Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid‐state polarization enhancement at ambient conditions, and the maximization of 13C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's 13C behavior in nano‐ and micro‐particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid‐state experiments. It was found that 13C NMR signals could be boosted by orders of magnitude in either low‐ or room‐temperature solid‐state DNP experiments by utilizing naturally occurring paramagnetic P1 substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin‐lattice relaxation times characteristic of diamond, coupled with a time‐independent cross‐effect‐like polarization transfer mechanism facilitated by a matching of the nitrogen‐related hyperfine coupling and the 13C Zeeman splitting. The efficiency of this solid‐state polarization process, however, is harder to exploit in dissolution DNP‐enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed. 相似文献
Hyperpolarized [1-13C]fumarate is a promising magnetic resonance imaging (MRI) biomarker for cellular necrosis, which plays an important role in various disease and cancerous pathological processes. To demonstrate the feasibility of MRI of [1-13C]fumarate metabolism using parahydrogen-induced polarization (PHIP), a low-cost alternative to dissolution dynamic nuclear polarization (dDNP), a cost-effective and high-yield synthetic pathway of hydrogenation precursor [1-13C]acetylenedicarboxylate (ADC) was developed. The trans-selectivity of the hydrogenation reaction of ADC using a ruthenium-based catalyst was elucidated employing density functional theory (DFT) simulations. A simple PHIP set-up was used to generate hyperpolarized [1-13C]fumarate at sufficient 13C polarization for ex vivo detection of hyperpolarized 13C malate metabolized from fumarate in murine liver tissue homogenates, and in vivo13C MR spectroscopy and imaging in a murine model of acetaminophen-induced hepatitis. 相似文献
Dynamic nuclear polarization (DNP) is a technique to polarize the nuclear spin population. As a result of the hyperpolarization, the NMR sensitivity of the nuclei in molecules can be dramatically enhanced. Recent application of the hyperpolarization technique has led to advances in biochemical and molecular studies. A major problem is the short lifetime of the polarized nuclear spin state. Generally, in solution, the polarized nuclear spin state decays to a thermal spin equilibrium, resulting in loss of the enhanced NMR signal. This decay is correlated directly with the spin‐lattice relaxation time T1. Here we report [13C,D14]tert‐butylbenzene as a new scaffold structure for designing hyperpolarized 13C probes. Thanks to the minimized spin‐lattice relaxation (T1) pathways, its water‐soluble derivative showed a remarkably long 13C T1 value and long retention of the hyperpolarized spin state. 相似文献
A scalable and versatile methodology for production of vinylated carboxylic compounds with 13C isotopic label in C1 position is described. It allowed synthesis of vinyl acetate‐1‐13C, which is a precursor for preparation of 13C hyperpolarized ethyl acetate‐1‐13C, which provides a convenient vehicle for potential in vivo delivery of hyperpolarized acetate to probe metabolism in living organisms. Kinetics of vinyl acetate molecular hydrogenation and polarization transfer from para‐hydrogen to 13C via magnetic field cycling were investigated. Nascent proton nuclear spin polarization (%PH) of ca. 3.3 % and carbon‐13 polarization (%P13C) of ca. 1.8 % were achieved in ethyl acetate utilizing 50 % para‐hydrogen corresponding to ca. 50 % polarization transfer efficiency. The use of nearly 100% para‐hydrogen and the improvements of %PH of para‐hydrogen‐nascent protons may enable production of 13C hyperpolarized contrast agents with %P13C of 20–50 % in seconds using this chemistry. 相似文献
We report on the assembly and performance evaluation of a 180‐GHz/6.4 T dynamic nuclear polarization (DNP) system based on a cryogen‐free superconducting magnet. The DNP system utilizes a variable‐field superconducting magnet that can be ramped up to 9 T and equipped with cryocoolers that can cool the sample space with the DNP assembly down to 1.8 K via the Joule–Thomson effect. A homebuilt DNP probe insert with top‐tuned nuclear magnetic resonance coil and microwave port was incorporated into the sample space in which the effective sample temperature is approximately 1.9 K when a 180‐GHz microwave source is on during DNP operation. 13C DNP of [1‐13C] acetate samples doped with trityl OX063 and 4‐oxo‐TEMPO in this system have resulted in solid‐state 13C polarization levels of 58 ± 3% and 18 ± 2%, respectively. The relatively high 13C polarization levels achieved in this work have demonstrated that the use of a cryogen‐free superconducting magnet for 13C DNP is feasible and in fact, relatively efficient—a major leap to offset the high cost of liquid helium consumption in DNP experiments. 相似文献
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.
