Rearrangement Of Ions Research Articles

On the limited electroactivity of Li2NiTiO4 nanoparticles in lithium batteries

The electroactivity of the rock-salt structure Li2NiTiO4 in lithium batteries containing LiBOB as electrolyte salt was examined. The compound exhibits a random distribution of the metal ions in octahedral 4a positions. The combined use of electrochemical impedance spectroscopy, step potential spectroscopy and thermogravimetric analysis revealed that the electrode undergoes various changes during the charging process. Thus, Ni(II) is initially oxidised to Ni(IV) through Ni(III) as an intermediate state over the region from OCV to 4.6V versus Li+/Li, which provides a high capacity (180mAhg−1). Upon charging, however, highly charged Ni(IV) ions hinder charge carrier motion in both ions and electrons. In fact, the lithium diffusion coefficient was also very low (DLi+≈10−17 cm2 s−1), which suggests a low ionic conductivity. From impedance studies, it seems that a quite stable polymer film is formed in the electrolyte/electrode interface during the first charge. The region between 4.6 and 4.8V exhibited an additional capacity of 23mAhg−1 that was assigned to the release of oxygen if the electrolyte oxidation at this stage is discarded. The electrode impedance increased three times after one cycle, which is consistent with irreversible rearrangement of lithium ions during the first oxidation process. Furthermore, a very resistive solid electrolyte interface is developed after a few cycles. Therefore, the capacity fading observed can be ascribed to deterioration of both, the electrolyte and the electrode conduction properties, by effect of hindered lithium and electron motion.

Reduction and Oxidation of Transition-Metal Oxide Thin Films: Solid-State Chemistry with Epitaxially Grown Thin Films

Abstract Reduction and oxidation of perovskite-structure transition-metal oxide thin films are highlighted. Oxygen ions are released from and incorporated into the perovskite-structure framework during the reduction and oxidation. Low-temperature topochemical reduction reaction with CaH2 enables us to prepare infinite-layer structure oxide thin films containing Fe and Ni. With the epitaxially grown thin film samples, anisotropic rearrangement and transfer of oxygen ions in the structures have been revealed. Selective reduction of layers in artificial superlattices was also found, and the observed behavior suggests that the oxygen-ion mobility in the artificial superlattices was confined within the two-dimensional brownmillerite layer. Specific structural features play important roles in the oxygen-ion transfer in solids at low temperatures. The obtained results would be a key to develop technologies related to energy and the environment.

Correlations of ion structure with multiple fragmentation pathways arising from collision‐induced dissociations of selected α‐hydroxycarboxylic acid anions

Under conditions of collision-induced dissociation (CID), anions of α-hydroxycarboxylic acids usually fragment to yield the distinctive hydroxycarbonyl anion (m/z 45) and/or the complementary product anion formed by neutral loss of formic acid (46 u). Further support for the known two-step mechanism, involving an ion-neutral complex for the formation of the hydroxycarbonyl anion from the carboxyl group, is herein provided by tandem mass spectrometric results and density functional theory computations on the glycolate, lactate and 3-phenyllactate ions. A fourth, structurally related α-hydroxycarboxylate ion, obtained by deprotonation of mandelic acid, showed only loss of carbon dioxide upon CID. Density functional theory computations on the mandelate ion indicated that similar energy inputs were required for a direct, phenyl-assisted decarboxylation and a postulated novel rearrangement to a carbonate ester, which yielded the benzyl oxide ion upon loss of CO2. Rearrangement of the glycolate ion led to expulsion of carbon monoxide, whereas the 3-phenyllactate ion showed the loss of water and formation of the benzyl anion and the benzyl radical as competing processes. The fragmentation pathways proposed for lactate and 3-phenyllactate are supported by isotopic labeling. The relative computed energies of saddle points and product ions for all proposed fragmentation pathways are consistent with the energies supplied during CID experiments and the observed relative intensities of product ions. The diverse reaction pathways characterized for this set of four α-hydroxycarboxylate ions demonstrate that it is crucial to understand the effects of structural variations when attempting to predict the gas-phase reactivity and CID spectra of carboxylate ions.

