论文标题
飞秒X射线排放研究的旋转跨界动力学
Femtosecond X-ray emission study of the spin cross-over dynamics in haem proteins
论文作者
论文摘要
在血红蛋白（由四个球状肌红蛋白样的亚基组成）中，从低旋转（LS）六型六边形的出血到配体脱离后的高旋转（HS）五型五型五齿状末期形式，以及在配体结合后的反向过程，代表了最终驱动呼吸器的过渡状态。长期以来，可见光 - 硫化光长期以来通过光解离来模仿血肠中的配体释放，同时使用时间分辨的红外线对紫外线光谱工具监测其重组。但是，这些既不是元素，也不是自旋敏感的。在这里，我们使用飞秒Fe Kalpha和KBETA非共振X射线发射光谱（XES）在X射线自由电子激光器上使用FE-NO键的光分析时，研究了肌红蛋白-NO（MBNO）的过渡态。我们发现，光诱导的从LS（s = 1/2）MBNO变为HS（s = 2）脱氧 - 甲状腺蛋白（脱氧症）的变化发生在CA中。 800 fs，并通过中间体（s = 1）旋转状态进行。 XES可观察物还表明，在没有重组脱氧分子时，返回平面MBNO基态是从HS到LS的电子松弛。 30 ps。因此，MBNO中的整个配体分解重组循环是自旋交叉，然后是反向自旋交叉过程。
In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from the haem by photodissociation, while its recombination was monitored using time-resolved infrared to ultraviolet spectroscopic tools. However, these are neither element- nor spin-sensitive. Here we investigate the transition state in the case of Myoglobin-NO (MbNO) using femtosecond Fe Kalpha and Kbeta non-resonant X-ray emission spectroscopy (XES) at an X-ray free-electron laser upon photolysis of the Fe-NO bond. We find that the photoinduced change from the LS (S = 1/2) MbNO to the HS (S = 2) deoxy-myoglobin (deoxyMb) haem occurs in ca. 800 fs, and that it proceeds via an intermediate (S = 1) spin state. The XES observables also show that upon NO recombination to deoxyMb, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in ca. 30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process.
