Dynamic nuclear polarization studies on deuterated nitroxyl spin probes

Detailed dynamic nuclear polarization and electron spin resonance studies were carried out for 3‐carbamoyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl, 3‐carboxy‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl,3‐methoxycarbonyl‐2,2,5,5‐tetramethy pyrolidine‐1‐oxyl nitroxyl radicals and their corresponding deuterated nitroxyl radicals, used in Overhauser‐enhanced magnetic resonance imaging for the first time. The dynamic nuclear polarization parameters such as dynamic nuclear polarization (DNP) factor, longitudinal relaxivity, saturation parameter, leakage factor and coupling factor were estimated for deuterated nitroxyl radicals. DNP enhancement increases with agent concentration up to 3 mm and decreases above 3 mm . The proton spin–lattice relaxation time and the longitudinal relaxivity parameters were estimated. The leakage factor increases with increasing agent concentration up to 3 mm and reaches plateau in the region 3–5 mm . The coupling parameter shows the interaction between the electron and nuclear spins to be mainly dipolar in origin. DNP spectrum exhibits that the full width at half maximum values are higher for undeuterated nitroxyl radicals compared with deuterated nitroxyl radicals, which leads to the increase in DNP enhancement. The ESR parameters such as, the line width, line shape, signal intensity ratio, rotational correlation time, hyperfine coupling constant and g‐factor were calculated. The narrow line width was observed for deuterated nitroxyl radicals compared with undeuterated nitroxyl radicals, which leads to the higher saturation parameter value and DNP enhancement. The novelty of the work permits clear understanding of the DNP parameters determining the higher DNP enhancement compared with the undeuterated nitroxyl radicals. Copyright © 2017 John Wiley & Sons, Ltd.     

Low‐frequency ESR studies on permeable and impermeable deuterated nitroxyl radicals in corn oil solution

Low‐frequency electron spin resonance studies were performed for 2 mM concentration of deuterated permeable and impermeable nitroxyl spin probes, 3‐methoxycarbonyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl and 3‐carboxy‐2,2,5,5,‐tetramethyl‐1‐pyrrolidinyloxy in pure water and various concentrations of corn oil solution. The electron spin resonance parameters such as the line width, hyperfine coupling constant, g factor, rotational correlation time, permeability, and partition parameter were estimated. The broadening of line width was observed for nitroxyl radicals in corn oil mixture. The rotational correlation time increases with increasing concentration of corn oil, which indicates the less mobile nature of spin probe in corn oil mixture. The membrane permeability and partition parameter values were estimated as a function of corn oil concentration, which reveals that the nitroxyl radicals permeate equally into the aqueous phase and oil phase at the corn oil concentration of 50%. The electron spin resonance spectra demonstrate the permeable and impermeable nature of nitroxyl spin probes. From these results, the corn oil concentration was optimized as 50% for phantom studies. In this work, the corn oil and pure water mixture phantom models with various viscosities correspond to plasma membrane, and whole blood membrane with different hematocrit levels was studied for monitoring the biological characteristics and their interactions with permeable nitroxyl spin probe. These results will be useful for the development of electron spin resonance and Overhauser‐enhanced magnetic resonance imaging modalities in biomedical applications.     

Electron spin resonance studies on deuterated nitroxyl spin probes used in Overhauser‐enhanced magnetic resonance imaging

