Multiply Charged Cations Research Articles

Extraction of Lithium Using TBP and the Noncoordinating Cation Exchanger Tetraphenylborate: Principles of Selectivity from Sodium and Higher-Valent Cations

Extraction of lithium, calcium, and some other metal cations using tetraphenylborate/tributyl phosphate mixtures has been studied. The possibility of a qualitative change in the cation exchange extraction series towards the preferential recovery of lowly-charged (singly-charged) metal cations was shown for these systems. A change in the separation factors for singly- over multiply-charged cations in this system, compared to the known commercially available extractants such as alkylphosphoric, carboxylic, and other organic acids, is several orders of magnitude and increases when passing from doubly- to triply-charged metal cations, reaching, for example, values of 103 and more for the lithium/yttrium couple. It was assumed that the change in the extraction series was caused by the instability of the salts of the multiply-charged metal cations compared to that for the singly-charged cations due to the ionic character of the bond with the extracted metals and structural problems caused by the large volume of the tetraphenylborate anion. The investigated system can serve as a model for the development of a new class of extractants having a higher selectivity for singly-charged metal cations, in particular, for lithium.

Dynamics of chemical reactions of multiply-charged cations: Information from beam scattering experiments

Resultof beam scattering experiments on dynamics of chemical (bond-forming) reactions of molecular dications and trications are briefly reviewed. Both studies of crossed-beam scattering experiments and experiments using advanced position-sensitive coincidence method and their achievements that added to a better understanding of collisional mechanisms and energy deposition in products of this class of processes are discussed. In addition, results of other non-scattering methods (mass spectrometric, guided beam, time-of-flight) are briefly mentioned, if relevant to the subject of the paper.

Exploiting the Twofold Donor Ability of Carbodiphosphoranes: Theoretical Studies of [(PPh3 )2 C→EH2 ]q (Eq =Be, B+ , C2+ , N3+ , O4+ ) and Synthesis of the Dication [(Ph3 P)2 CCH2 ]2.

Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level of theory have been performed for the isoelectronic series of compounds [(PPh3 )2 C→EH2 ]q (Eq =Be, B+ , C2+ , N3+ , O4+ ). The equilibrium geometries and bond dissociation energies were calculated and the nature of the C→E bond was investigated with charge and energy decomposition methods. The dication [(PPh3 )2 C→CH2 ]2+ could become isolated as a salt compound with two counter ions [AlBr4 ]- . The X-ray structure analysis of [(PPh3 )2 C→CH2 ]2+ gave bond lengths and angles that are in good agreement with the calculated data. The geometry optimization of [(PPh3 )2 C→OH2 ]4+ gave [(PPh3 )2 C→OH]3+ as the equilibrium structure. Bonding analysis of [(PPh3 )2 C→EH2 ]q shows that [(PPh3 )2 C→BeH2 ] and [(PPh3 )2 C→BH2 ]+ possess donor-acceptor bonds in which the σ and π lone-pair electrons of (PPh3 )2 C donate into the vacant orbitals of the acceptor fragment. The multiply charged compounds are better described as substituted olefins [(PPh3 )2 CCH2 ]2+ , [(PPh3 )2 CNH2 ]3+ , and [(PPh3 )2 COH]3+ , which possess electron-sharing σ and π bonds that arise from the interaction between the triplet states of [(PPh3 )2 C]2+ and the respective fragment CH2 , (NH2 )+ , and (OH)+ . The multiply charged cations [(PPh3 )2 CCH2 ]2+ , [(PPh3 )2 CNH2 ]3+ , and [(PPh3 )2 COH]3+ are calculated to be stable toward dissociation.

Ions interacting with planar aromatic molecules: Modeling electron transfer reactions

We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C(14)H(10), coronene C(24)H(12), or circumcoronene C(54)H(18). These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

Electrosurface characteristics of bulk titanium dioxide in solutions of simple electrolytes. III. Effect of multiply charged cations on adsorption and electrokinetic parameters of TiO2

The electrosurface characteristics of titanium oxide nanoparticles synthesized by the sol-gel method are studied in relation to the pH and concentration of solutions of sodium, potassium, barium, and lanthanum chlorides. The surface charges and electrokinetic potentials are found, and the positions of the points of zero charge are analyzed as depending on the type and concentration of cations. The absence of a negative region of the electrokinetic potential, which results from the superequivalent adsorption in the Stern layer, is revealed for BaCl2 and LaCl3 solutions.

