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 similar to 185 K, the pure dephasing, T-2*, 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, T-2* is exponentially activated.