A general strategy for the NMR observation of half-integer quadrupolar nuclei in dilute environments.
A general strategy for the observation of low gamma half-integer quadrupolar nuclides in biological systems is presented. The methodology combines low-temperature (4-100 K) techniques with cross-polarization (CP) experiments while employing a so-called Carr-Purcell-Meiboom-Gill spin-echo sequence (CPMG). This combined approach is termed CP/QCPMG. Also discussed are data processing issues that are unique to the induced signals that result from the QCPMG pulse sequence. Central to this strategy is the development of a stable low-temperature (4 to 250 K) NMR double-resonance probe. The probe is robust enough to handle multiple contact experiments and long acquisition periods with 1H decoupling. This approach is illustrated with low-temperature solid-state 67Zn and 25Mg NMR CP/QCPMG experiments on model compounds. The conclusion reached is that the strategy affords sufficient sensitivity to examine Zn2+ and/or Mg2+ binding sites in metalloproteins.
Lipton
A S
AS
Macromolecular Structure and Dynamics Directorate, WR Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Sears
J A
JA
Ellis
P D
PD
D005583:Fourier Analysis; D008274:Magnesium; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011868:Radioisotopes; D013696:Temperature; D015037:Zinc Radioisotopes
D011868:Radioisotopes; D015037:Zinc Radioisotopes; D008274:Magnesium