high frequency dynamic nuclear polarization · •magic angle adjustment ... l the full system was...
TRANSCRIPT
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Biomolecular NMR Winter School Trapp Family Lodge January 7-12, 2018
High Frequency Dynamic Nuclear Polarization
Francis Bitter Magnet Laboratoryand
Department of ChemistryMassachusetts Institute of Technology
AMUPol
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• Background and RationaleDNP, EPR, and Signal to NoiseDNP Enhancements of 100-400 in MAS Spectra @ 90 KDNP functions quite effectively in multiple classes of systems
• Instrumentation for DNPQuadruple Resonance, LT MAS ProbesSuperconducting Sweep CoilsGyrotron Microwave Oscillators and Amplifiers
• CW DNP Mechanisms and Polarizing AgentsSolid Effect — δ ~Δ << ω0I
two spins, without e- - 1H hyperfine couplingOverhauser Effect — δ ~Δ << ω0I
two spins, with e- - 1H hyperfine coupling Cross Effect — δ < ω0I < Δ
three spins, with e- -e--1H dipole coupling
• Time Domain DNPNOVEL — lab frame-rotating frame cross-polarizationIntegrated Solid EffectStretched Solid Effect
NEW
NEW
DNP Outline
Melanie Rosay
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• Background and RationaleDNP, EPR, and Signal to NoiseDNP Enhancements of 100-400 in MAS Spectra @ 90 KDNP functions quite effectively in multiple classes of systems
• Instrumentation for DNPQuadruple Resonance, LT MAS ProbesSuperconducting Sweep CoilsGyrotron Microwave Oscillators and Amplifiers
• CW DNP Mechanisms and Polarizing AgentsSolid Effect — δ ~Δ << ω0I
two spins, without e- - 1H hyperfine couplingOverhauser Effect — δ ~Δ << ω0I
two spins, with e- - 1H hyperfine coupling Cross Effect — δ < ω0I < Δ
three spins, with e- -e--1H dipole coupling
• Time Domain DNPNOVEL — lab frame-rotating frame cross-polarizationIntegrated Solid EffectStretched Solid Effect
DNP Outline
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What are the THREE most important parameters in magnetic resonance
Signal-to-noise Signal-to-noise
Signal-to-noise
4
Dynamic Nuclear Polarization
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Nuclear Spin PolarizationTemperature and Field Dependence
1 10 100 300
0.01
0.1
100
Temperature (K)
10
1
0.001
0.0186 % 1H polarization @ 700 MHz / 90 K
POLARIZATION
• Current strategy -- increase the polarization by increasing B0 ! • Result -- “modest” increases in sensitivity and resolution ! Increases in magnet cost are non-linear !
P = n+ - n-
n+ + n- = tanh γ !B0
2kT⎛⎝⎜
⎞⎠⎟
500 MHz
900 MHz
P = γ !B0
2kT
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Electron and Nuclear PolarizationTemperature and Field Dependence
12.24 % e- polarization @ 700 MHz / 90 K
0.0186 % 1H polarization @ 700 MHz / 90 K
POLARIZATION
• Much larger spin polarization is present in the electron spin reservoir •Transfer the electron polarization to the nuclear spins by irradiating the electrons with high frequency microwaves !
P = n+ - n-
n+ + n- = tanh γ !B0
2kT⎛⎝⎜
⎞⎠⎟
(γe/γ1H) ~ 660 P = γ !B0
2kT
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Components of a DNP System
Barnes, et al. (2009) Bajaj, et al. (2007) Joye, et al., (2006)
Woskow, et al. (2005) Song, et al. (2006) Matsuki, et al. (2009)
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Quadruple Resonance DNP/MAS Probew/ Optical Irradiation of the Sample
• Quadruple resonance -- 1H, 13C, 15N, and e-
• Routine low temperature spinning at 85-90 K, ωr/2π ~10 kHz• Optical irradiation (532/650 nm) of samples to generate photochemical
intermediates
Barnes, et. al. JMR (2009)
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MAS and Sample Exchange
3D printed eject pipe
tapped waveguide
Barnes et al. JMR, 198(2), 261
custom 3.2 mm Lewis stator
• Changes samples in minutes • Reduces risk of damage
90° turn
80-100 K
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Cambridge Instruments DNP Cryogenic MAS Probe
Challenges for cryogenic sample exchange:
•Magic angle adjustment•Limited space•Seals at low temperature•Physical restrictions under the magnet•Prevent damage to rotor
LT dewar
Sample eject
Waveguide
Optic fiber
Alexander Barnes
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Simulation of EM Coupling to Sample
l The full system was modeled in HFSS l Internal Reflections
Top View
Side View
Sapphire Rotor
EM Waves Launched
NMR Coil
• Modeling useful to optimize coupling of EM radiation to sample
8 mm
E. Nanni and R. Temkin, 2010
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Frequency Calibration• NMR frequencies ---
– generally refer to 1H frequencies – 42.577 MHz/Tesla
• EPR frequencies --- – dealing with g=2 electrons – 28.0 GHz/Tesla
Magnetic Field (Tesla)
1H NMR Frequency (MHz)
g=2 EPR Frequency (GHz)
5 211 1408.93 380 25014.09 600 39516.44 700 46018.79 800 527
(γe/γH) = (2800/42.577) =657
(⅔)𝜈H(MHz)≈𝜈e(GHz)
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460 GHz/ 700 MHz GyrotronOscillator
Hornstein,Kreischer, Temkin, et al (2004)
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250/ 460 GHz GyrotronFunctional Details
A: Electron emission from an annular ring
B: Bunching in the cavity and emission of microwaves
C: Quasi optic coupling of the microwaves out to the sample. Electrons continue to the collector.
