Dimer Ions Research Articles

Reply to “Comment on ‘Effect of Pore Size and Nickel Content of Ni-MCM-41 on Catalytic Activity for Ethene Dimerization and Local Structures of Nickel Ions’”

Reply to “Comment on ‘Effect of Pore Size and Nickel Content of Ni-MCM-41 on Catalytic Activity for Ethene Dimerization and Local Structures of Nickel Ions’”

Pulsed microplasmas generated in truncated paraboloidal microcavities: simulations of particle densities and energy flow

Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al (2009 Appl. Phys. Lett. 94 011503), have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150 µm and 75 µm in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200 kHz. For a Ne pressure of 500 Torr and 2 µs, 290 V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ∼10 nJ of energy is delivered to each parabolic cavity, of which 26–30% is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion currents, respectively, and the peak electron density of ∼6 × 1012 cm−3 is attained ∼90 ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150 kW cm−3 and the loss of power to the wall of the microcavity drops by as much as 24% when the excitation voltage is increased from 280 to 310 V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600 Torr accounting for <20% of the total electron energy.

Metastable fragmentation of photoionized styrene cluster ions: Implications for cluster ion structure

Styrene clusters are produced by supersonic expansion of a styrene/Ar mixture, photoionized with 193 or 248nm light, and analyzed in a reflectron time-of-flight mass spectrometer. The styrene cluster ions Stn+, n≤10, show an alternation in intensity that favors cluster ions containing an even number of molecules. Mass-selected cluster ions, n=2–8, are allowed to undergo metastable fragmentation, and the fragment ions are separated from the parent ions in the reflectron. For n=4–8, fragmentation proceeds exclusively by elimination of a series of styrene molecules. Loss of as many as five styrene molecules is observed for n=6–8. For n=4, the St+ fragment signal is very small, and for n=3 it is nonexistent. A robust signal for St2+ indicates the major product channel in both cases. These results are interpreted in terms of formation of covalently bound styrene dimer ions within the ionized clusters, especially n=3 and 4. The present fragmentation results are also discussed in relation to earlier work. Internal energy considerations show that there should be sufficient energy present to cause fragmentation of the structures proposed in the prior work, but no fragments corresponding to such fragmentation are observed. Thus the present work does not support the cluster ion structures proposed earlier, though it also does not completely rule them out.

Interatomic Coulombic decay of fixed-in-space neon dimers

The detailed theoretical and experimental analysis of the angular distributions of electrons from interatomic Coulombic decay (ICD) of the Ne dimer in the molecular frame is performed. In the initial state the doubly charged dimer ion has one $2s$ vacancy and one $2p$ vacancy on one atom. After the ICD process the neutral neon atom is ionized and the triply charged molecular ion dissociates into singly and doubly charged atomic ions, ${\text{Ne}}^{2+}(2{p}^{\ensuremath{-}2})+{\text{Ne}}^{+}(2{p}^{\ensuremath{-}1})$. From the coincident measurement of kinetic energy release (KER) of the ions and the ICD electron the decay channel can be identified unambiguously. The most detailed experimental data have been obtained for the singlet dicationic state Ne${}^{2+}(2{p}^{\ensuremath{-}2}){[}^{1}\phantom{\rule{-0.16em}{0ex}}D]$. Different KER energies correspond to different internuclear distances at which the ICD process takes place. In experiment the data have been presented for three regions of KER energies, and the corresponding calculations have been performed for three fixed internuclear distances. In calculations we imply that all the electrons in Ne${}_{2}$ to a good approximation are localized. However, we need to retain the molecular character of the dimer wave functions which opens the possibility for the ICD process. To do it, we calculate at first the Hartree-Fock ground state wave functions of the neutral Ne${}_{2}$ dimer using the standard procedure for homonuclear diatomic molecules corresponding to the ${D}_{\ensuremath{\infty}h}$ symmetry group. For the doubly charged ion Ne${}_{2}{}^{2+}$ with two vacancies on one atom the symmetry is lowered to ${C}_{\ensuremath{\infty}v}$, and we are looking now for the set of one-electron Hartree-Fock wave functions which are localized either on the left or on the right atom as a linear combination of symmetry-adopted wave functions. The theory correctly reproduces the experimental data and predicts the sharp variation of the angular distributions as a function of internuclear distance.