On the mechanisms of radiation damage and prospects of their suppression in complex metal oxides

AbstractThe influence of some impurity ions on the increase/decrease in the resistance against irradiation of metal oxides with X‐rays and electrons (low‐dense excitation) or ∼2 GeV Au198 and U238 ions providing a superhigh density of electronic excitations along cylindrical tracks (LET > 30 keV nm−1) has been investigated for fcc MgO single crystals with close ion masses or Lu3Al5O12 and Gd2SiO5 with large unit cells and heavy cations. The radiation effects have been studied using the methods of low‐temperature vacuum ultraviolet spectroscopy (up to 40 eV), cathodoluminescence and thermoactivation spectroscopy. The step‐by‐step annealing of the radiation‐induced absorption, scattering, and luminescence has been performed at the heating of irradiated crystals up to ∼70% of a melting point. Possible experimental manifestations of the temperature‐stable nanosize 3D defects created, according to theoretical predictions, via rearrangement of many host ions at the collapse of discrete solitons (breathers) are detected in Lu3Al5O12 and Gd2SiO5 crystals irradiated with swift heavy ions (fluence of 1012 ions cm−2).

Electrospray ionization tandem mass spectrometry of protonated and alkali‐cationized Boc‐N‐protected hybrid peptides containing repeats of D‐Ala‐APyC and APyC‐D‐Ala: Formation of [bn–1 + OCH3 + Na]+ and [bn–1 + OH + Na]+ ions

Differentiation and structural characterization of positional isomers of non-natural amino acid hybrid peptides by using electrospray ionization tandem mass spectrometry (ESI-MS(n) ) is desirable because of their fundamental importance from the view point of peptide mass spectrometry and also of their increasing importance in the area of research towards biomedical and material applications; hence, the present study is undertaken. Electrospray ionization ion-trap tandem mass spectrometry (ESI-MS(n)) was used to characterize and differentiate three pairs of positional isomers of Boc-N-protected hybrid peptides containing repeats of D-Ala-APyC and APyC-D-Ala (D-Ala = D-alanine and APyC = trans-3-aminopyran-2-carboxylic acid). ESI-MS(n) spectra of protonated and alkali-cationized positional isomeric peptides display characteristic fragmentation involving the peptide backbone, the Boc group, and the side chain. It is observed that abundant rearrangement ions [b(n-1) + OCH(3) + Na](+) or [b(n-1) + OH + Na](+) are formed when D-Ala is present at C-terminus and the presence of APyC at the C-terminus inhibits the formation of rearrangement ions. In addition, abundant b(n-1)(+) ions are formed, presumably with stable oxazolone structures, when the C-terminus of b(n-1) (+) ions possessed D-Ala. The present study demonstrates that ESI tandem mass spectrometry is very useful for differentiating positional isomers of hybrid peptides containing D-Ala and APyC amino acids. While the protonated peptides give rise to characteristic sequencing ions, the cationized peptides produce additional rearrangement ions ([b(n-1) + OCH(3) + Na](+) and [b(n-1) + OH + Na](+)) which helps distinguish between the presence of D-Ala and APyC amino acids at the C-terminus.

Gas chromatography and mass spectrometry: a practical guide

Preface. Part I: The Fundamentals of GC/MS: What Is GC/MS. Mass Spectral Interpretation. Quantitation. Additional Literature Pertaining to Part I. Part II: GC Conditions, Derivatization, and Mass Spectral Interpretation of Specific Compound Types: Acids. Alcohols. Aldehydes. Amides. Amines. Amino Acids. Common Contaminants. Drugs and Metabolites. Esters. Ethers. Fluorinated Compounds. Gases. Glycols. Halogenated Compounds. Hydrocarbons. Isocyanates. Ketones. Nitriles. Nitroaromatics. Nitrogen-Containing Hetrocyclics. Nucleosides. Pesticides. Phenols. Phosphorus Compounds. Plasticizers. Prostaglandins. Solvents and Impurities. Steriods. Sugars. Sulfur Compounds. Additional Literature Pertaining to Part II. Part III: Ions for Determining Unknown Structures: M 1 to M 200. Part IV: Appendices: Definitions of Terms Related to Gas Chromatography. Tips for Gas Chromatography. Derivatives Found Useful in GC/MS. Cross Index Chart for GC Phases. McReynolds' Constants. Simple GC Troubleshooting. Definitions of Terms Related to Mass Spectrometry. Tips and Troubleshooting for Mass Spectrometry. Atomic Masses and Isotope Abundances. Structurally Significant McLafferty Rearrangement Ions. Isotope Patterns for ClxBry. Mixtures for Determining Mass Spectral Resolution. Additional Literature Pertaining to Part IV. Index.

Electrochemical cycling reversibility of LiMoS2 using first-principles calculations

A static computational model based on chemical hardness is proposed for the prediction and modification of the electrochemical cycling reversibility in Li-ion battery electrode materials. As an example, it is demonstrated that the cycling reversibility of high capacity anode material LiMoS2 is governed by a principle of maximum hardness, which correlates ion rearrangement with the hardness of electron transfer, accompanying the formation of charge density wave. Using the model, we show that the modifications or doping that soften the hardness of electron transfer of MoS2 (e.g., electron-donor doping) can promote Li ion extraction and improve the electrochemical cycling reversibility.