D: Electrons are collected in the collector
• Generates microwaves with a frequency of ~28 GHz/Tesla
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Corrugated Waveguide
1.3 m
Wall thickness 300 microns
λ/4 Corrugation depth
•Very low insertion loss (0.01dB/m)
•Cryogenic Operation
•Excellent mode and polarization characteristics
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Sample Preparation
• TOTAPOL is soluble in water and stable
• Cryoprotection is critical to minimize inhomogeneous broadening
• Polarization diffuses throughout the macromolecule
H2Oe
-
H2OH2Oe-
e-
e-
e-
e- H2O
H2O
H2O
H2O
H2O
H2Oe-
Purple membrane
Cryoprotected sample
Cryoprotectant (e.g. glycerol)
bacteriorhodopsin
1. Resuspension
2. centrifugation
TOTAPOL Sedimented Proteins
“DNP Juice”
d8-glycerol/D2O/H2O
60:30:10
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DNP in Nonconducting Solids
♦ Requires microwaves and cryogenic temperatures
2H
2H
2H2H 2H
2H
2H2H
2H
2H
2H2H
2H
2H
2H
2H
2H2H
2H
2H
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DNP Sensitvity Enhancement
♦ ε = 40: DNP – 1 Day; no DNP – 4.38 years
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AMUPol Biradical Paul Tordo and Co.
Aux Marseille Universite
♦ ε = 420: DNP – 1 Day; no DNP – 483 years !
ε = 420
Qing Zhe Ni1M-13C-urea / 10 mM radical 60/30/10 (v/v/v)
380 MHz / 250 GHz - mw ~ 12 W
T=78 K, 13C{1H} CPMAS, 5.5 kHz
35 MHz e--e-
coupling
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DNP WorldwideWS 2010 -- One student remarked that he/she “will not try DNP very soon” since ... there
will not be access to DNP hardware in the future !
Other efforts: A, Barnes, R. Tycko, Y. Matsuki, K. Zilm, M. Ernst, M. Levitt, C. Hilty, W. Koeckenberger, Dan Vigernon, etc.
