Mass spectrometry of steroid systems—XXI Appearance and ionization potentials for the stereo‐isomers of the D‐homoestrane series

Abstract

The ionization potentials of methyl ethers of D-homoequilenine, its 14@-isomer, Dhomoestrone and its 8cc-isomer, as well as appearance potentials of certain fragment ions have been determined by means of electron-impact. The dissociation energies of the bonds which are split in the course of formation of these ions have been calculated.

Reactions between neutral molecules and cation-radicals in the gas-phase: Can protonation occur without proton transfer?

“…It should be noted that present AE of the immonium ion in Gly is very close to the most recent photoionization value 9.38  0.05 eV [29] which are lower than previous EI data 10.1 0.2 eV [7], 10.23  0.09 eV [8], 10.27  0.05 eV [9] and 10.1 0.1 eV [22,23] obtained via vanishing current method, semilogarithmic plot of the ionization curve and similar to the present fitting technique. A possible explanation of the discrepancy between photo- [29] and earlier electron ionization techniques [8,9] was in better detection efficiency at threshold in the case of photoionization MS in comparison to EI MS [29]. Analysis of the immonium ion ionization efficiency curve for Gly with a non-linear Marquardt-Levenberg algorithm fitting technique clearly demonstrates two features on the curve at 9.4 and 10.25 eV (Fig.…”

“…As was mentioned above, the previously reported EI appearance energies for the Gly immonium RCHNH 2 + ions provided substantially higher onset values (10.23  0.09 eV [8] and 10.27  0.05 eV [9]) than the present data (9.40.10 eV). We also detect an analogous onset at 10.250.10 eV (Fig.…”

“…The unexpected observation of [M+H] + protonated species in electron ionization (EI) mass spectra is considered a secondary process [4,6] and thus confounds interpretation of experimental data. The first reports on EI mass spectra of common amino acids [7][8][9] do not mention registration of protonated species and unlike their ester derivatives [10]. However, despite these early reports, EI spectra in the NIST data base, clearly indicate the formation of protonated ions for some amino acids [11] has occurred.…”

Photoionization studies on various quinones by an infrared laser desorption/tunable VUV photoionization TOF mass spectrometry

“…In addition, fragmentation mechanisms of some substituted quinones, especially for substituted 1,4‐naphthoquione14–16 and substituted anthraquinone13, 17 have been well established. Ionization energies (IEs) of some quinones have been measured by different groups with photoionization (PI) and photoelectron spectroscopy (PE) methods 18–21. However, there are no previous reports on near‐threshold PI studies of (M − CO) + and (M − 2CO) + fragments of quinones.…”

Molecular Evolution Using Intramolecular Acyl Migration on myo‐Inositol Benzoates with Thermodynamic and Kinetic Selectors

“…Because it is well known that the appearance potentials of the main fragment ions are different for stereoisomers,63–66 the low‐energy spectra (15 eV) of compounds 1a and 1b were recorded and are shown in Fig. 2.…”