Guanine REMPI

The vibration spectrum of the first excited state of guanine was measured using laser desorption jet-cooled resonance-enhanced multiphoton ionization (REMPI) spectrometry <1999JA4896>. The millimeter wave spectrum of purine was collected using a free jet spectrometer, and the observed rotational spectrum was assigned to the N(9)-H tautomer <1996CPL189>. 

Until recently gas phase studies have been limited to molecules that can be heated without degradation. For the nucleobases this includes adenine (A), but not, for example guanine (G) and none of the nucleosides. Since the first report of the resonance enhanced multiphoton ionization (REMPI) spectrum of laser desorbed guanine in 1999, laser desorption has essentially rendered all bases and their clusters amenable to study as neutral species in the gas phase [3],... 

UV spectroscopy in molecular beams involves either laser-induced fluorescence (LIP) or resonance-enhanced multiphoton ionization (REMPI) methods. The latter method has the advantage that the resulting ionized molecules can be mass-analysed in a TOP mass spectrometer. The application of either REMPI or LIP spectroscopy requires the molecule of interest to incorporate a UV chromophore, such as an aromatic moiety. The DNA and RNA bases adenine, guanine, cytosine, thymine and uracil are aromatic molecules with well-known UV absorptions. Of the 20 naturally occurring proteinogenic amino acids, 3 - phenylalanine, tyrosine and tryptophan - feature an aromatic side chain, as do many neurotransmitter molecules. To study molecules that lack a UV chromophore, such as peptides without Trp, Tyr and Phe residues and carbohydrates, a UV chromophore needs to be chemically attached [47, 48, 74]. 

Figure 7.J Tautomer selective REMPI spectra of guanine obtained b...

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