Stability Of Anions Research Articles

Fragmentation of deprotonated nitrophenol anions

This work examined the dissociation reactions and energetics of deprotonated nitrophenols. All species were generated using an atmospheric pressure chemical ionization source and were studied using tandem mass spectrometry. Collision induced dissociation studies revealed three common fragments: C6H4O−, NO2−, and C6H4O2−. Energy dependent collision induced dissociation showed the formation of C6H4O2− by the loss of NO is the lowest energy pathway for each isomer. The CN dissociation energy to yield NO2− is large, and is due to the stability of the nitrophenoxide anion.

Preferential geminal bis-silylation of 3,4-benzothiophane is caused by the dominance of electron withdrawal by R3Si over steric shielding effects.

Benzylic C–H lithiation of 3,4-benzothiophane and subsequent treatment with triphenyl- or trimethylchlorosilane under a variety of conditions leads to α,α- rather than α,α′-bis-silylation products as a consequence of anion stabilization by R3Si and very fast deprotonation of the intermediate monosilylated product, even with a sterically bulky base such as lithium diisopropylamide.

Synthesis and Survey Magnetic Properties of Fe2O3 Nanoparticles Coated With Different Surfactant

Fe2O3 nanoparticles were synthesized using a modified coprecipitation technique. For the optimal results, Ferric chloride was added to different surfactant with different ratio of metal ions/surfactant. Surfactants were employed with various charge such as anionic cetyl trimethyl ammonium bromide (CTAB), cationic sodium dodecyl sulfate (SDS), and neutral TritonX-100. The size and crystalline structure of these nanoparticles were controlled by changing the surfactant and ratio of metal ions/surfactant. Anionic stabilizer leads to smallest size and narrowest size distribution and the most crystalline. The samples were characterized using transmission electron microscopy, X-ray diffraction, FT-IR spectroscopy, and vibrating sample magnetometer.

A preorganized hydrogen bond network and its effect on anion stability.

Rigid tricyclic locked in all axial 1,3,5-cyclohexanetriol derivatives with 0-3 trifluoromethyl groups were synthesized and photoelectron spectra of their conjugate bases and chloride anion clusters are reported along with density functional computations. The resulting vertical and adiabatic detachment energies span 4.07-5.50 eV (VDE) and 3.75-5.00 (ADE) for the former ions and 5.60-6.23 eV (VDE) and 5.36-6.00 eV (ADE) for the latter species. These results provide measures of the anion stabilization due to the hydrogen bond network and inductive effects. The latter mechanism is found to be transmitted through space via hydrogen bonds, and the presence of three ring skeleton oxygen atoms and up to three trifluoromethyl groups enhance the ADEs by 1.61-2.88 eV for the conjugate bases and 1.01-1.60 eV for the chloride anion clusters. Computations indicate that the most favorable structures of the latter complexes have two hydrogen bonds to the chloride anion and one bifurcated interaction between the remote OH substituent and the two hydroxyl groups that directly bind to Cl(-).

A role of lithiated sarcosine TFSI on the formation of single crystalline SrTiO3 nanocubes via hydrothermal method

Effective capping activity of lithiated sarcosine TFSI on the formation of single crystalline SrTiO3 nanocubes via hydrothermal method has been investigated. Lithiated sarcosine TFSI formation by zwitterionic transformation was confirmed by NMR and FTIR studies. 13C and 7Li NMR studies showed the stabilization of metal hydroxide anions by the secondary ammonium cations (–NH2+–) of lithiated sarcosine. The FESEM results revealed the formation of SrTiO3 nanocubes. TEM images showed the spherical and square shaped defects within the round edged cubic particles with the average size of 90nm and SAED pattern indicates the single crystalinity. The crystalinity and nanocubic shape of SrTiO3 were strongly influenced by lithiated sarcosine TFSI. Hence, we propose lithiated sarcosine TFSI as an effective capping agent for the synthesis of single crystalline SrTiO3 nanocubes.

Photoelectron spectroscopic and computational study of hydrated pyrimidine anions.