The electron spin resonance studies were carried out for 2 mm concentration of ¹⁴N‐labeled and ¹⁵N‐labeled 3‐carbamoyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl, 3‐carboxy‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl, 3‐methoxycarbonyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl and their deuterated nitroxyl radicals using X‐band electron spin resonance spectrometer. The electron spin resonance line shape analysis was carried out. The electron spin resonance parameters such as linewidth, Lorentzian component, signal intensity ratio, rotational correlation time, hyperfine coupling constant and g‐factor were estimated. The deuterated nitroxyl radicals have narrow linewidth and an increase in Lorentzian component, compared with undeuterated nitroxyl radicals. The dynamic nuclear polarization factor was observed for all nitroxyl radicals. Upon ²H labeling, about 70% and 40% increase in dynamic nuclear polarization factor were observed for ¹⁴N‐labeled and ¹⁵N‐labeled nitroxyl radicals, respectively. The signal intensity ratio and g‐value indicate the isotropic nature of the nitroxyl radicals in pure water. Therefore, the deuterated nitroxyl radicals are suitable spin probes for in vivo/in vitro electron spin resonance and Overhauser‐enhanced magnetic resonance imaging modalities. Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamic Nuclear Polarization in Suspensions Consisting of Xylene Isomers and Asphaltene Extracted from MC‐800 Liquid Asphalt

Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers (o‐, m‐, p‐) at a low magnetic field of 1.44 mT and three different temperatures (15, 25, and 35°C). The asphaltene was extracted from MC‐800 liquid asphalt. Intermolecular spin‐spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The electron paramagnetic resonance spectrum of the asphaltene was obtained and the saturation experiments were applied to the samples prepared in vacuum. For all media, the dipole‐dipole interaction is predominant due to the negative signal enhancements. In all temperatures, the ultimate enhancement is the smallest for the p‐xylene solvent medium which has the lowest electrical dipole moment. The normalized low frequency relaxation components were calculated for 25°C, and the behavior of the nuclear‐electron coupling parameter according to this component is in agreement with the other works in the literature.     

ESR line width and line shape dependence of Overhauser‐enhanced magnetic resonance imaging

Electron spin resonance and Overhauser‐enhanced magnetic resonance imaging studies were carried out for various concentrations of ¹⁴N‐labeled 3‐carbamoyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl in pure water. Overhauser‐enhancement factor attains maxima in the range of 2.5–3 mm concentration. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameter showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. The electron spin resonance parameters, such as the line width, line shape and g‐factor, were determined. The line width analysis confirms that the line broadening is proportional to the agent concentration, and also the agent concentration is optimized in the range of 2.5–3 mm . The line shape analysis shows that the observed electron spin resonance line shape is a Voigt line shape, in which the Lorentzian component is dominant. The contribution of Lorentzian component was estimated using the winsim package. The Lorentzian component of the resonance line attains maxima in the range of 2.5–3 mm concentration. Therefore, this study reveals that the agent concentration, line width and Lorentzian component are the important factors in determining the Overhauser‐enhancement factor. Hence, the agent concentration was optimized as 2.5–3 mm for in vivo/in vitro electron spin resonance imaging and Overhauser‐enhanced magnetic resonance imaging phantom studies. Copyright © 2016 John Wiley & Sons, Ltd.     

Phenylazide Hybrid‐Silica – Polarization Platform for Dynamic Nuclear Polarization at Cryogenic Temperatures

Hyperpolarization of NMR‐active nuclei is key to gather high quality spectra of rare species and insensitive isotopes. We have recently established that silica‐based materials containing regularly distributed nitroxyl radicals connected to the silica matrix by flexible linkers can serve as promising polarization matrices for dynamic nuclear polarization (DNP). Here we investigate the influence of the linker on the efficiency of the polarization. The materials were fully characterized and exhibit high surface areas and narrow pore size distributions with a tunable amount of phenyl azide groups over a broad range of concentrations. The phenyl azide groups can be easily functionalized via a two‐step procedure with 4‐carboxy‐2,2,6,6‐tetramethyl‐1‐oxylpiperidine (TEMPO) to give polarizing matrices with controllable radical content. The DNP efficiency was found to be similar as in materials with flexible linkers, both for magic angle spinning at 105 K and dissolution DNP at 4 K.     

