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Determination of molecular structure of isomers by Mass Spectrometry

Determination of molecular structure of isomers by Mass Spectrometry. YKO9030 Spektroskoopia erikursus 04. April 2014 Maksim Osheka. Isomerism. Differentiation of Diastereoisomers by Mass Spectrometry and Density Functional Theory. MS: EI-DF

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Determination of molecular structure of isomers by Mass Spectrometry

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  1. Determination of molecular structure of isomers by Mass Spectrometry YKO9030 Spektroskoopiaerikursus 04. April 2014 Maksim Osheka

  2. Isomerism

  3. Differentiation of Diastereoisomers by MassSpectrometry and Density Functional Theory • MS: EI-DF • Idea: The loss of a diethoxyphosphoryl radical and the elimination of diethyl phosphonate are competitive fragmentation processes and their rate is different for diastereoisomers. E. Drabiket al. J. Am. Soc. Mass Spectrom.2013, 24, 388-398.

  4. The loss of a diethoxyphosphoryl radical

  5. Elimination of diethyl phosphonate

  6. Fragmetation of diastereoisomers of protected 1,2-diaminoalkylphosphonic dcids • For the trans isomer, the leading fragmentation pathway is the elimination of (EtO)2POHc (highest TS1=17.1 kcal/mol). • In case of the cis isomer, the leading reaction pathway is the loss of (EtO)2PO* (highest TS=20.8 kcal/mol).

  7. Ion mobility-mass spectrometry • Ion mobility spectrometry (IMS) is an analytical technique that separates gas-phase ions based on their size and shape, analogous to electrophoresis in the condensed phase. • DTIMS • TWIMS • FAIMS Claire E. Eyers, C. E. at al. Nature Chemistry2014, 16, 281-294.

  8. Drift-time ion mobility spectrometry (DTIMS) • Separation is achieved by passing the ions through a drift gas along the axis of an applied electric field. • The flight of a small ion (red) is retarded to a lesser degree than a large ion (blue), owing to fewer interactions with the drift gas. • The time taken to traverse the device (the drift time) is correspondingly shorter. • Used for direct calculation of an ion’s CCS (Ω) by means of the Mason–Schamp equation.

  9. Travelling-wave ion mobility spectrometry (TWIMS) • Application of a travelling voltage wave (T-wave) to a series of electrically connected ring electrodes (stacked ring ion guide; SRIG) pushes ions through the device. • Separation is achieved because, for a given wave speed and magnitude, higher-mobility ions (red) will be carried forward by the wave, whereas lower-mobility species (blue) will roll over the wave, thus taking longer to exit the device. • Used for both CCS calculation and differential separation of ions in a complex mixture.

  10. Field-asymmetric ion mobility spectrometry (FAIMS) • FAIMS, used primarily for differential separation of ions in a complex mixture. • Introduction of ions into an alternating asymmetric electric field (E) causes them to drift towards the two electrodes at different rates. • Time at positive voltage (t1) is shorter than the time at negative voltage (t2), although an equal (voltage × time) product for each part of the waveform is maintained. • Compensation voltage (CV) repels the ions and refocuses their flight through the device. • Different analytes require different CVs to prevent collision with the electrodes.

  11. Application: Regioisomers by TWIMS-MS Dear, G. J. et al. Rapid Commun. Mass Spectrom. 2010, 24, 3157–3162.

  12. Application: Enatiomers by DTIMS-MS • Superimposed spectrum of (S)- and (R)-atenolol obtained after introduction 10 ppm (S)-(+)-2-butanol as the chiral modifier in the inert nitrogen drift gas. • The separation of the enantiomers from their racemic mixture. Hill, H. H. Jr. Analytical Chemistry2006, 78, 8200-8206.

  13. ENANTIOSELECTIVITY OF MASS SPECTROMETRY • Traditionally MS is considered as a “chiral-blind” technique. MS—hyphenated techniques: • LC-MS (normal and reversed phase) • GC-MS • CE-MS • Capillary ElectroChromatography-MS (CEC-MS) • Supercritical Fluid Chromatography-Mass • Spectrometry (SFC-MS) MS chiral recognition mechanisms: • Host–Guest (H–G) Associations • Guest Exchange Ion–Molecule Reactions • Chiral Recognition Based on Complex Dissociation • Chiral Ion Mobility Spectrometry (previous slide). Hanan, A., El-Aneed, A. MassSpectrometry Reviews2013, 32, 466–483

  14. Host–Guest (H–G) Associations (FAB-MS EL) Kim et al. Bull. Korean Chem. Soc.2008, 29, 1069-1072

  15. Guest Exchange Ion–Molecule Reactions • The diastereomeric complex ions are mass selected by FT-ICR-MS. • Exchange reaction between diastereomeric complexes and gas reagent (chiral) giving different peak intensities for replaced and unreplaced ions. • Relative abundance depends on the enantiomeric ratio of the used chiral analyteand the time of the exchange reaction. • The quantification is performed by plotting a calibration curve between the analyteenantiomeric ratios (R/R+S) and the intensity ratios of the replaced and unreplaced ions. Hanan, A., El-Aneed, A. MassSpectrometry Reviews2013, 32, 466–483

  16. Ranjbar, B. & Gill, P. Chem. Biol. Drug Des.2009, 74, 101–120. Roberts, G. & Lian, L. Y. Protein NMR Spectroscopy: Practical Techniques and Applications (Wiley, 2011). Murray, K. K. et al. Pure Appl. Chem.2013, 85, 1515–1609.

  17. Thank you for your kind attention

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