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ENDOR Subgroup |
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Electron Nuclear DOuble Resonance
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ENDOR = EPR detected NMR |
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The energy levels of an unpaired electron in a magnetic field (B) are modified by the interaction of the electron spin and nuclear spin. This interaction is described by the hyperfine tensor, and is effectively unique to each nucleus. ENDOR is the measurement of NMR transitions by observation of changes to the EPR intensity at a specific magnetic field. |
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ENDOR splittings
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e.g. 1H, 13C, 15N
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e.g. 2H, 14N, 17O
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Larmor frequency regions
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2H
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13C
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31P
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1H
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14N
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35 GHz, g = 2.0 (B = 12500 G)
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We study the electronic, magnetic, and structural properties of metalloenzymes and model complexes through use of advanced paramagnetic resonance techniques
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ENDOR targets
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[14,15N] His
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[1,2H, 13C] Cys
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Large, well-resolved couplings Ž CW ENDOR
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Traditional
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Non-traditional
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Small, poorly resolved couplings Ž pulse techniques
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HxO [1,2H, 17O]
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NH – SH Bond
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Cavity-bound substrate or other distant species
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The Hoffman Group |
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The ENDOR spectrum for a single nucleus is characterized by two features (n+ and n-) that are centered at the nuclear larmor frequency, nn (for nn > A/2) or at A/2 (A/2 > nn). For nuclei with a nuclear spin (I) greater than 1/2, the nuclear quadrupole interaction further splits each feature into a doublet split by the magnitude of the quadrupole (3P). |
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In the microwave frequency regime most utilized by the Hoffman group (35 GHz), the above diagram demonstrates the RF frequency regimes within which the most relevant nuclei we study are observed. |
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Traditional target systems in our group involve ligands directly coordinated to the metal center(amino acid residues such as histidine and cystine, water, etc.). These species generally have large, well-resolved hyperfine couplings and are well-suited to study by continuous-wave (CW) ENDOR techniques. Less traditional target systems possess more distant nuclei that are not directly coordinated to the metal. These include cavity-bound subtrates and through-space metal-amino acid interactions. Such species show smaller hyperfine couplings that are not as clearly resolved. These systems are well-suited to study by the numerous pulsed ENDOR techniques. |
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Useful resources about EPR and ENDOR |
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1. Abragam, A, Bleaney, B. Electron Paramagnetic Resonance of Transition Ions. Oxford University Press, Oxford, 1970. 2. Hoffman, B.M., Electron-nuclear double resonance spectroscopy (and electron spin-echo envelope modulation) in bioinorganic chemistry, Proc. Natl. Acad. Sci., 2003, 100, 3575-3578. 3. Lowe, D.J., ENDOR and EPR of Metalloproteins, R.G. Landes, Austin, TX. 4. Schweiger, A., Jeschke, G., Principle of pulse electron paramagneti resonance, Oxford University Press, Oxford, U.K., 2001. |
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Funding |