Search

We synthesised and characterised the racemic and chiral versions of two Zn salan fluorine-based complexes from commercially available materials. The complexes are susceptible to absorbing H2O from the atmosphere. In solution (DMSO–H2O) and at the millimolar level, experimental and theoretical studies identify that these complexes exist in a dimeric-monomeric equilibrium. We also investigated their ability to sense amines via19F NMR. In CDCl3 or d6-DMSO, strongly coordinating molecules (H2O or DMSO) are the limiting factor in using these easy-to-make complexes as chemosensory platforms since their exchange with analytes requires an extreme excess of the latter.

Solvent-free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic acid (Br2-NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)2) and are tolerant to air and atmospheric moisture. Furthermore, the real-world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs.

Analysis of smokeless powders is of interest from forensics and security perspectives. This article reports the detection of smokeless powder organic additives (in their pre-detonation condition), namely the stabiliser diphenylamine and its derivatives 2-nitrodiphenylamine and 4-nitrodiphenylamine, and the additives (used both as stabilisers and plasticisers) methyl centralite and ethyl centralite, by means of swab sampling followed by thermal desorption and direct injection soft chemical ionisation-mass spectrometry. Investigations on the product ions resulting from the reactions of the reagent ions H3O+ and O2+ with additives as a function of reduced electric field are reported. The method was comprehensively evaluated in terms of linearity, sensitivity and precision. For H3O+, the limits of detection (LoD) are in the range of 41–88 pg of additive, for which the accuracy varied between 1.5 and 3.2%, precision varied between 3.7 and 7.3% and linearity showed R2 ≥ 0.9991. For O2+, LoD are in the range of 72 to 1.4 ng, with an accuracy of between 2.8 and 4.9% and a precision between 4.5 and 8.6% and R2 ≥ 0.9914. The validated methodology was applied to the analysis of commercial pre-blast gun powders from different manufacturers.

Manganese neurotoxicity is a hallmark of hypermanganesemia with dystonia 2, an inherited manganese transporter defect caused by mutations in SLC39A14. To identify novel potential targets of manganese neurotoxicity, we performed transcriptome analysis of slc39a14−/− mutant zebrafish that were exposed to MnCl2. Differentially expressed genes mapped to the central nervous system and eye, and pathway analysis suggested that Ca2+ dyshomeostasis and activation of the unfolded protein response are key features of manganese neurotoxicity. Consistent with this interpretation, MnCl2 exposure led to decreased whole-animal Ca2+ levels, locomotor defects and changes in neuronal activity within the telencephalon and optic tectum. In accordance with reduced tectal activity, slc39a14−/− zebrafish showed changes in visual phototransduction gene expression, absence of visual background adaptation and a diminished optokinetic reflex. Finally, numerous differentially expressed genes in mutant larvae normalised upon MnCl2 treatment indicating that, in addition to neurotoxicity, manganese deficiency is present either subcellularly or in specific cells or tissues. Overall, we assembled a comprehensive set of genes that mediate manganese-systemic responses and found a highly correlated and modulated network associated with Ca2+ dyshomeostasis and cellular stress. This article has an associated First Person interview with the first author of the paper.

In this paper we report a method for the comparative analysis of volatile organic compounds (VOCs) at physiologically representative concentrations by different analytical methods Standard aqueous solutions of acetone, ethanol, methanol, 1-propanol, 2-propanol and acetaldehyde were prepared by adding a specific mass of compound to a known volume of water, calculated using published Henry’s law constants for individual compounds. Headspace concentrations are thus known from established partitioning from dilute aqueous phase in accordance with Henry’s law. Selected Ion Flow Tube Mass Spectrometry (SIFT-MS), Proton Transfer Reaction Mass Spectrometry (PTR-MS), and Gas Chromatography–Mass Spectrometry (GC–MS) coupled to thermal desorption have been used to study and evaluate the performance of the instruments in the analysis of these VOCs. These analytical techniques have been widely used in the identification and quantification of trace concentrations of VOCs in biological samples. Quantitative determination of VOC concentration was achieved and the performance of the instruments compared with one another. Calibration curves are given within the range 101–103 ppbv.

In this study we present an investigation of the negative ion-molecule chemistry of pentachloroethane (PCE) in air based ion mobility spectrometry and ion mobility spectrometry–mass spectrometry systems. The observed product ions are Cl − , produced by dissociative electron attachment, and Cl − ·HOO resulting from a reaction with O 2 − . Based upon the moisture content of the system, these ions can be observed as a doublet in a ‘dry’ system or as a singlet in a ‘wet’ system. The nature of the Cl − ·HOO product ion was investigated by using isoflurane (ISOF) as a probe to monitor the changing ratios of Cl − and Cl − ·HOO as the PCE concentration decreased. This confirmed the origins of the two product anions. Electronic structure calculations are provided. These have aided the understanding of the reaction processes observed.

