Yan Zubavichus

Soft X-ray-induced decomposition of amino acids: an XPS, mass spectrometry, and NEXAFS study.

Abstract Zubavichus, Y., Fuchs, O., Weinhardt, L., Heske, C., Umbach, E., Denlinger, J. D. and Grunze, M. Soft X-Ray-Induced Decomposition of Amino Acids: An XPS, Mass Spectrometry, and NEXAFS Study. Radiat. Res. 161, 346–358 (2004). Decomposition of five amino acids, alanine, serine, cysteine, aspartic acid, and asparagine, under irradiation with soft X rays (magnesium KαX-ray source) in ultra-high vacuum was studied by means of X-ray photoelectron spectrometry (XPS) and mass spectrometry. A comparative analysis of changes in XPS line shapes, stoichiometry and residual gas composition indicates that the molecules decompose by several pathways. Dehydration, decarboxylation, decarbonylation, deamination and desulfurization of pristine molecules accompanied by desorption of H2, H2O, CO2, CO, NH3and H2S are observed with rates depending on the specific amino acid. NEXAFS spectra of cysteine at the carbon, oxygen and nitrogen K-shell and sulfur L2,3edges complement the XPS and mass spectrometry data and show that the exposure of the sample to an intense soft X-ray synchrotron beam results in the formation of C-C and C-N double and triple bonds. Qualitatively, the amino acids studied can be arranged in the following ascending order of radiation stability: serine < alanine < aspartic acid < cysteine < asparagine.

CdS and Cd(OH)2 formation during Cd treatments of Cu(In,Ga)(S,Se)2 thin-film solar cell absorbers

The surface modifications induced by treating Cu(In,Ga)(S,Se)2 films in an aqueous ammonia hydroxide-based solution of Cd2+ ions—as used in record Cu(In,Ga)(S,Se)2 solar cells without a CdS buffer layer—have been investigated for different Cd2+ concentrations. Employing a combination of x-ray photoelectron spectroscopy, Auger electron spectroscopy, and x-ray emission spectroscopy, it is possible to distinguish two different surface modifications. For Cd2+ concentrations below 4.5 mM in the solution we observe the formation of a CdS monolayer, while higher Cd2+ concentrations lead to the additional deposition of a cadmium hydroxide film on the CdS/Cu(In,Ga)(S,Se)2 surface.

X-ray Absorption Spectroscopy of the Nucleotide Bases at the Carbon, Nitrogen, and Oxygen K-Edges

Near-edge X-ray absorption fine structure spectra of three pyrimidine (viz., cytosine, uracil, and thymine) and two purine (viz., adenine and guanine) nucleobases, which are the key constituents of DNA and RNA, were measured at the C, N, and O K-edges using the self-absorption-free partial electron yield mode. The nucleobase samples were prepared as highly pure native polycrystalline powder films. The spectra are analyzed in terms of the electronic structure of the nucleobases. Subtle chemical effects related to the molecular structures of these heterocyclic compounds with extended pi-electron systems are considered and discussed.

Is X-ray Absorption Spectroscopy Sensitive to the Amino Acid Composition of Functional Proteins?

We report, compare, and analyze near-edge X-ray absorption fine structure (NEXAFS) spectra of powder samples of four different functional proteins, namely, lysozyme, ovalbumin, bovine serum albumin, and type-I collagen, at all relevant absorption edges. The spectra of all of the above proteins were found to be quite similar and to exhibit minor differences only. Nevertheless, despite the general similarity, the spectra of the individual proteins are distinguishable, and some of the respective differences clearly correlate with their amino acid compositions. Further factors affecting the NEXAFS spectra of proteins beyond the building block approach are discussed.