Infrared’s One-Two Punch: Studies and Applications of Azido- and Cyano- as Vibrational Reporters Using Multidimensional Spectroscopic Techniques

Abstract

Infrared (IR) spectroscopy is utilized to measure vibrational states in molecular systems. Information of the molecule can be obtained via these vibrations; such as structure, interactions with different environments, along with inter- and intramolecular interactions. With advancements in technology, IR studies have evolved to measuring vibrations over the femtosecond time scales to give molecular snapshots using non-linear techniques. Monitoring specific transitions over femtosecond time scales yields more information about dynamics such as changes in conformation, local environment, intramolecular interactions, and even intermolecular interactions. Some intrinsic transitions, such as amides and tyrosine ring modes, are less perturbative for peptides and proteins. However, non-intrinsic transitions, incorporated by different synthetic methods have been utilized effectively without significant perturbation. Two such probes are azido- and cyano-. These probes are relatively small, exist outside of the biological IR fingerprint region, and possess relatively high IR signal strengths. Even with these advantages, at times the vibrational lifetimes are short limiting the timescale for the window of dynamics. However, addition of heavy metals between the reporters and the molecular system of interest have shown to extend the vibrational lifetimes by around 100 times. Such extension of vibrational lifetimes allows for a longer timescale to monitor molecular dynamics. Dynamics that can be monitored at such long timescales are protein confirmation, long scale environmental interactions, and intermolecular energy transfer.