. http://dx.doi.org/10.1071/ch11389.
Testo completoAbstract (sommario):
The host–guest binding properties of a tri-thiourea cyclophane receptor (1) with several common anions have been investigated using density functional theory (DFT) and molecular dynamics calculations. Receptor 1 is predicted to be an effective receptor for binding small halogen and Y-shaped (NO3– and AcO–) anions in the gas phase, cyclohexane and chloroform. The calculated order of anion binding affinity for the receptor 1 in chloroform is F– > Cl– > AcO– > NO3– >Br– > H2PO4– > HSO4–. The binding free energies are strongly influenced by a dielectric solvent medium. The structures of the receptor–anion complexes are characterized by multiple (typically 6) hydrogen bonds in all cases. The overall binding affinity of various anions is determined by the basicity of anion, size and shape of the binding site, and solvent medium. Explicit chloroform solvent molecular dynamics simulations of selected receptor–anion complexes reveal that the anions are strongly bound within the binding pocket via hydrogen-bonding interactions to all the receptor protons throughout the simulation. A sulfur analogue of receptor 1 (2), with a larger central cavity, is shown to be a more effective sensor than 1 for small anions. Two different approaches to develop the thiourea-based cyclophane receptor into a chromogenic sensor were examined.
12
Smith, Stephen S., Erich D. Steinle, Mark E. Meyerhoff e David C. Dawson. "Cystic Fibrosis Transmembrane Conductance Regulator". Journal of General Physiology 114, n. 6 (29 novembre 1999): 799–818. http://dx.doi.org/10.1085/jgp.114.6.799.
Testo completoAbstract (sommario):
The cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel exhibits lyotropic anion selectivity. Anions that are more readily dehydrated than Cl exhibit permeability ratios (PS/PCl) greater than unity and also bind more tightly in the channel. We compared the selectivity of CFTR to that of a synthetic anion-selective membrane [poly(vinyl chloride)–tridodecylmethylammonium chloride; PVC-TDMAC] for which the nature of the physical process that governs the anion-selective response is more readily apparent. The permeability and binding selectivity patterns of CFTR differed only by a multiplicative constant from that of the PVC-TDMAC membrane; and a continuum electrostatic model suggested that both patterns could be understood in terms of the differences in the relative stabilization of anions by water and the polarizable interior of the channel or synthetic membrane. The calculated energies of anion–channel interaction, derived from measurements of either permeability or binding, varied as a linear function of inverse ionic radius (1/r), as expected from a Born-type model of ion charging in a medium characterized by an effective dielectric constant of 19. The model predicts that large anions, like SCN, although they experience weaker interactions (relative to Cl) with water and also with the channel, are more permeant than Cl because anion–water energy is a steeper function of 1/r than is the anion–channel energy. These large anions also bind more tightly for the same reason: the reduced energy of hydration allows the net transfer energy (the well depth) to be more negative. This simple selectivity mechanism that governs permeability and binding acts to optimize the function of CFTR as a Cl filter. Anions that are smaller (more difficult to dehydrate) than Cl are energetically retarded from entering the channel, while the larger (more readily dehydrated) anions are retarded in their passage by “sticking” within the channel.
13
Wilkinson, Hazel S., e William T. A. Harrison. "2-Methylpiperazinium bis(dihydrogenarsenate)". Acta Crystallographica Section E Structure Reports Online 63, n. 3 (28 febbraio 2007): m900—m901. http://dx.doi.org/10.1107/s1600536807008392.
Testo completoAbstract (sommario):
The title compound, C5H14N2 2+·2H2AsO4 −, contains a network of centrosymmetric doubly protonated 2-methylpiperazinium cations, showing disorder of the methyl group, accompanied by dihydogenarsenate anions. The component species interact by way of cation-to-anion N—H...O and anion-to-anion O—H...O hydrogen bonds, the latter leading to infinite sheets of the H2AsO4 − anions containing R 6 6(24) supramolecular loops.
14
Kellum, J. A., R. Bellomo, D. J. Kramer e M. R. Pinsky. "Hepatic anion flux during acute endotoxemia". Journal of Applied Physiology 78, n. 6 (1 giugno 1995): 2212–17. http://dx.doi.org/10.1152/jappl.1995.78.6.2212.
Testo completoAbstract (sommario):
We sought to determine the role the liver might play in the regulation of anion-cation balance during both stable baseline conditions and acute endotoxemia. Ten pentobarbital sodium-anesthetized dogs were instrumented at laparotomy with ultrasonic flow probes around the left renal artery, portal vein, and hepatic artery, and catheters were inserted into the hepatic vein, portal vein, pulmonary artery, left renal vein, and abdominal aorta. Measurements were obtained from each site at baseline and 30-45 min after the intravenous infusion of endotoxin. The total anion flux across the liver was calculated from the strong-ion difference. At baseline, the liver removed anions from the circulation (-0.34 meq/min). With early endotoxemia, however, the liver switched to the release of anions (0.12 meq/min; P = 0.0046). After endotoxin administration, the gut, which was neutral at baseline, began to take up anions (-0.47 meq/min; P = 0.008). Anion flux across the lung and kidney was unchanged. We conclude that in the dog the liver, which removes anions at baseline, switches to release anions during early endotoxemia and may be a major site of acid production in early sepsis.
15
Kusama, Nobuyoshi, Mamta Gautam, Anne Marie S. Harding, Peter M. Snyder e Christopher J. Benson. "Acid-sensing ion channels (ASICs) are differentially modulated by anions dependent on their subunit composition". American Journal of Physiology-Cell Physiology 304, n. 1 (1 gennaio 2013): C89—C101. http://dx.doi.org/10.1152/ajpcell.00216.2012.