Traveling‐wave ion mobility mass spectrometry of protein complexes: accurate calibrated collision cross‐sections of human insulin oligomers

The collision cross-section (Ω) of a protein or protein complex ion can be measured using traveling-wave (T-wave) ion mobility (IM) mass spectrometry (MS) via calibration with compounds of known Ω. The T-wave Ω-values depend strongly on instrument parameters and calibrant selection. Optimization of instrument parameters and calibration standards are crucial for obtaining accurate T-wave Ω-values. Human insulin and the fast-acting insulin aspart under native-like conditions (ammonium acetate, physiological pH) were analyzed on Waters SYNAPT G1 and G2 HDMS instruments. The calibrated T-wave Ω-values of insulin monomer, dimer, and hexamer ions were measured using many different combinations of denatured and native-like calibrants (masses between 2.85 and 256 kDa) and T-wave conditions. Drift-tube Ω-values were obtained on a modified SYNAPT G1. Insulin T-wave Ω-values were measured at 26 combinations of T-wave velocity and amplitude. Optimal sets of calibrants were identified that yield Ω-values with minimal dependence on T-wave conditions and calibration plots with high R(2)-values. The T-wave Ω-values determined under conditions satisfying these criteria had absolute errors <2%. Structural differences between human insulin and fast-acting insulin aspart were probed with IM-MS. Insulin aspart monomers have increased flexibility, while hexamers are more compact than human insulin. Accurate T-wave Ω-values that are indistinguishable from drift-tube values are obtained when using (1) native-like calibrants with masses that closely bracket that of the analyte, (2) T-wave velocities that maximize the R(2) of the calibration plot for those calibrants, and (3) at least three replicates at T-wave velocities that yield calibration plots with high R(2).

Mass spectrometric study of the vaporization of N,N′-o-phenylene-bis(salicylideniminate) nickel(II), copper(II), and zinc(II) and N,N′-ethylene-bis(salicylaldiminate) zinc(II) complexes

The thermodynamics of vaporization of Ni(saloph), Cu(saloph), Zn(saloph), and Zn(salen) complexes are studied by Knudsen effusion method with mass spectrometric control of the vapor composition. It is noted that in the mass spectra of Zn(saloph) and Zn(salen), there are low-intensity peaks corresponding to ions of dimer. The effect of the nature of a metal and a ligand on the behavior of fragmentation of the complexes during their ionization with electrons is discussed. The enthalpies of sublimation, ΔH ○ (T), are calculated by second law of thermodynamics: Ni(saloph) (502–578 K), 163 ± 1 kJ/mol; Cu(saloph) (475–550 K), 162 ± 1 kJ/mol; Zn(saloph) (571–637 K), 176 ± 4 kJ/mol; Zn(salen) (568–634 K), 169 ± 2 kJ/mol.

On-line chiral analysis of benzylmercapturic acid and phenylmercapturic acid in human urine using UPLC-QToF mass spectrometry with the kinetic method

A novel analytical method was developed for chiral analysis utilizing on-line ultra-performance liquid chromatography (UPLC) coupled with a quadrupole time-of-flight mass spectrometry (QToF-MS). This developed method was applied to discriminate and quantify accurately the chiral biomarkers, d/l-phenylmercapturic acid (PMA) and d/l-benzylmercapturic acid (BMA), in urine samples. Initially, UPLC was used to separate achirally the mixture of two biomarkers and then sequential on-line mass spectrometry differentiated successfully the enantiomers of each biomarker. After separating the two molecular species, a mixture of metal ion and reference ligand was added to the eluent of UPLC to produce trimeric M(II)-bound complex ion, [MII(A)(ref*)2-H]+ (MII, divalent transition metal ion; A, analyte; ref*, reference ligand). The collision-induced dissociation (CID) of the trimeric complex ion resulted in two dimeric complex ions, [MII(A)(ref*)-H]+ and [MII(ref*)2-H]+. The ratio of the abundances for the two product ions, the branching ratio, was established for one enantiomer relative to the other, which affects chiral discrimination. The compounds, Cu(II) as a central metal ion and L-Pro as a reference ligand were selected for the optimum distinction of chiral PMA and BMA. Rapid quantitative chiral analysis of PMA and BMA was achieved by constructing calibration curves derived from the kinetic method, related to the ratio of the branching ratios against the enantiomeric composition of their mixture.

