Macroscopic sample shape effect on pulse electron double resonance (PELDOR) signal.

Pulse electron double resonance (PELDOR), also called double electron-electron resonance (DEER), is a technique capable of measuring the strength of electron spin dipolar interactions, revealing spin-spin distance distributions in ordered and disordered solid materials. Previous work has shown that PELDOR signals acquire an out-of-phase component under conditions of high electron spin polarization, such as at low temperatures and high fields. In this paper, we show theoretically and experimentally that the size and sign of this effect depends on the macroscopic shape of the sample and its orientation in the external magnetic field.

C Hyperpolarization of Viscous Liquids by Transfer of Solid-Effect H Dynamic Nuclear Polarization at High Magnetic Field.

Dynamic nuclear polarization (DNP) is routinely used as a method for increasing the sensitivity to nuclear magnetic resonance (NMR). Recently, high-field solid-effect DNP in viscous liquids on H nuclei was demonstrated using narrow-line polarizing agents. Here we expand the applicability of DNP in viscous media to C nuclei.

Solid-Effect Dynamic Nuclear Polarization in Viscous Liquids at 9.4 T Using Narrow-Line Polarizing Agents.

Dynamic nuclear polarization (DNP) is a hyperpolarization method that is widely used for increasing the sensitivity of nuclear magnetic resonance (NMR) experiments. DNP is efficient in solid-state and liquid-state NMR, but its implementation in the intermediate state, namely, viscous media, is still less explored. Here, we show that a H DNP enhancement of over 50 can be obtained in viscous liquids at a magnetic field of 9.

DOPA Residues Endow Collagen with Radical Scavenging Capacity.

Here we uncover collagen, the main structural protein of all connective tissues, as a redox-active material. We identify dihydroxyphenylalanine (DOPA) residues, post-translational oxidation products of tyrosine residues, to be common in collagen derived from different connective tissues. We observe that these DOPA residues endow collagen with substantial radical scavenging capacity.

The effect of spin polarization on double electron-electron resonance (DEER) spectroscopy.

Double electron-electron resonance (DEER) spectroscopy measures the distribution of distances between two electron spins in the nanometer range, often on doubly spin-labeled proteins, via the modulation of a refocused spin echo by the dipolar interaction between the spins. DEER is commonly conducted under conditions where the polarization of the spins is small. Here, we examine the DEER signal under conditions of high spin polarization, thermally obtainable at low temperatures and high magnetic fields, and show that the signal acquires a polarization-dependent out-of-phase component both for the intramolecular and intermolecular contributions.

A triple resonance (e, H, C) probehead for liquid-state DNP experiments at 9.4 Tesla.

In DNP experiments, NMR signal intensity is increased by transferring the much larger electron spin polarization to nuclear spins via microwave irradiation. Here we describe the design and performance of a probehead that makes it possible to perform Overhauser DNP experiments at H and C in liquid samples with a volume of up to 100 nl. We demonstrate on a C-labeled sodium pyruvate sample in water that proton decoupling under DNP conditions is possible with this new triple-resonance DNP probehead.

Solid-like Dynamic Nuclear Polarization Observed in the Fluid Phase of Lipid Bilayers at 9.4 T.

Dynamic nuclear polarization (DNP) is a powerful method to enhance NMR sensitivity. Much progress has been achieved recently to optimize DNP performance at high magnetic fields in solid-state samples, mostly by utilizing the solid or the cross effect. In liquids, only the Overhauser mechanism is active, which exhibits a DNP field profile matching the EPR line shape of the radical, distinguishable from other DNP mechanisms.

Room-temperature dynamic nuclear polarization enhanced NMR spectroscopy of small biological molecules in water.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful and popular technique for probing the molecular structures, dynamics and chemical properties. However the conventional NMR spectroscopy is bottlenecked by its low sensitivity. Dynamic nuclear polarization (DNP) boosts NMR sensitivity by orders of magnitude and resolves this limitation.

Increased flow rate of hyperpolarized aqueous solution for dynamic nuclear polarization-enhanced magnetic resonance imaging achieved by an open Fabry-Pérot type microwave resonator.

A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized state of water protons can be achieved by flowing aqueous liquid through a microwave resonator placed directly in the bore of a 1.5 T MRI magnet.

Mechanoradicals in tensed tendon collagen as a source of oxidative stress.

As established nearly a century ago, mechanoradicals originate from homolytic bond scission in polymers. The existence, nature and biological relevance of mechanoradicals in proteins, instead, are unknown. We here show that mechanical stress on collagen produces radicals and subsequently reactive oxygen species, essential biological signaling molecules.

Dynamic Nuclear Polarization of C Nuclei in the Liquid State over a 10 Tesla Field Range.

Nuclear magnetic resonance (NMR) techniques play an essential role in natural science and medicine. In spite of the tremendous utility associated with the small energies detected, the most severe limitation is the low signal-to-noise ratio. Dynamic nuclear polarization (DNP), a technique based on transfer of polarization from electron to nuclear spins, has emerged as a tool to enhance sensitivity of NMR.

Liquid state DNP at high magnetic fields: Instrumentation, experimental results and atomistic modelling by molecular dynamics simulations.

Dynamic nuclear polarization (DNP) at high magnetic fields has recently become one of the major research areas in magnetic resonance spectroscopy and imaging. Whereas much work has been devoted to experiments where the polarization transfer from the electron spin to the nuclear spin is performed in the solid state, only a few examples exist of experiments where the polarization transfer is performed in the liquid state. Here we describe such experiments at a magnetic field of 9.

Characterization and optimization of the visualization performance of continuous flow overhauser DNP hyperpolarized water MRI: Inversion recovery approach.

