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Resource in
Pulsed EPR Spectroscopy
An NIH funded facility that provides the investigator with a means for measuring hyperfine interactions between
magnetic nuclei such as 1H, 2H, 13C, 14N, 15N, 31P and 23Na and paramagnetic centers encountered in
biological samples, including Cu2+, Fe3+, Co2+, Mn2+, Ni3+, free radicals and iron-sulfur clusters, through
the use of electron spin echo (ESE) envelope modulation techniques and electron-nuclear double resonance
ENDOR spectroscopy. For both ESE and ENDOR, one can relate the observed spectroscopic splittings to the
identity of the nuclei giving rise to the effect and can quantify the magnetic coupling between those nuclei and the
paramagnetic center. These coupling parameters provide a means for characterizing ligand bonding and in some
cases, the distance of a particular ligand nucleus from the paramagnetic center and the relative orientation of a
ligand molecule with respect to a structural component of the paramagnetic center. In this way, data forthcoming
from frozen solution samples provide information normally obtained from single crystal X-ray measurements. ESE
envelope modulation studies provide additional information concerning ligand group identity and the number of such
ligands bound. Therefore, these studies can yield information concerning the structure surrounding a paramagnetic
center and how that structure is altered by chemical or biochemical processes. Linear electric field effect (LEFE)
measurements using the ESE technique can provide information concerning crystal field symmetry for paramagnetic
metalloproteins and transition metal model compounds.
ESE envelope modulation studies of metalloproteins, metal-drug complexes, transition metal model complexes,
and radical species of biological importance, including single crystal studies are carried out at the Resource.
Questions being addressed concern the ligation structure surrounding paramagnetic metal centers in these
systems and how those structures change when various substrates or inhibitors are added. Model compound
studies have focused on providing the framework for interpreting protein data and understanding ESE envelope
modulation data from first principles. The development of computer software for analysis of these data and the
development of pulsed EPR instrumentation to enhance sensitivity for the study of biological materials are also
primary functions of the Resource.
The Resource includes a pulsed EPR spectrometer for performing ESEEM and pulsed ENDOR experiments
in the range of 8-15 GHz excitation frequency and at temperatures spanning 300-1.2 K. CW spectrometers
include a Varian E-112 (300 - 4 K), a Varian E-109 (300-77 K) and a Bruker ER 200 D with an EN-810
ENDOR accessory (300-4 K). (Construction of a high frequency (130 GHz) CW and pulsed spectrometer has begun.)
The Scientific Director is Dr. Jack Peisach
(2175).
Updated 12/16/05. Description
taken from Molecular Biophysics facilities page.
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