Thermospray mass spectrometry of N-methylcarbamates

The thermospray mass spectrometry (TSP/MS) of five N-methylcarbamates is presented. This is the first time that ions other than [M + H]⁺ and [M + NH₄]⁺ have been reported using positive TSP/MS. Protonation of ROCONHCH₃ yields the [CH₃NH₂CO]^+· ion, with formation of the ion–molecule adduct [ROCONHCH₃ · CH₃NH₂CO]^+· through elimination of CO^+· from [CH₃NH₂CO]^+·, and the adduct [M + 75]^+·, [ROCONHCH₃ · OCONH₂CH₃]^+·, is also obtained.     

Gas‐phase fragmentation of metal adducts of alkali‐metal oxalate salts

Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO₂, followed by an ejection of CO to generate a product ion that retains all three metals atoms of the precursor. Spectra recorded even at very low collision energies (2 eV) showed peaks for a 44‐Da neutral fragment loss. Density functional theory calculations predicted that the ejection of CO₂ requires less energy than an expulsion of a Na⁺ and that the [Na₃CO₂]⁺ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na₃C₂O₄]⁺ and [³⁹K₃C₂O₄]⁺ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na₂CO₂]^+? and [K₂CO₂]^+?, respectively, which represented a loss of an M^? from the precursor ions. Moreover, [Na₃CO₂]⁺, [³⁹K₃CO₂]⁺ and [Li₃CO₂]⁺ ions also undergo a CO loss to form [M₃O]⁺. Furthermore, product‐ion spectra for [Na₃C₂O₄]⁺ and [³⁹K₃C₂O₄]⁺ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na₂OH]⁺ and m/z 95 for [³⁹K₂OH]⁺, respectively. An additional peak observed at m/z 65 for [Na₂¹⁸OH] ⁺ in the spectrum recorded for [Na₃C₂O₄]⁺, after the addition of some H₂¹⁸O to the collision gas, confirmed that the [Na₂OH] ⁺ ion is formed by an ion–molecule reaction with residual water in the collision cell. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of thin films and molecular orientation using cluster SIMS

A study of phenylalanine films of different thicknesses from submonolayer to 55 nm on Si wafers has been made using Bi_n⁺ and C₆₀⁺ cluster primary ions in static SIMS. This shows that the effect of film thickness on ion yield is very similar for all primary ions, with an enhanced molecular yield at approximately 1 monolayer attributed to substrate backscattering. The static SIMS ion yields of phenylalanine at different thicknesses are, in principle, the equivalent of a static SIMS depth profile, without the complication of ion beam damage and roughness resulting from sputtering to the relevant thickness. Analyzing thin films of phenylalanine of different thicknesses allows an interpretation of molecular bonding to, and orientation on, the silicon substrate that is confirmed by XPS. The large crater size for cluster ions has interesting effects on the secondary ion intensities of both the overlayer and the substrate for monolayer and submonolayer quantities. This study expands the capability of SIMS for identification of the chemical structure of molecules at surfaces. © Crown copyright 2010.     

Ammonium and caesium carbonate peroxosolvates: supramolecular networks formed by hydrogen bonds

Diammonium carbonate hydrogen peroxide monosolvate, 2NH₄⁺·CO₃²⁻·H₂O₂, (I), and dicaesium carbonate hydrogen peroxide trisolvate, 2Cs⁺·CO₃²⁻·3H₂O₂, (II), were crystallized from 98% hydrogen peroxide. In (I), the carbonate anions and peroxide solvent molecules are arranged on twofold axes. The peroxide molecules act as donors in only two hydrogen bonds with carbonate groups, forming chains along the a and c axes. In the structure of (II), there are three independent Cs⁺ ions, two of them residing on twofold axes, as are two of the four peroxide molecules, one of which is disordered. Both structures comprise complicated three‐dimensional hydrogen‐bonded networks.     

