Coherent dynamics and ultrafast excited state relaxation of blue copper protein; plastocyanin.
Ultrafast transient absorption measurements in the femtosecond to picosecond time region were carried out for a blue copper protein, plastocyanin (Pc). To compare the dynamical profiles after photoexcitation upon the ligand-to-metal-charge-transfer (LMCT) band and the d-d transition band, the pump wavelength was set at wavelengths of 597 and 895 nm, respectively. The results were nearly identical, indicating that the transition from the LMCT to the lower ligand field (LF) states takes place in an ultrafast time regime of less than 40 fs. Subsequently, relaxation in the LF state occurs with a time constant of 90 fs and the system returns to the ground state with that of 250 fs. The longest time constant of 1.8 ps was attributed to the vibrational cooling in the ground state. Several wavepacket motions were observed, including Franck-Condon type motion at approximately 510 nm and a Herzberg-Teller type motion at 660-720 nm. Critically damped low-frequency oscillation of approximately 30 cm(-1) was also observed with both excitation wavelengths with the strongest amplitude around 600 nm. This oscillation could be due to the motion of the protein that is ballistically stimulated by ultrafast relaxation.
Nagasawa
Yutaka
Y
Division of Frontier Materials Science, Graduate School of Engineering Science, Center for Quantum Science and Technology under Extreme Conditions, Osaka University and CREST, JST, Toyonaka, Osaka 560-8531, Japan. nagasawa@chem.es.osaka-u.ac.jp
Fujita
Kenji
K
Katayama
Tetsuro
T
Ishibashi
Yukihide
Y
Miyasaka
Hiroshi
H
Takabe
Teruhiro
T
Nagao
Satoshi
S
Hirota
Shun
S
D007700:Kinetics; D008024:Ligands; D056004:Molecular Dynamics Simulation; D010970:Plastocyanin / Q000737:chemistry*; D013053:Spectrophotometry; D013997:Time Factors; D014732:Vibration
D008024:Ligands; D010970:Plastocyanin