ChemInform Abstract: Substituted Azabicyclo[2.2.1]heptanes via Nitrenium Ion Rearrangement.

AbstractN‐Chlorination of exo‐arylated bicyclic substrates and subsequent AgNO3‐mediated nitrenium ion rearrangement produces endo‐arylated products, which represent the skeleton of pharmaceutically important alkaloid systems.

Local environment of optically active Nd3+ions in the ultratransparent BaMgF4ferroelectric crystal

A comprehensive study of the site location of Nd${}^{3+}$ ions in the BaMgF${}_{4}$ ultratransparent ferroelectric crystal is presented. By combining different low-temperature optical spectroscopies and electron paramagnetic resonance, the crystal field energy levels of Nd${}^{3+}$ ions and the gyromagnetic factors are experimentally determined. These results are employed to perform the crystal field analysis of Nd${}^{3+}$ ions considering a Cs point symmetry. The crystal field calculation yields a small root-mean-square deviation of 18 cm${}^{\ensuremath{-}1}$ and reveals a large crystal field strength (621 cm${}^{\ensuremath{-}1}$), verifying the assignment of the Ba${}^{2+}$ cationic site as the location for Nd${}^{3+}$ ions in this fluoride host. The results suggest a slight displacement of Nd${}^{3+}$ from the barium regular site with a rearrangement of the fluorine ions around it. The work gives a deep insight into the properties of the Nd${}^{3+}$-doped BaMgF${}_{4}$ crystal, a ferroelectric widely ultra-transparent material with potential applications as optical device operating in the Vacuum Ultraviolet-Ultraviolet and midinfrared spectral regions.

Thermal stability of (MgO)12 dimers

The cagelike (MgO)12 clusters were suggested to assemble the low-density nanoporous crystalline phases by connecting in the edge-to-edge, tetragonal face-to-face and hexagonal face-to-face manners. The stabilities of the (MgO)12 dimers bound in the above manners are investigated using methods of molecular dynamics (MD) and density functional theory (DFT). The MD simulations show that the (MgO)12 dimer connected in the hexagonal face-to-face manner can transform to a group of the hexagonal tubelike structures, and the dimer connected in the tetragonal face-to-face manner can change to other isomers through a 2 × 4 × 6 slab structure. Both isomerizations do not require rearrangements of the ions and they occurs at about 700 K and 1000 K, respectively. The DFT calculations indicate that the energy barriers of the isomerizations are about 1 eV, which suggests a lower isomerization temperature.

Improved electrochemical performances of nanocrystalline Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material for Li-ion batteries

Layered Li[Li0.2Co0.13Ni0.13Mn0.54]O2 nanoparticles were synthesized by a simple polymer-pyrolysis method and then coated with 3 wt% Al2O3 to form a ∼4 nm thick protective skin. The Al2O3-coated Li[Li0.2Co0.13Ni0.13Mn0.54]O2 electrode demonstrates a high initial coulombic efficiency of 96.1%, a large reversible capacity of ∼311 mAh g−1, and a good cyclability with 83.8% capacity retention after 70 cycles. Particularly, this material can deliver a quite high capacity of ∼239 mAh g−1 at a high rate of 400 mA g−1. This superior electrochemical performance results from the well-crystallized nanocores and effective surface modification of the material. The former provides a short diffusion path and fast transport channels for lithium ion insertion/extraction reactions and the latter restrains the elimination of oxide ion vacancies and metal ion rearrangement during charge–discharge cycling. Due to their simplicity and applicability, the synthetic method along with the surface modification technique is easily adopted to make high performance xLi2MnO3·(1 − x)LiMO2 materials for practical battery applications.

Long-term WGS stability of Fe/Ce and Fe/Ce/Cr catalysts at high and low steam to CO ratios—XPS and Mössbauer spectroscopic study