Generation of gas‐phase sodiated arenes such as [(Na3(C6H4)+] from benzene dicarboxylate salts

Upon collision‐induced activation, gaseous sodium adducts generated by electrospray ionization of disodium salts of 1,2‐ 1,3‐, and 1,4‐benzene dicarboxylic acids (m/z 233) undergo an unprecedented expulsion of CO₂ by a rearrangement process to produce an ion of m/z 189 in which all three sodium atoms are retained. When isolated in a collision cell of a tandem‐in‐space mass spectrometer, and subjected to collision‐induced dissociation (CID), only the m/z 189 ions derived from the meta and para isomers underwent a further CO₂ loss to produce a peak at m/z 145 for a sodiated arene of formula (Na₃C₆H₄)⁺. This previously unreported m/z 145 ion, which is useful to differentiate meta and para benzene dicarboxylates from their ortho isomer, is in fact the sodium adduct of phenelenedisodium. Moreover, the m/z 189 ion from all three isomers readily expelled a sodium radical to produce a peak at m/z 166 for a radical cation [(^?C₆H₄CO₂Na₂)⁺], which then eliminated CO₂ to produce a peak at m/z 122 for the distonic cation (^?C₆H₄Na₂)⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Tricaesium tris(oxalato‐κ2O1,O2)chromate(III) dihydrate

The title compound, Cs₃[Cr(C₂O₄)₃]·2H₂O, has been synthesized for the first time and the spatial arrangement of the cations and anions is compared with those of the other members of the alkali metal series. The structure is built up of alternating layers of either the d or l enantiomers of [Cr(oxalate)₃]³⁻. Of note is that the distribution of the [Cr(oxalate)₃]³⁻ enantiomers in the Li⁺, K⁺ and Rb⁺ tris(oxalato)chromates differs from those of the Na⁺ and Cs⁺ tris(oxalato)chromates, and also differs within the corresponding BEDT‐TTF [bis(ethylenedithio)tetrathiafulvalene] conducting salts. The use of tris(oxalato)chromate anions in the crystal engineering of BEDT‐TTF salts is discussed, wherein the salts can be paramagnetic superconductors, semiconductors or metallic proton conductors, depending on whether the counter‐cation is NH₄⁺, H₃O⁺, Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺. These materials can also be superconducting or semiconducting, depending on the spatial distribution of the d and l enantiomers of [Cr(oxalate)₃]³⁻.     

Reactivity of gaseous sodiated ions derived from benzene dicarboxylate salts toward residual water in the collision gas

The sodium adduct of disodium salts of benzene dicarboxylic acids (m/z 233), when subjected to collision‐induced dissociation (CID), undergoes a facile loss of CO₂ to produce an ion of m/z 189, which retains all the three sodium atoms of the precursor. The CID spectrum of this unusual m/z 189 ion shows significant peaks at m/z 167, 63 and 85. The enigmatic m/z 167 ion, which appeared to represent a loss of a 22‐Da neutral fragment from the precursor ion is in fact a fragment produced by the interaction of the m/z 189 ion with traces of water present in the collision gas. The change of the m/z 167 peak to 168, when D₂O vapor was introduced to the collision gas of a Q‐ToF instrument, proved that such an intervention of water could occur even in collision cells of tandem‐in‐space mass spectrometers. The m/z 189 ion has such high affinity for water; it forms an ion/molecule complex even during the brief residence time of ions in collision cells of triple quadrupole instruments. The complex formed in this way then eliminates elements of NaOH to produce the ion observed at m/z 167. In an ion trap, the relative intensity of the m/z 167 peak increases with longer activation time even at the lowest possible collision energy setting. Similarly, the m/z 145 ion (which represents the sodium adduct of phenelenedisodium, formed by two consecutive losses of CO₂ from the m/z 233 ion of meta‐ and para‐isomers) interacts with water to produce a fragment ion at m/z 123 for the sodium adduct of phenylsodium. Other uncommon ions that originate also from water/ion interactions are observed at m/z 85 and 63 for [Na₃O]⁺ and [Na₂OH]⁺, respectively. Tandem mass spectrometric experiments conducted with appropriately deuterium‐labeled compounds confirmed that the proton required for the formation of the [Na₂OH]⁺ ion originates from traces of water present in the collision gas and not from the ring protons of the aromatic moiety. Copyright © 2010 John Wiley & Sons, Ltd.     

