Time Domain DNP NOVEL NOVEL lab frame-rotating frame cross-polarization

Transcription

1 DNP Outline Background and Rationale DNP, EPR, Signal to Noise and br DNP Enhancements of in MAS 90 K DNP functions quite effectively in multiple classes of systems CW DNP Mechanisms and Polarizing Agents Solid Effect δ ~Δ << ω 0I two spins, without e H hyperfine coupling Overhauser Effect δ ~Δ << ω 0I two spins, with e H hyperfine coupling Cross Effect δ < ω 0I < Δ three spins, with e - -e H dipole coupling NEW Time Domain DNP NOVEL NOVEL lab frame-rotating frame cross-polarization NEW Instrumentation for DNP Quadruple Resonance, LT MAS Probes Superconducting Sweep Coils Gyrotron Microwave Oscillators and Amplifiers

2 CW Dynamic Nuclear Polarization Mechanisms Thermal Mixing (TM) -- many electrons, insulating solids, but. δ, Δ >> ω 0 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 0 > δ CE -- operative at high fields where Δg >> δ, the line is inhomogeneously broadened.

3 DNP DNP Mechanisms Cross effect -- three spins Δ> ω0i/2π> δ Solid effect -- two spins ω0i/2π > δ,δ Overhauser effect - mobile electrons? ω n e 1 e 2 δ ~5 MHz Thermal mixing - many electrons, homogeneous EPR Time domain DNP electron spin locking -400 ω0i Frequency (MHz) Δ 600 MHz Mechanism determined by relative size of Δ, ω0i,δ

4 DNP Polarizing Agents Monoradicals -- Solid and Overhauser Effect Biradicals -- Cross Effect AMUPol

5 DNP Cross Effect DNP Inhomogeneously broadened EPR spectrum so that Δ > ω0i > δ 600 MHz > 211 MHz > 5 MHz CE is a three spin processes involving a coupled electron spin system -- flip two electrons and a nuclear spin. ω0 1 H CE is inefficient since only a fraction of the spins in a powder have the correct distance and relative orientations to contribute to DNP! ω 2e - ω 1e = ω n Kessenikh, A. V.; Manenkov, A. A. Soviet Physics- Solid State 5, 835 (1963). C.F. Hwang and D.A. Hill, PRL18, (1967) Kan Hu, Ph.D. 2007

6 DNP Cross Effect DNP Inhomogeneous EPR 1. µwave irradiation and e - -e - cross-relaxation burn a hole in the EPR line. µ-waves EPR Intensity 3. ω 2e ω 1e = ω n TEMPO EPR Absorption Lineshape 4. Enhancement Frequency (MHz) ω n ε γ e γ N 657 for 1 H 2615 for 13 C ε TM B 2 1 T T 1e 1n B 0 2. Two electrons separated by ω n flip-flop and the difference in energy is used to flip a nucleus. ( τ een ) 1 = 4 q 2 1 SS T 2e g(ω )g(ω ω n ) g(0) -400 e 1 e Frequency (MHz)

7 Monomeric Polarizing Agents 4-amino TEMPO H 2 N N O Cryoprotectant (e.g. glycerol) 1. Resuspension 2. centrifugation weak e - -e - coupling Purple membrane bacteriorhodopsin strong e - -e - coupling Randomly oriented and dispersed paramagnetic centers Suboptimal utilization of e- -e - dipolar coupling

8 DNP Biradical Polarizing Agents Bis TEMPO n-ethylene glycol (BTnE) Kan Hu Bruce Yu Biradical consists of two stable radicals (TEMPO) tethered together by a linker (ethylene glycol). Used extensively in the 70 s for the study of dynamics with EPR. Currently employed in pulsed EPR investigations of distances in a variety of systems.

9 DNP Enhancement v.s. Polyethylene Glycol Length 5 Tesla T= 90 K ν r = 3.5 khz Bis TEMPO n-ethylene glycol (BTnE) e - - e - dipole coupling R O-O -3 R O-O, distance between the two TEMPO radicals, is determined by the length of the all-trans ethylene glycol linker. Electron concentration drops from 40 mm to 10 mm! Enhancements increase by a factor of ~4 in going from n= (monomeric) to n= to 175! Hu et al, JACS (2004)

10 Inter-Electron Distances in BTnE CW EPR Lineshapes Simulation of 9 and 140 GHz EPR spectra 15N, 2 H-labeled BTnE DNP enhancement vs. (R e-e ) -3 Relative g-tensor orientations were permitted to vary. R e-e was determined by a regression analysis. Distance in 40 mm TEMPO ~35 Å In BTnE, decreasing R e-e increases e - -e - dipole coupling and the 1 H enhancement! !

