Remacle F, Levine R D
The Fritz Haber Research Center for Molecular Dynamics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Proc Natl Acad Sci U S A. 2006 May 2;103(18):6793-8. doi: 10.1073/pnas.0601855103. Epub 2006 Apr 24.
Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine.
基于计算研究讨论了小肽中超快、亚飞秒级的电荷迁移，并与施拉格和温考夫观察到的电离后的选择性键解离进行了比较。如果能在阿秒时间尺度上实现电子的移除，那么所报道的弛豫过程就可以实时探测。此时电子所感受到的平均场变化会足够快，从而引发迁移。酪氨酸末端的四肽具有特别快的电荷迁移，电荷在不到1飞秒的时间内就能到达另一端。飞秒脉冲可用于观察由不同自旋电子之间的相关性引起的稍慢一些的弛豫。移除更深层的价电子时也表明弛豫较慢。当发色氨基酸位于肽的一端时，电荷可以沿着肽主链一直迁移到N端，但色氨酸的位点选择性电离可能比酪氨酸更容易检测。
