Long-lived amide I vibrational modes in myoglobin

Pump-probe experiments in the infrared measure vibrational relaxation rates. Myoglobin, which is almost entirely α helix in secondary structure, has an unusually long, nonexponential excited state relaxation generated by optically pumping at the blue side (5.85μm) of the amide I band. The amino acid alanine and the predominantly β sheet protein photoactive yellow protein do not have such a long-lived state, suggesting that the a helix in proteins can support nonlinear states of 15 ps characteristic times.