Collecting multiple 2D IR spectra as a function of time turns these static snapshots into a movie. 1, 6, 7 Thus, a 2D IR spectrum provides a snapshot of water and ion dynamics around static protein structures. About the only things that move on a 1 ps time scale are water molecules and ions as they make and break hydrogen bonds protein backbones are essentially fixed in space, as are side chains, on this picosecond time scale. With a subpicosecond time resolution, there is essentially no protein or biological structural change that is too fast for it to follow. 2D IR spectroscopy provides the ideal time resolution to measure structural change. 4, 5 Of course, for a technique to measure kinetics, the time resolution of the technique needs to be shorter than the time scale of structural change.
1– 3 Knowledge of the kinetics of the interconversion between members of a structural ensemble can lead to fundamental insights into the mechanisms of these processes. The structural evolution of proteins, designed to accomplish precise functions, is at the heart many processes in biology.
