Photofragmentation of guanine, cytosine, leucine and methionine

An analysis of the NEXAFS spectra of a molecular crystal: α-glycine

“…47 The importance of conformation in gas phase amino acids has been examined experimentally by XPS and x-ray absorption. 12,48,49 It has occasionally been difficult to reproduce spectra of solid glycine, even under nominally identical conditions. 4,11,[15][16][17][18] While early spectral inconsistencies could have been due to sample preparation techniques, previous experiments supported the notion that linear dichroism could be a source of irreproducibility; however, our calculations on the nitrogen Kedge indicate that this effect is limited.…”

“…4,11,[15][16][17][18] This is similar to the form found when solvated in water, but different from that in the gas phase. 8,12 The N K-edge spectra are largely unchanged between crystalline glycine and glycine chloride (s), a protonated form of glycine where the NH 3 + group remains, but changes drastically upon being switched to sodium glycinate (s), where the NH 3 + group becomes an NH 2 group. 4,11,15,17,18 The N K-edge spectrum of zwitterionic glycine (s) exhibits a single peak centered at ~407 eV in energy, but when the NH 2 group is present several prominent features appear before the major peak at approximately ~402 eV.…”

“…4,11,15,17,18 The gas phase spectrum of glycine(g), which is terminated in an NH 2 group, is significantly different from the solid forms of glycine even when they are terminated with an NH 2 group. 12 It has been noted previously that the condensed phase spectrum of glycine(s) is different from that of the gaseous phase largely due to either the conversion or quenching of spatially extended Rydberg states in the gas to excitons in the solid. 11,18 As noted, a variety of different spectra of nominally identical solid glycine samples have been published.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] These studies began with single amino acids, and progressed to dipeptides, wherein it was noted that the formation of a peptide bond causes significant spectral changes. 4,7,15,18 The belief that one could use a "building block" approach to untangle the spectra of proteins was a large driving force behind this approach, viz.…”

Experimental Observation of Guanine Tautomers with VUV Photoionization

“…Nir et al report an R2PI ionization energy measurement of 7.905 eV for the enol-N7H (tautomer 5) form of guanine. 7 Plekan et al 19 performed photofragmentation studies using fixed wavelength VUV radiation and attempted to explain the fragmentation patterns by relating them to published photoelectron spectra.…”