400 MHz/263 GHz
H. Oschkinat/Berlin G. Bodenhausen/Lausanne
M. Baldus/Utrecht G. DePaepe/Grenoble x2
C. Glaubitz/Frankfurt M. Pruski/Iowa State
S. Han/ UCSB Kyoto and Tsukuba, Japan
600 MHz/395 GHz
A. McDermott/ Columbia V. Ladizhansky/Guelph
C. Greisinger/Goettingen J. Long, T. Cross/ Florida State
G. Debelouchina, S. Opella/UCSD V. Michaelis/ Alberta
C. Coperet/ETH-Zurich C.P. Jaroniec/OHio State
K, Frederik/ UTSW
800 MHz/527 GHz
M. Baldus, Utrecht Lesage, Pintacuda, Emsley/Lyon
G. Bodenhausen/Paris B. Reif/Munich
H. Oschkinat/Berlin H. Heise/ Dusseldorf
900 MHz/593 GHz L.Emsley/Lausanne
~17 Total
~13 Total
6 Total
1 Total
30-40
gyrotrons
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• Background and RationaleDNP, EPR, and Signal to NoiseDNP Enhancements of 100-400 in MAS Spectra @ 90 KDNP functions quite effectively in multiple classes of systems
• Instrumentation for DNPQuadruple Resonance, LT MAS ProbesSuperconducting Sweep CoilsGyrotron Microwave Oscillators and Amplifiers
• CW DNP Mechanisms and Polarizing AgentsSolid Effect — δ ~Δ << ω0I
two spins, without e- - 1H hyperfine couplingOverhauser Effect — δ ~Δ << ω0I
two spins, with e- - 1H hyperfine coupling Cross Effect — δ < ω0I < Δ
three spins, with e- -e--1H dipole coupling
• Time Domain DNPNOVEL — lab frame-rotating frame cross-polarizationIntegrated Solid EffectStretched Solid Effect
DNP Outline
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DNP Polarizing AgentsMonoradicals -- Solid and Overhauser Effect
Biradicals -- Cross Effect
AMUPol
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EPR spectra and DNP Zeeman field profiles
• EPR spectra of polarizing
agents -- ~100 mT (1000 G)
• Variety of polarizing agents
allows for optimal DNP in
different situations
140 GHz EPR spectra
DNP Zeeman field profiles
Mn2+
Gd3+
NO• BDPAtrityl
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DNP
0 200-200-400Frequency (MHz)
e1 e2
ωn
Δ 600 MHz
δ ~5 MHz
ω0I
• Mechanism determined by relative size of Δ, ω0I ,δ in EPR
•Cross effect -- three spins Δ> ω0I/2π> δ
•Solid effect -- two spins ω0I/2π > δ,Δ
•Overhauser effect - liquids, mobile electrons (?)
•Thermal mixing - many electrons, homogeneous EPR
• Time domain DNP — electron spin locking
DNP Mechanisms Δ, ω0I ,δ
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CW Dynamic Nuclear Polarization Mechanisms
Solid Effect (SE) -- single electron,insulating solids (organic, biological systems) when .…
δ ~Δ << ωδ = homogeneous linewidth of the EPR spectrumΔ = breadth of the EPR spectrum ω = nuclear Larmor frequency (1H, 13C, 15N)
Overhauser Effect (OE) -- applicable to systems with mobile electrons -- i.e., metals, liquids, 1D conductors (Carver and Slichter, Li metal) and strong 1H hyperfine couplings
δ ~Δ << ω
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CW Dynamic Nuclear Polarization Mechanisms
Thermal Mixing (TM) -- multiple electrons, insulating solids, but ….
δ, Δ >> ω TM -- dominates when the g anisotropy is small, and/or the EPR line is homogeneously broadened, and ω is small
Cross Effect (CE) -- two electrons, insulating solids, but ….
Δ> ω>δ CE -- operative at high fields where Δg >> δ, the line is inhomogeneously broadened.
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CW Dynamic Nuclear Polarization Mechanisms
Solid Effect (SE) -- single electron,insulating solids (organic, biological systems) when .…
δ ~Δ << ωδ = homogeneous linewidth of the EPR spectrumΔ = breadth of the EPR spectrum ω = nuclear Larmor frequency (1H, 13C, 15N)
Overhauser Effect (OE) -- applicable to systems with mobile electrons -- i.e., metals, liquids, 1D conductors (Carver and Slichter, Li metal) and strong 1H hyperfine couplings
δ ~Δ << ω
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DNP Polarizing AgentsMonoradicals -- Solid and Overhauser Effect -- Δ=25-60 MHz
9 GHz EPR spectra16 1H couplings 21 1H couplings
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Paramagnetic Centers for DNP
BDPA
Galvinoxyl
TEMPO
49.949.849.749.649.5Field (kilogauss)
• EPR lineshapes are Dominated by g- anisotropy
• BDPA linewidth ~21 MHz ---- Solid effect
• TEMPO powder pattern~600 MHz ---- Thermal mixing or
cross effect
ωe/2π = 28 GHz/T
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DNP with Gyrotrons
e- →1H→13C e- → 13Cεmax @ ωe ± ωn
ε~10 ε~40
1.5% efficient
(γe/γn) ~ 660
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Trityl Radical Structure and FT EPR Spectrum
• Small g-anisotropy yields a solid effect enhancement mechanism
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Dynamic Nuclear PolarizationSolid State EffectDNPDNPDNP
• Enhancement ~ (γ ε / γ n ) (ω1 /ω0 )2 (Ne / δ )T1n
• Irradiate the flip-floptransitionsW±
NuclearZeeman
Bath
ElectronZeeman
Bath
EquilibriumNegative
EnhancementPositive
EnhancementNo
Enhancement
νε−νn νε+νnνε
|--) + q |-+)
|+-) - q |++)|++)+ q* |+-)
WEPRWEPR
W±
|-+) - q* |--)Wnmr
Wnmr
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Solid Effect @ 400 MHz/263 GHz
• Mediated by single electron-nuclear spin flips •Transitions are partially allowed due to state mixing.