Effect of Pore Size and Nickel Content of Ni-MCM-41 on Catalytic Activity for Ethene Dimerization and Local Structures of Nickel Ions

The catalytic activity of nickel ion-loaded mesoporous silica MCM-41 (Ni-M41) for ethene dimerization was investigated as a function of the pore size and the amount of nickel. In addition, the silica wall and the loading of the nickel species were characterized. The Ni-M41 samples with smaller pore size and higher Si/Ni ratio exhibited greater reaction rate constants. The Fourier transform infrared (FT-IR) spectra indicated the formation of 2:1 nickel phyllosilicate-like species along the pore wall. Furthermore, the IR band at approximately 570 cm–1 and the X-ray absorption fine structure (XAFS) spectra indicated the existence of five-membered rings consisting of Si–O on the M41 pore wall in addition to the typical six-membered ones. On the basis of the UV–vis–NIR diffuse reflectance (UV–vis–NIR DR), FT-IR, and XAFS data, we propose that the three- and four-coordinated Ni2+ ions lie on the five- and six-membered Si–O rings of silica, respectively. Nitrogen monoxide was employed as a probe molecule in the ...

Determination of triacylglycerol regioisomers using electrospray ionization-quadrupole ion trap mass spectrometry with a kinetic method

The kinetic method was applied to differentiate and quantify mixtures of regioisomeric triacylglycerols (TAGs) by generating and mass selecting alkali ion bound metal dimeric clusters with a TAG chosen as reference (ref) and examining their competitive dissociations in a quadrupole ion trap mass spectrometer. This methodology readily distinguished pairs of regioisomers (AAB/ABA) such as LLO/LOL, OOP/OPO and SSP/SPS and consequently distinguished sn-1/sn-3, sn-2 substituents on the glycerol backbone. The dimeric complex ions [ref, Li, TAG(AAB and/or ABA)]+ generated by electrospray ionization mass spectrometry were subjected to collision induced dissociation causing competitive loss of either the neutral TAG reference (ref) leading to [Li(AAB and/or ABA)]+ or the neutral TAG molecule (TAG(AAB and/or ABA)) leading to [ref, Li]+. The ratio of the two competitive dissociation rates, defined by the product ion branching ratio (Riso), was related via the kinetic method to the regioisomeric composition of the investigated TAG mixture. In this work, a linear correlation was established between composition of the mixture of each TAG regioisomer and the logarithm of the branching ratio for competitive fragmentation. Depending on the availability of at least one TAG regioisomer as standard, the kinetic method and the standard additions method led to the quantitative analysis of natural TAG mixtures.

On the stability of an unsupported mercury–mercury bond linking group 15 Zintl clusters

The dimeric Zintl ion [Hg(2)(As(7))(2)](4-) has been synthesized with high crystalline yield from the reaction of an ethylendiamine solution of the intermetallic Zintl phase K(3)As(7) with diphenyl mercury. Single crystal X-ray diffraction of [K(2,2,2-crypt)](4)[Hg(2)As(14)], 1 (2,2,2-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane), reveals that the cluster anion exhibits a Hg-Hg bond and the compound has been further characterized using Raman spectroscopy, cyclic voltammetry and its band gap energy was measured. Theoretical studies provide a microscopic understanding of the bonding in this unusual compound.