When Do Molecular Bowls Encapsulate Metal Cations?

Curved carbon π surfaces have chemical and physical properties suitable for exploitation for chemical microencapsulation and the self-assembly of nanoscale materials. Advances will greatly benefit from more understanding of their host-guest interactions with guests such as metal cations. Here, quantitative predictions are made for the binding of metal cations to three prototypical surfaces using density functional theory calculations: the buckybowls C(20)H(10), C(30)H(10), and C(40)H(10). The focus was on finding the most favorable binding sites, assessing whether binding is more favorable inside or outside the bowl, and exploring factors influencing the binding site preference. Classes of cations studied included small and large monocations and cations with multiple charges: Na(+), Cs(+), NH(4)(+), Ba(+), Ba(2+), and La(3+). Factors found to favor inside binding were large ion size and high ion charge, suggesting that polarization interactions as well as short-range interactions are important in determining the preferred binding sites inside and outside these buckybowls. Unlike monocations, which at best have only a weak tendency toward encapsulation, the multiply charged cations Ba(2+) and La(3+) were found to have a strong driving force toward containment inside the bowls. Coulomb potentials were found to favor cation binding on the outside surface of the bowls, but cation microsolvation through polarization interactions presents a compensating factor that can tip the balance in favor of encapsulation. Knowledge of these factors will be a valuable tool in the design of nanocontainers and the diverse architecture possible with these structural elements.

Effect of multiply charged paramagnetic metal cations on J-aggregation of thiacyanine dyes

J-Aggregation of thiacyanine dyes with a different length of the polymethine chain has been studied in aqueous solutions in the presence of paramagnetic metal cations. The introduction of multiply charged metal cations stimulates J-aggregation. The number of molecules involved in the composition of J-aggregates has been calculated to be four on the basis of analysis of the absorption spectra. The equilibrium constants and the thermodynamic parameters of J-aggregation have been determined. The effect of the dye structure and the metal cation nature on J-aggregation has been revealed.

Multiply-charged ions and interstellar chemistry

Gaseous molecules and ions, and even dust grains, can accumulate charge in the interstellar medium (ISM) by harvesting the energy of UV photons, cosmic rays, helium ions and metastable atoms. This Perspective views the various modes of gas-phase formation of multiply-charged cations and the possible impact of their reactions on the chemical and ionization structure of the ISM, in the light of what is still very limited knowledge. Emphasis is given to gas-phase reactions of multiply-charged cations with atoms, molecules and electrons that lead to charge reduction, charge separation and chemical bond formation and these are examined for multiply-charged atoms, small molecules, hydrocarbons, polycyclic aromatic hydrocarbons and fullerenes, primarily as dications but also as a function of charge state. The increased electrostatic interaction due to multiple charge is seen to promote bonding to individual charge sites on large molecules (e.g. fullerenes) and allow ensuing "surface" chemistry under the influence of Coulomb repulsion. The unique ability of multiply charged cations to undergo charge separation reactions, either unimolecular or bimolecular, can feature in the production in the ISM of internally cold, but translationally hot, cations of lower charge state or hot atoms that may provide the driving force for subsequent chemical reactions in what is otherwise an ultracold environment. Available chemical kinetic models that account for the role of multiply-charged ions in the ISM are few and of limited scope and the observation of these ions in the ISM has remained elusive.

The Generating Function of CID, ETD, and CID/ETD Pairs of Tandem Mass Spectra: Applications to Database Search