Testo completoAbstract (sommario):
Acid-sensing ion channels (ASICs) are sodium channels gated by extracellular protons. ASIC1a channels possess intersubunit Cl−-binding sites in the extracellular domain, which are highly conserved between ASIC subunits. We previously found that anions modulate ASIC1a gating via these sites. Here we investigated the effect of anion substitution on native ASICs in rat sensory neurons and heterologously expressed ASIC2a and ASIC3 channels by whole cell patch clamp. Similar to ASIC1a, anions modulated the kinetics of desensitization of other ASIC channels. However, unlike ASIC1a, anions also modulated the pH dependence of activation. Moreover, the order of efficacy of different anions to modulate ASIC2a and -3 was very different from that of ASIC1a. More surprising, mutations of conserved residues that form an intersubunit Cl−-binding site in ASIC1a only partially abrogated the effects of anion modulation of ASIC2a and had no effect on anion modulation of ASIC3. The effects of anions on native ASICs in rat dorsal root ganglion neurons mimicked those in heterologously expressed ASIC1a/3 heteromeric channels. Our data show that anions modulate a variety of ASIC properties and are dependent on the subunit composition, and the mechanism of modulation for ASIC2a and -3 is distinct from that of ASIC1a. We speculate that modulation of ASIC gating by Cl− is a novel mechanism to sense shifts in extracellular fluid composition.
16
Fortenberry, R. C. "Theoretical Electronic and Rovibrational Studies for Anions of Interest to the DIBs". Proceedings of the International Astronomical Union 9, S297 (maggio 2013): 344–48. http://dx.doi.org/10.1017/s1743921313016098.
Testo completoAbstract (sommario):
AbstractThe dipole-bound excited state of the methylene nitrile anion (CH2CN−) has been suggested as a candidate carrier for a diffuse interstellar band (DIB) at 803.8 nm. Its corresponding radical has been detected in the interstellar medium (ISM), making the existence for the anion possible. This work applies state-of-the-art ab initio methods such as coupled cluster theory to reproduce accurately the electronic excitations for CH2CN− and the similar methylene enolate anion, CH2CHO−. This same approach has been employed to indicate that 19 other anions may possess electronically excited states, five of which are valence in nature. Concurrently, in order to assist in the detection of these anions in the ISM, work has also been directed towards predicting vibrational frequencies and spectroscopic constants for these anions through the use of quartic force fields (QFFs). Theoretical rovibrational work on anions has thus far included studies of CH2CN−, C3H−, and is currently ongoing for similar systems.
17
González-Ruiz, Víctor, Ángel Cores, M. Mar Caja, Vellaisamy Sridharan, Mercedes Villacampa, M. Antonia Martín, Ana I. Olives e J. Carlos Menéndez. "Fluorescence Sensors Based on Hydroxycarbazole for the Determination of Neurodegeneration-Related Halide Anions". Biosensors 12, n. 3 (14 marzo 2022): 175. http://dx.doi.org/10.3390/bios12030175.
Testo completoAbstract (sommario):
The environmental presence of anions of natural origin or anthropogenic origin is gradually increasing. As a tool to tackle this problem, carbazole derivatives are an attractive gateway to the development of luminescent chemosensors. Considering the different mechanisms proposed for anion recognition, the fluorescence properties and anion-binding response of several newly synthesised carbazole derivatives were studied. Potential anion sensors were designed so that they combined the native fluorescence of carbazole with the presence of hydrogen bonding donor groups in critical positions for anion recognition. These compounds were synthesised by a feasible and non-expensive procedure using palladium-promoted cyclodehydrogenation of suitable diarylamine under microwave irradiation. In comparison to the other carbazole derivatives studied, 1-hydroxycarbazole proved to be useful as a fluorescent sensor for anions, as it was able to sensitively recognise fluoride and chloride anions by establishing hydrogen bond interactions through the hydrogen atoms on the pyrrolic nitrogen and the hydroxy group. Solvent effects and excited-state proton transfer (ESPT) of the carbazole derivatives are described to discard the role of the anions as Brönsted bases on the observed fluorescence behaviour of the sensors. The anion–sensor interaction was confirmed by 1H-NMR. Molecular modelling was employed to propose a mode of recognition of the sensor in terms of complex stability and interatomic distances. 1-hydroxycarbazole was employed for the quantitation of fluoride and chloride anions in commercially available medicinal spring water and mouthwash samples.
18
Shafei, Gamal M. S. El, e Afaf A. Zahran. "Structural and Textural Properties of Perchlorated and Persulphated Mixed (Hydr)Oxides of Zirconium and Titanium". Adsorption Science & Technology 20, n. 8 (ottobre 2002): 707–22. http://dx.doi.org/10.1260/026361702321104219.
Testo completoAbstract (sommario):
Perchlorated and persulphated mixed hydroxides of zirconium and titanium were prepared by coprecipitation and impregnation in aqueous HClO4 or (NH4)2S2O8 solutions of 0.05, 0.10, 0.20 and 0.40 M concentrations. An alternate sequence of impregnation followed by calcination or vice versa was conducted and the samples obtained studied using XRD, FT-IR, pyridine titration and low-temperature (–196°C) nitrogen adsorption methods. XRD indicated that the presence of titanium stabilized the tetragonal modification of zirconia and almost completely prevented the usual tetragonal → monoclinic transformation upon calcination at 650°C. Both S2O82– and ClO4− anions at their lowest concentration level (0.05 M) partially retarded the crystallization which occurred upon calcination at 650°C in their absence. However, the two anions showed different effects. Whereas the perchlorate anion prevented the formation of a crystalline titania phase (anatase) to a greater extent than that of crystalline zirconia, the persulphate anion showed the opposite effect. Complete inhibition was observed with both anions at a concentration of 0.4 M. This effect was attributed to adsorption of the anions on the hydroxy species of zirconium and titanium formed initially, as demonstrated by IR spectroscopy which showed that the anions were of lower symmetry, viz. C2v, due to their bonding to the hydroxy species. Calcination at 650°C caused the material formed initially to lose virtually all its initial high surface area because of crystallization. The prevention of crystallization by added anions was reflected in the retention of a relatively high surface area even after calcination at 650°C. The recorded difference in the interactions of the anions with the hydroxy species formed initially was also reflected in the texture of the anion-modified solids. The protecting influence of the ClO4− anion increased with its increasing concentration in the system, whereas the corresponding effect with the S2O82– anion increased up to 0.10 M concentration and then decreased at higher concentrations.
19
Joseph, Stefanie, Christof Suchentrunk e Nikolaus Korber. "Dissolving Silicides: Syntheses and Crystal Structures of New Ammoniates Containing Si52– and Si94– Polyanions and the Role of Ammonia of Crystallisation". Zeitschrift für Naturforschung B 65, n. 9 (1 settembre 2010): 1059–65. http://dx.doi.org/10.1515/znb-2010-0901.