Convenient Synthesis of 7H-Naphtho-[1,8-gh]quinolin-7-one

7H-Naphtho[1,8-gh]quinolin-7-one was prepared by the glycerol condensation of 3-aminophenalenone in good yields. This method provides a new and convenient synthesis of the compound. NMR spectra of its related compounds were measured, and the rapid interchange between two equivalent α-enone structures was found, which is well known as the phenomenon for the formation of carboxylic acid dimer or hydrogen difluoride ion.

Initiating molecular growth in the interstellar medium via dimeric complexes of observed ions and molecules

A feasible initiation step for particle growth in the interstellar medium (ISM) is simulated by means of ab quantum chemistry methods. The systems studied are dimer ions formed by pairing nitrogen containing small molecules known to exist in the ISM with ions of unsaturated hydrocarbons or vice versa. Complexation energies, structures of ensuing complexes and electronic excitation spectra of the encounter complexes are estimated using various quantum chemistry methods. Moller-Plesset perturbation theory (MP2, Z-averaged perturbation theory (ZAP2), coupled cluster singles and doubles with perturbative triples corrections (CCSD(T)), and density functional theory (DFT) methods (B3LYP) were employed along with the correlation consistent cc-pVTZ and aug-cc-pVTZ basis sets. Two types of complexes are predicted. One type of complex has electrostatic binding with moderate (7-20 kcal per mol) binding energies, that are nonetheless significantly stronger than typical van der Waals interactions between molecules of this size. The other type of complex develops strong covalent bonds between the fragments. Cyclic isomers of the nitrogen containing complexes are produced very easily by ion-molecule reactions. Some of these complexes show intense ultraviolet visible spectra for electronic transitions with large oscillator strengths at the B3LYP, omegaB97, and equations of motion coupled cluster (EOM-CCSD) levels. The open shell nitrogen containing carbonaceous complexes especially exhibit a large oscillator strength electronic transition in the visible region of the electromagnetic spectrum.

Effects of B18Hx+ and B18Hx dimer ion implantations on crystallinity and retained B dose in silicon

The effects of B18Hx+ and B18Hx dimer ion (B36Hy+) implantations on Si crystallinity and the retained B dose in Si were investigated using B18Hx bombardment and compared with the effects of B+ implantation. Crystallinity was estimated for the implantation dose using molecular dynamic simulations (MDSs) and was quantified using the optical thickness obtained from spectroscopic ellipsometry. The authors focused on the crystallinity at a low B dose and compared the amorphized zones predicted by MDS for B18Hx+ implantation with those measured using transmission electron microscopy; the predicted and measured results were in reasonable agreement. The authors then used their understanding of B18Hx bombardment to discuss the process for the generation of larger amorphized zones and thicker amorphized layers, as observed in B36Hy+ implantation. The retained B dose and the sputtering were examined with secondary ion mass spectroscopy, focusing on a comparison of the retained B and the sputtering of Si and SiO2 surfaces. The retained B dose was lower for B18Hx+ and B36Hy+ implantations, with and without surface SiO2, than for B+ implantation, although no sputtering was observed. The reduction of the retained B dose was more severe in the samples with SiO2. The origin of the differences between Si and SiO2 surfaces was considered to be Si melting; this was predicted by the MDSs, and observed indirectly as flat B profiles in the Si region. To examine the effects of both crystallinity and retained B dose on the electrical characteristics, the sheet resistance (RS) was measured. The RS for B18Hx+ implantation was lower than that for B+ implantation at both B doses studied. Additionally, the B36Hy+ implantation under conditions that produced a thicker amorphized layer led to lower RS than B18Hx+ implantation. These results indicate that both the amorphized layer and the amorphized zone contribute to the activation of more B atoms.

Steroid/Triterpenoid Functional Molecules based on “Click Chemistry”

This Focus Review highlights the design and synthesis of various functional molecules based on steroid/triterpenoid as building blocks through the copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction, as well as their applications in bioactivity, recognition, and assembly. This method shows great promise to allow us to develop novel molecules with characteristic functions using the CuAAC "click" reaction.

