Spin-Label EPR T<sub>1</sub> Values Using Saturation Recovery from 2 to 35 GHz

Hyde, James S.; Yin, Jun‐Jie; Subczynski, Witold K.; Camenisch, Theodore G.; Ratke, Joseph J.; Froncisz, Wojciech

doi:10.1021/jp036329z

Cited by 49 publications

(96 citation statements)

References 23 publications

(46 reference statements)

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“…5. This point was made previously in an SR experiment at Q-band [17]. Observing microwave powers can be higher in spin labels in viscous solution or at high microwave frequencies because of shorter T 2 values, which improves the signal-to-noise ratio.…”

Section: Sr Epr and Sr Eldor Of Ctpo And Temponesupporting

confidence: 54%

“…3. The overall multi-arm bridge configuration is based on the double-sideband fixed-filter approach previously developed at X-band [30] and Q-band [17]. Multi-arm bridges enable multiple frequency experiments such as multiquantum (MQ) EPR and MQ ELDOR.…”

Section: Spectrometer Systemmentioning

confidence: 99%

“…We have previously presented SR data acquired at Q-band [17]. The bridge that is described in that paper has multiple arms and also is suitable for SR ELDOR experiments, which have been performed at Q-band but as yet are unpublished.…”

Section: Introduction Overview Of Saturation Recovery Epr and Eldor Amentioning

confidence: 99%

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Saturation recovery EPR and ELDOR at W-band for spin labels

Froncisz

Camenisch

Ratke

et al. 2008

Journal of Magnetic Resonance

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A reference-arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) (J.W. Sidabras et al., Rev. Sci. Instrum. 78 (2007) 034701). The high efficiency parameter (8.2 GW −1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE.

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Section: Sr Epr and Sr Eldor Of Ctpo And Temponesupporting

confidence: 54%

Section: Spectrometer Systemmentioning

confidence: 99%

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Saturation recovery EPR and ELDOR at W-band for spin labels

Froncisz

Camenisch

Ratke

et al. 2008

Journal of Magnetic Resonance

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“…Both relaxation parameters are in good agreement with the literature values. 19,20 As a check for the assumption used above (negligible w n at concentrations Z 5 mM) we have recorded similar curves for the 0.5 mM concentrated sample (data not shown) and we obtain (2w n + w x ) À1 Z 1 ms. This indicates that 1/(2w n ) Z 1 ms and the assumption is valid.…”

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confidence: 56%

Saturation factor of nitroxide radicals in liquid DNP by pulsed ELDOR experiments

Türke

Bennati

2011

Phys. Chem. Chem. Phys.

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We propose the use of the pulse electron double resonance (ELDOR) method to determine the effective saturation factor of nitroxide radicals for dynamic nuclear polarization (DNP) experiments in liquids. The obtained values for the nitroxide radical 15 N at different concentrations are rationalized in terms of spin relaxation and are shown to fulfil the Overhauser theory.Dynamic nuclear polarization (DNP) in aqueous solution at ambient conditions is a major topic of current efforts to enhance the sensitivity of high resolution NMR and magnetic resonance imaging. [1][2][3] In the liquid state, DNP is governed by the Overhauser mechanism, 4,5 in which polarization is transferred from paramagnetic centers to coupled nuclear spins by microwave pumping of the EPR line. The enhancements e depend on four factors, i.e. the ratio of the gyromagnetic constants of the electron spin g s and the target nucleus g I , the coupling factor x, the leakage factor f and the effective saturation factor s eff of the EPR line: 6In recent studies, nitroxide radicals have been favoured as polarizing agents for DNP since they are soluble in water, well compatible with biological systems, non-toxic and have been found to account for large DNP enhancements at magnetic fields up to 9 T. 7,8 However, the determination of the saturation factor for this class of polarizers has emerged as one of the major difficulties in rationalizing the observed DNP enhancements in terms of the Overhauser equation (1). [8][9][10][11][12] Due to the strong hyperfine coupling between the electron and the nitrogen nucleus, which splits the EPR spectrum into two ( 15 N) or three ( 14 N) separate lines, the saturation factor, defined as s eff = (S B À hS z i)/S B with S B the Boltzmann polarization of the electron spin, cannot be simply extracted from the saturation behaviour of the pumped line according to the Bloch equation, as formerly suggested for trityl radicals. 13 Moreover, the expectation value of the electron spin polarization hS z i depends on the population of all energy levels involved. In recent years, this issue has been debated in the literature and several theoretical models were proposed to calculate the saturation factor for nitroxides 9-11 but to date no direct experimental approach has been provided. In this paper, we show that the effective saturation factor in Overhauser DNP can be determined by a pulsed electron double resonance (ELDOR) experiment, 14 which measures the intensity of a hyperfine line when pumping a coupled hyperfine line. This approach is demonstrated with a 15 N containing nitroxide because this gives the maximum enhancement for DNP and is relevant for future DNP applications. However, it is fully applicable to radicals incorporating a 14 N nucleus as well. Our experiments were performed at X-band (9.7 GHz electron Larmor frequency) in a commercial dielectric EPR/ENDOR resonator (Bruker EN4118X-MD4), as used for DNP, 12 that is overcoupled to permit irradiation at two frequencies with Dn up to 100 MHz. The saturation factors...