Long term time on stream stability of Fe/Ce and Fe/Ce/Cr catalysts has been investigated for high temperature water gas shift (WGS) reaction. Excellent WGS stability was observed for the Fe/Ce catalyst at steam to CO ratio of 3.5 and temperature of 500 °C for 30 days. The Fe/Ce catalyst also exhibited remarkable stability in presence of sulfur since no deactivation was observed in the presence of 400 ppm of sulfur. However, at steam to CO ratio 1.5, Fe/Ce deactivated continuously with time due to continuous formation of carbon and methane. X-ray diffraction measurements reveal that all the catalysts are stable in terms of composition during the WGS reaction irrespective of the steam to CO ratio. However, sintering of the magnetite phase is rapid in the experiment at steam to CO ratio of 1.5. XPS and Mössbauer spectroscopic measurements show that surface and local structural rearrangement of iron ions are taking place in the experiment at steam to CO ratio 1.5. XPS measurements also indicate the carbonate formation during the activation of Fe/Ce catalyst. The present study shows that Ce is a good stabilizer for iron oxide for high temperature WGS reaction only for higher steam to CO ratio applications. At low steam to CO ratio, Ce does not stabilize the Fe 3+/Fe 2+ redox couple during the WGS reaction. Addition of Cr to the Fe/Ce catalyst improves the WGS long term stability of Fe/Ce catalyst at steam to CO ratio 1.5. Remarkably, no deactivation was observed for the Fe/Ce/Cr catalyst at steam to CO ratio 1.5 and in presence of 400 ppm of sulfur. Structural and surface characterization measurements suggest that both Ce and Cr prevent the magnetite phase from sintering of and local structural rearrangement of iron ions during the WGS reaction at steam to CO ratio 1.5.

Bending of Layered Silicates on the Nanometer Scale: Mechanism, Stored Energy, and Curvature Limits

Bending and failure of aluminosilicate layers are common in polymer matrices although mechanical properties of curved layers and curvature limits are hardly known. We examined the mechanism of bending, the stored energy, and failure of several clay minerals. We employed molecular dynamics simulation, AFM data, and transmission electron microscopy (TEM) of montmorillonite embedded in epoxy and silk elastin polymer matrices with different weight percentage and different processing conditions. The bending energy per layer area as a function of bending radius can be converted into force constants for a given layer geometry and is similar for minerals of different cation exchange capacity (pyrophyllite, montmorillonite, mica). The bending energy increases from zero for a flat single layer to ∼10 mJ/m2 at a bending radius of 20 nm and exceeds 100 mJ/m2 at a bending radius of 6 nm. The smallest observed curvature of a bent layer is 3 nm. Failure proceeds through kink and split into two straight layers of shorter length. The mechanically stored energy per unit mass in highly bent aluminosilicate layers is close to the electrical energy stored in batteries. Molecular contributions to the bending energy include bond stretching and bending of bond angles in the mineral as well as rearrangements of alkali ions on the surface of the layers. When embedded in polymers, average radii of curvature of aluminosilicates exceed hundreds of nanometers. The small fraction of highly bent layers (<20 nm radius) can be increased by extrusion, especially in stacked layers, and by an increase in weight percentage of layered silicates above 5%. Extrusion also promotes failure and shortening of isolated layers.

The dynamic shape of ceria nanoparticles

Ceria with other oxides constitutes an important class of catalysts that can exchange oxygen rapidly under variable reducing or oxidizing conditions. Surfaces play a crucial role in many of the catalytic applications of cerium-based oxides. The bond breaking and formation between cerium and oxygen lead to the surface layer reconstruction of the nanoparticles, accompanied by shape changes. Here we show by direct atomic imaging of the dynamic surface rearrangement of cerium ions on ceria nanoparticles during in situ observation in an atomic resolution transmission electron microscope.

Charging current probing of the slow relaxation of the ionic liquid double layer at the Pt electrode

Abstract The slow relaxation of the electrical double layer on the ionic liquid (IL) side of the electrified interface, which was recently found at the IL|water interface, is detected voltammetrically also at a polycrystalline Pt electrode in two ionic liquids, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA + ][C 4 C 4 N − ]) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C 2 mim + ][C 1 C 1 N − ]). The potential-step transients at the Pt electrode show exponential decays, in which the slower relaxation time is on the order of 0.1–0.4 s in both [TOMA + ][C 4 C 4 N − ] and [C 2 mim + ][C 1 C 1 N − ]. The slow relaxation commonly seen at the Pt electrode in highly viscous [TOMA + ][C 4 C 4 N − ] (2.0 Pa s) and much less viscous [C 2 mim + ][C 1 C 1 N − ] (0.0325 Pa s), which was also seen at the IL|water interface, suggests the presence of a common origin of the slow relaxation on the ionic liquid side of the electrified interface, possibly the slow rearrangement of ions in the electrical double layer that consists of an ionic liquid. An even slower mode of the relaxation was detected in cyclic voltammograms as the time-dependent double layer capacitance.

