Dynamic nuclear polarization at 700MHz/460GHz

Barnes, Alexander B.; Markhasin, Evgeny; Daviso, Eugenio; Michaelis, Vladimir K.; Nanni, Emilio A.; Jawla, Sudheer; Mena, Elijah L.; DeRocher, Ronald; Thakkar, Ajay; Woskov, P.; Herzfeld, Judith; Temkin, Richard J.; Griffin, Robert G.

doi:10.1016/j.jmr.2012.08.002

Cited by 86 publications

(56 citation statements)

References 38 publications

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“…4) by repeating the computation for our reference sample at higher field (parameters were set as follow, according to reference [22]: B 0 = 4.64 T, T = 1.2 K, T 1e = 1 s, ∆ω e = 63 MHz). The extension of our calculations to a model representing different radicals and eventually higher temperatures, for comparison with the experimental observations achieved under such conditions [23][24][25][26], will be faced in a next dedicated study.…”

Section: Discussionmentioning

confidence: 99%

On the role of electron–nucleus contact and microwave saturation in thermal mixing DNP

Serra

Rosso

Tedoldi

2013

Phys. Chem. Chem. Phys.

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We have explored the manifold physical scenario emerging from a model of Dynamic Nuclear Polarization (DNP) via thermal mixing under the hypothesis of highly effective electron-electron interaction. When the electron and nuclear reservoirs are also assumed to be in strong thermal contact and the microwave irradiation saturates the target electron transition, the enhancement of the nuclear polarization is expected to be considerably high even if the irradiation frequency is set far away from the centre of the ESR line (as already predicted by Borghini) and the typical polarization time is reduced on moving towards the boundaries of said line. More reasonable behaviours are obtained by reducing the level of microwave saturation or the contact between electrons and nuclei in presence of nuclear leakage. In both cases the function describing the dependency of the steady state nuclear polarization on the frequency of irradiation becomes sharper at the edges and the build up rate decreases on moving off-resonance. If qualitatively similar in terms of the effects produced on nuclear polarization, the degree of microwave saturation and of electron-nucleus contact has a totally different impact on electron polarization, which is of course strongly correlated to the effectiveness of saturation and almost insensitive, at the steady state, to the magnitude of the interactions between the two spin reservoirs. The likelihood of the different scenario is discussed in the light of the experimental data currently available in literature, to point out which aspects are suitably accounted and which are not by the declinations of thermal mixing DNP considered here.

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Section: Discussionmentioning

confidence: 99%

On the role of electron–nucleus contact and microwave saturation in thermal mixing DNP

Serra

Rosso

Tedoldi

2013

Phys. Chem. Chem. Phys.

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“…Likewise for solid-state dynamic nuclear polarization (DNP), MAS technology has been adapted to low-temperature operation and microwave irradiation, see e.g. [52,53].…”

Section: Introductionmentioning

confidence: 99%

Fluid flow dynamics in MAS systems

Wilhelm

Purea

Engelke

2015

Journal of Magnetic Resonance

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“…In these experiments, NOVEL showed very modest efficiency. An enhancement of ∼10 was obtained for 29 Si in uniaxially stressed silicon doped with boron acceptors, 33 and ε ∼ 200 was observed for 1 H using a photoexcited triplet state of pentacene doped naphthalene. 37 In both cases, the efficiency is less than 1%.…”

Section: Introductionmentioning

confidence: 99%

“…[14][15][16][17][18][19] Enhancements on the order of 10 2 − 10 3 were made possible via the solid effect using narrow-line radicals [20][21][22][23] and cross effect using biradicals [24][25][26][27] as polarizing agents and high frequency gyrotrons as microwave sources. [28][29][30] The latter operate in the 140-560 GHz regime and enable DNP to be performed at magnet field strengths used in contemporary NMR experiments (5-20 T).…”