Repair of defects created by Ar+ sputtering on graphite surface by annealing as confirmed using ToF‐SIMS and XPS

Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar⁺ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp³ carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the C_x⁻ and C_xH⁻ ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of C_xH₂^+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp³ carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the C_xH⁻ and C_xH₂^+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.     

Dissolution of uranium oxides under alkaline oxidizing conditions

Bench scale experiments were conducted to determine the dissolution characteristics of UO₂, U₃O₈, and UO₃ in aqueous peroxide-containing carbonate solutions. The experimental parameters investigated included carbonate countercation (NH₄ ⁺, Na⁺, K⁺, and Rb⁺) and H₂O₂ concentration. The carbonate countercation had a dramatic influence on the dissolution behavior of UO₂ in 1 M carbonate solutions containing 0.1 M H₂O₂, with the most rapid dissolution occurring in (NH₄)₂CO₃ solution. The initial dissolution rate (y) of UO₂ in 1 M (NH₄)₂CO₃ increased linearly with peroxide concentration (x) ranging from 0.05 to 2 M according to: y = 2.41x + 1.14. The trend in initial dissolution rates for the three U oxides under study was UO₃ ≫ U₃O₈ > UO₂.     

The sodium salt of 2‐hydroxy‐5‐nitrobenzylsulfonic acid

The structural data for sodium 2‐hydroxy‐5‐nitro­benzyl­sulfonate monohydrate, Na⁺·C₇H₆NO₆S^?·H₂O, which mimics an artificial substrate for human aryl­sulfatase A, viz. p‐­nitrocatechol sulfate, reveal that the geometric parameters of the substrate and its analogue are very similar. Two water mol­ecules, the phenolic O atom and three sulfonate O atoms form the coordination sphere of the Na⁺ ion, which is a distorted octahedron. The Na⁺ cations and the O atoms join to form a chain polymer.     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.     

Hydroxylation of the silica in microfabricated thin layer chromatography plates as probed by time‐of‐flight secondary ion mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy

Microfabricated silica thin layer chromatography (TLC) plates have previously been prepared on patterned carbon nanotube forests. The high temperatures used in their fabrication reduce the number of hydroxyl groups on their surfaces. Fortunately, silica can be rehydroxylated. In diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), a silanol peak below 3740 cm^?1 indicates a well‐hydroxylated silica surface that is fit for chromatography. Hydroxylations of our materials with HF are so effective that it is not possible to discern the position of this peak. In contrast, this signal is discernable when the plates are treated with NH₄OH. To find a more convenient method for studying the surfaces of TLC plates, time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) was considered. ToF‐SIMS is advantageous because multiple microfabricated TLC plates must be scraped to obtain enough silica for one DRIFT analysis, while static SIMS can be performed on very small regions (500 × 500 µm² or less) of individual plates. Ratios of the SiOH⁺ and Si⁺ ToF‐SIMS signals for microfabricated TLC plates correlated well with ~3740 cm^?1 silanol peaks from DRIFT. Thus, SIMS allows direct analysis of all of our treated and untreated plates, including those hydroxylated with HF. The best hydroxylation condition for HF, which was better than any studied for NH₄OH, was around 150 ppm at room temperature. The best hydroxylation condition for NH₄OH was 50 °C for 72 h. ToF‐SIMS versus DRIFT results of commercial TLC plates were also obtained and evaluated. Copyright © 2014 John Wiley & Sons, Ltd.     

Electron impact mass spectra of some salts of carboxylic acids with alkali (group Ia) metals

Thirteen of the salts of the alkali metals (Li, Na, K, Rb, Cs) with acetic, 2,2-dimethylpropionic, trifluoroacetic and heptafluorobutyric acid have been found to be sufficiently volatile to give mass spectra under normal electron impact conditions. The metal containing ions observed include (M=metal): [M]⁺, [MO]⁺, [MCO₂]⁺, [M₂]^+·, [M₂O]^+·, [M₂CO₂]^+· and the cluster ions [M_n (carboxylate)_n-1]⁺ for n = 2–8.     

