Keith J. Fisher

Sub-ppt detection limits for copper ions with Gly-Gly-His modified electrodes

An electrochemical metal ion sensor has been developed with a detection limit of less than 0.2 ppt by the covalent attachment of the tripeptide Gly-Gly-His as a recognition element to a 3-mercaptopropionic acid modified gold electrode.

Fullerenes : preparation, properties, and carbon chemistry

Abstract This article reviews the current literature on the new form of carbon based on the fullerene structure. It is now clear that fullerenes can be made from sources other than graphite. Progress has been made in characterising this material by Fourier transform infra red (FTIR), nuclear magnetic resonance (NMR) and mass spectrometric techniques and a wide range of physical measurements have been completed. Potential uses of fullerenes have also been outlined. Fullerene chemistry may also be useful in understanding both coking and soot-forming processes.

THE GAS PHASE REACTIVITY AND THEORETICAL STRUCTURES OF GERMANIUM IONS GENERATED BY DIRECT LASER VAPORISATION

Abstract The ion series Gex±, x=1–7, have been generated using direct laser vaporisation and detected using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Optimised non-local spin density approximation-density functional theory (NLSD) structures for these ions and their corresponding neutrals are presented. These results are used to interpret the relative intensity variation in positive-ion and negative-ion mass spectra and deduce the most prevalent neutral species in the laser plume. Ion–molecule reaction studies confirm the transitions to closed cyclic structures, as predicted by the NLSD calculations, at x=3 for the anions and x=4 for the cations. The ions most reactive towards CH3OH, CH3CH2OH, H2S and c-C3H6, were found to be the small cations with terminal, electron-rich (radical) Ge centres, while all the anions, with the exception of Ge2−, were essentially unreactive. The NLSD results reveal that there is little structural change upon either electron attachment or ionisation of the neutral structures. Small energy separations are predicted between the a 3 Π u and X 3 Σ − g states of Ge2 (6.2 kcal mol−1), the a 3 B 1 and X 1 A 1 spin states of Ge3 (4.6 kcal mol−1) and the singlet and triplet spin states of Ge5 (about 4 kcal mol−1 vertical separation). A Rydberg-like “square” quartet state of Ge4− was also discovered, 30 kcal mol−1 higher in energy than the lowest energy D2h doublet structure. NLSD did not locate minima corresponding to the anticipated 2 Π u ground states of the mixed valence dimers Ge2+ and Ge2−, instead locating the states 4 Σ + g Ge + 2 and 2 Σ + g Ge − 2 both of which have electron vacancies below the HOMO. Collision induced dissociation (CID) results from FTICR-MS studies, and the recent literature laser photoelectron-zero electron kinetic energy (LPES–ZEKE) results for the anions Ge2− through to Ge7− were interpreted using the theoretical results from this study.

The catalytic activation of primary alcohols on niobium oxide surfaces unraveled: the gas phase reactions of NbxOy− clusters with methanol and ethanol

Abstract The reactions of oligomeric niobium oxide anions (up to Nb 6 O 15 − ), generated by laser ablation and studied using a Fourier transform ICR mass spectrometer, have been used to deduce the roles of (i) Nb(III,IV,V) centers, (ii) Nb/O double bonds and (iii) proximal Nb centers, in the catalytic activation of methanol and ethanol. The most important recurring mechanism involves initial alcohol condensation at a cluster metal-oxygen double bond to yield Nb(OH)(OCH 3 ). There is no change in the oxidation state of the cluster during this step. The so-formed niobium-hydroxyl bond is the new reactive site in the cluster, and undergoes ligand switching in a follow-up collision to yield a bis-methoxy cluster and neutral water. Dehydrogenation is only observed to occur with clusters possessing two Nb/O double bonds at a single metal center, and involves reduction of the participating Nb(V) center to Nb(III). An ion ejection/selection step was used to monitor the activity of a number of the ionic reaction products towards the alcohols, and in most instances spontaneous or kinetically-activated decomposition resulted in regeneration of the parent cluster from the substituted species.