Real‐Time Interrogation of Aspirin Reactivity,Biochemistry, and Biodistribution by Hyperpolarized Magnetic Resonance Spectroscopy

Hyperpolarized magnetic resonance spectroscopy enables quantitative, non‐radioactive, real‐time measurement of imaging probe biodistribution and metabolism in vivo. Here, we investigate and report on the development and characterization of hyperpolarized acetylsalicylic acid (aspirin) and its use as a nuclear magnetic resonance (NMR) probe. Aspirin derivatives were synthesized with single‐ and double‐¹³C labels and hyperpolarized by dynamic nuclear polarization with 4.7 % and 3 % polarization, respectively. The longitudinal relaxation constants (T₁) for the labeled acetyl and carboxyl carbonyls were approximately 30 seconds, supporting in vivo imaging and spectroscopy applications. In vitro hydrolysis, transacetylation, and albumin binding of hyperpolarized aspirin were readily monitored in real time by ¹³C‐NMR spectroscopy. Hyperpolarized, double‐labeled aspirin was well tolerated in mice and could be observed by both ¹³C‐MR imaging and ¹³C‐NMR spectroscopy in vivo.     

Construction and 13C hyperpolarization efficiency of a 180 GHz dissolution dynamic nuclear polarization system

Dynamic nuclear polarization (DNP) via the dissolution method has become one of the rapidly emerging techniques to alleviate the low signal sensitivity in nuclear magnetic resonance (NMR) spectroscopy and imaging. In this paper, we report on the development and ¹³C hyperpolarization efficiency of a homebuilt DNP system operating at 6.423 T and 1.4 K. The DNP hyperpolarizer system was assembled on a wide‐bore superconducting magnet, equipped with a standard continuous‐flow cryostat, and a 180 GHz microwave source with 120 mW power output and wide 4 GHz frequency tuning range. At 6.423 T and 1.4 K, solid‐state ¹³C polarization P levels of 64% and 31% were achieved for 3 M [1‐¹³C] sodium acetate samples in 1 : 1 v/v glycerol:water glassing matrix doped with 15 mM trityl OX063 and 40 mM 4‐oxo‐TEMPO, respectively. Upon dissolution, which takes about 15 s to complete, liquid‐state ¹³C NMR signal enhancements as high as 240 000‐fold (P=21%) were recorded in a nearby high resolution ¹³C NMR spectrometer at 1 T and 297 K. Considering the relatively lower cost of our homebuilt DNP system and the relative simplicity of its design, the dissolution DNP setup reported here could be feasibly adapted for in vitro or in vivo hyperpolarized ¹³C NMR or magnetic resonance imaging at least in the pre‐clinical setting. Copyright © 2017 John Wiley & Sons, Ltd.     

Peptide Conjugates of a Nonsteroidal Anti‐Inflammatory Drug as Supramolecular Gelators: Synthesis,Characterization, and Biological Studies

Indomethacin ( IND ), which is a well‐known nonsteroidal anti‐inflammatory drug (NSAID), was conjugated with various naturally occurring amino acids. Most of these bioconjugates were capable of gelling pure water, a solution of NaCl (0.9 wt %), and phosphate‐buffered saline (pH 7.4), as well as a few organic solvents. The gels were characterized by table‐top and dynamic rheology, and electron microscopy. Variable‐temperature ¹H NMR spectroscopy studies on a selected gel were performed to gain insights into the self‐assembly process during gel formation. Both 1D and 2D hydrogen‐bonded networks were observed in the single‐crystal structures of two of the gelators. Plausible biological applications of the hydrogelators were evaluated with the ultimate aim of drug delivery in a self‐delivery fashion. All hydrogelators were stable in phosphate‐buffered saline at pH 7.4 at 37 °C, and biocompatible in mouse macrophage RAW 264.7 cell line (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay). Two of the most biocompatible hydrogelators displayed an anti‐inflammatory response comparable to that of the parent drug IND in prostaglandin E₂ assay. Release of the bioconjugates into the bulk solvent interfaced with the corresponding hydrogels indicated their plausible future application in drug delivery.     