Testo completoAbstract (sommario):
The dissolution of the ternary material K6Rb6Si17 in liquid ammonia yields the solvate compound Rb4Si9 ・ 5NH3, which contains fourfold negatively charged nine atom silicon clusters Si94−. Using additionally the [2.2.2] cryptand during the dissolution results in the solvate [K(2.2.2- crypt)]2Si5 ・ 4NH3 , in which the Si52− anion is present in the crystal structure. The Si52− anion has the shape of a nearly ideal trigonal bipyramid. The starting material K6Rb6Si17 contains both Si44− and Si94− Zintl anions. In ammoniate crystal structures, Si94− anions are accessible independently of Si44− anions, and ammonia of crystallisation plays a major role in the observed crystal symmetry. For the cryptate structures of Si52− and Ge52− anions ammonia of crystallisation is obligatory despite the loss of crystal symmetry compared to the crystal structures of the heavier homologues Pb52− and Sn52−.
20
Haider, Azeem, Mukhtiar Ahmed, Muhammad Faisal e Muhammad Moazzam Naseer. "Isatin as a simple, highly selective and sensitive colorimetric sensor for fluoride anion". Heterocyclic Communications 26, n. 1 (17 marzo 2020): 14–19. http://dx.doi.org/10.1515/hc-2020-0003.
Testo completoAbstract (sommario):
AbstractHerein, we report the fluoride anion sensing properties of a commercially available and inexpensive organic compound, isatin, which is found to be a highly selective and sensitive sensor. In naked-eye experiments, by addition of fluoride anions, isatin shows a dramatic color change from pale yellow to violet at room temperature, while the addition of other anions, i.e. $\mathrm{Cl}^-,$$\mathrm{Br}^-,\mathrm I^-,\mathrm{ClO}_4^-,{\mathrm H}_2\mathrm{PO}_4^-\,\mathrm{and}\,\mathrm{PF}_6^-,$did not induce any colour change. Additionally, recognition and titration studies have also been done through UV/Vis spectroscopy. Isatin displayed a new absorption band at 533 nm after the addition of fluoride anions, which is presumably due to acid-base interaction between isatin and fluoride anions, while other anions did not trigger noticeable spectral changes. The detection limit was observed to be 0.367 ppm. DFT calculations were also performed to further explain the behavior of receptor 1 towards the Fˉ anion. Owing to high sensitivity and selectivity, isatin can be useful in the detection of biologically or environmentally important fluoride anions at very low concentration.
21
Akaike, N., N. Inomata e T. Yakushiji. "Differential effects of extra- and intracellular anions on GABA-activated currents in bullfrog sensory neurons". Journal of Neurophysiology 62, n. 6 (1 dicembre 1989): 1388–99. http://dx.doi.org/10.1152/jn.1989.62.6.1388.
Testo completoAbstract (sommario):
1. Kinetic properties of gamma-aminobutyric acid (GABA)-gated inward and outward anion currents were investigated in the frog sensory neurons perfused internally and externally with various anions with the use of a rapid concentration-jump (termed as 'concentration-clamp') technique. 2. Extracellular Br- [( Br-]o) shifted the dose-response curves of GABA-induced inward anion currents to the left without affecting the maximum values, whereas [Cl-]o, [I-]o, [No3-]o, [HCOO-]o, and [CH3COO-]o altered the rate of desensitization differently without shifting the GABA dose-response curves, indicating that the kinetics of desensitization phase are affected differently by various extracellular anions. 3. [CH3COO-]o suppressed the maximum current of the dose-response curve of the GABA-induced inward ICl without affecting Kd. 4. Both activation and desensitization phases of GABA-induced ICl consisted of fast and slow components, respectively. [Br-]o, [I-]o, and [NO3-]o significantly prolonged the slow desensitization component, whereas both [HCOO-]o and [CH3COO-]o shortened it. The fast desensitization and the fast and slow activation components were also affected by these foreign anions. 5. GABA dose-response curves of inward currents carried by various intracellular anions (Cl-, Br-, NO3-, I-, SCN-, HCOO-, F-, CH3COO-, CH3CH2COO-, BrO3-, and ClO3-) while keeping a constant [Cl-]o had a constant Kd value but different saturating maximum currents. There were no marked differences among their current kinetics except in the case of SCN-, indicating that the current kinetics is not affected by replacing intracellular Cl- [( Cl-]i) with various foreign anions. 6. The configuration and amplitude of GABA-gated outward anion currents at a constant [Cl-]i reflected the extracellular action of individual anions on the anion-binding site of GABA receptor associated with the anion-selective channel. 7. The relative conductances of the various anions, calculated from the maximum peak currents in dose-response curves of the GABA-induced inward anion currents at a constant [Cl-]o, was in the sequence: I- greater than Br- greater than or equal to NO3- greater than ClO3- greater than SCN- greater than or equal to Cl- greater than HCOO- greater than BrO3- greater than CH3COO- greater than F- greater than CH3CH2COO-.(ABSTRACT TRUNCATED AT 400 WORDS)
22
Talanov, M. V., V. B. Shirokov e V. M. Talanov. "Anion order in perovskites: a group-theoretical analysis". Acta Crystallographica Section A Foundations and Advances 72, n. 2 (29 gennaio 2016): 222–35. http://dx.doi.org/10.1107/s2053273315022147.
Testo completoAbstract (sommario):
Anion ordering in the structure of cubic perovskite has been investigated by the group-theoretical method. The possibility of the existence of 261 ordered low-symmetry structures, each with a unique space-group symmetry, is established. These results include five binary and 14 ternary anion superstructures. The 261 idealized anion-ordered perovskite structures are considered as aristotypes, giving rise to different derivatives. The structures of these derivatives are formed by tilting ofBO6octahedra, distortions caused by the cooperative Jahn–Teller effect and other physical effects. Some derivatives of aristotypes exist as real substances, and some as virtual ones. A classification of aristotypes of anion superstructures in perovskite is proposed: theAXclass (the simultaneous ordering ofAcations and anions in cubic perovskite structure), theBXclass (the simultaneous ordering ofBcations and anions) and theXclass (the ordering of anions only in cubic perovskite structure). In most perovskites anion ordering is accompanied by cation ordering. Therefore, the main classes of anion order in perovskites are theAXandBXclasses. The calculated structures of some anion superstructures are reported. Comparison of predictions and experimentally investigated anion superstructures shows coherency of theoretical and experimental results.
