Extracting accurate infrared lineshapes from weak vibrational probes at low concentrations

Fourier-transform infrared (FTIR) spectroscopy using vibrational probes is an ideal tool to detect changes in structure and local environments within biological molecules. However, challenges arise when dealing with weak infrared probes, such as thiocyanates, due to their inherent low signal strengths and overlap with solvent bands. In this protocol we demonstrate: • A streamlined approach for the precise extraction of weak infrared absorption lineshapes from a strong solvent background. • A protocol combining a spectral filter, background modeling, and subtraction. • Our methodology successfully extracts the CN stretching mode peak from methyl thiocyanate at remarkably low concentrations (0.25 mM) in water, previously a challenge for FTIR spectroscopy. This approach offers valuable insights and tools for more accurate FTIR measurements using weak vibrational probes. This enhanced precision can potentially enable new approaches to enhance our understanding of protein structure and dynamics in solution.