Solid-state 67Zn NMR spectroscopy in bioinorganic chemistry. Spectra of four- and six-coordinate zinc pyrazolylborate complexes obtained by management of proton relaxation rates with a paramagnetic dopant
Solid-state 67Zn NMR spectroscopy in bioinorganic chemistry. Spectra of four- and six-coordinate zinc pyrazolylborate complexes obtained by management of proton relaxation rates with a paramagnetic dopant
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DOI：
10.1021/ja0127133
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发表时间：
2002-05-22
影响因子：
15
通讯作者：
Ellis, PD
中科院分区：
文献类型：
--
作者：
Lipton, AS;Wright, TA;Ellis, PD
用低温(10K)增强Boltzmann因子和交叉极化(CP)相结合的方法，获得了[H_2B(3，5-Me(2)PZ)(2)](2)[H_2B(3，5-Me(2)PZ)(2)](2)Zn(PZ代表吡唑环)等金属配位体模型化合物的固体Zn-67核磁共振谱。对于其他模型化合物，如[H_2B(PZ)(2)](2)Zn，由于质子弛豫时间较长，对其光谱的观察受到阻碍。为了缩短质子弛豫时间，研究了高自旋六配位络合物[Hb(3，4，5-Me(3)pz)(3)](2)Fe的掺杂。核磁共振和电子顺磁共振测量表明，在5-10K的温度范围内，这种Fe(II)掺杂有效地降低了锌样品的H-1自旋晶格驰豫时间T-1，而旋转坐标系下的H-1自旋晶格驰豫时间T-1的微扰很小。用这种方法，我们已经测定了四配位和六配位锌(II)多(吡唑基)硼酸盐配合物的锌-67核磁共振参数，这些参数是具有重要生物学意义的系统的有用模型。对比了类似化合物的锌-67核磁共振参数和CD-113核磁共振参数的相应变化。此外，这些研究还表明，[Hb(3，5-Me(2)Pz)(3)](2)Zn在185K附近发生了温度相关的相变；我们所研究的其他聚吡唑基硼酸盐配合物没有表现出这种温度相关的行为。这一结论被室温高场(18.8T)固体锌-67核磁共振谱和低温X射线方法相结合所证实。顺磁性掺杂剂的使用将使低温交叉极化实验能够在生物无机化学中重要的各种核素上进行，例如镁-25、钙-43和锌-67。
Solid-state Zn-67 NMR spectra of model compounds for metallophoteins, such as [H2B(3,5-Me(2)pz)(2)](2)Zn (pz denotes pyrazolyl ring), have been obtained using low temperatures (10 K) to enhance the Boltzmann factor in combination with cross polarization (CP) from H-1 to Zn-67. Attempts to observe spectra of other model compounds, such as [H2B(pz)(2)](2)Zn, were hindered by long relaxation times of the protons. To decrease the proton relaxation times, the high-spin six-coordinate complex [HB(3,4,5-Me(3)pz)(3)](2)Fe has been investigated as a dopant. NMR and EPR measurements have shown that this Fe(II) dopant effectively reduces the H-1 spin lattice relaxation time, T-1, of the zinc samples in the temperature range 5-10 K with minimal perturbations of the H-1 spin lattice relaxation time in the rotating frame, T-1rho. Using this methodology, we have determined the Zn-67 NMR parameters of four- and six-coordinate zinc(II) poly(pyrazolyl) borate complexes that are useful models for systems of biological importance. The Zn-67 NMR parameters are contrasted to the corresponding changes in the Cd-113 NMR parameters for the analogous compounds. Further, these investigations have demonstrated that a temperature-dependent phase transition occurs in the neighborhood of 185 K for [HB(3,5-Me(2)pz)(3)](2)Zn; the other poly(pyrazolyl) borate complexes we investigated did not show this temperature-dependent behavior. This conclusion is confirmed by a combination of room-temperature high-field (18.8 T) solid-state Zn-67 NMR spectroscopy and low-temperature X-ray methods. The utilization of paramagnetic dopants should enable low-temperature cross polarization experiments to be performed on a wide variety of nuclides that are important in bioinorganic chemistry, for example, Mg-25, Ca-43, and Zn-67.