Thermal desorption of quasimolecular ions

The thermal desorption of [M + Alkali]⁺ quasimolecular ions from a heated metal surface is reported for some alkali salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. No quasimolecular ion could be detected from sucrose. With benzo[15]crown-5 the desorption of [M + Na]⁺ ions takes place even below the threshold temperature for thermionic emission of alkali ions. In addition, the desorption of intact [B(C₆H₅)₄]^? ions from a layer of NaB(C₆H₅)₄ is reported.     

Spontaneous Hierarchical Assembly of Crown Ether‐like Macrocycles into Nanofibers and Microfibers Induced by Alkali‐Metal and Ammonium Salts

Schiff base macrocycle 1 , which has a crown ether like central pore, was combined with different alkali‐metal and ammonium salts in chloroform, resulting in one‐dimensional supramolecular aggregates. The ion‐induced self‐assembly was studied with solid‐state NMR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was found that the lengths and widths of the superstructures depend on the cation and counteranion of the salts. Among the salts being used, Na⁺ and NH₄⁺ ions with BF₄^? ions showed the most impressive fibrous structures that can grow up to 1 μm in diameter and hundreds of microns in length. In addition, the size of the fibers can be controlled by the evaporation rate of the solvent. A new macrocycle with bulky triptycenyl substituents that prevent supramolecular assembly was prepared and did not display any nanofibers with alkali‐metal ions in chloroform when studied with TEM.     

Mass-spectrometry of frozen matrix-assisted water in environmental analysis

Summary CO₂ laser evaporation/KrF-laser ionization combined with reflectron time-of-flight mass-spectrometry have been used for the analysis of drinking water polluted with phenol. A minimum phenol concentration level of 10^–8% was detected. Considerable temperature reduction (up to 50 K) due to laser evaporated molecules from the frozen water surface has been observed.     

Mass spectral fragmentation of metal dithiocarbamate complex salts

A summary of the mass spectra of metal dithiocarbamate complex salts (ML₂ and ML₃) is presented. Only divalent metal dithiocarbamate ions without an electronic configuration containing an inert s-orbital electron pair exhibited both expulsion of a ligand radical (L) and the neutral even electron species (L–H) generated from the ligand via hydrogen transfer to the metal-containing fragment ion. Divalent metal dithiocarbamate ions can be generated either by direct electron impact ionization of gas phase ML₂ molecules or ionization of ML₃ molecules followed by loss of a ligand radical. A highly stable sp² hybridized, gas phase ion of a monobidentate lead dithiocarbamate complex is proposed.     

Determination of alkali metal ion binding selectivities of calixarenes by matrix-assisted laser desorption ionization and electrospray ionization in a quadrupole ion trap

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) are used to evaluate the alkali metal ion binding selectivities of a series of calixarenes. Each calixarene of interest is mixed with one or more alkali metal salts (1:100 ratio of calixarene to metal), either in the ESI solution or on the MALDI probe surface, and the relative binding selectivities are directly determined from the intensities of the calixarene/metal complexes in the mass spectra. For t-butylcalix[4]arene-tetraacetic acid tetraethyl ester (calixarene 1), complexation of Na⁺ is favored over complexation of K⁺, in agreement with prior solution results obtained by conventional methods. For the three calixarenes that do not have t-butyl groups on the upper rims, the calixarenes preferentially bind K⁺ over Na⁺, thus demonstrating that size selective complexation can be probed with both the ESI and MALDI methods. Collision-activated dissociation results indicate that the phenyl oxygens, but not necessarily the ethoxy ethyl oxygens of the lower rims, are the primary binding sites for the alkali metal ions.     

Alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates: Radical polymerization and copolymerization

A new preparation of alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates, by reaction of alkali salts of acrylic and methacrylic acids with cyclic sulphates, is described; spectral characterization of the products is described. The kinetics of the radical polymerization of sodium (2-sulphoxyethyl)methacrylate (SSEM) were studied; monomer reactivity ratios for copolymerization with methacrylic acid were: r₁ = 1.1 ± 0.15 and r₂ = 0.73 ± 0.05. Dark electrical surface conductivity of some homopolymers and copolymers with methacrylic acid was found to be 10⁴–10¹¹$\text{Ω}{}^{\mathrm{?1}}$, depending on relative humidity.     

Further evidence for the stability of methylenechloronium ylide,H2CCIH. A neutralization-reionization ion-dissociation experiment

Recent theoretical and experimental studies are in conflict with our previous neutralization–reionization evidence for the surprising stability of simple ylides such as H₂CCIH. Neutralization of [H₂CCIH]⁺˙ ions from CICH₂COOH with Hg followed by reionization of the resulting neutral molecules with O₂ produces intense [CCIH₃]⁺˙ parent ions. Collisionally activated dissociation of these mass-selected ions shows that 47 ± 5% are the [H₂CCIH]⁺˙ isomer. This demonstrates that stable H₂CCIH molecules can be formed by neutralization, surviving intact for the lifetime of the experiment (10^?6 s). Field ionization conditions effective in ionizing excited argon atoms do not produce appreciable ionization of the neutrals from [H₂CCIH]⁺˙, suggesting that the stable H₂CCIH neutrals are not Rydberg state molecules.     

