arXiv 1502.007372015-02physics.optics

使用较长X射线laser脉冲的单分子成像

Single molecule imaging with longer x-ray laser pulses

Andrew V. Martin, Justine K. Corso, Carl Caleman, Nicusor Timneanu, Harry M. Quiney

备注：: 23 pages; 5 figures

摘要：

在过去的五年里，使用X射线激光脉冲的连续飞秒晶体学已发展成为一种强大的技术，用于从微米和亚微米尺寸的晶体中确定蛋白质分子的原子结构。这种成功的关键原因之一是“自选通”脉冲效应，由此X射线激光脉冲不需要跑过所有辐射损伤过程。相反，X射线引起的损伤在脉冲完成其通过样品之前终止布拉格衍射，就好像布拉格衍射是由相等强度的较短脉冲产生的一样。因此，连续飞秒晶体学不需要像曾经认为的那样用短至5- 10 fs的脉冲来执行，而是可以在持续时间为50- 100 fs的脉冲下成功。我们在这里表明，类似的门效应适用于单分子衍射相对于空间不相关的损伤过程，如电离和离子扩散。在衍射对比度的计算中，通过将平均结构的衍射与来自由于损伤（“损伤噪声”）引起的结构的统计波动的衍射分开计算，可以清楚地看到该效果。我们的研究结果表明，亚纳米单分子成像与30- 50飞秒脉冲，像那些在目前运行的设施，还不应该被排除在外。我们提出的理论开辟了新的实验途径来测量损伤对单颗粒衍射的影响，这是需要测试损伤模型和确定最佳成像条件。

英文摘要：

During the last five years, serial femtosecond crystallography using x-ray laser pulses has developed into a powerful technique for determining the atomic structures of protein molecules from micrometer and sub-micrometer sized crystals. One of the key reasons for this success is the "self-gating" pulse effect, whereby the x-ray laser pulses do not need to outrun all radiation damage processes. Instead, x-ray induced damage terminates the Bragg diffraction prior to the pulse completing its passage through the sample, as if the Bragg diffraction was generated by a shorter pulse of equal intensity. As a result, serial femtosecond crystallography does not need to be performed with pulses as short as 5--10 fs, as once thought, but can succeed for pulses 50--100 fs in duration. We show here that a similar gating effect applies to single molecule diffraction with respect to spatially uncorrelated damage processes like ionization and ion diffusion. The effect is clearly seen in calculations of the diffraction contrast, by calculating the diffraction of average structure separately to the diffraction from statistical fluctuations of the structure due to damage ("damage noise"). Our results suggest that sub-nanometer single molecule imaging with 30--50 fs pulses, like those produced at currently operating facilities, should not yet be ruled out. The theory we present opens up new experimental avenues to measure the impact of damage on single particle diffraction, which is needed to test damage models and to identify optimal imaging conditions.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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