Nitrile IR intensities characterize electric fields and hydrogen bonding in protic, aprotic, and protein environments

17 January 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Nitriles are widely used as vibrational probes; however, the interpretation of their IR frequencies is complicated by hydrogen bonding (H-bonding) in protic environments. We report a new vibrational Stark effect (VSE) that correlates the electric field projected on the nitrile bond to the transition dipole moment and, by extension, the nitrile peak area or integrated intensity. This linear VSE applies to both H-bonding and non-H-bonding interactions. It can therefore be generally applied to determine electric fields in all environments. Additionally, it allows for semi-empirical extraction of the H-bonding contribution to the blueshift of the nitrile frequency. Nitriles were incorporated at H-bonding and non-H-bonding protein sites using amber suppression, and each nitrile variant was structurally characterized at high resolution. We exploited the combined information now available from variations in frequency and integrated intensity and demonstrate that nitriles are a generally useful probe for electric fields.


vibrational Stark effect
hydrogen bonding
amber suppression
peak intensity
electric field

Supplementary materials

Supporting Information
Supporting Information for "Nitrile IR intensities characterize electric fields and hydrogen bonding in protic, aprotic, and protein environments"


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