X-Ray Spectroscopy of Heterocyclic Biochemicals: Xanthine, Hypoxanthine and Caffeine

Plekan, O.; Richter, R.; Moise, A.; Coreno, M.; Moskovskaya, T.E.; Zaytseva, I.L.; Feyer, V.; Soshnikov, D. Y.; Trofimov, A. B.; Prince, I.K.

doi:10.1021/jp300459p

Journal Article

X-Ray Spectroscopy of Heterocyclic Biochemicals: Xanthine, Hypoxanthine and Caffeine

Plekan, O. ; Feyer, V.FZJ* ; Richter, R. ; Moise, A. ; Coreno, M. ; Prince, I. K. ; Zaytseva, I. L. ; Moskovskaya, T. E. ; Soshnikov, D. Y. ; Trofimov, A. B.FZJ*

2012
American Institute of Physics Melville, NY

The journal of chemical physics 116, 5653 - 5664 (2012) [10.1021/jp300459p]

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Please use a persistent id in citations: http://hdl.handle.net/2128/7508 doi:10.1021/jp300459p

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.

Keyword(s): Caffeine: chemistry (MeSH) ; Carbon: chemistry (MeSH) ; Gases (MeSH) ; Hypoxanthine: chemistry (MeSH) ; Models, Chemical (MeSH) ; Molecular Structure (MeSH) ; Nitrogen: chemistry (MeSH) ; Oxygen: chemistry (MeSH) ; Quantum Theory (MeSH) ; Spectrometry, X-Ray Emission: methods (MeSH) ; X-Ray Absorption Spectroscopy: methods (MeSH) ; Xanthine: chemistry (MeSH) ; Gases ; Caffeine ; Hypoxanthine ; Xanthine ; Carbon ; Nitrogen ; Oxygen ; J

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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.

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