23
Zaleskaya, Marta, Łukasz Dobrzycki e Jan Romański. "Highly Efficient, Tripodal Ion-Pair Receptors for Switching Selectivity between Acetates and Sulfates Using Solid–Liquid and Liquid–Liquid Extractions". International Journal of Molecular Sciences 21, n. 24 (12 dicembre 2020): 9465. http://dx.doi.org/10.3390/ijms21249465.
Testo completoAbstract (sommario):
A tripodal, squaramide-based ion-pair receptor 1 was synthesized in a modular fashion, and 1H NMR and UV-vis studies revealed its ability to interact more efficiently with anions with the assistance of cations. The reference tripodal anion receptor 2, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by presence of cations. Besides the ability to bind anions in enhanced manner by the “single armed” ion-pair receptor 3, the lack of multiple and prearranged binding sites resulted in its much lower affinity towards anions than in the case of tripodal receptors. Unlike with receptors 2 or 3, the high affinity of 1 towards salts opens up the possibility of extracting extremely hydrophilic sulfate anions from aqueous to organic phase. The disparity in receptor 1 binding modes towards monovalent anions and divalent sulfates assures its selectivity towards sulfates over other lipophilic salts upon liquid–liquid extraction (LLE) and enables the Hofmeister bias to be overcome. By changing the extraction conditions from LLE to SLE (solid–liquid extraction), a switch of selectivity from sulfates to acetates was achieved. X-ray measurements support the ability of anion binding by cooperation of the arms of receptor 1 together with simultaneous binding of cations.
24
Brown, J. C., R. K. Packer e M. A. Knepper. "Role of organic anions in renal response to dietary acid and base loads". American Journal of Physiology-Renal Physiology 257, n. 2 (1 agosto 1989): F170—F176. http://dx.doi.org/10.1152/ajprenal.1989.257.2.f170.
Testo completoAbstract (sommario):
Bicarbonate is formed when organic anions are oxidized systemically. Therefore, changes in organic anion excretion can affect systemic acid-base balance. To assess the role of organic anions in urinary acid-base excretion, we measured urinary excretion in control rats, NaHCO3-loaded rats, and NH4Cl-loaded rats. Total organic anions were measured by the titration method of Van Slyke. As expected, NaHCO3 loading increased urine pH and decreased net acid excretion (NH4+ + titratable acid - HCO3-), whereas NH4Cl loading had the opposite effect. Organic anion excretion was increased in response to NaHCO3 loading and decreased in response to NH4Cl loading. We quantified the overall effect of organic ion plus inorganic buffer ion excretion on acid-base balance. The amounts of organic anions excreted by all animals in this study were greater than the amounts of NH4+, HCO3-, or titratable acidity excreted. In addition, in response to acid and alkali loading, changes in urinary organic anion excretion were 40-50% as large as changes in net acid excretion. We conclude that, in rats, regulation of organic anion excretion can contribute importantly to the overall renal response to acid-base disturbances.
25
Edwards, Nicola. "Fluorescent sensors for detecting anions". Open Access Government 43, n. 1 (10 luglio 2024): 232–33. http://dx.doi.org/10.56367/oag-043-11152.
Testo completoAbstract (sommario):
Fluorescent sensors for detecting anions Nicola Edwards, Associate Professor of Chemistry at the University of St. Joseph, is conducting research on the development of fluorescent sensors for anion detection. Fluorescent (chemo)sensors are molecules that register changes in their “glow” (fluorescence ) when bound to an analyte (the substance of interest that is being studied), thus reporting the presence of that analyte. These changes can be detected with the naked eye. and/or instrumentation. Therefore, the presence of this invisible substance can now be detected. Fluorescent sensors are generally more sensitive and have lower limits of detection for a particular analyte compared to colorimetric sensors. Anions—chemical entities with an overall negative charge—are found everywhere and are involved in numerous chemical, biological, and industrial processes. As an example, cavity-fighting kinds of toothpaste and gels contain anion and fluoride. Additionally, chemical compounds containing anions, nitrate and phosphate are used in fertilizers. In this piece, Dr. Nicola Edwards discusses her ongoing work on developing fluorescent sensors for anions.
26
Durkin, Kathleen Anne, Richard Francis Langler e Nancy Ann Morrison. "Sulfonyl esters 1: The reduction of tribromophenyl sulfonates with mercaptide anions". Canadian Journal of Chemistry 66, n. 12 (1 dicembre 1988): 3070–76. http://dx.doi.org/10.1139/v88-475.
Testo completoAbstract (sommario):
2,4,6-Tribromophenyl sulfonates have been shown to undergo unusually efficient reduction by mercaptide anions in hexamethylphosphoramide. The reduction products include the sulfinate anion derived from the sulfonate ester and the disulfide derived from the mercaptide anions.
27
Marin, B. P., e X. Gidrol. "Chloride-ion stimulation of the tonoplast H+-translocating ATPase from Hevea brasiliensis (rubber tree) latex. A dual mechanism". Biochemical Journal 226, n. 1 (15 febbraio 1985): 85–94. http://dx.doi.org/10.1042/bj2260085.
Testo completoAbstract (sommario):
The effect of Cl- and other anions on the tonoplast H+-translocating ATPase (H+-ATPase) from Hevea brasiliensis (rubber tree) latex was investigated. Cl- and other anions stimulated the ATPase activity of tightly sealed vesicles prepared from Hevea tonoplast, with the following decreasing order of effectiveness: Cl- greater than Br- greater than SO4(2-) greater than NO3-. As indicated by the changes of the protonmotive potential difference, anion stimulation of tonoplast H+-ATPase was caused in part by the ability of these anions to dissipate the electrical potential. This interpretation assumes not a channelling of these anions against a membrane potential, negative-inside, but a modification of the permeability of these ions through the tonoplast membrane. In addition, Cl- and the other anions stimulated the ATPase activity solubilized from the tonoplast membrane. Consequently, the tonoplast H+-pumping ATPase can be considered as an anion-stimulated enzyme. These results are discussed in relation to various models described in the literature for the microsomal H+-ATPase systems claimed as tonoplast entities.