The high sensitivity of proton transfer reaction-mass spectrometry (PTR-MS) makes it a suitable analytical tool for detecting trace compounds. Its specificity is primarily determined by the accuracy of identifying the m/ z of the product ions specific to a particular compound. However, specificity can be enhanced by changing the product ions (concentrations and types) through modifying the reduced electric field. For current PTR-MS systems, this is not possible for trace compounds that would only be present in the reaction chamber of a PTR-MS for a short time (seconds). For such circumstances, it is necessary to change the reduce electric field swiftly if specificity enhancements are to be achieved. In this paper we demonstrate such a novel approach, which permits any compound that may only be present in the drift tube for seconds to be thoroughly investigated. Specifically, we have developed hardware and software which permits the reaction region's voltages to be rapidly switched at a frequency of 0.1-5 Hz. We show how this technique can be used to provide a higher confidence in the identification of compounds than is possible by keeping to one reduced electric field value through illustrating the detection of explosives. Although demonstrated for homeland security applications, this new technique has applications in other analytical areas and disciplines where rapid changes in a compound's concentration can occur, for example, in the Earth's atmosphere, plant emissions and in breath. Importantly, this adaptation provides a method for improved selectivity without expensive instrumental changes or the need for high mass resolution instruments.

A novel thermal desorption unit (TDU) has been developed and specifically designed for the detection of trace quantities of explosives using a proton transfer reaction mass spectrometer (PTR-MS). For the first time details on recovery times and instrumental limits of detection for the screening of explosives with this TDU/PTR-MS system are reported. We demonstrate that traces (nanograms or less) of explosives deposited on swabs are desorbed within less than a second upon insertion into the TDU. For a short period of time (seconds) a concentration “pulse” of an explosive enters the drift (reaction) tube of the PTR-MS. This temporal concentration pulse of material is monitored in real-time by recording the product ion intensities for a given explosive as a function of time. By changing the reduced electric field in the drift tube region of the PTR-MS, we demonstrate how selectivity can be improved. This study demonstrates that the TDU/PTR-MS instrument meets security application criteria in terms of sensitivity, selectivity and recovery times.

a b s t r a c t Negative ion formation through dissociative electron attachment to the gas-phase volatile anaesthetics enflurane and isoflurane (C3H2ClF5O) and to two chlorinated ethanes, pentachloroethane (C2HCl5) and hexachloroethane (C2Cl6), have been studied in a crossed electron-molecular beam two sector field mass spectrometer experiment. Anion efficiency curves for the negatively charged fragments have been mea- sured over an electron energy range of approximately 0-17 eV, with an energy resolution of ∼1 eV. For the chlorinated ethanes, resonance features were generally found at ∼0 eV and at 7.5 eV. For the volatile anaesthetics, no zero energy resonances were observed. Instead, product anions were detected mainly in the 2-3 eV and 9 eV energy regions, with the exception of Cl − , whose dominant resonance occurs at approximately 0.6 eV and 0.9 eV for isoflurane and enflurane, respectively. To aid in the interpretation of the experimental results, quantum chemical calculations providing thermochemical thresholds of anion formation are also presented.

Here we demonstrate the use of a switchable reagent ion proton transfer reaction mass spectrometry (SRI-PTR-MS) instrument to improve the instrument's selectivity for the detection of the explosive compounds 2,4,6 trinitrotoluene (TNT), 1,3,5 trinitrobenzene (TNB), pentaerythritol tetranitrate (PETN), and cyclotrimethylenetrinitramine (RDX). Selectivity is improved owing to the production of different product ions resulting from changes in the reagent ion-molecule chemistry. To be of use as an analytical tool for homeland security applications, it is important that the reagent ions (and hence product ions) can be rapidly changed (within seconds) from H 3 O + to another dominant ion species if the technology is to be acceptable. This paper presents measurements that show how it is possible to rapidly switch the reagent ion from H 3 O + to either O 2 + or NO + to enhance selectivity for the detection of the four explosives named above. That switching reagent ions can be done quickly results from the fact that the recombination energies of O 2 + and NO + are less than the ionisation potential of H 2 O, i.e. charge transfer cannot occur which otherwise would result in ions that can react efficiently with water (e.g. H 2 O + + H 2 O → H 3 O + + OH) leading to H 3 O + becoming the dominant reagent ion. Reaction processes observed are non-dissociative charge transfer (O 2 + with TNT and TNB), dissociative charge transfer (O 2 + with TNT) and adduct formation (NO + with PETN and RDX). O 2 + is found to be unreactive with PETN and RDX, and under the conditions operating in the reaction region of the PTR-MS only a low signal associated with NO + ·TNT was observed. No NO + ·TNB was detected.