11 Biradical Models from EPR Analyses A longer tether reduces constraints on relative g-tensor orientation.

12 DNP Thermal Mixing/ Cross Effect DNP NO! EPR spectrum is ~600 MHz wide Thermal mixing and the cross effect are three spin process involving the irradiation of a dipolar coupled electron spin system Flip two electrons and then a nuclear spin. C.F. Hwang and D.A. Hill, PRL18, (1967)

13 DNP Qualitative Thermal Mixing/Cross Effect DNP g-tensor Orientations Correct relative orientations of the TEMPO molecules are required to yield two lines separated by ω 2e - ω 1e =ω n efficient thermal mixing/cross effect polarization transfer Simulations suggest that the TEMPO molecules in BTnE s are oriented at approximately 90º with respect to one another 3 B 0 O N N O N O g-tensor orientations yield two lines separated by ~ ω n /2π?

14 DNP Semi-quantitative Thermal Mixing/Cross Effect DNP g-tensor Orientations e2 e1 O N N O N O 3 B 0 Several different orientations satisfy the frequency difference ω 2e - ω 1e =ω n

15 ε = 420 AMUPol Biradical Paul Tordo and Co. Aux Marseille Universite 35 MHz e - -e - coupling ε = 420: DNP 1 Day; no DNP 483 years! 1M- 13 C-urea / 10 mm radical 60/30/10 (v/v/v) 380 MHz / 250 GHz - mw ~ 12 W T=78 K, 13 C{ 1 H} CPMAS, 5.5 khz Qing Zhe Ni

16 DNP Three-Spin Process in Cross Effect DNP SSI l++-> SSI l+++> DNP(+) MW DNP(-) NMR NMR ω e2 ω e1 l-++> ω e1 ω e2 l-+-> l+--> l+-+> If ω e2 -ω e1 ~ω n Equilibrium Δω e < ω n Equilibrium Δω e > ω n l---> Equilibrium Δω e = ω n l--+> l-+->, l+-+> degenerate Kan Hu PhD Thesis 2006 Positive Enhancement Negative Enhancement

17 Hamiltonian: Three Spin Cross Effect DNP Matrix form in direct product basis: Total Unperturbed Perturba&on = + Thurber and Tycko, JCP (2012) Cody Can (2012)

18 Cross Effect Matching Conditions!Diagonalizing!the!unperturbed!H 0! E 3 = 1 2 E 6 = 1 2 ω 0I D d 2 ω 0I D d 2 ω Δ + A Δ 2 ω Δ A Δ D D 0 2!1 st!matching!condi8on:!!1:1!state!mixing! due!to!the!degenerate!perturba8on! ω 0I ω Δ 2 + D 0 2!2 nd!matching!condi8on:!where!to!set!the! microwave!frequency!

19 Cross Effect Matching Conditions Spinning frequency dependence data suggest it is constant? Matching condition is satisfied at level crossings Anti crossings deplete Boltzmann polarization

20 Mixed radicals 86

21 Cross Effect in TEMPO / Trityl Mixtures An Approximation to an Ideal Polarizing Agent Ideal polarizing agent -- tethered radicals small g-anisotropies TEMPO g 22 Trityl ω 1e -ω 2e ~ ω n + TEMPO/ trityl mixture ε 165 trityl TEMPO Notice that. g 22 (TEMPO)-g(trityl) 80 G = 224 MHz! --- which is comparable to ω 1H /2π = 211 MHz! Demonstrates the importance of satisfying ω 1e -ω 2e ~ ω n!

22 DNP in Trityl-TEMPO Mixtures Trityl TEMPO Trityl +TEMPO ε~±15 ε~±50 ε~±160 Notice that g 22 (TEMPO)-g(trityl) 80 G = 224 MHz! Demonstrates the importance of satisfying ω 1e -ω 2e ~ ω n! Hu, Bajaj, Rosay, Griffin, J. Chem. Phys. (2007)

23 BDPA-TEMPO Biradical BDPA-TEMPO E. Dane and T. Swager T. Maly and G. Delbouchina TEMPO Biradical approximately satisfying the matching condition ω e1 -ω e2 = ω n

24 Gael De Paepe TEMTriPol Biradical Polarizing Agent Narrow and Broad EPR Zeeman Field Profiles Jennifer Mathies TEMTriPol-1 Mentink-Vigier, et al., Chem Science (2017) Maximum enhancement at the trityl line Enhancement scales less with field No quenching/bleaching! Mathies, et al Angwandte Chemie (2015)