Solvent effect on complexation reactions

The inclusion complexation of aromatic amines with cucurbit[6]uril (CB[6]) capped with alkali metal cations was studied spectrophotometrically. We showed that CB[6] capped with alkali metal cations forms a 1:1 inclusion complex with the aromatic amine guests (neutral organic molecules), independent of the length of guest molecules. The effects of salts on the inclusion constants of CB[6] in the presence of different alkali salts were examined and it was found that the inclusion constants increased in the order of alkali cation Cs⁺ < Na⁺ < K⁺, suggesting the interaction of amine guests with the capped alkali metal cation. Further, the structures of the inclusion complexation of aromatic amines with CB[6] were characterized by ¹H NMR measurements. Based on the results, the inclusion abilities of CB[6] capped with alkali metal cations are discussed.     

Ion-pair formation in fast collisions of metastable argon with iodine

Differential ion-pair production cross sections for Ar^*—I₂ collisions at center of mass energies of 25–133 eV are quite similar to analogous alkali—I₂ results despite the addition of competing channels (Penning ionization and excitation transfer) and possible multiple electronic surface crossings.     

Salt effects in the synergistic solvent extraction of Co2+

The extraction of Co²⁺ by mixtures of acetylacetone (acac) and either pyridine (Py), benzylamine (ba), triethylamine (tea) or tripyridylamine (tpa) bases in xylene solvent was investigated from an aqueous phase containing salts of LiCl, NaCl, KCl, RbCl and CsCl in concentrations varying up to 3M. The different hydration properties of the alkali metal cations is show to affect very slightly the synergistic solvent extraction of Co²⁺. This result, together with previously obtained thermodynamic data indicating the nonexistence of water molecules in the extracted synergistic species, may explain the fact that these salts have no effect on the extraction of Co(acac)₂ (N-base)₂.     

Comparison of ionization behaviors of ring and linear carbohydrates in MALDI-TOFMS

Ionization efficiencies of cyclodextrins and their linear compounds in matrix-assisted laser desorption and ionisation (MALDI) analysis were compared, and differences in the ionization efficiencies of α- and β-cyclodextrins were also studied. The mass spectra showed a series of the [M+cation]⁺ ions but not the [M+H]⁺ ions. Alkali metal salts of Li⁺, Na⁺, K⁺, and Cs⁺ were used as the cationizing agents to enhance the ionization efficiency. Relative ion intensities of the ring compounds (α- and β-cyclodextrins) were much larger than those of the linear ones (maltohexaose and maltoheptaose), and the difference showed an increasing trend with the size of the alkali metal cation. β-Cyclodextrin had higher ionization efficiency than α-cyclodextrin and the difference increased by increasing the size of the alkali metal cation. It was also found that the ionization efficiency was affected by the counter anion of the salt. The higher ionization efficiencies of cyclodextrins were explained with the number of coordination sites and the binding energies.     

Calcium ion generation from calcium iodide by surface ionization in mass spectrometry

The process of calcium ionization on a rhenium filament was studied at different heating conditions of the evaporation filament (EF) loaded with a CaI₂ sample. The analysis indicated that three different ionization processes are involved in the ionization; (1) CaI₂ → Ca⁺, (2) CaI → Ca⁺, and (3) Ca → Ca⁺. Reaction (1) appears at the low temperatures of EF, reaction (2) is dominant in the medium temperature region, and reaction (3) appears at the high temperature of EF. These facts suggest that the EF assists the dissociation of CaI₂. Experiments are extended to the isotopic ratio measurement using different materials of Ta, Re, and Pt for the evaporation filament.     

The effect of sample salt additives on capillary electrophoresis analysis of intact proteins using surface modified capillaries

The effect of adding alkali salts to protein samples for capillary electrophoretic (CE) analysis of intact proteins was studied. A high degree of peak stacking, even for large proteins, was found to occur when alkali salts were added to the sample. The addition of salt to the protein sample promotes a strong improvement in the peak efficiency of individual proteins giving up to 2.1 × 10⁶ apparent plates/m. The concentration of salt required in the sample to reach optimal peak efficiency show dependency on both the molecular weight and molar concentration of the protein. However, adding salt will, at a sufficiently high concentration, cause a mixture of proteins to co-migrate to one very sharp peak. The observed sample stacking effect was obtained with a number of different surface modified silica capillaries indicating a general phenomenon and not surface coating specific.     

Evidence that gas-phase ion-molecule reactions are responsible for the behaviour of crown ethers under fast atom bombardment conditions

The fast atom bombardment mass spectrometry of some crown ethers shows the formation of both [M + H]⁺ and [M ? H]⁺ ions, paralleling behaviour already observed using electron impact ionization. The study of these oily samples with and without a glycerol matrix, trifluoroacetic acid or alkali metal salts, suggests that the ionization process does not occur in the condensed phase, but in the selvedge region by gas-phase ion-molecule reactions in accordance with the ‘gas-phase explosion model’. Positive-ion chemical ionization experiments support this proposal.     

Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2‐ethylhexyl)sulfosuccinate

The behavior of aqueous solutions of sodium bis(2‐ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N⁰_AOT AOT^? anions (N⁰_AOT = 0, 5, 10) and N⁰_Na sodium ions (N⁰_Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N⁰_AOT and N⁰_Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Organocatalysis of nucleophilic substitution reactions by the combined effects of two promoters fused in a molecule: oligoethylene glycol substituted imidazolium salts

Oligoethylene glycol substituted imidazolium salts were synthesized as promoters for a range of S_N2 reactions, and their efficiency was examined. These tailor-made organic promoters enhanced the nucleophilicity of alkali metal salts significantly through the combined effects of two promoters (oligoethylene glycols and imidazolium salts) in a single molecule. The effects of the oligoethylene glycol side chain length, ionic liquid anions, nucleophiles, and substrates were investigated systematically. [hexaEGmim][OMs] and [dihexaEGim][OMs] showed the highest efficiency for S_N2 reactions using alkali metal salts. The role of the terminal hydroxyl groups of the oligoethylene glycol moiety was assessed by examining the relative S_N2 yields of chlorination and bromination. The results showed that the hydrogen bonding strength of the hydroxyl groups with the nucleophile is very important. The mechanism for the excellent promotion of S_N2 reactions by oligoEGILs was examined by quantum chemical calculations. The results showed that the oxygen atoms in the oligoethylene glycol portion and the ionic liquid anion act on the counter cation K⁺ or Na⁺ as a Lewis base, to enhance the reactivity of the metal salts significantly.     

New Low‐Molecular‐Mass Gelators Based on L‐Lysine: Amphiphilic Gelators and Water‐Soluble Organogelators

The new L ‐lysine alkali‐metal salts 1 – 5 (M⁺=Na⁺ and K⁺) with different alkyl groups at the N^α‐position were easily synthesized, and their hydro‐ and organogelation properties were investigated. All compounds were H₂O‐soluble, and some salts, especially the potassium salts, functioned as a hydrogenator that could gel water below 2 wt‐%. These salts also had organogelation abilities for many organic solvents.     

Salt effects in the binding of 4-(1-pyrenyl)-butyltrimethylammonium to poly(vinylbenzo-18-crown-6) and poly(vinylbenzoglyme) in water

The binding of 4¹-(1-pyrenyl)butyltrimethylammonium bromide (PN⁺) to the neutral poly-soap-type polymers poly(vinylbenzo-18-crown-6) (P18C6) and poly(vinylbenzoglyme) (PVBG) was studied by optical spectroscopy and fluorescence in the presence and absence of salts. Measurements of the respective binding constants were based on distinct differences in the optical absorption spectra of free and polymer-bound PN⁺. When crown ether-compelxable cations (e.g., K⁺) were added the adsorption of PN⁺ to P18C6 decreased as the neutral polymer was converted to a polycation. No decrease was found with PVBG because alkali ions do not complex significantly to this polymer in water. PN⁺ adsorption to both polymers rose rapidly, however, as the salt concentration increased. This effect was strongly anion-dependent and increased in the order of Cl^? < Br^? < I^? < CNS^? < BPh₄?. The increased binding was reflected in a higher binding constant and also in a larger number of bound PN⁺ molecules per polymer chain under saturation conditions. It is argued that the formation of ion pairs or larger ion clusters in the aqueous phase when anions are added forces more PN⁺ molecules to adsorb on the surface of the polymer coil to which they are bound as ion pairs or higher aggregates. Under saturation conditions enough PN⁺ molecules are bound to convert the pyrene monomer fluorescence spectrum into that of the excimer. These results are compared with data obtained for the anionic solute 4-(1-pyrenyl)butanoate in the presence of salts.     

Laser desorption mass spectrometry of squaric acid and its salts

The laser desorption mass spectrometry of the oxocarbon squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) and its salts of the form A₂C₄O₄ (A = cation) is described. Both positive and negative ion spectra were obtained. The positive ion spectrum of the acid is characterized by an ion corresponding to loss of CO from [M + H]⁺. The negative ion spectrum shows an intense [M ? H]^? peak in addition to a dimer species. The alkali salt spectra contain [M + A]⁺ in the positive mode and [M ? A]^? and an intense [C₄HO₄]^? in the negative mode. The smaller alkali salts also have an [M + H]⁺ adduct ion. Unlike the alkali squarates, the ammonium salt shows ions corresponding to losses of neutrals from the molecular adduct in the positive ion spectrum and a dimer species in the negative ion spectrum. Molecular weight information was obtained in all cases. A (bis) dicyanomethylene derivative of potassium squarate was also studied. Some field desorption mass spectrometry results are presented for comparison.     

Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M₁ + Cat + M₂)⁺, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M₁ + Cat)⁺ and (M₂ + Cat)⁺ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li⁺, Na⁺, and K⁺ than the larger ions such as Cs⁺ and Rb⁺. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.