Nitrile groups as vibrational probes of biomolecular structure and dynamics: an overview

This paper presents an overview of recent experiments and theoretical developments aimed at using vibrational spectroscopy to understand the structure and dynamics of nitrile-labeled biomolecules. Nitrile groups are excellent vibrational probes of proteins and DNA because they absorb in a region of the spectrum that is relatively free of absorption due to the biomolecule, and they have high extinction coefficients. The vibrational frequency of nitrile groups is also extraordinarily sensitive to its local environment, and thus CN bonds have been employed in both linear and 2-D infrared (IR) spectroscopy experiments and also as vibrational Stark probes of electric fields in proteins. The interpretation and design of these experiments would be enhanced by accurate calculations of IR spectra from molecular dynamics simulations. Recently, theoretical developments towards computing the vibrational spectrum of nitrile groups in the condensed-phase have been highly successful. A strong synergy between experiment and theory will further promote the use of vibrational spectroscopy of nitrile-labeled biomolecules to address fundamental questions of structure and dynamics that are elusive to other techniques.