[PDF] NMR of Paramagnetic Molecules - Sites at Penn State

Chapter 3: Biological Molecules - WOU

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NMR of Paramagnetic Molecules - Sites at Penn State

Resources • Bertini & Luchinat, “NMR of Paramagnetic Molecules in Biological Systems,” 1986, Benjamin/Cummings: Menlo Park ISBN: 0-8053-0780-X • Bertini & Luchinat, “NMR of Paramagnetic Substances,”

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NMR of Paramagnetic Molecules

Kara L. Bren

University of Rochester

Outline

• Resources • Examples of effects on spectra • What we can learn (why bother?) • NMR fundamentals (review) • Relaxation mechanisms in NMR • Effects of unpaired electrons on relaxation • Effects of unpaired electrons on chemical shifts

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Resources

• Bertini & Luchinat, "NMR of Paramagnetic Molecules in Biological Systems," 1986, Benjamin/Cummings: Menlo Park. ISBN: 0-8053-0780-X • Bertini & Luchinat, "NMR of Paramagnetic Substances," Coord. Chem. Rev. 1996, 150, 1-296. • Banci, "Nuclear and Electron Relaxation. The Magnetic Nucleus-unpaired Electron Coupling in Solution," 1991, VCH: Weinheim. ISBN: 3-5272-8306-4 • Bren, "NMR Analysis of Spin States and Spin Densities," in Spin States in Biochemistry and Inorganic Chemistry: Influence on Structure and Reactivity, (Eds: Swart & Costas), 2016, Wiley: Chichester. DOI: 10.1002/9781118898277.ch16

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Outline

• Resources • Examples of effects on spectra • What we can learn (why bother?) • NMR fundamentals (review) • Relaxation mechanisms in NMR • Effects of unpaired electrons on relaxation • Effects of unpaired electrons on chemical shifts

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Effects of Unpaired Electrons

5

S = 1/2 Horse ferricytochrome c

2

6PSUBioinorganicWorkshop,Bren

Effects of Unpaired Electrons

6

S = 1/2 Horse ferricytochrome c

Heme methyls

2

6PSUBioinorganicWorkshop,Bren

Effects of Unpaired Electrons

JACS 1995, 8067

7

CN-Fe(III) M80A cytochrome c, D

2 O

S = 1/2

FeCNHNNHis

25 20 15 10 5 0 -5 -10 -15 δ, ppmH

2 O

CN-Fe(III) cytochrome c, D

2

O CN-Fe(III) M80A cytochrome c, D

2 O 2

6PSUBioinorganicWorkshop,Bren

********* = heme methyls

Effects of Unpaired Electrons

Bren group

8

H. thermophilus Fe(III)M61A cyt c S = 1/2, 5/2

45 °C 35 °C 25 °C 15 °C 5 °C

FeOH2NHNHis

2

6PSUBioinorganicWorkshop,Bren

a,b,c,d = heme methyls

Effects of Unpaired Electrons

JACS 2000, 3701

P. aeruginosa Cu(II) azurin

9

60 50403020100δ, ppm

CuSHisH2CNNHHisH2CNNHCysSOMet

S = 1/2

2

6PSUBioinorganicWorkshop,Bren

Effects of Unpaired Electrons

Biochemistry 1996, 1810

Ni(II) azurin

S = 1 2

6PSUBioinorganicWorkshop,Bren

Effects of Unpaired Electrons

JACS 1996, 11658

T. thermophilus Cu

A domain

CuSNNHHisNHNCysHSOMetCuSCysHis

Cu(I)Cu(II) S = 1/2

pH 4.5, H 2

OpH 8.0, H

2 O 2

6PSUBioinorganicWorkshop,Bren

Outline

• Resources • Examples of effects on spectra • What we can learn (why bother?) • NMR fundamentals (review) • Relaxation mechanisms in NMR • Effects of unpaired electrons on relaxation • Effects of unpaired electrons on chemical shifts

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6PSUBioinorganicWorkshop,Bren

What Can We Learn?

• Metal oxidation state and spin state • Electron spin relaxation time (estimate) • Presence of low-lying excited states • Pattern and amount of electron spin delocalization onto ligands; hyperfine coupling constants • Presence of hydrogen bonds • Magnetic anisotropy, magnetic axes • Structural refinement is possible • (In addition, 3D structure, exchange phenomena, dynamics, etc.)

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6PSUBioinorganicWorkshop,Bren

Outline

• Resources • Examples of effects on spectra • What we can learn (why bother?) • NMR fundamentals (review) • Relaxation mechanisms in NMR • Effects of unpaired electrons on relaxation • Effects of unpaired electrons on chemical shifts

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6PSUBioinorganicWorkshop,Bren

NMR Fundamentals

Some nuclei have spin angular momentum and an associated magnetic moment, µ I I = g N (e/2m p ) I g N 1

H) = 5.5856947

I | = (h/2π) I[I(I+1)] 1/2 Need nucleus with non-zero spin (I ≠ 0) Examples: 1 H, 13 C, 15 N, 19 F, 31

P (I = 1/2)

2 H, 14 N, (I = 1) Herein we will base examples in nuclei with I = 1/2 5 µI 2

6PSUBioinorganicWorkshop,Bren

NMR Fundamentals

A nucleus with spin I has states with associated M I values where M I I = ± 1/2

62 6PSUBioinorganicWorkshop,Bren

In the absence of a magnetic field, states with different M I are degenerate and their magnetic moments µ orient randomly

NMR Fundamentals

Applying a magnetic field lifts this degeneracy.

1

H with M

I 1

H with M

I = +1/2 have a lower energy.

72 6PSUBioinorganicWorkshop,Bren

The nuclear spins align with (M

I = +1/2) or opposed to (M I I h/2πB 0

NMR Fundamentals

The energies of the nuclei in the magnetic field are: E = >quotesdbs_dbs8.pdfusesText_14