Single-pass attenuated total reflection Fourier transform infrared spectroscopy for the analysis of proteins in H2O solution.

The application of single-pass attenuated total reflection Fourier transform infrared (ATR-FT-IR) microscopy was investigated for secondary structure analysis of 15 representative proteins in H2O solution. This is the first reported application of single-pass ATR-FT-IR for protein analysis; thus, the method was validated using transmission FT-IR and multipass ATR-FT-IR as referee methods. The single-pass ATR-FT-IR technique was advantageous since the single-pass geometry permits rapid secondary structure analysis on small volumes of protein in H2O solution without the use of demountable thin path length sample cells. Moreover, the fact that H2O backgrounds were small allowed the simultaneous observation of the amide I-III, A, and B regions without having to perform H2O subtraction. A comparison of replicate protein spectra indicated that the single-pass ATR-FT-IR method yields more reproducible data than those acquired by transmission FT-IR. The observed trends for the amide I-III and A bands obtained by single-pass ATR-FT-IR agreed with those in the literature for conventional transmission FT-IR.