The stabilization of the pyrimidine anion by the addition of water molecules is studied experimentally using photoelectron spectroscopy of mass-selected hydrated pyrimidine clusters and computationally using quantum-mechanical electronic structure theory. Although the pyrimidine molecular anion is not observed experimentally, the addition of a single water molecule is sufficient to impart a positive electron affinity. The sequential hydration data have been used to extrapolate to -0.22 eV for the electron affinity of neutral pyrimidine, which agrees very well with previous observations. These results for pyrimidine are consistent with previous studies of the hydrated cluster anions of uridine, cytidine, thymine, adenine, uracil, and naphthalene. This commonality suggests a universal effect of sequential hydration on the electron affinity of similar molecules.

Structure and stability of phenoxide and fluorophenoxide anions investigated with infrared multiple-photon dissociation and detachment spectroscopy and tandem mass spectrometry.

The gas-phase infrared multiple-photon dissociation and detachment (IRMPD) vibrational action spectra of the unsubstituted phenoxide anion and a series of fluorine- and trifluoromethyl-substituted phenoxide anions in the spectral region between 600 and 1800 cm(-1) are presented along with density functional theory (DFT) harmonic vibrational frequency calculations to establish the characteristic vibrations of the phenoxide functionality. The fluorophenoxide anions studied include the conjugate bases of o-, m-, and p-fluorophenol (C6H4FO(-)) as well as o-, m-, and p-α,α,α-trifluorocresol (CF3C6H4O(-)). The influence of the substituent on the characteristic vibrational frequencies is interpreted in terms of inductive and resonance shifts. In addition to the dissociation induced by infrared multiple-photon excitation, the electron detachment is also shown to play an important role in the decomposition of the unsubstituted phenoxide. It is demonstrated that the amount of electron detachment relative to dissociation is strongly mitigated by fluorination, and interpretations aided by DFT energy calculations suggest this is primarily due to the increased availability of low-energy dissociation pathways in the substituted phenoxides. Collision-induced dissociation (CID) mass spectrometry of the parent ions is used to estimate relative energies of the dissociation processes, and particular fragmentation motifs are elucidated. In particular, overall HF and CO losses provide facile decomposition pathways, yielding interesting fragment ions such as C6H(-) or C3H2FO(-) from the CF3C6H4O(-) parent anions.

Influence of anionic stabilization of alumina particles in 2-propanol medium on the electrophoretic deposition and mechanical properties of deposits

Abstract The ceramic dispersions were prepared using 0.85, 1.70, 4.25, 12.75 or 21.25 wt.% of monochloroacetic, dichloroacetic or trichoroacetic acid, 15 wt.% alumina and 2-propanol. The mechanism of anionic stabilization in 2-propanolic media was described. Alumina green bodies were prepared from the stable dispersion via electrophoretic deposition (EPD). It was found that increasing dispersion conductivity significantly influenced the EPD yields. The most effective electrophoretic depositions were performed from dispersions with conductivity in range 4.0–5.3 × 10 −4 S m −1 . Deposits with the highest green density were prepared from the dispersion stabilized by trichloroacetic acid. This behavior was explained by low voltage drop during deposition. The surface roughness was high at low dispersion conductivity and with increasing acid concentration in dispersion the surface of deposits was smoother. The mechanism of particle arrangement in deposit was discussed. Influence of stabilizer amount in the dispersion on the hardness and fracture toughness was described.

DFT Study of the Effects of Halogen Anions on the Stability of Alanine Zwitterion