28
Jarjis, Hayfa M., e Salim M. Khalil. "MINDO-Forces Study of Phenyl and Cyclopropyl Substituted Allyl Cations and Anions". Zeitschrift für Naturforschung A 42, n. 3 (1 marzo 1987): 297–304. http://dx.doi.org/10.1515/zna-1987-0317.
Testo completoAbstract (sommario):
MINDO-force calculations have been performed on phenyl and cyclopropyl substituted allyl cations and anions with complete energy minimization. It is found that the phenyl ring destabilizes the allyl cations when substituted at the terminal and at the center carbon atom of the cation, while the cyclopropyl ring stabilizes the allyl cation when substituted at the terminal carbon atoms, but destabilizes the cation when substituted at the center carbon atom of the cation. These results agree with the experimental ones. In the case of the allyl anions, it is found that the phenyl ring destabilizes the allyl anions when substituted on the terminal and on the center carbon atoms of the allyl anions, while the cyclopropyl ring stabilizes the allyl anion when substituted on the terminal carbon atom but destabilizes the anion when substituted on the center carbon atom. Also, it is found that both the phenyl and cyclopropyl rings are electron withdrawing when substituted on the allyl anions, while they are electron donating when substituted on the allyl cations.
29
Stafström, Sven. "GEOMETRICAL AND ELECTRONIC STRUCTURE OF C60 ANIONS". International Journal of Modern Physics B 06, n. 23n24 (dicembre 1992): 3853–58. http://dx.doi.org/10.1142/s0217979292001924.
Testo completoAbstract (sommario):
The geometrical and electronic structure of various C 60 anions is calculated using a model which couples the bond length to the bond order and to Coulomb interactions between adjacent sites. The total energy of the C 60 anions is minimized with respect to variations in the bond length. The geometrical relaxations of the anions, relative to the neutral molecule, are such that the symmetry of the molecule is lowered (Jahn-Teller distortion). In the case of the mono-anion and the di-anion, the geometrical distortions and the charge are localized to one equatorial line around the spherical molecule. We term this type of self-localized defect a cyclon. The distortions of higher anions are best described as resulting from interacting cyclons. These distortions and the corresponding charges are delocalized over practically the whole system. The Jahn-Teller distortions of the C 60 anions result in a breaking of the degeneracy of the electronic levels and, generally speaking, a broadening of the peaks in the density of states compared to neutral C 60.
30
Keshavarzi, Ezat, e Mahsa Abareghi. "The Effect of Stern Layer Thickness on the Diffuse Capacitance for Size Asymmetric Electrolyte inside the Charged Spherical Cavities by Density Functional Theory". Journal of The Electrochemical Society 169, n. 2 (1 febbraio 2022): 020547. http://dx.doi.org/10.1149/1945-7111/ac52fe.
Testo completoAbstract (sommario):
The Modified Fundamental Measure Theory was used within the Primitive Model to determine Stern layer thickness in charged spherical cavity. The different behaviors for mean electric potential in Stern region with those one in the diffuse region was considered as the best criteria to determine this thickness. Depending on concentration, ion charge and size, and cavity charge the cations or anions may be found at the closest distance from the cavity’s wall, which lead two values for Stern thickness. In the present case study in which anions are assumed to be larger than cations, at zero or low positive values of cavity surface charge, the cations are found at the cavity wall, although the anion’s contact density is larger. But, by increasing the surface charge to a specific level, the cations are repelled away from the wall so that Stern thickness increases and becomes equal to anion radius. It is shown that this specific surface charge decreases not only with anion size, concentration and cation charge but also with rising cavity curvature. Also, we studied that how the diffuse capacitance for size-asymmetric electrolytes is affected by variation in Stern layer thickness.
31
Zhou, Benhua, e Hongxia Liu. "Tetrakis(4-chloroanilinium) hexachloridostannate(IV) dichloride". Acta Crystallographica Section E Structure Reports Online 68, n. 6 (19 maggio 2012): m782. http://dx.doi.org/10.1107/s1600536812021666.
Testo completoAbstract (sommario):
The asymmetric unit of the title compound, (C6H7ClN)4[SnCl6]Cl2, comprises two 4-chloroanilinium cations, half of an [SnCl6]2− anion and a Cl− anion. The SnIV atom, located on a special position on a twofold rotation axis, exhibits an octahedral environment. In the crystal, molecules are linked by N—H...Cl hydrogen bonds between the 4-chloroanilinium cations, [SnCl6]2− anions and Cl− anions.
32
Pitchay*, Dharmalingam S., Jonathan M. Frantz e James C. Locke. "Anion Species in Fertilizers Affect Growth and Development in Bedding Plants". HortScience 39, n. 4 (luglio 2004): 776E—777. http://dx.doi.org/10.21273/hortsci.39.4.776e.
Testo completoAbstract (sommario):
Currently, formulation of inorganic fertilizers is based on cation amounts such as NH4, K, Mg, Ca, Fe, MN Cu, and Zn, whereas anion species and amounts are viewed, with few exceptions, as necessary fillers. The delivery of cations in the nutrient solution is associated with an anion such as Cl, SO4, NO3, PO4 or CO3. These anions at higher concentrations can result in different growth responses by altering the rhizosphere pH, soluble salts, and influencing the uptake of both cations and anions. The impact of these anions has not been extensively studied in the formulation of inorganic fertilizers. Several experiments assessed the effect of SO4 and Cl on root and shoot growth and development of bedding plants represented by petunia, impatiens, and vinca. In all treatments, plant height, shoot and root dry weight, and flower number decreased with an increase in Cl concentration. Root morphology was marked by fewer total roots and shorter primary and secondary roots when grown with Cl anions compared to the plants grown with SO4 anions. This indicates that anions have a larger role in determining optimum fertilizer formulation than previously believed. This information provides an additional tool in formulating fertilizers for greenhouse bedding plant production.
33
Qi, Ting, Zhen-Bing Si, Li-Juan Liu, Hong-Mei Yang, Zhou Huang, Hua-Qing Yang e Chang-Wei Hu. "Mechanistic study of cellobiose conversion to 5-hydroxymethylfurfural catalyzed by a Brønsted acid with counteranions in an aqueous solution". Physical Chemistry Chemical Physics 22, n. 17 (2020): 9349–61. http://dx.doi.org/10.1039/c9cp06944e.
