NUCLEAR MAGNETIC RESONANCE OF PARAMAGNETIC METAL CENTERS
IN PROTEINS AND SYNTHETIC COMPLEXES
Li-June Ming
Department of Chemistry and
Institute for Biomolecular Science
University of South Florida
Tampa, Florida 33620-5250
I. Basic NMR Principles for Paramagnetic Molecules
A. NMR transition
B. Chemical Shift
1. Fermi
Contact interaction
2. Dipolar
Interaction and Molecular Structure
C. Nuclear Relaxation
1. Dipolar
Relaxation
2. Curie
Relaxation
3. Contact
Relaxation
4. Application
of Nuclear Relaxation
D. NMR Properties of Multinuclear Paramagnetic
Metal Centers
1. Magnetic
Coupling
2. Chemical
Shift
3. Electron
and Nuclear Relaxations
II. Practical Aspects: Acquiring NMR Spectra of Paramagnetic
Molecules
A. I just want a spectrum!
1. Spectral
width—the window in the frequency domain
2. Radio
Frequency Pulse
3. Free
induction decay—the window in the time domain
4. Choice
of window function
5. Baseline
correction
6. Water
suppression
7. Temperature
control
8. Relaxation
times
B. Nuclear Overhauser Effect
C. 2D NMR
1. Bond
Correlation (COSY, TOCSY, and HMQC)
2. Internuclear
Distance (NOESY and ROESY)
3. Chemical
Exchange (EXSY)
III. Perspectives
Acknowledgments
Appendix I. Derivation of Fermi Contact Shift
Appendix II. Nuclear Overhauser Effect (NOE)
A. Steady-State NOE
B. Transient NOE and NOESY
C. Rotating Frame NOE
Appendix III. Chemical Exchange
I. Basic NMR Principles for Paramagnetic Molecules
Nuclear magnetic resonance (NMR), a versatile tool
for the study of molecular structure and dynamics, has been used to solve
problems in bioinorganic chemistry, despite the fact that many systems
of interest contain a paramagnetic metal center. The basic principles
of NMR in diamagnetic species can be applied, in principle, to the understanding
of the NMR properties of paramagnetic species by taking into account the
significant influence of electron magnetic moment (which is 658 times larger
than that of the proton). The unpaired electrons in these paramagnetic
molecules present some challenges and require some adaptation of approaches
used for NMR studies of diamagnetic molecules. Nevertheless useful
information can be extracted from the NMR spectra of paramagnetic metal
complexes and metalloproteins. This chapter is intended to serve
as an illustration how NMR can be applied to the investigation of paramagnetic
systems.
(Back to Current Publications)