Alanine is the most abundant and important amino acid found in proteins, and is present on both the interior and exterior surface of proteins in contact with water. The structure of alanine has been studied both experimentally and theoretically by many researchers. Using a highpressure mass spectrometer (HPMS) and ab initio calculations, Wu et al. showed that certain organic ammonium ions are able to stabilize the zwitterionic structure of amino acids. Amino acids in aqueous solutions also exist in the zwitterionic form over a wide range of pH. However, they do not exist in the zwitterionic form in the gas phase. Zwitterions play an important role in variety of biological reactions. The electric fields of zwitterionic structures serve as the driving force that determines the activity of amino acids, peptides, and proteins. In particular, many drugs are present in their zwitterionic form and exhibit strong electrostatic interactions with protein receptors. Because of the instability of amino acid zwitterions in the gas phase, direct experimental evidence of their behavior is lacking; therefore, numerous attempts were made to stabilize gas-phase zwitterions. On the basis of ab initio calculations, Jensen et al. reported that two water molecules can stabilize the glycine zwitterion. Metalation and protonation also stabilize the amino acid zwitterions. Kass stabilized the zwitterionic glycine using oxalic and malonic dianions, which cannot exist independently in the gas phase. He also examined the utility of self-stabilized anionic species to stabilize amino acid zwitterionic structures. On the basis of this finding, and as continuation of our studies on organic radicals and alanine radical cations, we report the effects of halogen anions on the stability of the alanine zwitterion in this paper. All theoretical calculations on structures considered in this study were carried out with the Gaussian 09 series of programs. The relativistic effects play important roles in the Br and I elements, and accordingly their electrons near the nuclei are represented with the LanL2DZ basis set containing effective core potential (ECP). In accordance with ref 13, F and Cl elements were treated the same method as Br and I. DFT calculations were evaluated at the B3LYP level, and ab initio calculations were performed using the MP2 level of theory. Equilibrium geometries of each structures were fully optimized without any restriction on symmetries. Vibration frequencies were also calculated to confirm whether all the stationary points correspond to the true minima. The stationary structures were obtained by verifying if the harmonic frequencies for the local minimum were real. In this study, halogen anions (X = F−, Cl−, Br−, and I−) were used as the anionic stabilizer for zwitterionic alanine in the gas phase. Through interactions with binding sites of halogen anionic stabilizers (2X−), alanine zwitterions (AZW) can be stabilized and form AZW–2X− complexes. The dissociation energy (DE) of the AZW–2X− complexes were estimated using the following equation:

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

Abstract Gas-phase acidities of polyfluorinated hydrocarbons have been determined by measuring proton-transfer equilibria and by computing the free energies of deprotonated carbanions and the corresponding neutrals. An excellent linear relationship between acidities and the accumulated inductive effects of fluorine atoms contained in a molecule was observed for the perfluoroalkyl-substituted neopentanes, (Rf1)(Rf2)(Rf3)CCH3, and polyfluorinated bridgehead carbon acids where the contribution of negative hyperconjugation of the Cβ–F bond to the stability of the conjugate anions is absent or negligibly small. On the basis of this relationship, the extent of β-fluorine negative hyperconjugation involved in acidities of polyfluorinated hydrocarbons could be evaluated quantitatively. The negative hyperconjugation was found to be negligibly small in the stable tertiary polyfluorinated carbanions while in the less stable primary and secondary carbanions the contribution of this effect is present certainly, indicating that the negative fluorine hyperconjugation is complementary to the stabilization by the accumulated inductive effect of fluorine atoms. The extent of negative hyperconjugation was found to increase in order of CF3CH2− < C2F5CH2− ≈ C3F7CH2− < i-C3F7CH2−, being qualitatively consistent with the elongation of the Cβ–F bond by deprotonation. The effect of α-fluorine on acidity was found to change complicatedly with the carbanion, e.g., the α-fluorine substitution in CF3CH3 strengthens acidity, no effect in (CF3)2CH2, and strengthens again acidity in (i-C3F7)2CH2. Such varying effect of α-fluorine in the polyfluorinated hydrocarbons would be caused by a subtle balance of effective electronegativity of an anionic center carbon, a varying p–p lone pair repulsion depending on the net negative charge at the formal charge center carbon, and the change in ability of β-F negative hyperconjugation caused by α-F substitution.

Solubility and Stability of Superoxide Radical Anions in Room-Temperature Ionic Liquids

Because superoxide anion is easily decomposed by the presence of proton, it is known that superoxide anion only dissolves in specific highly polar aprotic solvents such as dimethylsulfoxide. Organic solvents are dangerous due to their high volatility and flammability, while ionic liquids possess inflammability, nonvolatility, and high ion conductivity. Additionally, in the area of organic synthesis, there is a potential for a new reaction media different from existing organic reaction media. Therefore, it would be attractive to use ILs as a new reaction media and an electrolyte of batteries. In this study, we studied solubility and stability of superoxide anion in five kinds of ILs. It was found that P14,6,6,6Cl was the most suitable solvent in terms of the solubility and stability of superoxide anion.