Purpose: Overhauser dynamic nuclear polarization (DNP) allows the production of liquid hyperpolarized substrate inside the MRI magnet bore as well as its administration in continuous flow mode to acquire MR images with enhanced signal-to-noise ratio. We implemented inversion recovery preparation in order to improve contrast-to-noise ratio and to quantify the overall imaging performance of Overhauser DNP-enhanced MRI.

Method: The negative enhancement created by DNP in combination with inversion recovery (IR) preparation allows canceling selectively the signal originated from Boltzmann magnetization and visualizing only hyperpolarized fluid.

Dynamic nuclear polarization-enhanced NMR on aligned lipid bilayers at ambient temperature.

Dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy has been shown to hold great potential for functional studies of membrane proteins at low temperatures due to its great sensitivity improvement. There are, however, numerous applications for which experiments at ambient temperature are desirable and which would also benefit from DNP signal enhancement. Here, we demonstrate as a proof of concept that a significant signal increase for lipid bilayers under room-temperature conditions can be achieved by utilizing the Overhauser effect.

High-field liquid state NMR hyperpolarization: a combined DNP/NMRD approach.

Here we show how fast dynamics between radicals and solvent molecules in liquid solutions can be detected by comparison of coupling factors determined by nuclear magnetic relaxation dispersion (NMRD) measurements and dynamic nuclear polarization (DNP) enhancement measurements at high magnetic field (9.2 T). This is important for a theoretical understanding of the Overhauser DNP mechanism at high magnetic fields and thus for optimization of the DNP agent/target system for high resolution liquid state NMR applications.

Host-guest complexes as water-soluble high-performance DNP polarizing agents.

Dynamic nuclear polarization (DNP) enhances the sensitivity of solid-state NMR (SSNMR) spectroscopy by orders of magnitude and, therefore, opens possibilities for novel applications from biology to materials science. This multitude of opportunities implicates a need for high-performance polarizing agents, which integrate specific physical and chemical features tailored for various applications. Here, we demonstrate that for the biradical bTbK in complex with captisol (CAP), a β-cyclodextrin derivative, host-guest assembling offers a new and easily accessible approach for the development of new polarizing agents.

Liquid state DNP of water at 9.2 T: an experimental access to saturation.

We have performed liquid state ("Overhauser") Dynamic Nuclear Polarization (DNP) experiments at high magnetic field (9.2 T, corresponding to 260 GHz EPR and 400 MHz (1)H-NMR resonance frequency) on aqueous solutions of (14)N-TEMPOL nitroxide radicals. Integrated signal enhancements exceeding -80 were observed for the water protons at microwave superheated temperatures (160 °C) and still -14 at ambient temperatures (45 °C) relevant to biological applications.

Liquid state Dynamic Nuclear Polarization probe with Fabry-Perot resonator at 9.2 T.

Recent achievements in liquid state DNP at high magnetic fields showing significant enhancements on aqueous solutions have initiated strong interest in possible applications of this method to biomolecular research. However, in situ DNP of biomolecules at ambient temperatures is a challenging task due to high microwave losses leading to excessive sample heating. To avoid such heating the sample volume has to be reduced strongly to keep it away from the electric component of the microwave field.

DNP in MRI: an in-bore approach at 1.5 T.

We have used liquid state ("Overhauser") Dynamic Nuclear Polarization (DNP) to significantly enhance the signal to noise ratio (SNR) of Magnetic Resonance Imaging (MRI). For the first time this was achieved by hyperpolarizing directly in the MRI-scanner field of 1.5 T in continuous flow mode and immediately delivering the hyperpolarized substance to the imaging site to ensure maximum contrast between hyperpolarized sample and sample at thermal polarization.

Conformational flexibility of DNA.

Pulsed Electron-Electron Double Resonance (PELDOR) on double-stranded DNA (ds-DNA) was used to investigate the conformational flexibility of helical DNA. Stretching, twisting, and bending flexibility of ds-DNA was determined by incorporation of two rigid nitroxide spin labels into a series of 20 base pair (bp) DNA duplexes. Orientation-selective PELDOR experiments performed at both X-band (9 GHz/0.

Multifrequency electron paramagnetic resonance characterization of PpoA, a CYP450 fusion protein that catalyzes fatty acid dioxygenation.

PpoA is a fungal dioxygenase that produces hydroxylated fatty acids involved in the regulation of the life cycle and secondary metabolism of Aspergillus nidulans . It was recently proposed that this novel enzyme employs two different heme domains to catalyze two separate reactions: within a heme peroxidase domain, linoleic acid is oxidized to (8R)-hydroperoxyoctadecadienoic acid [(8R)-HPODE]; in the second reaction step (8R)-HPODE is isomerized within a P450 heme thiolate domain to 5,8-dihydroxyoctadecadienoic acid. In the present study, pulsed EPR methods were applied to find spectroscopic evidence for the reaction mechanism, thought to involve paramagnetic intermediates.

Liquid state DNP using a 260 GHz high power gyrotron.

Dynamic nuclear polarization (DNP) at high magnetic fields (9.2 T, 400 MHz (1)H NMR frequency) requires high microwave power sources to achieve saturation of the EPR transitions. Here we describe the first high-field liquid-state DNP results using a high-power gyrotron microwave source (20 W at 260 GHz).

Dynamic nuclear polarization of water by a nitroxide radical: rigorous treatment of the electron spin saturation and comparison with experiments at 9.2 Tesla.

The interaction between nuclear and electronic spins is of interest for structural characterization of biomolecules and biomedical imaging based on nuclear magnetic resonance. The polarization of the nuclear spins can be increased significantly if the electron spin polarization is kept out of equilibrium. We employ semiclassical relaxation theory to analyze the electronic polarization of the two-spin system characteristic of nitroxide radicals.