Vanadium oxide anion cluster reactions with methyl isobutyrate and methyl methacrylate monomer and dimer: a study by FT/ICR mass spectrometry

Laser ablation of vanadium pentoxide (V2O5) powder produces VO3-, V2O5-, V3O7-, V3O8-, and V4O10- cluster ions which have subsequently been reacted with methyl isobutyrate, methyl methacrylate monomer and its dimer in the ion cell region of a Fourier transform ion cyclotron resonance mass spectrometer. Gas phase ion/molecule chemistry has revealed that reactivity decreases with increased mass of the vanadium oxide cluster anions. VO3-, V2O5-, and V3O7- ions react with the three reagents, methyl isobutyrate, methyl methacrylate and its dimer, respectively, either by addition of a whole reagent molecule or an associated fragment. All products formed are a result of parallel processes. V4O10- undergoes no reaction for reaction times of up to 500 s, while V3O8- adds a water molecule. Although the ions possess a net negative charge, the reactive site toward electron rich reagents such as methyl isobutyrate, methyl methacrylate and its dimer is the under-coordinated vanadium atom. This observation is supported by the lack of reactivity toward the studied reagents by those anions (V3O8- and V4O10-) whose most likely stable structures contain fully coordinated vanadium atoms

Some reactions and thermochemistry of NbO3−: oxidation and reduction, hydrogen bond strength, and catalytic activation of primary alcohols

Abstract Some reactions of the Nb(V) anion NbO3− have been studied in the gas phase using Fourier transform ion cyclotron resonance mass spectrometry. In most instances, this ion behaves as a closed shell species, however, reactions where both the ion and neutral products were radicals were also observed. In these cases, the niobium was invariably reduced to a lower oxidation state. A value for the NbO3−–H bond strength is proposed, based on the observed reactivity: D(NbO3−–H) = 103 ± 9 kcal mol−1. The reactions of NbO3− with methanol and ethanol were also studied due to their relevance in catalytic processes. For the NbO3−/CH3OH couple, the favoured pathway involves reduction of the parent ion to NbO3H2−, dihydroxyniobium(III) oxide, and concomitant liberation of formaldehyde in a single step dehydrogenation reaction. The dehydration pathway, which liberates the neutral H2O, competes less efficiently with the oxidation/reduction pathway. The primary product NbO3H2− does not appear to react with methanol. In contrast, the dehydration pathway is kinetically favoured for ethanol, with liberation of neutral ethene and formation of NbO4H2− observed. This reaction is extremely inefficient (kexp/kADO = 0.02). The primary hydration product reacts even less efficiently with ethanol, in a two step process, ultimately resulting in formation of NbO4C2H6−. Radio-frequency acceleration of NbO4H2− results in regeneration of the parent ion. Overall, the results are in agreement with the hypothesis that higher order Nb–O bonds are the catalytically active centres on Nb–O surfaces.

Carbon phosphide anions

Stable carbon phosphide anions have been prepared by the reaction of small carbon anions (C n − n = 3–9) with gaseous P4. The C n − anions, produced by laser ablation, were trapped and reacted in a Fourier transform ion cyclotron resonance mass spectrometer. The compositions of the anions formed were C n P, C n P2, C4P4, C n P5. All the anions for n = 3–9 are covered in this paper and have been investigated theoretically using density functional calculations, incorporating gradient corrections and numerical basis sets. The [C n P]− and [C n P2]− anions are calculated to be linear, with the P atoms at one and both ends of the C n chain, respectively. The [C4P4]− anion is the only ion containing four P atoms, and never has more than minor intensity; three structures close in energy are calculated for [C4P4]−, with the most stable possessing a CP4 mononocycle at the end of the C4 chain. The [C n P5]− anions observed when n = 4, 6 or 8 have a lowest energy structure with one phosphorus atom at one end of the chain and a P4 ring at the other end.

