Probing the reaction coordinate for ligand binding in hemoglobin using ultrafast transient Raman spectroscopy

© 1893 SPIE. Transient picosecond Raman spectroscopy is capable of differentiating vibrational relaxation from conformational changes by comparing the Stokes and anti-Stokes dynamics. We report pump-probe picosecond Raman experiments on oxy-and deoxyhemoglobin (oxyHb and deoxyHb, respectively) using 8 ps 532 nm pump pulses and 8 ps 355 nm probe pulses. Heme-to-protein vibrational cooling has been directly observed in deoxyHb for the first time, and the deconvolved cooling time constant is measured to be 2-5 ps.1-2 By applying our mode-specific Stokes and anti-Stokes technique to oxyHb, we find that any geminate recombination of photodeligated O2 must occur in either less than two picoseconds or longer than a nanosecond