Methionine by X-ray Photoelectron Spectroscopy

Methionine is one of the 20 amino acids, and one of the two sulfur-containing amino acids. Observations of chemical shifts in various constituents of methionine are important in determining its interaction with a surface in a thin film. As such, spectra of bulk films of methionine, as in this work, serve as a baseline for the thin film studies. In this work, an aqueous solution prepared from methionine powder was poured into a recessed sample holder and allowed to dry. This formed a block of methionine approximately 1/4 in. thick. The spectra were acquired at liquid nitrogen temperature. The atomic concentrations measured with XPS agree well with those expected for methionine, assuming the small amount of excess carbon and oxygen is due to adventitious material. Predominantly zwitterionic character is observed in the O 1s and N 1s spectra. A small amount of either neutral species or condensed polypeptide is also observed. © 1997 American Vacuum Society.