Testo completoAbstract (sommario):
In the cellobiose conversion to HMF catalyzed by Brønsted acid, the halide anions (Cl− and Br−) act as promoters, whereas both NO3− anion and the carboxylate-containing anions behave as inhibiters.
34
Tamao, Kohei, Atsushi Kawachi, Yoko Tanaka, Hitoshi Ohtani e Yoshihiko Ito. "Synthetic applications of functionalized silyl anions: Aminosilyl anions as hydroxy anion equivalent". Tetrahedron 52, n. 16 (aprile 1996): 5765–72. http://dx.doi.org/10.1016/0040-4020(96)00212-8.
Testo completo
35
Shafei, Gamal M. S. El, e Christine A. Philip. "Solid Acids from Persulphated and Perchlorated Physical Mixtures of Zirconium and Titanium Hydroxides". Adsorption Science & Technology 20, n. 10 (dicembre 2002): 977–93. http://dx.doi.org/10.1260/026361702321705267.
Testo completoAbstract (sommario):
Calcination at 650°C of a physical mixture of zirconium and titanium hydroxides led to the formation of the corresponding oxides, monoclinic zirconia and anatase. The adsorption of perchlorate or persulphate anions (as 0.05, 0.1, 0.2 or 0.4 M aqueous solutions) before calcination did not inhibit crystallization; however, perchlorate anions activated the formation of rutile in addition to the predominant anatase phase. Indeed, the adsorption of perchlorated anions prior to calcination allowed the thermodynamically less stable tetragonal phase of zirconia to be detected in addition to monoclinic zirconia at ambient temperature. In contrast, the adsorption of persulphate anions before calcination stabilized the tetragonal phase with no rutile phase being detected in this case. Infrared spectroscopy showed that adsorbed S2O82– anions were held more strongly by the solid than ClO4− anions which tended to decompose when the solid was calcined. The acidities of the solid acids produced because of S2O82– or ClO4−anion adsorption were studied via the adsorption of pyridine (pKa = 5.3) from cyclohexane solution. The amounts and strengths of the acid sites formed during persulphate treatment were higher than those resulting from perchlorate adsorption. The strength of the acid sites formed on samples calcined before loading with S2O82– or ClO4− anions showed no significant differences. Variations detected in the structural aspects arising from S2O82– or ClO4− anion adsorption were reflected in the texture as assessed by nitrogen adsorption at −196°C.
36
Flood, Amar H. "Creating molecular macrocycles for anion recognition". Beilstein Journal of Organic Chemistry 12 (31 marzo 2016): 611–27. http://dx.doi.org/10.3762/bjoc.12.60.
Testo completoAbstract (sommario):
The creation and functionality of new classes of macrocycles that are shape persistent and can bind anions is described. The genesis of triazolophane macrocycles emerges out of activity surrounding 1,2,3-triazoles made using click chemistry; and the same triazoles are responsible for anion capture. Mistakes made and lessons learnt in anion recognition provide deeper understanding that, together with theory, now provides for computer-aided receptor design. The lessons are acted upon in the creation of two new macrocycles. First, cyanostars are larger and like to capture large anions. Second is tricarb, which also favors large anions but shows a propensity to self-assemble in an orderly and stable manner, laying a foundation for future designs of hierarchical nanostructures.
37
Liu, Shang Lin, Qing Shan Li e Wen Feng Lv. "Measuring Air Anion Concentration and Researching Development of Forest Health Tourism in Riyuexia National Forest Park". Applied Mechanics and Materials 320 (maggio 2013): 743–47. http://dx.doi.org/10.4028/www.scientific.net/amm.320.743.
Testo completoAbstract (sommario):
In this paper, air Anions functions such as cleaning air, resisting bacteria, health care and the seven evaluation criteria system of the air anions concentration were introduced. Air Anion Concentration of Riyuexia National Forest Park in Heilongjiang province was Measured and analyzed. After comparing the result of 10 samples to the Anions evaluation system we can see that the air quality of Riyuexia National Forest Park is very fresh, it helps to health and is fit for some ecotourism activities such as health preservation of forest and fresh air bath. The paper proposes that we should preserve forest and water tourism resources, construct featured green eco-system and publish air anion Concentration index regularly.
38
Zhang, Jian-Feng, Bo Wan, Wen Liu e Qian Shi. "Diaquadi-μ-formato-bis{μ-2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenolato}cadmium(II)dinickel(II) dihydrate". Acta Crystallographica Section E Structure Reports Online 68, n. 8 (28 luglio 2012): m1122—m1123. http://dx.doi.org/10.1107/s1600536812029583.
Testo completoAbstract (sommario):
In the centrosymmetric title compound, [CdNi2(C17H16N2O2)2(HCOO)2(H2O)2]·2H2O, The NiIIcation is chelated by a 2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenolate (salpn) anion, and further coordinated by a formate anion and a water molecule in a distorted NiN2O4octahedral geometry. The CdIIcation, located on an inversion center, is coordinated by four deprotonated hydroxy groups from two salpn anions and two carboxylate O atoms from formate anions in a distorted octahedral geometry. Both formate and salpn anions bridge the Cd and Ni cations, forming a trinuclear complex. Within the salpn anion, the benzene rings are twisted to each other at a dihedral angle of 61.46 (18)°. Intermolecular O—H...O hydrogen bonding is present in the crystal structure. The lattice water molecule is disorder over two positions with an occupancy ratio of 0.75:0.25.
39
Wang, Huali, Sichen Gu, Ying Bai, Shi Chen, Na Zhu, Chuan Wu e Feng Wu. "Anion-effects on electrochemical properties of ionic liquid electrolytes for rechargeable aluminum batteries". Journal of Materials Chemistry A 3, n. 45 (2015): 22677–86. http://dx.doi.org/10.1039/c5ta06187c.
Testo completoAbstract (sommario):
Anion-effects are embodied in: (1) halogen anions resulting from different halogenated imidazole salt species, which is the critical factor for electrochemical windows; (2) aluminum chloride anions resulting from different AlCl3/imidazole salt mole ratios, which is the determinant of electrochemical activities.
