2D IRphoton echo of azido-probes for biomolecular dynamics

Abstract

The vibrations in the azido-, N₃, asymmetric stretching region of 2′-azido-2′-deoxyuridine (N₃dU) are examined by two-dimensional infrared spectroscopy. In water and tetrahydrofuran (THF), the spectra display a single sharp diagonal peak that shows solvent sensitivity. The frequency–frequency correlation time in water is 1.5 ps, consistent with H-bond making and breaking dynamics. The 2D IR spectrum is reproduced for N₃dU in water based on a model correlation function and known linear response functions. Its large extinction coefficient, vibrational frequency outside the protein and nucleic acid IR absorption, and sensitivity to water dynamics render –N₃ a very useful probe for 2D IR and other nonlinear IR studies: its signal is ca. 100 times that of nitriles.