Recent emergence of new mass spectrometry techniques (e.g. electron transfer dissociation, ETD) and improved availability of additional proteases (e.g. Lys-N) for protein digestion in high-throughput experiments raised the challenge of designing new algorithms for interpreting the resulting new types of tandem mass (MS/MS) spectra. Traditional MS/MS database search algorithms such as SEQUEST and Mascot were originally designed for collision induced dissociation (CID) of tryptic peptides and are largely based on expert knowledge about fragmentation of tryptic peptides (rather than machine learning techniques) to design CID-specific scoring functions. As a result, the performance of these algorithms is suboptimal for new mass spectrometry technologies or nontryptic peptides. We recently proposed the generating function approach (MS-GF) for CID spectra of tryptic peptides. In this study, we extend MS-GF to automatically derive scoring parameters from a set of annotated MS/MS spectra of any type (e.g. CID, ETD, etc.), and present a new database search tool MS-GFDB based on MS-GF. We show that MS-GFDB outperforms Mascot for ETD spectra or peptides digested with Lys-N. For example, in the case of ETD spectra, the number of tryptic and Lys-N peptides identified by MS-GFDB increased by a factor of 2.7 and 2.6 as compared with Mascot. Moreover, even following a decade of Mascot developments for analyzing CID spectra of tryptic peptides, MS-GFDB (that is not particularly tailored for CID spectra or tryptic peptides) resulted in 28% increase over Mascot in the number of peptide identifications. Finally, we propose a statistical framework for analyzing multiple spectra from the same precursor (e.g. CID/ETD spectral pairs) and assigning p values to peptide-spectrum-spectrum matches.

Semiconductor-to-insulator transition of undoped-BaTiO3 in quenched state

It has been believed that the defect structure of “undoped” BaTi1−ηO3−δ be governed by background acceptor impurities, most likely AlTi′, in its near stoichiometry regime (δ≈0). Its electrical conductivity versus oxygen activity should, thus, be expected to be similar to that of Al-doped BaTiO3 not only in equilibrium state at elevated temperatures, but also in quenched state at low temperatures. In quenched state, however, the “undoped” BaTiO3 from various sources totally betray this expectation: A landmark of the quenched-state defect structure, semiconductor-to-insulator transition falls at an oxygen activity >10 orders lower than that of the Al-doped and it is rather similar to that of variable-valent Mn-doped BaTiO3. The transition is found to systematically depend on the nonmolecularity (η), suggesting the defect structure being governed by the multiply-charged cation vacancies. The hole-trapping energies of VBa″ and VTi⁗ are estimated and compared with those for the fixed-valent AlTi′ and variable-valent MnTi″.

Stability of multiply charged fullerene anions and cations

We present a systematic study of the stability of highly charged cationic and anionic fullerenes whose most stable neutral counterparts follow the isolated pentagon rule (IPR). In agreement with recent studies, we have found that, for many highly charged fullerenes, non-IPR isomers are significantly more stable than the IPR ones. To understand this behavior, we compare the results of elaborate density-functional theory (DFT) calculations to those of a simple H\uckel molecular-orbital theory in which the DFT energies of the corresponding neutral systems are used as a reference. The model leads to a reasonable estimate of the relative stability of the IPR and non-IPR isomers as a function of charge, which can be used to identify, among the thousands of possible isomers and charge states, the non-IPR species that are likely more stable than the IPR isomers.

A Computational Study on Some Viable Targets for Gas-Phase Synthesis of Metal Complexes of the Cyclic (B6C)−2and Their Bonding Pattern

In this account, a detailed computational study is conducted to verify the geometric, energetic, and electronic properties of the planar cyclic (B 6C) (-2) (as the simplest carrier of hexacoordinate carbon) within some metal complexes. The [M(B 6C)] ((-)) (M = Li, Na, K) and [M(B 6C)] (M = Be, Mg, Ca) series are employed for this purpose. Relevant ab initio calculations at both DFT and post-HF levels vividly demonstrate that this dianion is stabilized considerably in the electric field generated by cations, whereas the geometrical and electronic properties of this ring remain almost intact in these complexes. The complementary topological analysis of charge densities confirms that cyclic (B 6C) (-2) within these complexes exhibits the same topological patterns as the naked dianion, thus confirming the presence of an unusual charge density distribution in this dianion. An electrostatic model is proposed that not only qualitatively but also quantitatively explains the observed computational trends in these complexes. This model successfully traces the polarization of the central carbon atom of the ring in the presence of a hard, multiply charged cation. To facilitate experimental detection, the photoelectron spectra of the [M(B 6C)] ((-)) (M = Li, Na, K) series are computed and the dominant features are extracted. Although considered species are not global minima on their potential energy hypersurfaces, their kinetic stabilities are verified and demonstrated unequivocally.