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“…However, to obtain a wide range of tumbling correlation times the solvent and structure of the radical were varied, which complicates interpretation of the results. In another study, tumbling correlation times were varied by changing the size of doxyl radicals in lipids and relaxation rates were measured as a function of Zeeman frequency [23]. It was proposed that modulation of g-and A-anisotropy, spin rotation, and generalized spin diffusion were required to model the relaxation rates [9].…”

Section: J(ω) Is the Spectral Density Of The Solute Motion And The Fomentioning

confidence: 99%

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

Sato

Bottle

Blinco

et al. 2008

Journal of Magnetic Resonance

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Electron spin-lattice relaxation rates, 1/T 1 , at X-band of nitroxyl radicals (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl and 3-carbamoyl-2,2,5,5-tetramethylpyrrolin-1-oxyl) in glass-forming solvents (decalin, glycerol, 3-methylpentane, o-terphenyl, 1-propanol, sorbitol, sucrose octaacetate, and 1:1 water:glycerol) at temperatures between 100 K and 300 K were measured by long-pulse saturation recovery to investigate the relaxation processes in slow-to-fast tumbling regimes. A subset of samples was also studied at lower temperatures or at Q-band. Tumbling correlation times were calculated from continuous wave lineshapes. Temperature dependence and isotope substitution ( 2 H and 15 N) were used to distinguish the contributions of various processes. Below about 100 K relaxation is dominated by the Raman process. At higher temperatures, but below the glass transition temperature, a local mode process makes significant contributions. Above the glass transition temperature, increased rates of molecular tumbling modulate nuclear hyperfine and g anisotropy. The contribution from spin rotation is very small. Relaxation rates at X-band and Q-band are similar. The dependence of 1/T 1 on tumbling correlation times fits better with the Cole-Davidson spectral density function than with the Bloembergen-Purcell-Pound model.

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Spin-Label EPR T₁ Values Using Saturation Recovery from 2 to 35 GHz

Cited by 49 publications

References 23 publications

Saturation recovery EPR and ELDOR at W-band for spin labels

Saturation recovery EPR and ELDOR at W-band for spin labels

Saturation factor of nitroxide radicals in liquid DNP by pulsed ELDOR experiments

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

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Spin-Label EPR T1 Values Using Saturation Recovery from 2 to 35 GHz

Cited by 49 publications

References 23 publications

Saturation recovery EPR and ELDOR at W-band for spin labels

Saturation recovery EPR and ELDOR at W-band for spin labels

Saturation factor of nitroxide radicals in liquid DNP by pulsed ELDOR experiments

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

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Spin-Label EPR T₁ Values Using Saturation Recovery from 2 to 35 GHz