spin_relaxation_in_proteins_10

spin_relaxation_in_proteins_10 - Model-Free Approach to...

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Model-Free Approach to Internal Motions in Proteins • Lipari & Szabo, JACS 104, 4546 (1982) • Palmer AG. Ann. Rev. Biophys. Biomol. Struc., 30, 129-155 (2001) • Palmer AG, Kroenke CD, Loria JP, Meth. Enzymol. 339, 204-238 (2001)
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Spin Relaxation: Result of Modulation of Spin Interactions by Molecular Motion: D-D Example: Can probe structure, but also molecular motion R 1S = 1/T 1 = ( μ 2 0 h 2 γ I 2 γ S 2 r IS -6 / 64 π 4 )(J( ω I - ω S ) + 3J( ω S ) + 6J( ω I + ω S )) R 2S = 1/T 2 = ( μ 2 0 h 2 γ I 2 γ S 2 r IS -6 / 128 π 4 )(4J(0)+J( ω I - ω S )+3J( ω S )+6J( ω I )+6J( ω I + ω S )) J( ω ) = (2/5) τ c /(1 + ω 2 τ c 2 ) Note: if τ c is small (small molecule), R 1S = R 2S . if τ c is large, R 2S >> R 1S
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Generalized Order Parameters and Internal Motion Basis: fast internal motions scale interactions that are then modulated by molecular tumbling Methyl rotation a model specific example: H H H θ θ θ ’’ B 0 H 1 (t) (3cos 2 ( θ ’’(t) – 1) H 1 (t) (3cos 2 ( θ ’(t) – 1)(3cos 2 ( θ – 1)/2 H 1 (t) (3cos 2 ( θ ’(t) – 1)(-0.34) H 1 (t) (3cos 2 ( θ ’(t) – 1) S Order Parameter
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• Scaling due to motions too fast to affect relaxation directly • Efficiency of relaxation due to tumbling is
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This note was uploaded on 11/07/2011 for the course CHEM 8853R taught by Professor Gelbaum during the Fall '11 term at Georgia Institute of Technology.

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spin_relaxation_in_proteins_10 - Model-Free Approach to...

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