A chestnut-like hierarchical architecture of a SWCNT/microsphere composite on an electrode for electroanalysis

A new electrochemical interface of a chestnut-like hierarchical microsphere/SWCNT composite array was constructed. The composite was then characterized by means of scanning electron microscopy and cyclic voltammetry. The voltammetric response of SWCNT/microsphere-array electrodes was demonstrated by applying them to the analytical determination of the three different redox couples of the neutral molecule Fc(NH 2OH) 2, the multiply charged cation Ru ( NH 3 ) 6 3 + , and the multiply charged anion Fe(CN) 6 3 − . The effects of the CNT loading, the sample concentration, the pH, the sweep rates, and the ionic strength on the electrochemical properties of this new generation of hierarchical structure were studied. The stability of this composite in a solution was also investigated.

Direct characterization of intact polypeptides by matrix‐assisted laser desorption electrospray ionization quadrupole Fourier transform ion cyclotron resonance mass spectrometry

We report the characterization of a recently introduced hybrid ionization source, matrix-assisted laser desorption electrospray ionization (MALDESI), coupled to a quadrupole Fourier transform ion cyclotron resonance mass spectrometry (QFT-ICR-MS) system. We first demonstrate the ability of MALDESI-QFT-ICR MS to directly analyze and provide high mass measurement accuracy (approximately 1 part-per-million) of a polypeptide using internal calibration. Second, we show the potential of MALDESI-QFT-ICR MS for the top-down characterization of multiply charged polypeptide cations. Finally, we demonstrate sub-femtomole detection limits in MALDESI-QFT-ICR MS using a combination of naturally occurring peptides and their respective stable isotope labeled forms. The results presented herein demonstrate the feasibility of several potential applications for MALDESI-QFT-ICR MS for the direct analysis of intact biological molecules.

FT‐ICRMS distinguishes the mechanism of the charge state reduction for multiply charged protein cations admixed with redox reagents in ESI

Recently, we reported on a phenomenon in which multiply charged protein cations produced by electrospray ionization could be reduced to lower and narrower charge state distributions when admixed with reducing reagents 1,4-benzoquinone or quinhydrone. Circular dichroism spectra of the proteins indicated that secondary and tertiary structural changes upon addition of these reducing reagents were negligible, thus eliminating conformational effects as playing a role in the charge reduction mechanism. Furthermore, the extent of charge state reduction did not correspond with gas-phase basicities of the redox reagents, suggesting that solution-phase, and not gas-phase, behavior dominates the observed charge state reduction. The relatively low resolution of the triple quadrupole employed did not make it possible to distinguish isotopic distributions of the multiply charged cations in order to determine whether the observed phenomenon was the result of proton-transfer reactions between the multiply charged cations and the reducing reagent or because of electron transfer from the reducing reagent to the protein cations. Here, high-resolution ESI-Fourier transform ion cyclotron resonance mass spectrometry of several peptide amides in the presence of a redox reagent show isotopic distributions that are consistent only with the proton-transfer mechanism.

Appearance energies of singly, doubly, and triply charged coronene and corannulene ions produced by electron impact

Electron impact ionization near threshold has been studied for the polyaromatic hydrocarbons coronene and corannulene using a high resolution electron monochromator in conjunction with quadrupole mass spectrometry. The mass spectra determined at an electron energy of 100 eV show a rich fragmentation pattern (particularly for coronene) including the presence of multiply charged molecular cations for both compounds. For the singly and multiply charged parent ions of coronene and corannulene we present the ionization efficiency curves near threshold from which the corresponding appearance energies (AEs) are determined using a nonlinear least squares fitting routine. The AEs obtained here are compared where available with previous values reported for both compounds using electron impact ionization and photoionization as well as with theoretical predictions.

