Photoabsorption and photoionization studies of the amino acid proline in the VUV region

Abstract

Ionic fragmentation of the sublimated amino acid DL-proline has been studied using time-of-flight mass spectrometry and synchrotron radiation. Total ion yield and mass spectra were recorded in the 13 to 21.6 eV energy range. Partial ion yields have been calculated for the produced fragments and the results analyzed in a comparative way. Mass spectrum of proline previously obtained at 21.21 eV using photons from a discharge lamp (He I), was used as reference in the comparison to the synchrotron radiation based spectra. The loss of the COOH fragment represents the most probable dissociation pathway following the photoionization of DLproline in the valence region. These are the fi rst results of total and partial ion yields spectra for this molecule in its gas phase in the valence region using time-of-flight spectrometry.

Photofragmentation of guanine, cytosine, leucine and methionine

“…Due to the low energy of the excitation, only singly charged ions are present in the spectra. We have also measured the mass spectra of glycine, proline, adenine, uracil and thymine, for which data have already been reported in the literature [9,10,14]. The published spectra of proline [9] and glycine measured at 21.2 eV [7] were acquired with a TOF spectrometer, and are similar to our data.…”

“…We have also measured the mass spectra of glycine, proline, adenine, uracil and thymine, for which data have already been reported in the literature [9,10,14]. The published spectra of proline [9] and glycine measured at 21.2 eV [7] were acquired with a TOF spectrometer, and are similar to our data. The spectra of adenine, uracil and thymine [14] were measured with a quadrupole mass spectrometer, and show some differences in the intensity ratios with respect to our spectra at 21.2 eV.…”

“…Since the HOMO has mostly sulphur lone pair character, this explains why the parent ion is stronger than in leucine, or other amino acids such as glycine, proline, etc. [7,9,10]. Junk and Svec observed a parent ion peak intensity of 4.2% of total ion yield for electron bombardment, whereas we observe a total of 16% (including isotopes), indicating a clear difference between electron and photon impact ionization.…”

“…In the photon energy range of interest here, photofragmentation of various amino acids has been reported: glycine, alanine, valine and proline have been studied by Lago et al [7] at 21.2 eV; alanine and serine by Prü emper et al [8]; proline by Coutinho et al [9] between 13 and 21.6 eV; and glycine and related compounds by Jochims et al [10] in the range 6-22 eV. Lago of about 20 eV.…”

May interstellar leucine react with NO radicals present in interstellar/interplanetary medium? An ion-trap mass spectrometry study

“…The influence of space radiations on gas-phase amino acids and nucleobases was investigated by different groups [17][18][19][20][21][22][23]. Alternatively, gas-phase reactivity between amino acids and highly reactive species such as radicals, may also take place in the interstellar/interplanetary medium.…”