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@ARTICLE{Plekan:22160,
      author       = {Plekan, O. and Feyer, V. and Richter, R. and Moise, A. and
                      Coreno, M. and Prince, I.K. and Zaytseva, I.L. and
                      Moskovskaya, T.E. and Soshnikov, D. Y. and Trofimov, A. B.},
      title        = {{X}-{R}ay {S}pectroscopy of {H}eterocyclic {B}iochemicals:
                      {X}anthine, {H}ypoxanthine and {C}affeine},
      journal      = {The journal of chemical physics},
      volume       = {116},
      issn         = {0021-9606},
      address      = {Melville, NY},
      publisher    = {American Institute of Physics},
      reportid     = {PreJuSER-22160},
      pages        = {5653 - 5664},
      year         = {2012},
      note         = {O.P. acknowledges financial support from the CEI (Central
                      European Initiative). We thank Christian Leghissa for
                      excellent technical support, and our colleagues at Elettra
                      for their assistance, and for providing high quality
                      synchrotron light. The authors are grateful to E. V. Gromov
                      for help in conducting the ADC(4) calculations. We are also
                      thankful to Prof. J. Schirmer for useful suggestions and
                      interest in this work.},
      abstract     = {The electronic structures of the purine derivatives
                      xanthine, hypoxanthine and caffeine have been investigated
                      in the gas phase using C, N, and O 1s X-ray photoemission
                      (XPS) and near edge X-ray absorption fine structure (NEXAFS)
                      spectroscopy. The results have been interpreted by means of
                      ab initio calculations using the third-order
                      algebraic-diagrammatic construction (ADC(3)) method for the
                      one-particle Green's function and the second-order ADC
                      method (ADC(2)) for the polarization propagator. The carbon,
                      nitrogen and oxygen K-edge NEXAFS spectra of xanthine and
                      caffeine are very similar, since the molecules differ only
                      by substitution of three hydrogen atoms by methyl groups.
                      For hypoxanthine, the electronic structure and spectra
                      differ considerably from xanthine as the purine ring is more
                      highly conjugated, and there is one less oxo group. Effects
                      due to oxo-hydroxy tautomerism were not observed. However,
                      the two oxo tautomeric forms of hypoxanthine oxo-N(9)-H and
                      oxo-N(7)-H are populated in the gas phase, and the C 1s
                      spectra can be simulated only by taking account of these two
                      tautomers, with appropriate Boltzmann population ratios
                      which we have also calculated. For xanthine and caffeine,
                      single tautomeric forms were observed.},
      keywords     = {Caffeine: chemistry / Carbon: chemistry / Gases /
                      Hypoxanthine: chemistry / Models, Chemical / Molecular
                      Structure / Nitrogen: chemistry / Oxygen: chemistry /
                      Quantum Theory / Spectrometry, X-Ray Emission: methods /
                      X-Ray Absorption Spectroscopy: methods / Xanthine: chemistry
                      / Gases (NLM Chemicals) / Caffeine (NLM Chemicals) /
                      Hypoxanthine (NLM Chemicals) / Xanthine (NLM Chemicals) /
                      Carbon (NLM Chemicals) / Nitrogen (NLM Chemicals) / Oxygen
                      (NLM Chemicals) / J (WoSType)},
      cin          = {PGI-6},
      ddc          = {540},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {Grundlagen für zukünftige Informationstechnologien},
      pid          = {G:(DE-Juel1)FUEK412},
      shelfmark    = {Chemistry, Physical / Physics, Atomic, Molecular $\&$
                      Chemical},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:22620864},
      UT           = {WOS:000305355900014},
      doi          = {10.1021/jp300459p},
      url          = {https://juser.fz-juelich.de/record/22160},
}