G. John Langley

Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)

This document contains recommendations for terminology in mass spectrometry. Development of standard terms dates back to 1974 when the IUPAC Commission on Analytical Nomenclature issued recommendations on mass spectrometry terms and definitions. In 1978, the IUPAC Commission on Molecular Structure and Spectroscopy updated and extended the recommendations and made further recommendations regarding symbols, acronyms, and abbreviations. The IUPAC Physical Chemistry Division Commission on Molecular Structure and Spectroscopy’s Subcommittee on Mass Spectroscopy revised the recommended terms in 1991 and appended terms relating to vacuum technology. Some additional terms related to tandem mass spectrometry were added in 1993 and accelerator mass spectrometry in 1994. Owing to the rapid expansion of the field in the intervening years, particularly in mass spectrometry of biomolecules, a further revision of the recommendations has become necessary. This document contains a comprehensive revision of mass spectrometry terminology that represents the current consensus of the mass spectrometry community.

Chloride, carboxylate and carbonate transport by ortho-phenylenediamine-based bisureas

Highly potent but structurally simple transmembrane anion transporters are reported that function at receptor to lipid ratios as low as 1:1000000. The compounds, based on the simple ortho-phenylenediamine-based bisurea scaffold, have been studied for their ability to facilitate chloride/nitrate and chloride/bicarbonate antiport, and HCl symport processes using a combination of ion selective electrode and fluorescence techniques. In addition, the transmembrane transport of dicarboxylate anions (maleate and fumarate) by the compounds was examined. Molecular dynamics simulations showed that these compounds permeate the membrane more easily than other promising receptors corroborating the experimental efflux data. Moreover, cell based assays revealed that the majority of the compounds showed cytotoxicity in cancer cells, which may be linked to their ability to function as ion transporters.

Towards predictable transmembrane transport: QSAR analysis of anion binding and transport

The transport of anions across biological membranes by small molecules is a growing research field due to the potential therapeutic benefits of these compounds. However, little is known about the exact mechanism by which these drug-like molecules work and which molecular features make a good transporter. An extended series of 1-hexyl-3-phenylthioureas were synthesized, fully characterized (NMR, mass spectrometry, IR and single crystal diffraction) and their anion binding and anion transport properties were assessed using 1H NMR titration techniques and a variety of vesicle-based experiments. Quantitative structure–activity relationship (QSAR) analysis revealed that the anion binding abilities of the mono-thioureas are dominated by the (hydrogen bond) acidity of the thiourea NH function. Furthermore, mathematical models show that the experimental transmembrane anion transport ability is mainly dependent on the lipophilicity of the transporter (partitioning into the membrane), but smaller contributions of molecular size (diffusion) and hydrogen bond acidity (anion binding) were also present. Finally, we provide the first step towards predictable anion transport by employing the QSAR equations to estimate the transmembrane transport ability of four new compounds.

Effect of increasing concentration of ammonium acetate as an additive in supercritical fluid chromatography using CO2–methanol mobile phase

The effects of increasing concentrations of ammonium acetate additive in supercritical fluid chromatography were studied on silica, 2-ethyl-pyridine and endcapped 2-ethyl-pyridine stationary phases. The study involved the addition of increasing concentrations of the ammonium acetate either in the mobile phase modifier (methanol) or in the sample solvent. The effects of ammonium acetate on retention and peak shape of the analytes were evaluated. Compounds that exhibited satisfactory chromatographic behaviour in the absence of the additive were virtually unaffected by its presence in the mobile phase or sample solvent. Nevertheless, compounds that exhibited late elution and strongly tailing peak shapes when pure methanol was used showed dramatically improved chromatographic behaviour in the presence of the additive. Shorter retention was observed not only when the modifier was introduced in the mobile phase but also when it was in the sample solvent.

13 C NMR spectroscopy of C76, C78, C84 and mixtures of C86–C102; anomalous chromatographic behaviour of C82, and evidence for C70H12

