Investigation of S–H bonds in biologically important compounds by sulfur K-edge X-ray absorption spectroscopy
Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, 53115 Bonn,
2 Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, 50939 Köln, Germany
3 Physikalisches Institut, Rheinische Friedrich-Wilhelms-Universität Bonn, Nußallee 12, 53115 Bonn, Germany
Revised: 10 June 2002
Published online: 13 September 2002
X-ray Absorption Near Edge Structure (XANES) spectroscopy, often provides a direct correlation between observed resonances in the spectrum and molecular bonds in the sample. This can be used as a fingerprint for the presence of a given molecular environment of the absorber atom in a sample. As the white line is found at similar energy positions for S–C and S–H bonds, this approach is impossible when both types of bond are present simultaneously, as often in biological systems. To develop a criterium for the presence of S–H bonds in such samples, reduced glutathione, reduced coenzyme A, cysteine and their corresponding oxidized forms were investigated using sulfur K-edge XANES, revealing a unique feature at 2 475.8 eV in the respective difference spectra. To correlate this structure to S–H bonds, H2S and H2S2 were measured, whose difference spectrum also shows a structure at this energy position, whereas it is not present throughout a variety of C–S–C/C–S–S–C environments. Theoretical investigations suggest its correlation to a Rydberg transition occurring in the case of a S–H bond. Using this criterium, the presence of S–H bonds is in the purple sulfur bacterium Allochromatium vinosum during oxidation of intracellular accumulated sulfur, is proved, as expected from biological considerations.
PACS: 87.15.By – Structure and bonding / 87.64.Fb – EXAFS spectroscopy / 61.10.Ht – X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002