Ld. Book et al., ULTRAFAST PUMP-PROBE STUDIES OF EXCITED-STATE CHARGE-TRANSFER DYNAMICS IN BLUE COPPER PROTEINS, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 102(23), 1998, pp. 4350-4359
We report the results of ultrafast pump-probe measurements on three bl
ue copper proteins: spinach plastocyanin, poplar plastocyanin, and hum
an ceruloplasmin. Electronic population dynamics and vibrational coher
ences involving d --> d transitions of the blue copper active site are
observed using both wavelength-integrated and wavelength-resolved det
ection. Depending on the protein and the method of detection, the pump
-induced bleaches of the electronic ground state decay with time const
ants of 230-300 fs. The pump-probe signals are modulated by oscillatio
ns that correspond to vibrational coherences induced by the ultrashort
pulses. The frequencies of some of these oscillations can be matched
with modes observed in resonance Raman studies of these proteins. For
spinach plastocyanin and ceruloplasmin, wavelength-resolved signals re
veal a previously unreported vibration at similar to 500 cm(-1) whose
decay dynamics are consistent with the excited-state lifetime. The ori
gin of this mode is argued to result from Duschinsky rotation. The rel
evance of these pump-probe results to the development of a model for b
iological electron transport;in these proteins is discussed.