Novel Pulsed Electron Paramagnetic Resonance Techniques for the Studies of Structure and Dynamics of Photo‐excited Triplet State of Organic Molecules: A Professional Journey

We present a few novel pulsed electron paramagnetic resonance techniques developed in our laboratory for the studies of structure and dynamics of the photo‐excited triplet state of organic molecules. We discuss many aspects of these new techniques and the significances of these measurements: (1) enhancing NMR signal intensity by dynamic nuclear polarization ‐ integrated solid effect, (2) performing magnetic resonance in zero‐field and low‐field by pulsed microwave, (3) mapping molecular motion of organic crystals by pulsed zero‐field and low‐field experiments, (4) probing spin dynamics at level anti‐crossing by fast field switching, (5) measuring hyperfine interaction by electron spin echo envelop modulation and spin‐echo electron nuclear double resonance and (6) detecting spin dynamics, nuclear quantum oscillation, entanglements and new avenues for quantum computer. We have employed the highly electron spin polarized pentacene triplet state as the model system in all of our pulsed EPR experiments. We performed most of our experiments at room temperature. The goals of our studies are aiming to improve spin detectability, to probe molecular dynamics, to determine electronic structures, to measure molecular interaction and motion, and to examine quantum coherence and oscillation which may yield new avenues in the applications of pulsed EPR techniques to quantum computer.     

Level Anti‐Crossings are a Key Factor for Understanding para‐Hydrogen‐Induced Hyperpolarization in SABRE Experiments

Various hyperpolarization methods are able to enhance the sensitivity of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) by several orders of magnitude. Among these methods are para‐hydrogen‐induced polarization (PHIP) and signal amplification by reversible exchange (SABRE), which exploit the strong nuclear alignment of para‐hydrogen. Several SABRE experiments have been reported but, so far, it has not been possible to account for the experimentally observed sign and magnetic‐field dependence of substrate polarization. Herein, we present an analysis based on level anti‐crossings (LACs), which provides a complete understanding of the SABRE effect. The field‐dependence of both net and anti‐phase polarization is measured for several ligands, which can be reproduced by the theory. The similar SABRE field‐dependence for different ligands is also explained. In general, the LAC concept allows complex spin dynamics to be unraveled, and is crucial for optimizing the performance of novel hyperpolarization methods in NMR and MRI techniques.     

A Nanoparticle Catalyst for Heterogeneous Phase Para‐Hydrogen‐Induced Polarization in Water

Para‐hydrogen‐induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state‐of‐the‐art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand‐inhibited surface diffusion on the nanoparticles resulted in a ¹H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the ¹H polarization to a ¹³C nucleus using a para‐hydrogen polarizer yielded a polarization of 0.013 %. The nuclear‐spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water.     

Preparation and biodistribution study of technetium-99m-labeled quercetin as a potential radical scavenging agent

Free radicals and oxidative stress are the primary causes of several chronic diseases such as cancer and heart disease. Quercetin is a natural compound with potent antioxidant activity. We have prepared and evaluated technetium-99m (^99mTc)-labeled quercetin as a potential radical scavenging radiotracer. A ^99mTc-quercetin complex was prepared using quercetin, SnCl₂ and Na^99mTcO₄ in a buffered solution over 30 min. The participation coefficient was measured in octanol and queues solutions. The stability was determined in phosphate buffered saline and serum. The biodistribution in normal mice was evaluated at 0.5, 2, 6 and 24 h post-injection. The radiochemical purity (>99%) was determined by thin layer chromatography (TLC) in normal saline solution as the mobile phase. It has a log P of 0.204. It was mainly cleared by the kidneys and showed negligible brain uptake at four time points measured post-injection. The pharmacological properties of quercetin, mainly its free radical scavenging, may potentially cat as a radiopharmaceutical agent for radical-targeted imaging of tissue with high levels of reactive oxygen species.     

