Vibrational Dynamics of CO Bound to Myoglobin and Metallo-porphyrins

We have made direct measurements of the vibrational lifetimes of carbonmonoxide (CO) bound at the active site of wildtype myoglobin [1] and myoglobin with single residue mutations in the binding pocket. Measurements were also made for CO bound to water soluble metalloporphyrins with differing metals and peripheral substituents. A pump-probe technique using tunable microjoule pulses from an infrared free-electron laser was used to monitor the loss of vibrational energy from the CO ligand with 2 picosecond time resolution. Recovery to the CO vibrational ground state in both the protein and soluble porphyrin systems occurs in the range from 10 to 30 picoseconds. The vibrational lifetime of CO bound to myoglobin is essentially independent of temperature from 20 to 300 K.