Studies on phosphatidylserine by tandem quadrupole and multiple stage quadrupole ion-trap mass spectrometry with electrospray ionization: Structural characterization and the fragmentation processes

Low-energy CAD product-ion spectra of various molecular species of phosphatidylserine (PS) in the forms of [M−H]⁻ and [M−2H+Alk]⁻ in the negative-ion mode, as well as in the forms of [M+H]⁺, [M+Alk]⁺, [M−H+2Alk]⁺, and [M−2H+3Alk]⁺ (where Alk=Li, Na) in the positive-ion mode contain rich fragment ions that are applicable for structural determination. Following CAD, the [M−H]⁻ ion of PS undergoes dissociation to eliminate the serine moiety (loss of C₃H₅NO₂) to give a [M−H−87]⁻ ion, which equals to the [M−H]⁻ ion of a phoshatidic acid (PA) and give rise to a MS³-spectrum that is identical to the MS²-spectrum of PA. The major fragmentation process for the [M−2H+Alk]⁻ ion of PS arises from primary loss of 87 to give rise to a [M−2H+Alk−87]⁻ ion, followed by loss of fatty acid substituents as acids (R_xCO₂H, x=1,2) or as alkali salts (e. g., R_xCO₂Li, x=1,2). These fragmentations result in a greater abundance of [M−2H+Alk−87−R₂CO₂H]⁻ than [M−2H+Alk−87−R₁CO₂H]⁻ and a greater abundance of [M−2H+Alk−87−R₂CO₂Li]⁻ than [M−2H+Alk−87−R₁CO₂Li]⁻; while further dissociation of the [M−2H+Alk−87−R_{2(or 1)}CO₂Li]⁻ ions gives a preferential formation of the carboxylate anion at sn-1 (R₁CO₂⁻) over that at sn-2 (R₂CO₂⁻). Other major fragmentation process arises from differential loss of the fatty acid substituents as ketenes (loss of R_x′CH=CO, x=1,2). This results in a more prominent [M−2H+Alk−R₂′CH=CO]⁻ ion than [M−2H+Alk−R₁′CH=CO]⁻ ion. Ions informative for structural characterization of PS are of low abundance in the MS²-spectra of both the [M+H]⁺ and the [M+Alk]⁺ ions, but are abundant in the MS³-spectra. The MS²-spectrum of the [M+Alk]⁺ ion contains a unique ion corresponding to internal loss of a phosphate group probably via the fragmentation processes involving rearrangement steps. The [M−H+2Alk]⁺ ion of PS yields a major [M−H+2Alk−87]⁺ ion, which is equivalent to an alkali adduct ion of a monoalkali salt of PA and gives rise to a greater abundance of [M−H+2Alk−87−R₁CO₂H]⁺ than [M−H+2Alk−87−R₂CO₂H]⁺. Similarly, the [M−2H+3Alk]⁺ ion of PS also yields a prominent [M−2H+3Alk−87]⁺ ion, which undergoes consecutive dissociation processes that involve differential losses of the two fatty acyl substituents. Because all of the above tandem mass spectra contain several sets of ion pairs involving differential losses of the fatty acid substituents as ketenes or as free fatty acids, the identities of the fatty acyl substituents and their positions on the glycerol backbone can be easily assigned by the drastic differences in the abundances of the ions in each pair.     

Degree of hydration in cement paste and C<Subscript>3</Subscript>A-sodium carbonate-water systems

This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate (C₃A) paste at water to cement ratio of 0.5 and C₃A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted clinker minerals to gel-like hydration products in the cement-Na₂CO₃ pastes takes place rapidly between 1^st to 24^th h. Contrary the Ca(OH)₂ formation within the same time interval is retarded in the excess of CO₃²⁻ ions due to intensive rise and growth of CaCO₃ crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents of calcite and vaterite relative to that of Ca(OH)₂ in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na₂CO₃ are observed. C₃A hydrates very quickly with sodium carbonate between 1^st and 24^th h forming hydration products rich in bound water and characterized also by complex salts of (x)C₃A·(y)CO₂·(zH₂O type, whereas C₃A-H₂O system offers C₃AH₆ as the main hydration product. Higher content of the formed calcium aluminate hydrates in C₃A-Na₂CO₃-H₂O system also contributes to early strength increase of Portland cement paste.     