Thermal Stability and Fire Safety of Ionic Liquid-Based Electrolytes for Lithium-Ion Batteries

Due to environmental and energy concerns, batteries for electric vehicles are highly studied and developed. They are mainly based on lithium-ion technology, considered more efficient in energy density. Carbonate mixtures used as electrolyte solvents could lead to safety issues due to their high flammability and low flash points. Formulating electrolyte solutions with nonvolatile and nonflammable ionic liquids (ILs) instead of carbonate mixtures could be safer1 as they have low vapour pressure and high flash point.2 Moreover, they are good ionic conductors, present wide electrochemical window and high decomposition temperature (Td).3 But little information is available on their behaviour under abuse conditions like car crashes or any abnormal use (shortcut, overheat). In order to understand the possible decomposition mechanisms of ILs and their mixture with lithium salt during abuse tests, a thermodynamic study of these compounds was carried out. A critical literature study of the Td determined by thermogravimetric analysis (TGA) and consequent experiments highlighted the stability of the NTf2 anion combined with two cationic families: imidazolium and pyrrolidinium.4 We chose 1-butyl-3-methylimidazolium [C1C4Im] and 1-butyl-1-methylpyrrolidinium [PYR14] cations, bis(trifluoromethanesulfonyl)imide [NTf2] anion. The electrolytes were composed of their mixture with 1 mol.L-1 of LiNTf2 and referred to as [C1C4Im][Li][NTf2] and [PYR14][Li][NTf2]. Nevertheless, TGA does not give sufficient information on the nature of volatile emissions, so the thermal decomposition of [C1C4Im][NTf2] and [PYR14][NTf2] and their corresponding electrolytes was studied. Long term experiments with different techniques (2 to 15 h at 350°C) showed the highest stability of imidazolium-based solutions (Figure 1). For both families, the volatile decomposition products were mainly identified as butene isomers. Recombined alkyl cations (e.g. C1Im, C4Im, C4C4Im and C1C1Im) were detected in the residual liquid phases, implying that a degradation with no mass loss occurred.Figure 1: Long term stability test by TGA of IL-based electrolytes, neat ILs and lithium salt at 350 °C for 15 hFlammability and heat of combustion were studied with a fire propagation apparatus. The solutions were found very weakly combustible, and LiNTf2 showed a flame retardant effect. Flammable gases were emitted due to cation decomposition, and the anion decomposition formed toxic effluents.5 Figure 2: Heat release rate profiles of neat ILs and corresponding electrolytes showing good resistance to ignition (ca.5 min)Then the electrolytes [C1C4Im][Li][NTf2] and [PYR14][Li][NTf2] were used in batteries constituted of Li4Ti5O12 and LiNi1/3Co1/3Mn1/3O2 electrodes. The cells were submitted to abuse tests such as shortcut or overcharge. A specific setup coupled with a mass spectrometer was developed to analyse in situ the gaseous emissions.All these points will be developed during the communication.References 1 A. Lewandowski et al., J Power Sources, 2009, 194, 601. 2 A. O. Diallo et al., Sep Purif Technol, 2012, 97, 228. 3 P. Wasserscheid and T. Welton, Ionic liquids in synthesis, Wiley-VCH, 2003. 4 L. Chancelier et al., in preparation. 5 L. Chancelier et al., Phys. Chem. Chem. Phys., accepted.

Green and facile synthesis of Pt/{PW12-GN} composite film and its electrocatalytic activity for methanol oxidation