25 DNP Outline Background and Rationale DNP, EPR, and Signal to Noise DNP Enhancements of in MAS 90 K DNP functions quite effectively in multiple classes of systems Instrumentation for DNP Quadruple Resonance, LT MAS Probes Superconducting Sweep Coils Gyrotron Microwave Oscillators and Amplifiers CW DNP Mechanisms and Polarizing Agents Solid Effect δ ~Δ << ω 0I two spins, without e H hyperfine coupling Overhauser Effect δ ~Δ << ω 0I two spins, with e H hyperfine coupling Cross Effect δ < ω 0I < Δ three spins, with e - -e H dipole coupling Time Domain DNP NOVEL lab frame-rotating frame cross-polarization Integrated Solid Effect Stretched Solid Effect

26 Overhauser Effects in NMR Overhauser effects require mobil electrons or nuclei... Metals, 1D conductors, Na in NH 3, solu&on NOE s Overhauser DNP in insulators new mechanism! Heteronuclear Overhauser effects scale ~B 0 -n... Transla&onal and rota&onal spectral densi&es Heteronuclear ( 1 H- 13 C) NOE s are akenuated >2.3 T Should not do 13 C protein NMR above > MHz Overhauser DNP scales as B 0 +n! Time Domain Experiments are not field dependent... INEPT for 1 H- 13 C / 15 N polariza&on transfers Pulsed DNP experiments are not field dependent!

27 Time Domain DNP Mechanisms Pulsed DNP Weis and Griffin, SSNMR (2006); Can, et al. J. Chem. Physics Mathies, et al. J. Phys Chem Letters 2016 NOVEL -- Wenckebach, et al. (CPL, 1988) rotating frame / lab frame ω1e=ω0 Integrated Solid Effect -- Wenckebach, et al. (CPL, 1988) Stretched Solid Effect -- Can, et al. (submitted) High frequency microwave amplifiers are just becoming available.

28 Time Domain DNP NOVEL - ω0i =ω1s NOVEL matching condition -- ω0i =ω1s n=4096 τ90x= 15 ns, τmatch=100 ns, τ1=20 μs Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Use pulses on the e- to build up polarization Henstra and Wenckebach, Mol. Physics (2008) Can, et al, J. Chem Phys 143, (2015)

29 1H- 13 C/ 15 N Cross Polarization Hartmann-Hahn - ω1i =ω1s B0 B0 ω1i B0 B0 ω1s # 1 H spins # 13 C spins Generates transverse magnetization

30 Time Domain DNP NOVEL - ω0i =ω1s B0 B0 ω1s B0 Spin lock the electrons B0 ω0h # e- spins < # 1 H spins Substitute the B0 field for B1S Generates Z-polarization! Henstra and Wenckebach, Mol. Physics (2008)

31 Davies ENDOR Spectrum Benzophenone-Diphenylnitroxide Crystal structure and molecular structure 140 GHz Davies ENDOR spectrum Can, et al, J. Chem Phys 143, (2015)

32 Time Domain DNP NOVEL - ω0i =ω1s Saturate 1 H signals with a train of m pulses Spin lock the electrons n times using ω 0I =ω 1S! Detect the signal with a solid echo Can, et al, J. Chem Phys 143, (2015)

33 Microwave Field Profiles NOVEL - ω0i =ω1s ℇ~300 NOVEL matching condition -- ω0i =ω1s Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Henstra and Wenckebach, Mol. Physics (2008) T=300 K Can, et al, J. Chem Phys 143, (2015)

34 NOVEL - ω0i =ω1s Diphenyl-NO in Benzophenone 300 ns NOVEL matching condition -- ω0i =ω1s Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Henstra and Wenckebach, Mol. Physics (2008) Can, et al, J. Chem Phys 143, (2015)

35 NOVEL at 80 K (b) SA-BDPA in DNP juice A factor of ~3 improvement by deuteration Also works well at low temperature Can, et al, J. Chem Phys 143, (2015)

36 NOVEL - ω0i =ω1s Trityl DNP Juice NOVEL matching condition -- ω0i =ω1s Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Henstra and Wenckebach, Mol. Physics (2008) Mathies, et al JPC Lett (2016)

37 NOVEL - ω0i =ω1s Trityl DNP Juice 1 µs NOVEL matching condition -- ω0i =ω1s Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Henstra and Wenckebach, Mol. Physics (2008) Jennifer Mathies (2014)

