th  - 1987 - 51st ENC Conference

MF13
4=Ca NMR In The Solid State
S. D. Kennedy, S. Swanson, S. Ganapathy, R. G. Bryant
Department of Biophysics, University of Rocheste~
Rochester, New York 14642
Calcium ion like other group IIA metals has a significant
nuclear electric quadrupole moment that limits the resolution
possible in solution phase NMR. The poor resolution becomes
Norse when the ion interacts with large ligands such as
proteins which provide a large increase in the correlation
time for the line broadening interactions. The dynamical
broadening may be defeated in the solid, but other broadening
interactions remain that may be defeated by application of
the appropriate rf fields. The price is signal to noise~
since in such odd integral spin spectra narrowed by strong
proton decoupling and rapid sample rotation at the magic
angle, the central transition is observed, but usually not
the others. The signal to noise may be improved
significantly by exploiting magnetization transfer from the
protons. Since the ratio of the magnetogyric ratios is
14.86, the ma>:imum gain is significant. We have observed CP-
MASS spectra of 4=Ca and found that not only is the
e~:periment possible, but the spectra obtained hold promise
for excellent resolution among different calcium sites. This
poster presents representative CP-MASS calcium spectra, and
the conditions required to obtain them. Since the contact
times required for maximum signal are long, and the effective
gain in the signal strength for the rare spin may be severely
limited by the decay of the proton magnetization in the
rotating frame.