40
Siegel, Marshall M., e Norman B. Colthup. "Molecular Orbital Study of Remote Charge Site Decompositions in the Collision-Induced Decomposition Mass Spectra of Fatty Acid Carboxylate Anions". Applied Spectroscopy 42, n. 7 (settembre 1988): 1214–21. http://dx.doi.org/10.1366/0003702884429887.
Testo completoAbstract (sommario):
Molecular orbital calculations were used to study the energetics of four different mechanisms used to explain the collision-induced decomposition mass spectra of saturated fatty acid carboxylate anions produced by fast atom bombardment and chemical ionization. The most abundant homologous series of anions, terminally unsaturated carboxylate anions, arose from the concerted cleavage of gauche segments of the hydrocarbon backbone via a sixatom transition state. A series of anions of lower abundance arose by homolytic cleavage of anti segments of the hydrocarbon backbone into two radical fragments. The loss of methane from the parent anion is produced by the concerted cleavage of the terminal methyl group via a four-atom transition state. The computed activation energies for the reaction mechanisms were in the following order: sixatom transition state < four-atom transition state ≪ homolytic cleavage of hydrocarbon backbone. Dehydration of the parent anion is rationalized to occur by loss of a carboxylate oxygen and two hydrogen atoms on the alpha carbon from the carboxylate carbon.
41
Bull, James N., Christopher W. West e Jan R. R. Verlet. "On the formation of anions: frequency-, angle-, and time-resolved photoelectron imaging of the menadione radical anion". Chemical Science 6, n. 2 (2015): 1578–89. http://dx.doi.org/10.1039/c4sc03491k.
Testo completoAbstract (sommario):
Frequency-, angle-, and time-resolved photoelectron imaging of gas-phase menadione (vitamin K3) radical anions is used to show that quasi-bound resonances of the anion can act as efficient doorway states to produce metastable ground electronic state anions on a sub-picosecond timescale.
42
Noushija, Mannanthara Kunhumon, Ananthu Shanmughan, Binduja Mohan e Sankarasekaran Shanmugaraju. "Selective Recognition and Reversible “Turn-Off” Fluorescence Sensing of Acetate (CH3COO−) Anion at Ppb Level Using a Simple Quinizarin Fluorescent Dye". Chemistry 4, n. 4 (29 ottobre 2022): 1407–16. http://dx.doi.org/10.3390/chemistry4040092.
Testo completoAbstract (sommario):
A simple and cost-effective optical sensing system based on quinizarin fluorescent dye (QZ) for the selective and reversible sensing of CH3COO− anions is reported. The anion binding affinity of QZ towards different anions was monitored using electronic absorption and fluorescence emission titration studies in DMSO. The UV-visible absorption spectrum of QZ showed a decrease in the intensity of the characteristic absorption peaks at λ = 280, 323, and 475 nm, while a new peak appeared at λ = 586 nm after the addition of CH3COO− anions. Similarly, the initial strong emission intensity of QZ was attenuated following titration with CH3COO− anions. Notably, similar titration using other anions, such as F−, Cl−, I−, NO3−, NO2−, and H2PO4-, caused no observable changes in both absorption and emission spectra. The selective sensing of CH3COO− anions was also reflected by a sharp visual color change from bright green to faint green under room light. Further, the binding was found to be reversible, and this makes QZ a potential optical and colorimetric sensor for selective, reversible, and ppb-level detection of CH3COO− anions in a DMSO medium.
43
Makuc, Damjan, Jennifer R. Hiscock, Mark E. Light, Philip A. Gale e Janez Plavec. "NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas". Beilstein Journal of Organic Chemistry 7 (2 settembre 2011): 1205–14. http://dx.doi.org/10.3762/bjoc.7.140.
Testo completoAbstract (sommario):
The conformational properties of 1,3-diindolylureas and thioureas were studied by a combination of heteronuclear NMR spectroscopy and quantum mechanics calculations. NOE experiments showed that the anti–anti conformer along the C7–N7α bonds was predominant in DMSO-d 6 solution in the absence of anions. Anion-induced changes in the 1H and 15N chemical shifts confirm the weak binding of chloride anions with negligible conformational changes. Strong deshielding of ureido protons and moderate deshielding of indole NH was observed upon the addition of acetate, benzoate, bicarbonate and dihydrogen phosphate, which indicated that the predominant hydrogen bond interactions occurred at the urea donor groups. Binding of oxo-anions caused conformational changes along the C7–N7α bonds and the syn–syn conformer was preferred for anion–receptor complexes. The conformational changes upon anion binding are in good agreement with energetic preferences established by ab initio calculations.
44
Ngatijo, Ngatijo, Diah Riski Gusti, Abdurrazaq Habib Fadhilah e Resilta Khairunnisah. "Adsorben Magnetit Terlapis Dimerkaptosilika untuk Adsorpsi Anion Logam [AuCl4]- dan [Cr2O7]-". Jurnal Riset Kimia 11, n. 2 (27 agosto 2020): 113–20. http://dx.doi.org/10.25077/jrk.v11i2.353.
Testo completoAbstract (sommario):
Adsorbent magnetite-dimercapto-silica (Fe3O4 - DMS) is a synthesis of magnetite with 2,3-dimercapto-1-propanol which has been applied to adsorb anions [AuCl4] - and [Cr2O7]-2. The adsorption process of metal anion [AuCl4]- at pH 5 with a contact time of 100 minutes was found optimum results at an adsorption capacity of 77.58 mg/g and an adsorption efficiency value of 96.975%. While the optimum conditions of metal anion [Cr2O7]-2 after the adsorption process at pH 4 with a contact time of 90 minutes was found an adsorption capacity of 85.0426 mg/g and an adsorption efficiency value of 85.0426%. The adsorption efficiency of metal anions [AuCl4]- is higher than the adsorption efficiency of metal anions [Cr2O7] -2
45
Ren, Xiaoming, e Peter G. Pickup. "Ion–polymer interactions in polypyrrole films". Canadian Journal of Chemistry 75, n. 11 (1 novembre 1997): 1518–22. http://dx.doi.org/10.1139/v97-182.