Identification of Amino Acid Phosphorodiamidates of Antiviral Nucleosides Using Electrospray Ionisation Tandem Mass Spectrometry

Several amino acid phosphorodiamidate derivatives of d4T as anti-HIV prodrugs were synthesized and investigated using electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). A novel methyl group migration in gas phase was observed in ESI-MS(2) of the sodium adducts of amino acid methyl ester of phosphorodiamidates of 2',3'-didehydro-2',3'-dideoxythymidine (d4T). The proposed structures of the rearrangement ions were confirmed by high resolution tandem mass spectrometry. A possible mechanism involving the pentacoordinate phosphoric-carboxylic phosphate anhydride was proposed, in which a seven-membered ring intermediate was formed by coordination with the metal ion between the phosphoryl group and carbonyl oxygen atom. Thus, the intrinsic properties of phosphoryl group might be the key factors responsible for this migration.

A novel methyl migration to the phosphoryl group with the formation of cyclic aminoacylphosphoramidates in electrospray ionization tandem mass spectra of amino acid ester phosphoramidates of antiviral nucleosides

The mass spectral behavior of amino acid methyl ester phosphoramidate derivatives have been investigated using electrospray ionization multistage mass spectrometry (ESI-MS(n)) and moderate theoretical calculations at the B3LYP/6-31G(d) level. A novel methyl group migration to the phosphoryl group with the formation of the intermediate cyclic aminoacylphosphoramidate was found. The proposed structures of the rearrangement ions were confirmed by high-resolution tandem mass spectrometry. A possible mechanism involving the pentacoordinate phosphoric-carboxylic phosphate anhydride was proposed, in which the metal ion coordination with the phosphoryl and carbonyl groups and the intrinsic properties of phosphoryl group might be the key factors responsible for this novel migration.

ChemInform Abstract: Use of Functionalized β‐Lactams as Building Blocks in Heterocyclic Chemistry

AbstractReview: 58 refs.

Comparison of the isomeric α‐amino acyl adenylates and amino acid phosphoramidates of adenosine by electrospray ionization tandem mass spectrometry

The isomeric α-amino acyl adenylates and amino acid phosphoramidates of adenosine were synthesized and analyzed in detail by electrospray ionization tandem mass spectrometry (ESI-MS(n)). In ESI-MS/MS of α-amino acyl adenylates, the novel rearrangement ion [cAMP-H](-) observed as the most intense signal was formed through the pentacoordinate phosphorus intermediate with a six-membered ring by nucleophilic attack of the 3'-hydroxyl group on the phosphorus atom. In contrast, for the amino acid phosphoramidate of adenosine, the phosphorus atom could be attacked not only by the carboxylic group to form the cyclic aminoacyl phosphoramidates (CAPAs), but also by the nitrogen atom on the nucleobase leading to intramolecular phosphoryl group migration. It was found that the sodium ion having multidentate binding ability played an essential role in this characteristic rearrangement. The proposed mechanisms were supported by the MS/MS study, deuterium-labeled experiments, high-resolution tandem mass spectrometry and moderate calculations at the B3LYP/6-31G* level. The characteristic fragmentation patterns of α-amino acyl phosphates and amino acid phosphoramidates allows identification of stereoisomers when either the phosphorylation is at the N-terminus or C-terminus of amino acids.

Collision‐induced dissociation mass spectra of positive ions derived from tetrahydropyranyl (THP) ethers of primary alcohols

Peaks for [M + H](+) are not observed when electrospray ionization mass spectra of tetrahydropyranyl (THP) ethers are recorded under acidic conditions. However, gaseous [M + H](+) ions can be generated from ammonium adducts of THP ethers of primary alcohols by in-source fragmentation. The product ion spectra of these proton adducts show two significant peaks at m/z 85 and 103. Tandem mass spectrometric data obtained from appropriately deuteriated derivatives and ab initio calculations indicate that the m/z 85 ion originates from more than one mechanism and represents two structurally different species. A charge-directed E1-elimination mechanism or an inductive cleavage mechanism can produce the 3,4,5,6-tetrahydropyrylium ion as one of the structures for the m/z 85 ion, whereas a charge-remote process with ring contraction can generate the 5-methyl-3,4-dihydro-2H-furylium ion as the other structure. A comparison of the relative abundances of product ions from different isotopologues showed that the charge-remote process is the preferred mechanism. This is congruent with the ab initio calculations, which showed that the dihydrofurylium ion bears the lowest energy structure. The less abundant m/z 103 ion, which represents a protonated tetrahydropyran-2-ol, is formed by a charge-remote process via a proton transfer from the alkyl substituent. This process involves the formation and rearrangement of a carbenium ion in close association with a hydroxypentanal molecule. A proton transfer from the carbenium ion to the aldehyde is followed by elimination of an alkene.