VIBRATIONAL ECHO STUDIES OF PROTEIN DYNAMICS

The first picosecond infrared vibrational echo experiments on a protei n, myoglobin-CO, are described. The experiments were performed at temp eratures ranging from 60 to 300 K with a midinfrared free electron las er 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 temperat ure glasses (<5 K) but is observed here at much higher temperatures. A bove the solvent glass transition temperature, T-2 is exponentially a ctivated.