Gary D. Willett

Exploring the use of the tripeptide Gly–Gly–His as a selective recognition element for the fabrication of electrochemical copper sensors

The modification of electrodes with the tripeptide Gly-Gly-His for the detection of copper in water samples is described in detail. The tripeptide modified electrode was prepared by first self-assembling 3-mercaptopropionic acid (MPA) onto the gold electrode followed by covalent attachment of the tripeptide to the self-assembled monolayer using carbodiimide coupling. The electrodes were characterized using electrochemistry, a newly developed mass-spectrometry method and quantum mechanical calculations. The mass spectrometry confirmed the modification to proceed as expected with peptide bonds formed between the carboxylic acids of the MPA and the terminal amine of the peptide. Electrochemical measurements indicated that approximately half the MPA molecules in a SAM are modified with the peptide. The peptide modified electrodes exhibited high sensitivity to copper which is attributed to the stable 4N coordinate complex the peptide formed around the metal ion to give copper the preferred tetragonal coordination. The formation of a 4 coordinate complex was predicted using quantum mechanical calculation and confirmed using mass spectrometry. The adsorption of the copper to the peptide modified electrode was consistent with a Langmuir isotherm with a binding constant of (8.1 +/- 0.4) 10(10) M(-1) at 25 degrees C.

Translational spectroscopy of the triatomic dications CO2+2, OCS2+ and CS2+2

Measurement of single-electron capture (SEC) and translational energy spectroscopy (TES) of the triatomic dications CO2+2, OCS2+, CS2+2 at high product ion resolution (typically 0.6 eV) is facilitated by a novel translational spectrometer. Calibration of SEC spectra allows the detection and precise assignment of observed state-selective processes; TES data indicate the presence of dication state having the same spin symmetry. Since single and double ionisation of each triatomic neutral ACB (where A and B represent O and S) to low-lying cation states occurs by removal of essentially non-bonding electrons, the bond lengths and energies of each ACB, ACB+ and ACB2+ are similar. Therefore, current data permit the evaluation of electronic levels of the triatomic dications in excellent agreement with previous experimental and theoretical work. A systematic procedure for future investigations of multiply charged molecular ions is proposed.

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.

Laser ablation Fourier transform mass spectrometric investigation of coals and model materials

Abstract Several different rank Australian coals, two American anthracites, graphite and a selection of polynuclear aromatic hydrocarbons have been studied by laser ablation FT-m.s.. It is shown that by doping the samples with alkali metal salts, adduct ions are observed for the polycyclic hydrocarbon model compounds, while a range of various size carbon clusters are formed from graphite and the coals. There is an apparent relationship between the ease of large positive carbon cluster formation from the coals and the degree of polycyclic ring condensation. This suggests that the technique may be useful for estimating the ordering of aromatic lattices in higher ranked coals and graphitic material.

Photoelectron spectrum of methylenimine by spectrum stripping

The He I photoelectron spectrum of methylenimine, CH2NH, has been obtained from the spectra of methylamine pyrolysis products recorded at different temperatures. The time-averaged digitized spectra are relatively noise-free and the spectrum stripping was carried out using an interactive computer program producing visually displayed spectra.

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.