Title: Beyond FT-IR spectroscopy: EC-QCL based mid-IR transmission spectroscopy of proteins in the amide I and amide II region
Language: English
Authors: Schwaighofer, Andreas 
Montemurro, Milagros 
Freitag, Stephan  
Kristament, Christian 
Culzoni, Maria Julia 
Lendl, Bernhard  
Issue Date: 2018
Journal: Analytical Chemistry
In this work, we present a setup for mid-IR measurements of the protein amide I and amide II bands in aqueous solution. Employing a latest generation external cavityquantum cascade laser (EC-QCL) at room temperature in pulsed operation mode allowed implementing a high optical path length of 31 μm that ensures robust sample handling. By application of a data processing routine, which removes occasionally deviating EC-QCL scans, the noise level could be lowered by a factor of 4. The thereby accomplished signal-to-noise ratio is better by a factor of approximately 2 compared to research-grade Fourier transform infrared (FT-IR) spectrometers at equal acquisition times. Employing this setup, characteristic spectral features of three representative proteins with different secondary structures could be measured at concentrations as low as 1 mg mL−1. Mathematical evaluation of the spectral overlap confirms excellent agreement of the quantum cascade laser infrared spectroscropy (QCL-IR) transmission measurements with protein spectra acquired by FT-IR spectroscopy. The presented setup combines performance surpassing FT-IR spectroscopy with large applicable optical paths and coverage of the relevant spectral range for protein analysis. This holds high potential for future ECQCL-based protein studies, including the investigation of dynamic secondary structure changes and chemometrics-based protein quantification in complex matrices.
DOI: 10.1021/acs.analchem.8b01632
Library ID: AC15518671
URN: urn:nbn:at:at-ubtuw:3-7499
ISSN: 1520-6882
Organisation: E164 - Institut für Chemische Technologien und Analytik 
Publication Type: Article
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