Vibrational echo studies of protein dynamics

The first picosecond infrared vibrational echo experiments on a protein, myoglobin-CO, are described. The experiments were performed at temperatures ranging from 60 to 300 K with a midinfrared free electron laser tuned to 1945 cm^-1. Below ∼185 K, the pure dephasing, T₂*, displays a power law temperature dependence, T^1.3. This behavior is reminiscent of that associated with the properties of low temperature glasses (<5 K) but is observed here at much higher temperatures. Above the solvent glass transition temperature, T₂* is exponentially activated.