Seminars Archive

Photoionisation Spectroscopy of Biomolecules

Abstract
The physics and chemistry of biological molecules is fundamental for many fields from biology, to astrochemistry and astrobiology, as well as in biotechnological applications, such as sensors and molecular electronics. A comprehensive study of the photo-excitation and ionization of some amino-acids and RNA/DNA bases has been done combining laboratory sources and synchrotron radiation. Firstly the photofragmentation spectra of these molecules were measured with noble gas resonance radiation between 8.43 to 21.2 eV [1]. The fragmentation pattern of amino acids such as glycine proline, leucine with the same outer orbitals (oxygen and nitrogen lone pair character) are similar. Methionine with an outer orbital with sulphur lone pair character behaves very differently and displays reduced fragmentation. All nucleobases, namely guanine, adenine, cytosine, thymine and uracil, show relatively strong parent ions at all photon energies. The photoabsorption spectra [3] and the gas phase XPS spectra [2] near the carbon, nitrogen and oxygen K edge of the amino acids glycine, methionine and proline have been measured at the GasPhase beamline at Elettra. The most interesting result has been the observation of two peaks in the nitrogen XPS spectrum of proline, which contains only one nitrogen atom [2]. Electronic structure calculations demonstrate that the peaks are due to different conformers of proline. Valence spectra and measurements as a function of the temperature confirmed this observation. Finally the adsorption of the nucleobase adenine on iron pyrite minerals and on silicon dioxide surfaces has been studied by photoemission and soft x-ray photoabsorption spectroscopy at the Material Science beamline at Elettra [4]. Two different adsorbate species were observed: a weakly bound, randomly oriented adsorbate, and a chemisorbed species. In the case of the iron pyrite the chemisorbed species were bound edge-on to the surface plane, while the molecule is found to physisorb approximately parallel to the surface on silicon dioxide surface In this work we have shown that combining the gas phase and solid state data a complete characterization of biomolecules can be achieved. [1]. O. Plekan, V. Feyer, R. Richter, M. Coreno, M. de Simone, K.C. Prince. (submitted to Chem. Phys.). [2]. O. Plekan, V. Feyer, R. Richter, M. Coreno, M. de Simone, K.C. Prince, and V. Carravetta, (J. of Electron Spectroscopy and Related Phenomena, in press). [3] O. Plekan, V. Feyer, R. Richter, M. Coreno, M. de Simone, K.C. Prince, and V. Carravetta, (submitted to Chem. Phys. Lett.). [4] Plekan, V. Feyer, F. Šutara, T. Skála, M. Svec, V. Cháb, V. Matolín and K.C. Prince, (submitted to Surface Science).