A table‐top PXI based low‐field spectrometer for solution dynamic nuclear polarization

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of ¹H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced ¹H signal at 288 kHz was constructed with Litz wire. The largest observed ¹H enhancements (ε) at 6.7 mT for ¹⁴N‐CTPO radical in air saturated aqueous solution was ε~65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi‐frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.     

Simultaneous evaluation of one‐electron reducing systems and radical reactions in cells by nitroxyl biradical as probe

In the present study, a novel probe for the simultaneous evaluation of one‐electron reducing systems (electron transport chain) and one‐electron oxidizing systems (free radical reactions) in cells by electron chemical detection was developed. Six‐membered cyclic nitroxyl radicals (2,2,6,6‐tetramethylpiperidine‐1‐oxyl; TEMPO series) are sensitive to one‐electron redox systems, generating the hydroxylamine form [TEMPO(H)] via one‐electron reduction, and the secondary amine form [TEMPO(N)] via one‐electron oxidation in the presence of thiols. In contrast, the sensitivities of five‐membered cyclic nitroxyl radicals (2,2,5,5‐tetramethylpyrrolidine‐1‐oxyl; PROXYL series) to the one‐electron redox systems are comparatively low. The electron chemical detector can detect 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), TEMPO(H) and PROXYL but not TEMPO(N). Therefore, nitroxyl biradical, TEMPO‐PROXYL, as a probe for the evaluation of one‐electron redox systems was employed. TEMPO‐PROXYL was synthesized by the conjunction of 4‐amino‐TEMPO with 3‐carboxyl‐PROXYL via the conventional dicyclohexyl carbodiimide reaction. TEMPO‐PROXYL, TEMPO(H)‐PROXYL and TEMPO(N)‐PROXYL were simultaneously quantified by HPLC with Coularray detection. Calibration curves for the quantification of TEMPO‐PROXYL, TEMPO(H)‐PROXYL and TEMPO(N)‐PROXYL were linear in the range from 80 nm to 80 μm , and the lowest quantification limit of each molecule was estimated to be <80 nm . The relative standard deviations at 0.8 and 80 μm were within 10% (n = 5). Copyright © 2015 John Wiley & Sons, Ltd.     

Spin Noise Detection of Nuclear Hyperpolarization at 1.2 K

We report proton spin noise spectra of a hyperpolarized solid sample of commonly used “DNP (dynamic nuclear polarization) juice” containing TEMPOL (4‐hydroxy‐2,2,6,6‐tetramethylpiperidine N‐oxide) and irradiated by a microwave field at a temperature of 1.2 K in a magnetic field of 6.7 T. The line shapes of the spin noise power spectra are sensitive to the variation of the microwave irradiation frequency and change from dip to bump, when the electron Larmor frequency is crossed, which is shown to be in good accordance with theory by simulations. Small but significant deviations from these predictions are observed, which can be related to spin noise and radiation damping phenomena that have been reported in thermally polarized systems. The non‐linear dependence of the spin noise integral on nuclear polarization provides a means to monitor hyperpolarization semi‐quantitatively without any perturbation of the spin system by radio frequency irradiation.     

Parahydrogen‐Based Hyperpolarization for Biomedicine

Magnetic resonance (MR) is one of the most versatile and useful physical effects used for human imaging, chemical analysis, and the elucidation of molecular structures. However, its full potential is rarely used, because only a small fraction of the nuclear spin ensemble is polarized, that is, aligned with the applied static magnetic field. Hyperpolarization methods seek other means to increase the polarization and thus the MR signal. A unique source of pure spin order is the entangled singlet spin state of dihydrogen, parahydrogen (pH₂), which is inherently stable and long‐lived. When brought into contact with another molecule, this “spin order on demand” allows the MR signal to be enhanced by several orders of magnitude. Considerable progress has been made in the past decade in the area of pH₂‐based hyperpolarization techniques for biomedical applications. It is the goal of this Review to provide a selective overview of these developments, covering the areas of spin physics, catalysis, instrumentation, preparation of the contrast agents, and applications.     

