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 Para
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- 作者：Andrew S. Lipton ; Terri A. Wright ; Michael K. Bowman ; Daniel L. Reger ; and Paul D. Ellis
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：May 22, 2002
- 年：2002
- 卷：124
- 期：20
- 页码：5850 - 5860
- 全文大小：281K
- 年卷期：v.124,no.20(May 22, 2002)
- ISSN：1520-5126
文摘
Solid-state 67Zn NMR spectra of model compounds for metalloproteins, such as [H2B(3,5-Me2pz)2]2Zn (pz denotes pyrazolyl ring), have been obtained using low temperatures (10 K) to enhance theBoltzmann factor in combination with cross polarization (CP) from 1H to 67Zn. Attempts to observe spectraof other model compounds, such as [H2B(pz)2]2Zn, 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-Me3pz)3]2Fe hasbeen investigated as a dopant. NMR and EPR measurements have shown that this Fe(II) dopant effectivelyreduces the 1H spin lattice relaxation time, T1, of the zinc samples in the temperature range 5-10 K withminimal perturbations of the 1H spin lattice relaxation time in the rotating frame, T1
fchars/rho.gif" BORDER=0 >. Using this methodology,we have determined the 67Zn NMR parameters of four- and six-coordinate zinc(II) poly(pyrazolyl)boratecomplexes that are useful models for systems of biological importance. The 67Zn NMR parameters arecontrasted to the corresponding changes in the 113Cd NMR parameters for the analogous compounds.Further, these investigations have demonstrated that a temperature-dependent phase transition occurs inthe neighborhood of 185 K for [HB(3,5-Me2pz)3]2Zn; the other poly(pyrazolyl)borate complexes weinvestigated did not show this temperature-dependent behavior. This conclusion is confirmed by acombination of room-temperature high-field (18.8 T) solid-state 67Zn NMR spectroscopy and low-temperatureX-ray methods. The utilization of paramagnetic dopants should enable low-temperature cross polarizationexperiments to be performed on a wide variety of nuclides that are important in bioinorganic chemistry, forexample, 25Mg, 43Ca, and 67Zn.
fchars/rho.gif" BORDER=0 >. Using this methodology,we have determined the 67Zn NMR parameters of four- and six-coordinate zinc(II) poly(pyrazolyl)boratecomplexes that are useful models for systems of biological importance. The 67Zn NMR parameters arecontrasted to the corresponding changes in the 113Cd NMR parameters for the analogous compounds.Further, these investigations have demonstrated that a temperature-dependent phase transition occurs inthe neighborhood of 185 K for [HB(3,5-Me2pz)3]2Zn; the other poly(pyrazolyl)borate complexes weinvestigated did not show this temperature-dependent behavior. This conclusion is confirmed by acombination of room-temperature high-field (18.8 T) solid-state 67Zn NMR spectroscopy and low-temperatureX-ray methods. The utilization of paramagnetic dopants should enable low-temperature cross polarizationexperiments to be performed on a wide variety of nuclides that are important in bioinorganic chemistry, forexample, 25Mg, 43Ca, and 67Zn.