Testo completoAbstract (sommario):
Formal potentials from cyclic voltammetry and ionic conductivities from impedance measurements are used to probe anion–polymer interactions in electrochemically deposited films of polypyrrole. Hard anions (F−, Cl−, ClO4−) stabilize the oxidized form of the polymer more than soft anions (I−, SCN−). Anions of weak acids (F− and CN−) interact with the polymer particularly strongly and exhibit anomalously low mobilities. Hydrogen bonding with the N-H groups of oxidized polypyrrole is proposed. Keywords: conducting polymer, polypyrrole, impedance, ion transport, electrolyte effects, ion exchange.
46
Yadav, Monalisa, Hong Fang, Santanab Giri e Puru Jena. "Ligand stabilization of manganocene dianions – in defiance of the 18-electron rule". Physical Chemistry Chemical Physics 21, n. 44 (2019): 24300–24307. http://dx.doi.org/10.1039/c9cp02331c.
Testo completoAbstract (sommario):
Di-anions of manganocene derivatives complexes, in spite of being a 19-electron system, are found to be more stable than their mono-anions. This defiance of the 18-electron rule is linked to the geometrical distortion of the di-anion, akin to the Jahn-Teller-like mechanism.
47
Li, Chongyang, Yongli Huang, Chang Q. Sun e Lei Zhang. "Acidic Stabilization of the Dual-Aromatic Heterocyclic Anions". Catalysts 11, n. 7 (24 giugno 2021): 766. http://dx.doi.org/10.3390/catal11070766.
Testo completoAbstract (sommario):
Recently, we discovered that the delocalization of nitrogen lone-pair electrons (NLPEs) in five-membered nitrogen heterocycles created a second σ-aromaticity in addition to the prototypical π-aromaticity. Such dual-aromatic compounds, such as the pentazole anion, were proved to have distinct chemistry in comparison to traditional π-aromatics, such as benzene, and were surprisingly unstable, susceptible to electrophilic attack, and relatively difficult to obtain. The dual-aromatics are basic in nature, but prefer not to be protonated when confronting more than three hydronium/ammonium ions, which violates common sense understanding of acid−base neutralization for a reason that is unclear. Here, we carried out 63 test simulations to explore the stability and reactivity of three basic heterocycle anions (pentazole anion N5¯, tetrazole anion N4C1H1¯, and 1,2,4-triazole anion N3C2H2¯) in four types of solvents (acidic ions, H3O+ and NH4+, polar organics, THF, and neutral organics, benzene) with different acidities and concentrations. By quantum mechanical calculations of the electron density, atomistic structure, interatomic interactions, molecular orbital, magnetic shielding, and energetics, we confirmed the presence of dual aromaticity in the heterocyclic anions, and discovered their reactivity to be a competition between their basicity and dual aromaticity. Interestingly, when the acidic ions H3O+/NH4+ are three times more in number than the basic heterocyclic anions, the anions turn to violate acid−base neutralization and remain unprotonated, and the surrounding acidic ions start to show a significant stabilization effect on the studied heterocyclic anions. This work brings new knowledge to nitrogen aromatics and the finding is expected to be adaptable for other pnictogen five-membered ring systems.
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Moriyoshi, Chikako, Hirokazu Hoashi, Hiroaki Sato, Masatoshi Takegawa, Eisaku Nii, Ryo Sasai e Yoshihiro Kuroiwa. "Structure and Anion Exchangeability of Ni-Al-Type Layered Double Hydroxides". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C915. http://dx.doi.org/10.1107/s2053273314090846.
Testo completoAbstract (sommario):
Layered double hydroxide (LDH) is one of promising inorganic materials for cleaning the environmental water polluted by toxic anions. The crystal structure of LDH is composed of the positively-charged metal hydroxide nanosheets and the anions with water molecules intercalated between the nanosheet layers. To put LDHs for practical use, it is necessary to understand why only special anions can be intercalated into the crystal structure from the aqueous solution. In this study, the anion exchange experiments and the synchrotron radiation x-ray powder diffraction measurements of Ni-Al-type LDHs of several kinds of Ni/Al ratios with chlorine and nitrate anions were performed to investigate the relationship between the anion exchange selectivity and crystal structures. The nitrate ion selectivity is normally poor in most of LDHs with different metal ions in the hydroxide nanosheet [1]. However, the nitrate ions were preferred to the chlorine ions in Ni-Al-type LDH when Ni/Al = 4, whereas the chlorine ions were selected when Ni/Al = 2. The crystal structure analysis revealed that the interlayer distance decreased and the thermal motion of the nitrate ions suppressed in Ni-Al-nitrate-type LDH with increasing the Ni/Al ratio, whereas those of the chlorine ions in Ni-Al-chlorine-type LDH increased and enhanced with increasing the Ni/Al ratio. These results indicate that the nitrate ions are more stable than the chlorine ions in the crystal structure of the Ni-Al-type LDH when the positive charge of the nanosheet is small, i.e. the number of anions is small. The short interlayer distance and the small thermal vibration of anions in the crystal structure are the key to understand the anion selectivity of LDH.
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Tepuš, Brigita, e Marjana Simonič. "Uncertainty of nitrate and sulphate measured by ion chromatography in wastewater samples". Open Chemistry 5, n. 2 (1 giugno 2007): 557–69. http://dx.doi.org/10.2478/s11532-007-0002-3.
Testo completoAbstract (sommario):
AbstractThis paper presents an evaluation of measurement uncertainty regarding the results of anion (nitrate and sulphate) concentrations in wastewater. Anions were determined by ion chromatography (EN ISO 10304-2, 1996). The major sources of uncertainty regarding the measurements’ results were identified as contributions to linear least — square or weighted regression lines, precision, trueness, storage conditions, and sampling. Determination of anions in wastewater is very important for the purification procedure, especially the amount of nitrate in waste and potable waters. The determined expanded uncertainty was 6.1 % for nitrate anions and 8.3 % for sulphate anions. The difference between measurement uncertainties determined by the two methods, the weighted and linear least — square methods, is negligible.
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Maslowska-Jarzyna, Krystyna, Maria L. Korczak, Jakub A. Wagner e Michał J. Chmielewski. "Carbazole-Based Colorimetric Anion Sensors". Molecules 26, n. 11 (27 maggio 2021): 3205. http://dx.doi.org/10.3390/molecules26113205.
Testo completoAbstract (sommario):
Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.