In this paper, H3PW12O40 (PW12)-functionalized graphene nanosheets (PW12-GNs) were prepared using a green and facile method via a UV-irradiated photoreduction process, in which PW12 was directly deposited on the GNs as a reductant and also as an anionic stabilizer. The as-prepared water-dispersive PW12-GN composite is used as matrices for electrodeposition of the interesting orchidlike Pt nanoclusters in situ. The PW12-GN composite was characterized by transmission electron microscopy (TEM) and cyclic voltammetry (CV). It was shown that the electrochemical properties of PW12 were maintained in PW12-GNs. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) confirmed that Pt had been deposited on the PW12-GN composite surface. Field emission scanning electron microscopy (FE-SEM) showed that the interesting orchidlike Pt nanoparticles were uniformly immobilized on the surface of the {PW12-GN} composite film. Cyclic voltammetry and chronoamperometric curves were used to study the electrocatalytic activity of Pt/{PW12-GN} regarding methanol oxidation in 0.5 M H2SO4. It is worthy of note that the Pt/{PW12-GN} composite film-modified electrode presents a high catalytic activity (j = 353 mA mg−1) and better tolerance of CO towards methanol electrooxidation.

Methotrexate intercalated layered double hydroxides with different particle sizes: Structural study and Controlled release properties

To study the influence of particle size on release properties, drug efficacy and other properties, a series of methotrexate intercalated layered double hydroxides (MTX/LDHs) nanohybrids with different particle sizes were synthesized through traditional coprecipitation method, by using the mixture of water and polyethylene glycol (volume ratio is 3:1) as solvent. The relationship between particle size and hydrothermal treatment conditions (i.e., time and temperature) had been systematically investigated, and the results indicate that the particle size can be precisely controlled between 70 and 300nm. Elemental C/H/N and inductive coupled plasma (ICP) analysis indicated that different hydrothermal treatment almost has no effect on compositions of the nanohybrids. X-ray diffraction (XRD) patterns and fourier transform infrared spectroscopy (FTIR) investigations manifested the successful intercalation of MTX anions. MTX/LDHs particles exhibited hexagonal platelet morphology with round corner, due to the adsorption of MTX anions on positively charged LDHs surface. In addition, the crystallinity of MTX/LDHs increased with the particle diameters and the thermal stability of MTX anions was enhanced by holding together with LDHs layers. The in vitro release showed that bigger particles have much longer release duration, and the bioassay tests indicated that bigger particles are more efficient in the suppression of the tumor cells.

Phenyl- and Thienyl-Ended Symmetric Azomethines and Azines as Model Compounds for n-Channel Organic Field-Effect Transistors: An Electrochemical and Computational Study

The formation energy and stability of radical anions in a series of 12 phenyl- and 2-thienyl-ended linear, symmetric azomethines and azines were investigated by cyclic voltammetry. Replacing 1,4-phenylene with 2,5-thienylene cores and substitution with cyano or methyl moieties have allowed the lowering of lowest unoccupied molecular orbital energy levels even by 1 eV. Methyl capping stabilizes electron carriers (radical anions) toward dimerization, and the mechanism of such radical anion dimerization has been clarified by cyclic voltammetric kinetic analysis. The results have been compared with optical parameters and supported by density functional theory calculations.

Organic acid formation in steam–water cycles: Influence of temperature, retention time, heating rate and O2

Organic carbon breaks down in boilers by hydrothermolysis, leading to the formation of organic acid anions, which are suspected to cause corrosion of steam–water cycle components. Prediction of the identity and quantity of these anions, based on feedwater organic carbon concentrations, has not been attempted, making it hard to establish a well-founded organic carbon guideline. By using a batch-reactor and flow reactor, the influence of temperature (276–352 °C), retention time (1–25 min), concentration (150–2400 ppb) and an oxygen scavenger (carbohydrazide) on organic acid anion formation from organic carbon was investigated. By comparing this to data gathered at a case-study site, the validity of setups was tested as well. The flow reactor provided results more representative for steam–water cycles than the batch reactor. It was found that lower heating rates give more organic acid anions as degradation products of organic carbon, both in quantity and species variety. The thermal stability of the organic acid anions is key. As boiler temperature increases, acetate becomes the dominant degradation product, due to its thermal stability. Shorter retention times lead to more variety and quantity of organic acid anions, due to a lack of time for the thermally less stable ones to degrade. Reducing conditions (or the absence of oxygen) increase the thermal stability of organic acid anions. As the feedwater organic carbon concentration decreases, there are relatively more organic acid anions formed.