Using high pressure liquid chromatography, the fullerenes C76, C78. C84, and C86–C102 have been separated (in some cases partially) from soot produced by the arc-discharge procedure. The 13C NMR spectrum for C76 confirms that reported previously, whilst the spectrum for C78 indicates the presence of C2v, D3, C2v, isomers in the approximate relative yields (there is a small batch dependence) of 52 : 30 : 18%. The spectrum for the D3 isomer (confirmed from two separate batches) differs from that given in the literature with respect to the location of one peak. The relative peak heights in the C8413C NMR spectrum are similar to those reported for samples produced under different conditions. The stabilities of the component isomers must therefore be similar and so produced in a similar ratio irrespective of conditions; this indicates them to be the D2and a O2d isomers. The spectrum also contains over 70 minor peaks due to other isomers of C84. Eleven of the peaks are more intense than the others, consistent with the presence of the D3d and D6h isomers, predicted to be of relatively high stability. Two fractions (giving yellow solutions in hexane) eluted after C84: the first was separated into two components, shown by mass spectrometry to consist of minor amounts of C86–C92, and mainly C90 and C92 with lesser amounts of C94–C,102, respectively. The 13C NMR spectrum of the C94–C102 component indicated the presence of a fullerene isomer of high symmetry. The second yellow fraction consisted largely of C82 together with traces of fullerenes up to C108, but the quantity was insufficient for the 13C NMR spectrum to be obtained. The retention time of C82 is inconsistent with values for the other fullerenes indicating that it consists of the C3v isomer, predicted to be polar. C90 eluted with two different retention times suggesting that the second fraction is also a polar isomer. One sample of C84 contained a coeluent, identified by mass spectrometry as C70H12; proposals are made concerning its possible origin, structure, and stability relative to other hydrogenated derivatives.

Mass spectrometric analysis in combinatorial chemistry

The continuing success of the combinatorial approach is heavily reliant on analytical methodologies, which allow for the rapid and accurate characterisation of medicinally relevant molecules from compound libraries. Mass spectrometry has recently been touted as the most suitable tool for a range of combinatorial applications such as structural elucidation and screening. The refinement of conventional methods, developments of techniques such as Fourier transform ion cyclotron resonance and new screening methodologies have allowed the medicinal chemist to tackle the growing analytical challenges posed by combinatorial chemistry.

Simplified sample preparation for the analysis of oligonucleotides by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the analyses of oligonucleotides has generally been carried out using negative ionisation conditions, usually following ammonium ion-exchange chromatography and the addition of ammonium buffers to the MALDI matrix. The molecular ion region is complex, due to the varying degrees of ammoniation of the phosphate backbone of the oligonucleotide. This gives rise to an overall decrease in sensitivity compared with similar size peptides and can cause ambiguity of assignment of the relative molecular mass of the sample. This study describes the use of H(+) ion exchange resin in situ as the means of removing alkali metal ions from the phosphate backbone of the oligonucleotide. An increase in resolution, sensitivity and identification of the molecular species is reported, with little or no difference in sensitivity observed between positive or negative ionisation spectra. This method is now used for routine screening of synthetic oligonucleotides with a gain in sensitivity of 1-2 orders of magnitude compared with previous methods, and mass assignment errors of +/-0.1% are routinely recorded for externally calibrated data.

Fluorination of buckminsterfullerene

Fluorination of solid C60 with fluorine gas proceeds in a stepwise manner to give, after twelve days (10 mg scale), a colourless derivative indicated by a single line 19F NMR spectrum to be C60F60; reaction time is quantity dependent.

A mass spectrometric–NMR study of fullerene-78 isomers

Three isomers of C78 have been detected by 13C NMR spectroscopy; one of the signals ascribed in the literature to the D3 isomer is absent from our spectrum.

A predictive science approach to aid understanding of electrospray ionisation tandem mass spectrometric fragmentation pathways of small molecules using density functional calculations

RATIONALE Tandem mass spectrometry (MS/MS) dissociation pathways can vary markedly between compound classes and can result in challenging and time-consuming interpretation of the data. Compound, class and substructure specific fragmentation rules for protonated molecules require refinement to aid the structural elucidation process. METHODS The application of a predictive science approach using density functional theory (DFT) calculations has been investigated to estimate the abundances of first-generation product ions observed using an ion trap mass spectrometer. This has been achieved by application of Boltzmann population theory to electrospray ionisation (ESI)-MS and MS/MS data. RESULTS Tandem ESI-MS data for this preliminary study were used to investigate the internal stabilities of protonated species and their product ions. The calculated relative abundances of 11.3%, 96.5%, and 1.1% for the product ion (m/z 192) of three quinazoline structural isomers are compared with the experimental values of 16%, 90% and 0% observed in the first-generation product ion mass spectra. CONCLUSIONS Close correlation between calculated and experimental data has been demonstrated for these initial data. Applying this approach and establishing fragmentation rules, based on structure specific and common fragmentation behaviour, would improve and expedite the structural elucidation process.