Three hydrates of the bisphosphonate risedronate,consisting of one molecular and two ionic structures

Three different hydrates of risedronate were obtained by varying the pH of a solution containing the compound. At the pH values used, the N atom of the pyridine group is protonated and the compounds are zwitterionic. Crystals obtained directly from the synthesis resulted in risedronate monohydrate, or [1‐hydroxy‐1‐phosphono‐2‐(pyridinium‐3‐yl)­ethyl]phosphonate monohydrate, C₇H₁₁NO₇P₂·H₂O, (I), in which just one phosphonate group is negatively charged. Recrystallizations at pH values of 2 and 4 yielded risedronate dihydrate, or sodium [1‐hydroxy‐2‐(pyridinium‐3‐yl)­ethane‐1,2‐diyl]­bis­(phosphonate) dihydrate, Na⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (II). Finally, recrystallizations at pH values of 7 and 8 produced risedronate 2.5‐­hydrate, or sodium [1‐hydroxy‐2‐(pyridinium‐3‐yl)­ethane‐1,2‐diyl]­bis­(phosphonate) 2.5‐hydrate, Na⁺·C₇H₁₀NO₇P₂⁻·­2.5H₂O, (III). At these four pH values, both phosphonate groups in (II) and (III) are negatively charged and coordinated to an Na⁺ ion. Crystals of (II), i.e. those grown at pH values of 2 and 4, have isomorphous polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to the same Na⁺ ion. On the other hand, crystals of (III), i.e. those grown at pH values of 7 and 8, have isomorphism polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to different Na⁺ ions.     

A comparative study on the thermal decomposition of some transition metal maleates and fumarates

Thermal decomposition of M(mal/fum)·xH₂O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C employing TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320–360°C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than maleates.     

Sorption of uranyl ion on hydrous silica: Effects of ionic strength and ethylenediaminetetraacetic acid (EDTA)

The effects of ionic strength and of ethylenediamin et etraacetic acid (EDTA) on the sorption of uranyl ion, UO₂ ²⁺, to SiO₂·xH₂O (silica gel) were investigated. It was observed that pH and the ions present in the supporting electrolytes influence the ionic strength effects. The presence of different sodium salts in the concentration range (0.20 to 1.40M) suppressed the sorption of UO₂ ²⁺ in the order: NaNO₃ < NaClO₄ < NaCl < NaOCOCH₃ < Na₂SO₄ [pH 2.75(±0.05)], while the presence of perchlorate salts of Li⁺, Na⁺ and Ca²⁺ (0.20 to 1.40M) promoted the sorption of UO₂ ²⁺ on silica gel in the order: LiClO₄∼NaClO₄<Ca(ClO₄)₂ at pH 2.80(±0.05). The ionic strength effect on UO₂ ²⁺ sorption was studied in presence of EDTA (0–1.00·10⁻³M) in the pH range 2.90 to 5.57. The sorption data and speciation calculation suggest negligible complexation of UO₂ ²⁺ with EDTA at I≥1.00M NaClO₄. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.     

Zur Kenntnis des Natriumthioferrates(III)

The mixed valency compound Na₃Fe₂S₄, which is also formed in iron-sodium polysulfide melts, is oxidized and hydrated to NaFeS₂·H₂O (x ≈ 2) on air. It is shown by TGA that this hydrate loses the water reversibly between 80–140 °C. A crystal structure model for the water free phase NaFeS₂ is proposed (space group I 222,a=6.25 Å,b=10.83 Å,c=5.40 Å). The formation of NaFeS₂·xH₂O from Na₃Fe₂S₄ and the reversible phase transformation between NaFeS₂·xH₂O and NaFeS₂ are topotactic. Na⁺ ions in NaFeS₂·xH₂O are easily exchanged against K⁺, Rb⁺, Cs⁺, Tl⁺, Ca²⁺, Sr²⁺, and Ba²⁺. The high chemical reactivity of the sodium thioferrates is discussed and their crystal structures are compared with the other alkali metal thioferrate structures.