Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland.
Sci Rep. 2018 Mar 27;8(1):5281. doi: 10.1038/s41598-018-22944-z.
The rebinding kinetics of NO after photodissociation from microperoxidase (Mp-9) is studied in different solvent environments. In mixed glycerol/water (G/W) mixtures the dissociating ligand rebinds with a yield close to 1 due to the cavities formed by the solvent whereas in pure water the ligand can diffuse into the solvent after photodissociation. In the G/W mixture, only geminate rebinding on the sub-picosecond and 5 ps time scales was found and the rebinding fraction is unity which compares well with available experiments. Contrary to that, simulations in pure water find two time scales - ~10 ps and ~200 ps - indicating that both, geminate rebinding and rebinding after diffusion of NO in the surrounding water contribute. The rebinding fraction is around 0.63 within 1 ns which is in stark contrast with experiment. Including ions (Na and Cl) at 0.15 M concentration in water leads to rebinding kinetics tending to that in the glycerol/water mixture and yields agreement with experiments. The effect of temperature is also probed and found to be non-negligible. The present simulations suggest that NO rebinding in Mp is primarily driven by thermal fluctuations which is consistent with recent resonance Raman spectroscopy experiments and simulations on MbNO.
在不同溶剂环境中研究了微过氧化物酶（Mp-9）中 NO 光解后重新结合的动力学。在混合甘油/水（G/W）混合物中，由于溶剂形成的腔，解离配体的结合产率接近 1，而在纯水中，光解后配体可以扩散到溶剂中。在 G/W 混合物中，仅发现亚皮秒和 5 ps 时间尺度上的成对复合，并且结合分数为 1，这与可用的实验很好地吻合。与之相反，在纯水中的模拟发现了两个时间尺度——约 10 ps 和约 200 ps——表明，成对复合和 NO 在周围水中扩散后的复合都有贡献。在 1 ns 内，结合分数约为 0.63，这与实验形成鲜明对比。在水中加入浓度为 0.15 M 的离子（Na 和 Cl）会导致结合动力学趋于 G/W 混合物，并与实验结果一致。还研究了温度的影响，发现其不可忽略。目前的模拟表明，Mp 中 NO 的重新结合主要由热波动驱动，这与最近的共振拉曼光谱实验和 MbNO 的模拟一致。
