Studying the X-Ray Absorption Fine Structure Spectra of a Protein Monolayer on Liquids. The Possibilities of Multi-Pass Technique

For the first time, the extended fine structure of the absorption spectra for a protein monolayer on a liquid surface has been measured. We used as a test object human serum albumin treated with zinc chloride solution at a critically low concentration (3.6×10 M), which is comparable to the zinc concentration in blood serum. A multi-pass technique for detecting fluorescence radiation under total external reflection conditions was applied. The temporal stability of the Zn K-edge absorption spectra was examined using weighted regression analysis. It is shown that the error of the oscillating part of the total spectrum did not exceed 1%, which allowed to determine the radius of the first coordination sphere with an accuracy of ±0.01 Å.