Mass spectrometry and density functional studies of neutral and anionic tin clusters

Abstract The anionic tin clusters Sn x − , x = 2–7 have been generated and studied using laser ablation Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Gas phase ion-molecule chemistry has revealed that some clusters are reactive towards 2-propanol and hydrogen sulflde and all the clusters are unreactive towards methanol, ethanol, nitrous oxide and methane. Energy minimised structures, obtained from non-relativistic local spin density functional calculations including post-SCF non-local energy corrections, were doublets and favoured cyclic or closed structures for x ≥ 3 . Inspection of the highest occupied molecular orbitals for the anions revealed significant delocalisation of the additional electron, leading to cluster anions which resemble a sphere, with the charge distributed evenly over all the atoms. Adiabatic electron affinities and atomisation energies determined from energy minimised neutral and anion calculations compare well with literature values.

The crystallisation of polyoxo-molybdate and -tungstate anions with phenylated phosphonium and arsonium cations, in relation to the crystal packing and species in solution

Polyoxometallate anions often occur as mixtures of species in solution. We have investigated the possible selectivity of crystallisation of these anions using arylated cations that commonly adopt cation dominated crystal packing motifs known as multiple aryl embraces. The crystallisation and crystal structures of the compounds (Ph4P)2[Mo2O7], (Ph4P)2[Mo6O19](CH3CN)2, (Ph4P)2[W6O19](DMSO)2, (MePh3As)2[Mo6O19], (Ph4P)2(Na)2[Mo8O26](CH3CN)2(H2O), (Bu4P)3(NH4)[Mo8O26], (Ph4P)4[W10O32] and (MePh3P)4[W10O32] are described, and solution compositions measured by electrospray mass spectrometry. The crystal packing of these and some related literature compounds is analysed and interpreted. One- and two-dimensional nets of embracing Ph4P+ cations are general, with segregated cations and segregated anions, and it appears that Ph4P+ cation arrays control the separations of anions, with solvent occupying any gaps between anions. An embracing pair of MePh3As+ is cube-shaped, as is [Mo6O19]2−, and together they form a pseudo face-centered cubic array. In (MePh3P)4[W10O32] this fcc array is expanded by additional stuffed cations. The electrostatic energies of the ion arrays are discussed, in the context of the segregation of homo-charged ions, and the commensurabilities of the ion arrays. Using electrospray mass spectrometry of the solutions from which the crystals formed, we show that (Ph4P)2[Mo2O7] crystallises from a solution containing [Mo8O26]4−.

Gas phase reactions of the negative and positive ions of gold and platinum with aromatic hydrocarbons, thiols and H2S

Abstract The negative and positive ions of gold and platinum, Au−, Pt−, Au+, generated by the direct laser ablation of the metals, were reacted with benzene, alkyl substituted benzenes, benzenethiol, H2S, n-propanethiol and the four butanethiols in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS). Reactions were carried out with ions collisionally cooled, to reduce their kinetic energy and deactivate electronic excited states, and with “hot” ions directly after production by the laser. The negative ions of both metals react at a slower rate than the positive ions and their spectra show fewer products. No products were observed for the reaction of metal negative ions with the aromatic hydrocarbons except for the reaction of Pt− ions with mesitylene to give the (CH3)2C6H3CH2− anion as the major product. The reactions of Au− ions with most of the aryl and the alkyl thiols produced the SR− anion as the major product. The reactions of both Au+ and Pt+ ions with benzene and the substituted benzenes gave the charge transfer ions L+ (e.g. C6H6+) as the major products. Collisionally cooled Pt+ ions gave minor product ions identified as Pt-benzyne species (PtC6H4+), while “hot” Pt+ ions gave the Pt-benzyne species as the major ions. Benzenethiol reacted with both Au+ and Pt+ to yield the charge transfer ion C6H5SH+ as the major product, while the reactions of Au+ and Pt+ ions with H2S both gave addition complexes MH2S+ and M(H2S)2+, similar to the reactions of Ag+ and Cu+. The reactions of n-propanethiol and the four butanethiols with Au+ and Pt+ ions generally gave the protonated thiol as the major ion with significant quantities of other ions including addition complexes. These results are different from the previously reported reactions of Cu+ and Ag+ ions which gave the addition ions as the major products.