A key issue with any analytical system based on mass spectrometry with no initial separation of compounds is to have a high level of confidence in chemical assignment. This is particularly true for areas of security, such as airports, and recent terrorist attacks have highlighted the need for reliable analytical instrumentation. Proton transfer reaction mass spectrometry is a useful technology for these purposes because the chances of false positives are small owing to the use of a mass spectrometric analysis. However, the detection of an ion at a given m/z for an explosive does not guarantee that that explosive is present. There is still some ambiguity associated with any chemical assignment owing to the presence of isobaric compounds and, depending on mass resolution, ions with the same nominal m/z. In this article we describe how for the first time the use of a radio frequency ion-funnel (RFIF) in the reaction region (drift tube) of a proton transfer reaction−time-offlight− mass spectrometer (PTR-ToF-MS) can be used to enhance specificity by manipulating the ion−molecule chemistry through collisional induced processes. Results for trinitrotoluene, dinitrotoluenes, and nitrotoluenes are presented to demonstrate the advantages of this new RFIF-PTR-ToF-MS for analytical chemical purposes

We have investigated the reactions of NO(+), H3O(+), O2(+), and Kr(+) with picric acid (2,4,6 trinitrophenol, C6H3N3O7, PiA) using a time-of-flight mass spectrometer with a switchable reagent ion source. NO(+) forms a simple adduct ion PiA·NO(+), while H3O(+) reacts with PiA via nondissociative proton transfer to form PiAH(+). In contrast, both O2(+) and Kr(+) react with PiA by nondissociative charge transfer to produce PiA(+). For Kr(+), we also observe dissociation of PiA, producing NO2(+) with a branching percentage of approximately 40%. For the reagent ions H3O(+) and O2(+) (and operating the drift tube with normal laboratory air), we find that the intensities of the PiAH(+) and PiA(+) ions both exhibit a peak at a given drift-tube voltage (which is humidity dependent). This unusual behavior implies a peak in the detection sensitivity of PiA as a function of the drift-tube voltage (and hence E/N). Aided by electronic-structure calculations and our previous studies of trinitrotoluene and trinitrobenzene, we provide a possible explanation for the observed peak in the detection sensitivity of PiA.

This paper presents an investigation of proton and charge transfer reactions to 2-, 3- and 4-nitroanilines (C6H6N2O2) involving the reagent ions H3O+·(H2O)n (n = 0, 1 and 2) and O2+, respectively, as a function of reduced electric field (60–240 Td), using Selective Reagent Ion–Time-of-Flight–Mass Spectrometry (SRI–ToF–MS). To aid in the interpretation of the H3O+·(H2O)n experimental data, the proton affinities and gas-phase basicities for the three nitroaniline isomers have been determined using density functional theory. These calculations show that proton transfer from both the H3O+ and H3O+·H2O reagent ions to the nitroanilines will be exoergic and hence efficient, with the reactions proceeding at the collisional rate. For proton transfer from H3O+ to the NO2 sites, the exoergicities are 171 kJ mol−1 (1.8 eV), 147 kJ mol−1 (1.5 eV) and 194 kJ mol−1 (2.0 eV) for 2-, 3- and 4-nitroanilines, respectively. Electron transfer from all three of the nitroanilines is also significantly exothermic by approximately 4 eV. Although a substantial transfer of energy occurs during the ion/molecule reactions, the processes are found to predominantly proceed via non-dissociative pathways over a large reduced electric field range. Only at relatively high reduced electric fields (> 180 Td) is dissociative proton and charge transfer observed. Differences in fragment product ions and their intensities provide a means to distinguish the isomers, with proton transfer distinguishing 2-nitroaniline (2–NA) from 3- and 4-NA, and charge transfer distinguishing 4-NA from 2- and 3-NA, thereby providing a means to enhance selectivity using SRI–ToF–MS.

In the present work we present an investigation of the negative ion-molecule chemistry of the anaesthetics isoflurane, ISOF, and enflurane, ENF, in an ion mobility spectrometry/mass spectrometry (IMS/MS), in both air and nitrogen. Hexachloroethane (HCE) was introduced in both air and nitrogen to produce Cl– as a reactant ion. This study was undertaken owing to uncertainties in the chemical processes, which lead to the cluster ions reported in other work (Eiceman et al. Anal. Chem. 61, 1093–1099, 1). In particular for ISOF the product ion observed was ISOF.Cl–, and it was suggested that the Cl– was formed by dissociative electron attachment (DEA) although there was mention of a chlorine containing contaminant. We show in this study that ISOF and ENF do not produce Cl– in an IMS system either by capture of free electrons or reaction with O2 –. This demonstrates that the Cl– containing ions, reported in the earlier study, must have been the result of a chlorine containing contaminant as suggested. The failure of ISOF and ENF to undergo DEA was initially surprising given the high calculated electron affinities, but further calculations showed that this was a result of the large positive vertical attachment energies (VAEs). This experimental work has been supported by electronic structure calculations at the B3LYP level, and is consistent with those obtained in a crossed electron-molecular beam two sector field mass spectrometer. An unusual observation is that the monomer complexes of ISOF and ENF with O2 – are relatively unstable compared with the dimer complexes. Graphical Abstractᅟ Electronic supplementary material The online version of this article (doi:10.1007/s13361-017-1616-0) contains supplementary material, which is available to authorized users.