Photochemical pump and NMR probe: chemically created NMR coherence on a microsecond time scale.
Photochemical pump and NMR probe: chemically created NMR coherence on a microsecond time scale.
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DOI：
10.1021/ja504732u
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发表时间：
2014-06
影响因子：
15
通讯作者：
Olga Torres;B. Procacci;M. Halse;R. W. Adams;D. Blazina;S. Duckett;Beatriz Eguillor;R. A. Green;R. Perutz;D. C. Williamson
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文献类型：
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作者：
Olga Torres;B. Procacci;M. Halse;R. W. Adams;D. Blazina;S. Duckett;Beatriz Eguillor;R. A. Green;R. Perutz;D. C. Williamson
我们报道了利用激光同步反应对氢（para-H2）与过渡金属二氢化物配合物结合核磁共振（NMR）检测的泵浦探针实验。泵浦-探针实验包括一个纳秒级的激光泵浦脉冲，经过精确定义的延迟后，接着是一个射频（rf）探针脉冲。激光辐照消除了C6D6溶液中Ru(PPh3)3(CO)(H) 21或顺式Ru(dppe)2(H) 22中的H2。然后与对h2反应，在一个明确的核自旋状态下再生1和2。rf探针脉冲产生高分辨率，单扫描(1)H NMR谱，可以在泵浦探针延迟仅10 μs后记录。当泵浦-探针延迟以微或毫秒的增量增加时，可以跟踪光谱的演变。由于这个para-H2实验的灵敏度，得到的核磁共振光谱可以有超过750:1的氢化物信噪比。1的谱幅振荡频率为1101±3hz，为化学不等价氢化物之间的化学位移差。2对应的氢化物信号振荡频率为83±5 Hz，这与氢化物与赤道（31）P核耦合的差异相匹配。我们使用乘积算符的形式来证明这种振荡行为是由与磁场正交的平面上的磁相干性引起的，该平面是由使用没有射频初始化的激光脉冲产生的。此外，我们还演示了化学位移成像如何区分激光照射区域，从而区分核磁共振管内的热反应性和光化学反应性。
We report pump-probe experiments employing laser-synchronized reactions of para-hydrogen (para-H2) with transition metal dihydride complexes in conjunction with nuclear magnetic resonance (NMR) detection. The pump-probe experiment consists of a single nanosecond laser pump pulse followed, after a precisely defined delay, by a single radio frequency (rf) probe pulse. Laser irradiation eliminates H2 from either Ru(PPh3)3(CO)(H)2 1 or cis-Ru(dppe)2(H)2 2 in C6D6 solution. Reaction with para-H2 then regenerates 1 and 2 in a well-defined nuclear spin state. The rf probe pulse produces a high-resolution, single-scan (1)H NMR spectrum that can be recorded after a pump-probe delay of just 10 μs. The evolution of the spectra can be followed as the pump-probe delay is increased by micro- or millisecond increments. Due to the sensitivity of this para-H2 experiment, the resulting NMR spectra can have hydride signal-to-noise ratios exceeding 750:1. The spectra of 1 oscillate in amplitude with frequency 1101 ± 3 Hz, the chemical shift difference between the chemically inequivalent hydrides. The corresponding hydride signals of 2 oscillate with frequency 83 ± 5 Hz, which matches the difference between couplings of the hydrides to the equatorial (31)P nuclei. We use the product operator formalism to show that this oscillatory behavior arises from a magnetic coherence in the plane orthogonal to the magnetic field that is generated by use of the laser pulse without rf initialization. In addition, we demonstrate how chemical shift imaging can differentiate the region of laser irradiation thereby distinguishing between thermal and photochemical reactivity within the NMR tube.