Spin‐Labeled Heparins as Polarizing Agents for Dynamic Nuclear Polarization

A potentially biocompatible class of spin‐labeled macromolecules, spin‐labeled (SL) heparins, and their use as nuclear magnetic resonance (NMR) signal enhancers are introduced. The signal enhancement is achieved through Overhauser‐type dynamic nuclear polarization (DNP). All presented SL‐heparins show high ¹H DNP enhancement factors up to E=?110, which validates that effectively more than one hyperfine line can be saturated even for spin‐labeled polarizing agents. The parameters for the Overhauser‐type DNP are determined and discussed. A striking result is that for spin‐labeled heparins, the off‐resonant electron paramagnetic resonance (EPR) hyperfine lines contribute a non‐negligible part to the total saturation, even in the absence of Heisenberg spin exchange (HSE) and electron spin‐nuclear spin relaxation (T_1ne). As a result, we conclude that one can optimize the use of, for example, biomacromolecules for DNP, for which only small sample amounts are available, by using heterogeneously distributed radicals attached to the molecule.     

Diffusion characteristics of agarose hydrogel used in diffusive gradients in thin films for measurements of cations and anions

The agarose hydrogel has been increasingly used as a diffusive layer in diffusive gradients in thin films (DGT) measurements. However its diffusive characteristics have not been examined in detail. In this study, the performance of agarose gel was tested in DGT measurements of eight cations (Fe(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), and Cd(II)) and eight anions (P(V), As(V), Cr(VI), Mo(VI), Sb(V), Se(VI), V(V), and W(VI)). It was found that the thickness of agarose, a key parameter in the calculation of DGT measured concentration, remained unchanged after hydration followed by storage under the following conditions: pH 2–11, ionic strength 0–1.0 M, temperature 4–40 °C, and with the storage time extending to 300 d. Enrichment of cations and repelling of anions were observed in the gel under the ionic strengths of < 2–3 mM and <1 mM (NaNO₃), respectively, which was attributed to the electrostatic interactions of these ions with the fixed negatively charged groups (mainly pyruvate) in the gel. The diffusion coefficients of cations and anions through the agarose gel (plus a PVDF filter membrane) were on average 1.10 ± 0.04 times of the reported diffusion coefficients through the agarose cross-linked polyacrylamide (APA) hydrogel, typically used in DGT technique. The working pH ranges for the agarose gel-assembled DGTs were 4–10 and 5–9 for anions and cations, respectively. The use of agarose gel, either individually or along with different filter membranes, affected the overall diffusion rates of cations and anions. The measured DGT concentrations of cations and anions in filtered natural freshwater and seawater were mostly in line with those measured directly. The results showed that the agarose gel can be used as one of the standard diffusive layers in DGT measurements for a wide range of inorganic and organic analytes.     

Producing Radical‐Free Hyperpolarized Perfusion Agents for In Vivo Magnetic Resonance Using Spin‐Labeled Thermoresponsive Hydrogel

Dissolution dynamic nuclear polarization (DNP) provides a way to tremendously improve the sensitivity of nuclear magnetic resonance experiments. Once the spins are hyperpolarized by dissolution DNP, the radicals used as polarizing agents become undesirable since their presence is an additional source of nuclear spin relaxation and their toxicity might be an issue. This study demonstrates the feasibility of preparing a hyperpolarized [1‐¹³C]2‐methylpropan‐2‐ol (tert‐butanol) solution free of persistent radicals by using spin‐labeled thermoresponsive hydrophilic polymer networks as polarizing agents. The hyperpolarized ¹³C signal can be detected for up to 5 min before the spins fully relax to their thermal equilibrium. This approach extends the applicability of spin‐labeled thermoresponsive hydrogel to the dissolution DNP field and highlights its potential as polarizing agent for preparing neat slowly relaxing contrast agents. The hydrogels are especially suited to hyperpolarize deuterated alcohols which can be used for in vivo perfusion imaging.