Section: Introductionmentioning

confidence: 99%

“…[14][15][16][17][18][19] Enhancements on the order of 10 2 − 10 3 were made possible via the solid effect using narrow-line radicals 20-23 and cross effect using biradicals 24-27 as polarizing agents and high frequency gyrotrons as microwave sources. [28][29][30] The latter operate in the 140-560 GHz regime and enable DNP to be performed at magnet field strengths used in contemporary NMR experiments (5-20 T).All of the DNP mechanisms mentioned above employ continuous wave (CW) microwave irradiation. In addition, all of them, except for the OE in insulating solids, scale unfavorably with the magnetic field, displaying a B −n 0 field dependence where n ∼ 1-2 or larger.…”

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confidence: 99%

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Time domain DNP with the NOVEL sequence

Can

Walish

Swager

et al. 2015

The Journal of Chemical Physics

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We present results of a pulsed dynamic nuclear polarization (DNP) study at 0.35 T (9.7 GHz/ 14.7 MHz for electron/ 1 H Larmor frequency) using a lab frame-rotating frame cross polarization experiment that employs electron spin locking fields that match the 1 H nuclear Larmor frequency, the so called NOVEL (nuclear orientation via electron spin locking) condition. We apply the method to a series of DNP samples including a single crystal of diphenyl nitroxide (DPNO) doped benzophenone (BzP), 1,3-bisdiphenylene-2-phenylallyl (BDPA) doped polystyrene (PS), and sulfonated-BDPA (SA-BDPA) doped glycerol/water glassy matrices. The optimal Hartman-Hahn matching condition is achieved when the nutation frequency of the electron matches the Larmor frequency of the proton, ω 1S = ω 0I , together with possible higher order matching conditions at lower efficiencies. The magnetization transfer from electron to protons occurs on the time scale of ∼100 ns, consistent with the electron-proton couplings on the order of 1-10 MHz in these samples. In a fully protonated single crystal DPNO/BzP, at 270 K, we obtained a maximum signal enhancement of ε = 165 and the corresponding gain in sensitivity of ε(T 1 /T B ) 1/2 = 230 due to the reduction in the buildup time under DNP. In a sample of partially deuterated PS doped with BDPA, we obtained an enhancement of 323 which is a factor of ∼3.2 higher compared to the protonated version of the same sample and accounts for 49% of the theoretical limit. For the SA-BDPA doped glycerol/water glassy matrix at 80 K, the sample condition used in most applications of DNP in nuclear magnetic resonance, we also observed a significant enhancement. Our findings demonstrate that pulsed DNP via the NOVEL sequence is highly efficient and can potentially surpass continuous wave DNP mechanisms such as the solid effect and cross effect which scale unfavorably with increasing magnetic field. Furthermore, pulsed DNP is also a promising avenue for DNP at high temperature. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4927087] INTRODUCTIONDynamic nuclear polarization (DNP) is a process whereby the large polarization present in an electron spin reservoir of a paramagnetic polarizing agent is transferred via microwave irradiation to nuclei, thereby enhancing the nuclear spin polarization. The initial mechanism supporting the DNP process, the Overhauser effect (OE), was proposed in 1953 1 and confirmed experimentally 2,3 in samples with mobile electrons (i.e., metals, solutions, and 1D conductors). In contrast, in insulating solids, such as glycerol/water glasses and biological samples, the OE was thought to be forbidden, but we have recently observed Overhauser enhancements using polarizing agents with narrow EPR spectra that exhibit strong 1 H−e − hyperfine couplings. 4 Furthermore, in these sorts of samples, DNP processes can also be mediated by three other mechanisms -the solid effect (SE), 5,6 the cross effect, 7-11 and/or thermal mixing. 12 Initially, the primary application of DNP was preparation of p...

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Dynamic nuclear polarization at 700MHz/460GHz

Cited by 86 publications

References 38 publications

On the role of electron–nucleus contact and microwave saturation in thermal mixing DNP

On the role of electron–nucleus contact and microwave saturation in thermal mixing DNP

Fluid flow dynamics in MAS systems

Time domain DNP with the NOVEL sequence

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