Delfino Ines, Manzoni Cristian, Sato Katsuko, Dennison Christopher, Cerullo Giulio, Cannistraro Salvatore
Biophysics and Nanoscience Centre, CNISM - Università della Tuscia, I-01100 Viterbo, Italy.
J Phys Chem B. 2006 Aug 31;110(34):17252-9. doi: 10.1021/jp062904y.
We have applied femtosecond pump-probe spectroscopy to investigate the excited-state dynamics of umecyanin from horseradish roots, by exciting its 600-nm ligand-to-metal charge-transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching is modulated by clearly visible oscillations and occurs exponentially with a time constant depending on the observed spectral component of the transmission difference signal, ranging from 270 fs up to 700 fs. The slower decaying process characterizes the spectral component corresponding to the metal-to-ligand charge-transfer transition. The excited-state decay rate is significantly lower than in other blue copper proteins, probably because of the larger energy gap between ligand- and metal-based orbitals in umecyanin. Wavelength dependence of the recovery times could be due to either the excitation of several transitions or the occurrence of intramolecular vibrational relaxation within the excited state. We also find evidence of a hot ground-state absorption, at 700 nm, persisting for several picoseconds. The vibrational coherence induced by the ultrashort pump pulse allows vibrational activity to be observed, mainly in the ground state, as expected in a system with fast excited-state decay. However, we find evidence of a rapidly damped oscillation, which we assign to the excited state. Finally, the Fourier transform of the oscillatory component of the signal presents additional bands in the low-frequency region which are assigned to collective motions of the protein.
我们应用飞秒泵浦-探测光谱技术来研究辣根中伞形花青素的激发态动力学，用15飞秒脉冲激发其600纳米的配体到金属电荷转移带，并在可见光区域的宽范围内进行探测。泵浦诱导的基态漂白的衰减由清晰可见的振荡调制，并以指数形式发生，其时间常数取决于透射差信号的观测光谱成分，范围从270飞秒到700飞秒。较慢的衰减过程表征了与金属到配体电荷转移跃迁相对应的光谱成分。激发态衰减速率明显低于其他蓝铜蛋白，这可能是因为伞形花青素中基于配体和金属的轨道之间的能隙较大。恢复时间的波长依赖性可能是由于几种跃迁的激发或激发态内分子内振动弛豫的发生。我们还发现了在700纳米处持续数皮秒的热基态吸收的证据。超短泵浦脉冲诱导的振动相干使得振动活性得以观测，主要是在基态，这正如在具有快速激发态衰减的系统中所预期的那样。然而，我们发现了一个快速衰减振荡的证据，我们将其归因于激发态。最后，信号振荡成分的傅里叶变换在低频区域呈现出额外的谱带，这些谱带被归因于蛋白质的集体运动。
