Dispersion related coupling effects in IR spectra on the example of water and Amide I bands
Journal
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Date Issued
2023-03
Author(s)
Mayerhöfer, Thomas G.
Pahlow, Susanne
Popp, Jürgen
DOI
10.1016/j.saa.2022.122115
Abstract
We discuss coupling effects in infrared spectra which are caused by dispersion and local field effects. The first effect is instigated by changes of the refractive index
due to absorption which have an impact on the strength of adjacent absorptions. The second effect is a consequence of the light-induced polarization of one molecule
affecting neighboring ones. These coupling effects do not only effect band positions, but also influence relative intensities. They are particularly strong in case of
overlapping bands and complicate their deconvolution by band fitting. We investigated the corresponding challenges for the HO-stretching vibrations in water and
the Amide I band in proteins. Our findings show that the effects are significant and of high interest for protein and water structure determination. Especially, for the
water stretching vibrations we conclude that it is of utmost importance to consider such coupling effects in quantum mechanical calculations of water spectra.
Otherwise, progress in understanding band positions and profiles is likely to be hampered. Also, in case of the Amide I band we found a distinct impact of such
coupling effects. Accordingly, we strongly recommend consideration of dispersion and local field effects to ensure the possibility of an accurate, quantitative
determination of α-helix and β-sheet structures.
due to absorption which have an impact on the strength of adjacent absorptions. The second effect is a consequence of the light-induced polarization of one molecule
affecting neighboring ones. These coupling effects do not only effect band positions, but also influence relative intensities. They are particularly strong in case of
overlapping bands and complicate their deconvolution by band fitting. We investigated the corresponding challenges for the HO-stretching vibrations in water and
the Amide I band in proteins. Our findings show that the effects are significant and of high interest for protein and water structure determination. Especially, for the
water stretching vibrations we conclude that it is of utmost importance to consider such coupling effects in quantum mechanical calculations of water spectra.
Otherwise, progress in understanding band positions and profiles is likely to be hampered. Also, in case of the Amide I band we found a distinct impact of such
coupling effects. Accordingly, we strongly recommend consideration of dispersion and local field effects to ensure the possibility of an accurate, quantitative
determination of α-helix and β-sheet structures.