Rearrangements Leading to Fragmentations of Hydrocinnamate and Analogous Nitrogen-Containing Anions Upon Collision-Induced Dissociation

Tandem mass spectrometry (MS/MS) confirmed decarboxylation as the major collision-induced dissociation (CID) pathway of deprotonated hydrocinnamic acid (C6H5CH2CH2CO2H), N-phenylglycine (C6H5NHCH2CO2H) and 3-pyridin-2-ylpropanoic acid (C5H4NCH2CH2CO2H). The structure and stability of isomeric precursor and product anions were examined using density functional theory and ab initio methods. Geometry optimizations and frequency calculations were performed using the B3LYP/6-31++G(2d,p) level of theory and basis set with additional single point energies calculated at the MP2/6-311++G(2d,p) level. The formation of a delocalized product anion by carboxyl group-mediated migration of a benzylic proton to the ortho position of the ring and subsequent Cα-CO2(-) bond cleavage was energetically more favorable than direct decarboxylation and rearrangements of anions within ion-neutral complexes with carbon dioxide. The energy barrier for rearrangement of the delocalized product anion to the more stable benzylic anion was lowest in the fragmentation pathway of 3-pyridin-2-ylpropanoate. More energetically demanding fragmentation processes were indicated by the formation of other product anions at higher collision energy. Computations supported the feasibility of the formation of hydroxycarbonyl, styrene, and phenide ions from the benzylic anion of hydrocinnamate and the corresponding product anions from the nitrogen-containing analogues. The loss of dihydrogen from decarboxylated 3-pyridin-2-ylpropanoate was characterized computationally as hydride abstraction of an aryl proton. Overall, the results highlight the importance of exploring rearrangements in the fragmentation pathways of ions formed by electrospray ionization (ESI).

Theoretical study on structure, conformation, stability and electronic transition of C4 and C5 anions of ascorbic acid stereoisomers

The structures, stabilities, conformational analysis and electronic transitions of l-ascorbic acid anions (four stereoisomers) were studied theoretically. These anions are produced from the de-protonation of C4–H and C5–H sites of l-ascorbic acid stereoisomers. The geometries of these anions were fully optimized in gas phase and aqueous phase in order to determine their relative stabilities. It was observed that the de-protonation at C5 site of two stereoisomers leads to the ring opening in both phases. Isomerization of the l-form to one of the d-form was observed during the optimization of the anions at C5. Conformational analysis (potential energy surface scan) of the opened ring anions was performed in search of energy minima and/or maxima. The absorption electronic transitions of the anions in the UV region were calculated using Time-Dependent Density Functional Theory (TD-DFT).

Insights into the reversible oxygen reduction reaction in a series of phosphonium-based ionic liquids.

New findings supporting the stability of the superoxide ion, O2˙(-), in the presence of the phosphonium cation, [P6,6,6,14](+), are presented. Extended electrochemical investigations of a series of neat phosphonium-based ILs with different anions, including chloride, bis(trifluoromethylsulfonyl)imide and dicyanamide, demonstrate the chemical reversibility of the oxygen reduction process. Quantum chemistry calculations show a short intermolecular distance (r = 3.128 Å) between the superoxide ion and the phosphonium cation. NMR experiments have been performed to assess the degree of long term degradation of [P6,6,6,14](+), in the presence of superoxide and peroxide species, showing no chemically distinct degradation products of importance in reversible air cathodes.

Extended Hückel Method Calculation of Polarization Energies: The Case of a Benzene Dimer

We adapted Hoffmann's extended Hückel method to an interacting molecular system and use this approach to compute the electron affinity and ionization potential of benzene dimers. We restrict the added charge to one of the molecules and argue that the dimer energy computed in this manner is the relevant energy in any meaningful thermally activated hopping rate expression. The dimer electron affinity and ionization potential differs from the isolated molecule corresponding quantity by what is called polarization energy. The polarization energy normally stabilizes the anion and this is particularly relevant for benzene, given that its isolated anion is unstable with respect to charge detachment. We found that the anionic benzene dimer is only stabilized in certain conformations, suggesting that the stabilization of a benzene anion in an amorphous environment is very unlikely. The modest computational cost of the method makes it a viable alternative to compute the energy of charged molecules in amorphous molecular films, a central issue in the problem of charge transport in organic electronics.