Photostability of amino acids to Lyman α radiation: Glycine

The amino acids already detected in Solar System bodies and researched in Interstellar Medium are of particular importance for the chemistry related to the origin of life since they are constituents of all living organisms. Several amino acids have been identified in meteorites carbonaceous with significant concentration, while the existence of glycine in regions of star formation has been claimed. To interpret the viability of amino acids in pre-biotic astrochemistry is important to investigate the stability of these compounds in extraterrestrial surroundings. This study investigates, in the laboratory, the stability of glycine to the action of ultraviolet radiation, in spectral region around the wavelength of the Lyman α line (1216Å) produced by a hydrogen lamp. 252Cf-PDMS of positive and negative desorbed ions was performed for glycine, before and during the irradiation, and the dependence of the ion desorption yields on the irradiation time is determined. As a result, the relative photostability curves of the molecular and dimer ions are observed to be a single exponential decay with a time constant 376min for positive desorbed ions and 675min for negative ones. The photodissociation cross section found for glycine molecule at room temperature, when positive secondary ions are considered, is 17Mb; this value drops to 9Mb when negative secondary ions are analyzed. This new methodology offers a complementary way of understanding the photonic interaction in amino acids, allowing discussion on polymerization and/or radiation induced phase transition effects.

Optical absorption spectrum of the silver dimer ion: temperature dependence measured by photodissociation and photon-trap spectroscopy

The optical absorption spectrum is reported for the silver dimer cation, Ag2 +, which is temperature-controlled by buffer-gas cooling in an ion trap. The measurement is performed by two methods, photodissociation and photon-trap spectroscopy. The temperature of the trapped ions is estimated from the profiles of the spectrum. The spectrum is further analyzed to evaluate the bond length, r e , the vibrational frequency, ω e , and the anharmonic constant, ω e x e , in the first excited electronic state based on the molecular parameters reported for the ground state. Absorption and dissociation cross sections are compared as well.

Synthesis of (Ge9–Ge9)6– Dimeric Zintl Ions in Liquid Ammonia Solutions of K4Ge9: Low‐Dimensional Coordination Networks in the Crystal Structure of the Ammoniates Kn[K([2.2.2]crypt)]6–n[Ge9–Ge9](NH3)m (n = 2, 3, and 4)

AbstractThree new compounds of the dimeric cluster anion [Ge9–Ge9]6– were obtained from liquid ammonia solutions of the Zintl phase K4Ge9. All of them follow the general formula Kn[K([2.2.2]crypt)]6–n[Ge9–Ge9](NH3)m (1: n = 4, m = 14; 2: n = 3, m = 18; 3: n = 2, m = 17.28) and comprise sequestered and non‐sequestered K+ cations in different ratios. The non‐sequestered cations coordinate to the Ge9 cages and support the covalent intercluster bond. Additionally, they are in contact with each other by varying numbers of coordinative ammonia bridges leading to arrangement of the anions. The dimensionality of the cluster arrangements correlates with the amount of sequestering molecules. Layers, double chains and single chains are observed for 1, 2, and 3, respectively, according to an increase of [2.2.2]crypt) per formula unit for 1 to 3.

Elucidation of Reaction Mechanisms Responsible for Afterglow and Reagent-Ion Formation in the Low-Temperature Plasma Probe Ambient Ionization Source

