Studying the X-ray Absorption Fine Structure Spectra of Protein Monolayers on the Liquid Surface. The possibilities of Multi-pass Technique

For the first time X-ray absorption fine structure spectra were measured for a protein monolayer on the liquid surface. We used as the test object human serum albumin treated with a zinc chloride solution at a critically low concentration (3.6 × 10−7 M), which is comparable to the zinc concentration in blood serum. The multi-pass technique was applied for detecting the fluorescence yield under total external reflection conditions. The temporal stability of the zinc K-edge X-ray absorption spectra was examined using the weighted regression analysis. No changes in the absorption spectra were observed. It was shown that the measurement error of the oscillating part of the summed spectrum did not exeed 1%, allowing the determination of the radius of the first coordination sphere with an accuracy of ±0.01 Å.