Potential energy surfaces in Coulomb explosion of polyatomic molecules: Benzene and cyclohexane trications and acetylene dication

AbstractWe report density functional and ab initio calculations of potential energy surfaces (PES) for benzene and cyclohexane trications relevant to the Coulomb explosion mechanisms of C6H6 and C6H12. Numerous isomerization and dissociation mechanisms on these PES have been considered, and the products most favorable thermodynamically and kinetically have been predicted. We also demonstrate applications of RRKM theory to the calculation of product branching ratios in decomposition of multiply charged cations. Significant common features of PES related to Coulomb explosion experiments on hydrocarbon molecules have been described. Calculations along minimal energy reaction paths for some representative isomerization and dissociation channels have been carried out in the presence of strong external electric field for C6H and C2H and the influence of the field on molecular orientation and PES have been analyzed. The results show that proton mobility in nonaromatic hydrocarbon cations is high due to nearly zero barriers for the H+ migrations. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Toward a general mechanism of electron capture dissociation

The effects of positive charge on the properties of ammonium and amide radicals were investigated by ab initio and density functional theory calculations with the goal of elucidating the energetics of electron capture dissociation (ECD) of multiply charged peptide ions. The electronic properties of the amide group in N-methylacetamide (NMA) are greatly affected by the presence of a remote charge in the form of a point charge, methylammonium, or guanidinium cations. The common effect of the remote charge is an increase of the electron affinity of the amide group, resulting in exothermic electron capture. The N-Calpha bond dissociation and transition state energies in charge-stabilized NMA anions are 20-50 kJ mol(-1) greater than in the hydrogen atom adduct. The zwitterions formed by electron capture have proton affinities that were calculated as 1030-1350 kJ mol(-1), and are sufficiently basic for the amide carbonyl to exothermically abstract a proton from the ammonium, guanidinium and imidazolium groups in protonated lysine, arginine, and histidine residues, respectively. A new mechanism is proposed for ECD of multiply charged peptide and protein cations in which the electron enters a charge-stabilized electronic state delocalized over the amide group, which is a superbase that abstracts a proton from a sterically proximate amino acid residue to form a labile aminoketyl radical that dissociates by N-Calpha bond cleavage. This mechanism explains the low selectivity of N-Calpha bond dissociations induced by electron capture, and is applicable to dissociations of peptide ions in which the charge carriers are metal ions or quaternary ammonium groups. The new amide superbase and the previously proposed mechanisms of ECD can be uniformly viewed as being triggered by intramolecular proton transfer in charge-reduced amide cation-radicals. In contrast, remote charge affects N-H bond dissociation in weakly bound ground electronic states of hypervalent ammonium radicals, as represented by methylammonium, CH3NH3*, but has a negligible effect on the N-H bond dissociation in the strongly bound excited electronic states. This refutes previous speculations that loss of "hot hydrogen" can occur from an excited state of an ammonium radical.

Assembly, electrochemical characterisation and electrocatalytic ability of multilayer films based on [Fe(bpy) 3] 2+, and the Dawson heteropolyanion, [P 2W 18O 62] 6−

Successive adsorption onto a glassy carbon electrode of the Dawson heteropolyanion, [P 2W 18O 62] 6−, and the multiply charged cation [Fe(bpy) 3] 2+, resulted in the formation of stable multilayer assemblies on the electrode surface. Surface coverages were found to be typical of monolayer coverages for multilayer systems. Cyclic voltammetric studies of the assembly in aqueous 0.5 M NaHSO 4, gave a range of redox couples associated with the Fe 3+/2+ redox system, of the cationic [Fe(bpy) 3] 2+ moiety and the tungsten-oxo framework of the Dawson parent heteropolyanion, [P 2W 18O 62] 6−. It was possible to immobilise up to thirty monolayers, with the system exhibiting well-behaved redox behaviour. The stability of the assembly towards redox switching was investigated, with it being found to be extremely stable once the outer layer is anionic in nature. The immobilised film was also tested for electrocatalytic activity for the reduction of nitrite, hydrogen peroxide and bromate, and was shown to be an efficient electrocatalyst.

Polymeric sheets in Mg 4C 60

We present preliminary results on the preparation and structure of Mg 4C 60, a new fulleride polymer. A series of Mg x C 60 compositions (0< x<6) were prepared by solid state reaction. While most samples were multiphase, a single phase material was obtained at the nominal composition Mg 4C 60. The X-ray diffraction pattern of Mg 4C 60 was successfully indexed and fitted to a rhombohedral structure based on two-dimensional polymeric sheets of C 60 ions. This result extends the family of fulleride polymers to the salts of multiply charged cations and thus opens a new direction in this field.