Aqueous sample holders for high-frequency electron spin resonance

Barnes, Jeff P.; Freed, Jack H.

doi:10.1063/1.1148205

Cited by 51 publications

(71 citation statements)

References 22 publications

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“…[65][66][67] To study the hydration dynamics and lipid ordering slightly below the lipid headgroup in the presence and the vicinity of Chol, 23 we employed a nitroxide spin-labeled Chol analogue, 3β-doxyl-5α-cholestane (CSL) (see Chart 1), which has been used to study the dynamics and ordering of Chol in model membranes by cw EPR. 23,24,83 In CSL, the polar 3β-OH headgroup of Chol is replaced by a doxyl group, but still shows the same overall molecular characteristics and rotational diffusion rates as expected for Chol, according to a high-field EPR study.…”

Section: A Model Lipid Membrane Systemsmentioning

confidence: 72%

Cholesterol enhances surface water diffusion of phospholipid bilayers

Cheng

Olijve

Kausik

et al. 2014

The Journal of Chemical Physics

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Elucidating the physical effect of cholesterol (Chol) on biological membranes is necessary towards rationalizing their structural and functional role in cell membranes. One of the debated questions is the role of hydration water in Chol-embedding lipid membranes, for which only little direct experimental data are available. Here, we study the hydration dynamics in a series of Chol-rich and depleted bilayer systems using an approach termed 1 H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry that enables the sensitive and selective determination of water diffusion within 5-10 Å of a nitroxide-based spin label, positioned off the surface of the polar headgroups or within the nonpolar core of lipid membranes. The Chol-rich membrane systems were prepared from mixtures of Chol, dipalmitoyl phosphatidylcholine and/or dioctadecyl phosphatidylcholine lipid that are known to form liquid-ordered, raft-like, domains. Our data reveal that the translational diffusion of local water on the surface and within the hydrocarbon volume of the bilayer is significantly altered, but in opposite directions: accelerated on the membrane surface and dramatically slowed in the bilayer interior with increasing Chol content. Electron paramagnetic resonance (EPR) lineshape analysis shows looser packing of lipid headgroups and concurrently tighter packing in the bilayer core with increasing Chol content, with the effects peaking at lipid compositions reported to form lipid rafts. The complementary capability of ODNP and EPR to site-specifically probe the hydration dynamics and lipid ordering in lipid membrane systems extends the current understanding of how Chol may regulate biological processes. One possible role of Chol is the facilitation of interactions between biological constituents and the lipid membrane through the weakening or disruption of strong hydrogen-bond networks of the surface hydration layers that otherwise exert stronger repulsive forces, as reflected in faster surface water diffusivity. Another is the concurrent tightening of lipid packing that reduces passive, possibly unwanted, diffusion of ions and water across the bilayer.

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Section: A Model Lipid Membrane Systemsmentioning

confidence: 72%

Cholesterol enhances surface water diffusion of phospholipid bilayers

Cheng

Olijve

Kausik

et al. 2014

The Journal of Chemical Physics

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“…This reduction in sample volume oftentimes results in decreased concentration sensitivity at Wband, relative to X-band, even though the absolute spin sensitivity is enhanced due to increased magnetization at high field. Even when using a quasi-optical approach with no resonator, as in the present study, or even with a Fabry-Pérot resonator [50], the reduction in penetration depth with increasing frequency also results in an unavoidable decrease in active sample volume.…”

Section: Introductionmentioning

confidence: 69%

“…This modeling approach is similar to that described by Earle et al in [57]. The sample is assumed to have a complex permittivity appropriate to water at 94 GHz ( = 8.057, ' = 13.66) [50], and a complex permeability that is different for the two circular polarization states. The model then computes the reflected cross-polar amplitude in which the EPR signal is encoded.…”

Section: Figure 2 (A)mentioning

confidence: 99%

“…This is due to the many technical challenges associated with the detection of EPR signals from aqueous samples at W-band (94 GHz) and above. To design a sample holder at these high frequencies, the most common practice is to use a resonator [50,58,67]. All other things being equal, one would expect significantly enhanced sensitivity at higher fields and frequencies on account of the increased sample magnetization ( B 0 /T).…”

Section: Sensitivity Of Hiper Thin-layer Sample Holdersmentioning

confidence: 99%

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Toward increased concentration sensitivity for continuous wave EPR investigations of spin-labeled biological macromolecules at high fields

Song

Liu

Kaur

et al. 2016

Journal of Magnetic Resonance

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High-field, high-frequency electron paramagnetic resonance (EPR) spectroscopy at W-(~95 GHz) and D-band (~140 GHz) is important for investigating the conformational dynamics of flexible biological macromolecules because this frequency range has increased spectral sensitivity to nitroxide motion over the 100 ps to 2 ns regime. However, low concentration sensitivity remains a roadblock for studying aqueous samples at high magnetic fields. Here, we examine the sensitivity of a non-resonant thin-layer cylindrical sample holder, coupled to a quasi-optical induction-mode W-band EPR spectrometer (HiPER), for continuous wave (CW) EPR analyses of: (i) the aqueous nitroxide standard, TEMPO; (ii) the unstructured to -helical transition of a model IDP protein; and (iii) the base-stacking transition in a kink-turn motif of a large 232 nt RNA. For sample volumes of ~50 L, concentration sensitivities of 2-20 µM were achieved, representing a ~10-fold enhancement compared to a cylindrical TE 011 resonator on a commercial Bruker W-band spectrometer. These results therefore highlight the sensitivity of the thin-layer sample holders employed in HiPER for spin-labeling studies of biological macromolecules at high fields, where applications can extend to other systems that are facilitated by the modest sample volumes and ease of sample loading and geometry.2

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“…The FP resonator is the best resonator to accommodate aqueous liquid samples. Several arrangements have been demonstrated [77,78]. Möbius et al [79,80] presented a Fabry-Perot resonator operating at 360 GHz that allowed (CW) ENDOR experiments.…”

Section: Probe Headsmentioning

confidence: 99%

High-Frequency EPR Instrumentation

Reijerse¹

2009

Appl Magn Reson

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An overview of the most recent developments in high-frequency highfield electron paramagnetic resonance (EPR) instrumentation is given. In particular, the practical choices concerning sources, detectors, resonators, propagation systems as well as magnet technology are discussed in the light of various possible applications. Examples of particular homodyne and heterodyne quasi-optic EPR systems illustrate the potential for future developments in EPR technology.

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Aqueous sample holders for high-frequency electron spin resonance

Cited by 51 publications

References 22 publications

Cholesterol enhances surface water diffusion of phospholipid bilayers

Cholesterol enhances surface water diffusion of phospholipid bilayers

Toward increased concentration sensitivity for continuous wave EPR investigations of spin-labeled biological macromolecules at high fields

High-Frequency EPR Instrumentation

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