•Maximum and minimum enhancements at ω =ωe ± ωn
Trityl Radical triphenyl methyl radical
Magne&cField
Polarizeωe±ωn
C. Can, M.Caporini, F. Mentink-Vigier , S. Vega and M. Rosay, JCP (2014)
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Dynamic Nuclear PolarizationSolid State EffectDNPDNPDNP
• Enhancement ~ (γ ε / γ n ) (ω1 /ω0 )2 (Ne / δ )T1n
• Irradiate the flip-floptransitionsW±
NuclearZeeman
Bath
ElectronZeeman
Bath
EquilibriumNegative
EnhancementPositive
EnhancementNo
Enhancement
νε−νn νε+νnνε
|--) + q |-+)
|+-) - q |++)|++)+ q* |+-)
WEPRWEPR
W±
|-+) - q* |--)Wnmr
Wnmr
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State Mixing+ + S+ − − = + − S+ − + = 0 !
• Electron-nuclear transitions are forbidden
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Perturbation Theory Notes 1
ψ n1 =
ψ m0 ′H ψ n
0
En0 − Em
0m≠n∑ Ψm
0 !
En1 = ψ n
0 ′H ψ n0 !
En2 =
ψ m0 ′H ψ n
0 ψ n0 ′H ψ m
0
En0 − Em
0 =m≠n∑ ′Hmn ′Hnm
En0 − Em
0m≠n∑ !
•Hamiltonian of interest is the electron-nuclear dipolar coupling
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Electron-Nuclear Dipole Coupling
• C and D (C’) terms mix adjacent states
HIS =
γ Iγ Sr3 (A + B + C + D + E + F) !
A=(1− 3cos2θ) SZ IZ[ ]B = −
14
(1− 3cos2θ) S−I+ + S+I−[ ]
C = −32
sinθ cosθe− iφ S+IZ + SZ I+[ ]
D = C† = −32
sinθ cosθeiφ S−IZ + SZ I−[ ]
E = −34
sin2θe−2iφ S+I+[ ]
F = −34
sin2θe2iφ S−I−[ ]
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Electron-Nuclear Dipole Coupling
• Only terms with the nuclear frequency survive in the expansion
ψ 31 =
ψ m0 ′H ψ n
0
En0 − Em
0m≠3∑ ψ m
0 =ψ 1
0 ′H ψ 30
E30 − E1
0 ψ 10 +
ψ 20 ′H ψ 3
0
E30 − E2
0 ψ 20 +
ψ 40 ′H ψ 3
0
E40 − E1
0 ψ 40
E30 − E1
0 =12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟−
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= γ IB0 = ω0 I
E30 − E2
0 =12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟− −
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= γ SB0 = ω0S
E40 − E1
0 = −12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟−
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= −γ SB0 + γ IB0 ≈ −ω0S
!
ω 0S / 2π = 140 GHz ω 0 I / 2π = 211 MHz
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Electron-Nuclear Dipole Coupling
• Only terms with the nuclear frequency survive
ψ 31 =
ψ m0 ′H ψ n
0
En0 − Em
0m≠3∑ ψ m
0 =ψ 1
0 ′H ψ 30
E30 − E1
0 ψ 10 +
ψ 20 ′H ψ 3
0
E30 − E2
0 ψ 20 +
ψ 40 ′H ψ 3
0
E40 − E1
0 ψ 40
E30 − E1
0 =12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟−
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= γ IB0 = ω0 I
E30 − E2
0 =12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟− −
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= γ SB0 = ω0S
E40 − E1
0 = −12γ SB0 +
12γ IB0
⎛⎝⎜
⎞⎠⎟−
12γ SB0 −
12γ IB0
⎛⎝⎜
⎞⎠⎟
= −γ SB0 + γ IB0 ≈ −ω0S
!