38 NOVEL - ω0i =ω1s Trityl DNP Juice ℇ~ MHz NOVEL matching condition -- ω0i =ω1s Lab frame/rotating frame matching -- Z-polarization Should not manifest a B0 dependence! Henstra and Wenckebach, Mol. Physics (2008) Jennifer Mathies (2014)

39 Ramped Amplitude NOVEL Plateau at ~18 MHz of ramp size Slower buildup, larger efficiency A factor of 1.6 improvement SA-BDPA and BDPA-PS Can, et al., J. Chem Phys. 2016

40 Solid Effect vs. Integrated Solid Effect Solid effect field profile: bimodal Integrated solid effect field profile: EPR lineshape

41 Integrated Solid Effect (ISE) Sweeping B 0 Sweeping frequency (chirp pulse) Wenckebach et al., Phys. Lett. A (1988) Arbitrary waveform generator (AWG) Challenging, unfavorable At 800 MHz: ~0.1 T in ~1 ms! Convenient, suitable to NMR Broad sweep with a fast AWG

42 Integrated Solid Effect Field Profile ISE S 2 E ISE S 2 E Combination of stretched solid effect (S 2 E) and integrated solid effect (ISE) S 2 E peaks displace with the sweep width

43 Components of the ISE Field Profile Stretched Solid Effect Integrated Solid Effect Two components combination of stretched SE and ISE ISE field profile resembles the shape of the EPR spectrum

44 ISE Field Profile Experiment Simulation by Dr. Chen Yang Overlapping of stretched SE and ISE Qualitative agreement with experimental data

45 ISE at Low Power 15 MHz / 2 µs 1.5 MHz / 120 µs Same efficiency at low power (5% power) Slower sweep rate (~100 times slower)

46 Integrated Solid 94 GHz Stretched Solid Effect Constant Frequency Chirp Frequency ISE S 2 E ISE depends on the direction of the chip sweep Displace solid effect does not

47 140 GHz Pulsed DNP Spectrometer Gyro-Amplifier Gyroamplifier currently generating ~800 watts Quasioptical bridge for detection Time domain DNP -- no field dependence Experimental flexibility Andy Smith and Bjoern Corzilius

48 Time Domain DNP Spectrometer (of the future) Gyroamplifier, corrugated waveguide, NMR and EPR consoles Quasi-optic network -- λ ~ 2.14 mm (140 GHz) to 0.57 mm (527 GHz) Ernst and coworkers -- time domain NMR!

49 250 GHz Amplifier for Pulsed DNP Solid State Source 30mW 248 GHz 258 GHz Gyrotron Amplifier HV Modulator Transmission Line Electron Gun 9.6 T Magnet Control System Heterodyne Frequency Detector Nanni, PRL 111, (2013)

50 250 GHz High Gain/Wide Bandwidth Operation Device Gain (db) 8 GHz BW Nonlinear Theory V k = 23 kv I b = A α = 0.45 B 0 = 8.90 T 2% velocity spread Frequency (GHz) 7.5 mw Input Power (after isolator) 45 W Output Power 38 db Device Gain (55 db Circuit Gain)

51 Picosecond Pulse 250 GHz ω0/2π = 250 GHz BDPA and trityl have Δ~150 MHz For nitroxides at 9 T, Δ ~ 1.2 GHz ~1 ns pulses Picosecond pulses for electron excitation

52 140 GHz Pulsed DNP Spectrometer MAS Probe (a) μ-waves waveguide 1 H 1 H match source 1 H tune 13 C trap 13 C trap 1 H balance (b) 12.7 mm 2.7 mm 1 H trap 1 H trap 13 C 13 C match source 13 C tune resonator Probe 13 C balance (c) helix waveguide sample 5 mm Gyroamplifier generating ~ watts Quasioptical bridge for detection Time domain DNP -- no field dependence ω1s/2π~ MHz Fixed plunger R.F. leads Adjustable plunger Andy Smith and Bjoern Corzilius

53 Collaborators DNP Cody Can Bjoern Corzilius Eugenio Daviso Jennifer Mathies Vlad Michaelis Qing Zhe Ni Andy Smith Joe Walish Marc Caporini Melanie Rosay Werner Maas Gyrotrons Emilio Nanni Sudheer Jawal Michael Shapiro Paul Woskow Richard Temkin National Institute of Biomedical Imaging and Bioengineering Polarizing Agents Joe Walish Olesya Haze Tim Swager Paul Tordo Overhauser DNP Cody Can Bjoern Corzilius Fred Mentink-Vigier Marc Caporini Melanie Rosay Werner Maas Shimon Vega

54 Thank you for your attention!