The development of ambient desorption/ionization mass spectrometry has shown promising applicability for the direct analysis of complex samples in the open, ambient atmosphere. Although numerous plasma-based ambient desorption/ionization sources have been described in the literature, little research has been presented on experimentally validating or determining the desorption and ionization mechanisms that are responsible for their performance. In the present study, established spectrochemical and plasma physics diagnostics in combination with spatially resolved optical emission profiles were applied to reveal a set of reaction mechanisms responsible for afterglow and reagent-ion formation of the Low-Temperature Plasma (LTP) probe, which is a plasma-based ionization source used in the field of ambient mass spectrometry. Within the dielectric-barrier discharge of the LTP probe, He(2)(+) is the dominant positive ion when helium is used as the plasma supporting gas. This helium dimer ion (He(2)(+)) has two important roles: First, it serves to carry energy from the discharge into the afterglow region in the open atmosphere. Second, charge transfer between He(2)(+) and atmospheric nitrogen appears to be the primary mechanism in the sampling region for the formation of N(2)(+), which is an important reagent ion as well as the key reaction intermediate for the formation of other reagent ions, such as protonated water clusters, in plasma-based ambient ionization sources. In the afterglow region of the LTP, where the sample is usually placed, a strong mismatch in the rotational temperatures of N(2)(+) (B (2)Σ(u)(+)) and OH (A (2)Σ(+)) was found; the OH rotational temperature was statistically identical to the ambient gas temperature (~300 K) whereas the N(2)(+) temperature was found to rise to 550 K toward the tail of the afterglow region. This much higher N(2)(+) temperature is due to a charge-transfer reaction between He(2)(+) and N(2), which is known to produce rotationally hot N(2)(+) (B (2)Σ(u)(+)) ions. Furthermore, it was found that one origin of excited atomic helium in the afterglow region of the LTP is from dielectronic recombination of vibrationally excited He(2)(+) ions.

Gas-Phase Ions of Human Hemoglobin A, F, and S

Hemoglobin (Hb) (α(2)β(2)) is a tetrameric protein-protein complex. Collision cross sections, hydrogen exchange levels, and tandem mass spectrometry have been used to investigate the properties of gas-phase monomer, dimer, and tetramer ions of adult human hemoglobin (Hb A, α(2)β(2)), and two variant hemoglobins: fetal hemoglobin (Hb F, α(2)γ(2)) and sickle hemoglobin (Hb S, α(2)β(2), E6V[β]). All three proteins give similar mass spectra. Monomers of Hb S and Hb F have similar cross sections, ca. 10% greater than those of Hb A. Cross sections of dimer ions of Hb S are 11% greater than those of Hb A and 6% greater than those of Hb F. Tetramers of Hb S are 13% larger than tetramers of Hb A or Hb F. Monomers and dimers of all three Hb have similar hydrogen-deuterium exchange (HDX) levels. Tetramers of Hb S exchange 16% more hydrogens than Hb A and Hb F. In tandem mass spectrometry, monomers of Hb S and Hb F require ca. 10% greater internal energy for heme loss than Hb A. Dimers (+11) of Hb A and Hb S dissociate to monomers with asymmetrical charge division; dimers of Hb F (+11) dissociate with nearly equal charge division. Tetramer ions dissociate to monomers and trimers, unlike solution Hb, which dissociates to dimers. The most stable dimers are from Hb S; the most stable tetramers from Hb F. The results with Hb S show that a single mutation in the β chain can change the physical properties of this gas-phase protein-protein complex.

Orthoamide und Iminiumsalze, LXXI [1]. Zur Fixierung von Kohlendioxid mit organischen Basen (Teil 2) – Reaktionen von Guanidinen und ω-Aminoalkyl-guanidinen mit Kohlendioxid/ Orthoamides and IminiumSalts, LXXI [1]. Capturing of Carbon Dioxidewith OrganicBases (Part 2) – Reactions of Guanidines and ω-Aminoalkyl-guanidines with Carbon Dioxide

The guanidines 1, 4, 6, 8, 10, and 12 react with carbon dioxide in the presence of traces of water to give the guanidinium hydrogen carbonates 3, 5, 7, 9, 11, and 13. The crystal structures of the salts reveal the presence of centrosymmetric hydrogen carbonate ion dimers, which are connected by O-H・ ・ ・O hydrogen bonds. Additionally the cations are associated with the anions via N-H・ ・ ・O hydrogen bonds. The reaction of the N-(aminoalkyl)guanidine 14 with CO2 in the presence of traces of water affords a stable hygroscopic carbamic acid as the hydrogen carbonate salt 15. In the crystal structure of 15 the hydrogen carbonate ion is connected with the carbamic acid moiety by strong O-H・ ・ ・O hydrogen bonds