ω 0S / 2π = 140 GHz ω 0 I / 2π = 211 MHz
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Electron-Nuclear Dipole Coupling
• Only terms with the nuclear frequency survive
ψ 31 =
ψ m0 ′H ψ n
0
En0 − Em
0m≠3∑ ψ m
0 =ψ 1
0 ′H ψ 30
E30 − E1
0 ψ 10 +
ψ 20 ′H ψ 3
0
E30 − E2
0 ψ 20 +
ψ 40 ′H ψ 3
0
E40 − E1
0 ψ 40
q = −γ Iγ S
r3
32ω0 I
sinθ cosθe− iφ + + SZ I+ + −
ψ 3= + − − q + +
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Electron-Nuclear Dipole Coupling
• Only terms with the nuclear frequency survive
q = −γ Iγ S
r3
32ω0 I
sinθ cosθe− iφ + + SZ I+ + −
ψ 3= + − − q + +
ψ 1= + + + q * + −ψ 2 = − + − q * − −ψ 4 = − − + q − +
!
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Transition Probabilities
ψ 1 S+ ψ 42
= + +( ) + q + −( ) S+ − −( ) + q − +( ) 2= 2q = 4q2 !
ψ 2 S− ψ 32
= − +( ) − q − −( ) S− + −( ) + q + +( ) 2= 2q = 4q2 !
Double Quantum
Zero Quantum
q2 ω0 I
−2 !
• Solid effect scales as ω 0−2 !
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Solid Effect with Trityl Radical
• Soluble in aqueous media
• Frequency dependence shows a well resolved solid effect
• Peaks in the enhancement curves at ω e±ω n
δe < ω n90 MHz < 211 MHz• Enhancements are significant but modest only ±15 ! L !
K. Hu et. al (2004)
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Solid Effect DNP
•Sta&cHamiltonian: Huet.al.,JCP(2011)CorziliusJCP(2012)
•Hcanbediagonalizedin2subspaces
CodyCan(2012)
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Solid Effect Field Profile
• Resolved solid effect at 5 T
• Unresolved solid effect at 0.35 TCan et al., J. Chem. Phys. 141, 064202 (2014)
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• 3-spin mechanism
• Enhancement up to ~100 at 0.35 T
Experiment by Dr. Kong Tan
ω1S ± 2ω0I
9.72 9.74 9.76 9.78 9.8 9.82 9.84250
200
150
100
50
0
50
100
150
200
250
uw / GHz
Sign
al In
tens
ity
170423_trityl_80k_3484G_eldorsweep_SE_2MHz
ωe-2ωn
ωe-ωn
ωe+ωn
ωe+2ωn
deBoer, J. Low Temp. Phys. 22, 185(1976)
Trityl radical3-Spin Solid Effect
Zeeman Field Profile
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3-Spin Solid Effect
• 3-spin mechanism
• Enhancement up to ~100 at 0.35 T
Simulation by Dr. Chen YangExperiment by Dr. Kong Tan
ω1S ± 2ω0I
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• Background and RationaleDNP, EPR, Signal to Noise and bRDNP Enhancements of 100-400 in MAS Spectra @ 90 KDNP functions quite effectively in multiple classes of systems
• CW DNP Mechanisms and Polarizing AgentsSolid Effect — δ ~Δ << ω0I
two spins, without e- - 1H hyperfine couplingOverhauser Effect — δ ~Δ << ω0I
two spins, with e- - 1H hyperfine coupling Cross Effect — δ < ω0I < Δ
three spins, with e- -e--1H dipole coupling
• Time Domain DNP — NOVELNOVEL — lab frame-rotating frame cross-polarization
• Instrumentation for DNPQuadruple Resonance, LT MAS ProbesSuperconducting Sweep CoilsGyrotron Microwave Oscillators and Amplifiers
NEW
DNP Outline
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LessonsfromSolu9onNMR๏Overhausereffectsrequiremobileelectronsornuclei....Metals,1Dconductors,NainNH3,solu&onNOE’s
๏ HeteronuclearOverhausereffectsscale~B0-n.... Transla&onalandrota&onalspectraldensi&es Heteronuclear(1H-13C)NOE’sareaKenuated>2.3T
Shouldnotdo13CproteinNMRabove>60-100MHz
๏ TimeDomainExperimentsarenotfielddependent.... INEPTfor1H-13C/15Npolariza&ontransfers
OverhauserDNPininsulators—newmechanism!
OverhauserDNPscalesasB0+n!
PulsedDNPexperimentsarenotfielddependent!
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Overhauser Effect vs. ω0
• Overhauser effects commonly scale ~ω0-n
•13C NMR in proteins — only at <100 MHz
Hauser and Stehlik Adv in Mag. Res 1970
Oldfield, Norton and Allerhand J. Biol. Chem. 1975
electron-nuclear 1H-13C NOE’s in proteins
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7Li w/ DNP @ 84 MHz
7Li w/o DNP
1H glycerol
• 7Li NMR @ ω0/2π= 50 kHz (30.3 Gauss)
• EPR @ ω0/2π= 84 MHz
ε ~ 100
• Initial demonstration of the Overhauser effect -- DNP • Nuclear Overhauser effect is important in solution NMR !
Carver and Slichter, Phys. Rev. 92, 212-213 (1953) Phys. Rev. 102, 975-980 (1956)
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Water soluble BDPA
• Improved Solid Effect
performance with MAS 40 mM in d8-Glycerol/D2O/H2O (60:30:10) 4 mm rotor spinning at 5 kHz, 80 K 5 W cw microwave irradiation
Olesya Haze, Tim Swager, et al. JACS (2012)
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Solid and Overhauser Effects @ 400 MHz/263 GHz
•Small Overhauser enhancement for SA-BDPA •Well developed transition for BDPA •Trityl cannot make up its mind !
SolidEffectSolidEffect
+Overhauser
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect @ 600 MHz/395 GHz
• Overhauser enhancement for BDPA and SA-BDPA
• SA-BDPA -- 40 % of the SE enhancement
• g-anisotropy evident on the SE lineshape
• 800 and 1200 MHz ?
Abragam, A. Phys. Rev. 1955, 98, 1729–1735.Can, et al, J. Chem. Phys. 141, 064202 (2014)
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DNP Polarizing AgentsMonoradicals -- Solid and Overhauser Effect -- Δ=25-60 MHz
9 GHz EPR spectra16 1H couplings 21 1H couplings
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect HYperfine Coupling Zero Quantum
• Overhauser and solid effect enhancements
• Two spin model -- 5 MHz 1H-e- couplings
• Zero quantum relaxation mediates the OE enhancementCan, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect
• Overhauser and solid effect enhancements
• Two spin model, 1H hyperfine coupling
• Zero quantum relaxation mediates the OE enhancementCan, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect HYperfine Coupling Zero Quantum
58
• Overhauser and solid effect enhancements
• Two spin model -- 5 MHz 1H-e- couplings
• Zero quantum relaxation mediates the OE enhancement
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect Simulations
F. Mentink-Vigier and S. Vega
• Overhauser enhancement for BDPA and SA-BDPA
• Two spin model, 1H hyperfine coupling
• BDPA’s have 1H’s ! Trityl e--1H coupling weak !
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Overhauser Effect Power Dependence F. Mentink-Vigier and S. Vega
• Zero quantum relaxation OE enhancement
• High frequency sources (400-1000 GHz), <5 watts
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect Dipolar Coupling Double Quantum
• Overhauser and solid effect enhancements
• e- -1H dipolar coupling
• Double quantum relaxation mediates the OE enhancementCan, et al, J. Chem. Phys. 141, 064202 (2014)
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Solid + Overhauser Effect
• Overhauser and solid effect enhancements
• Two spin model, 1H hyperfine or dipolar coupling
• Zero or double quantum relaxation OE enhancement
e- -1H dipolar --DQe- -1H Hyperfine -- ZQ
Can, et al, J. Chem. Phys. 141, 064202 (2014)
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Overhauser Effect vs. ω0
• Overhauser effects commonly scale ω0-n
• Solid effect scales ℇ0 ~ω0-2
• Overhauser effect scales ~(ℇ0 +k’ω0) [rather than ω0-n]
Marc Baldus Utrecht Univ.
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BDPA/ortho-terphenyl at 14.1 T
• Ortho-terphenyl forms a excellent glass
• A factor of ~ 5 improvement compared to polystyrene
• Stable narrow line radicals with large 1H hyperfine couplings
Can, et al, (submitted) (2015)
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65
OverhauserDNPEnhancement@[email protected]
600MHz/395GHz T=1.2K
• Factor of ~ 5 improvement compared to polystyrene
• T=1.2 K eliminates many molecular fluctuations that could mediate the OE enhancement.
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OverhauserDNPEnhancement@800MHz,ωr/2π=40KHz
66
•BDPA in OTP (95% 2H)
• 13C enhancement =105
•No depolarization effects
• ℇ increases with ωr/2π
• Long build-up time — 40 s
•ω0/2π=800 MHz !
105
•Higher ωr/2π and ω0/2π yield larger the Overhauser enhancements !
43 s