The promise of hyperpolarized glucose as a non-radioactive imaging agent capable of reporting on multiple metabolic routes has led to recent advances in its dissolution-DNP (dDNP) driven polarization using UV-light induced radicals and trityl radicals at high field (6.7 T) and 1.1 K. However, most preclinical dDNP polarizers operate at the field of 3.35 T and 1.4–1.5 K. Minute amounts of Gd3+ complexes have shown large improvements in solid-state polarization, which can be translated to improved hyperpolarization in solution. However, this Gd3+ effect seems to depend on magnetic field strength, metal ion concentration, and sample formulation. The effect of varying Gd3+ concentrations at 3.35 T has been described for 13C-labeled pyruvic acid and acetate. However, it has not been studied for other compounds at this field. The results presented here suggest that Gd3+ doping can lead to various concentration and temperature dependent effects on the polarization of [13C6,2H7]glucose, not necessarily similar to the effects observed in pyruvic acid or acetate in size or direction. The maximal polarization for [13C6,2H7]glucose appears to be at a Gd3+ concentration of 2 mM, when irradiating for more than 2 h at the negative maximum of the DNP intensity profile. Surprisingly, for shorter irradiation times, higher polarization levels were determined at 1.50 K compared to 1.45 K, at a [Gd3+]=1.3 mM. This was explained by the build-up time constant and maximum at these temperatures. 相似文献
Dissolution dynamic nuclear polarization (DNP) enables high‐sensitivity solution‐phase NMR experiments on long‐lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution‐state 1H NMR upon polarizing low‐γ nuclear species. Following solid‐state hyperpolarization of both 13C and 1H, solution‐phase 1H NMR experiments on dissolved samples revealed transient effects, whereby peaks arising from protons bonded to the naturally occurring 13C nuclei appeared larger than the typically dominant 12C‐bonded 1H resonances. This enhancement of the satellite peaks was examined in detail with respect to a variety of mechanisms that could potentially explain this observation. Both two‐ and three‐spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization‐transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross‐relaxation models were examined, and found to well describe the distinct patterns of growth and decay shown by the 13C‐bound 1H NMR satellite resonances. The dynamics of these novel cross‐relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced‐sensitivity 1H NMR traces was explored. 相似文献
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. 相似文献
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. 相似文献
In this study, natural‐based ionic liquid (IL) using caffeine (Caff), trietahnolamine (TEA) and ZnBr2, [Caff‐TEA]+[ZnBr3]?, which features high catalytic activity and environmentally‐friendly nature was synthesized with melting point of 76 °C by a facile method. The synthesized [Caff‐TEA]+[ZnBr3]? has high catalytic activity as both of catalyst and solvent in condensation reactions for the synthesis of benzylidenes, bis‐hydroxyenones and xanthenes. Synthesized IL was characterized by proton nuclear magnetic resonance (1HNMR), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) and Energy‐dispersive X‐ray spectroscopy (EDX) analysis. Also synthesized heterocycles were characterized by FT‐IR, proton nuclear magnetic resonance (1HNMR) and carbon nuclear magnetic resonance (13CNMR). 相似文献
A novel poly (ethylene glycol) bridged primary amine functionalized dicationic ionic liquid ([PA‐PEG1000‐DIL][BF4]) was synthesized and characterized by 1H‐NMR, 13C‐NMR, FT‐IR and ESI‐MS. The thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis indicated the high thermal stability of [PA‐PEG1000‐DIL][BF4]. It was used as an efficient and recyclable catalyst for the synthesis of substituted tetrahydrobenzo[b]pyrans through a one‐pot three‐component condensation of aromatic aldehydes, malononitrile and dimedone in 86% ~ 96% yields within 10 ~ 30 min in water. This method offers several advantages such as mild reaction conditions, simple operation and environmental friendliness. Furthermore, the catalyst could be easily recovered and reused for at least five runs without obvious loss of catalytic activity. 相似文献
The crystal structure of a nitrilotriacetate (nta) oxidovanadium(IV) salt with 4‐methylpyridinium cation, [4‐Me(Py)H]+, of [4‐Me(Py)H][VO(nta)(H2O)] stoichiometry was determined. The complex comprises a discrete mononuclear [VO(nta)(H2O)]– coordination entity that can be rarely found among other known compounds containing nitrilotriacetate oxidovanadium(IV) moieties. The complex was characterized by spectroscopic (IR and EPR) methods, magnetic measurements, and thermogravimetry (TG‐FTIR). The stability of the title compound in aqueous solutions was investigated by using the potentiometric titration method. Furthermore, spectrophotometric (UV/Vis) studies have revealed that the compound is capable to scavenge the superoxide free radicals (O2 ? –) as well as stable organic radicals i.e. 2,2′‐azinobis(3‐ethylbenzothiazoline‐6 sulfonic acid) cation radical (ABTS+ ? ) and 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH ? ). Finally, biological properties of the complex studied were investigated in relation to its cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the HT22 hippocampal neuronal cell line (the MTT assay). Additionally, the biological action of the compound towards two human osteosarcoma HOS and MG‐63 cell lines (the MTT and BrdU tests) as well as the untransformed human osteoblast hFOB 1.19 cell line was tested. 相似文献
Samples prepared following dissolution dynamic nuclear polarization (DNP) enable the detection of NMR spectra from low‐γ nuclei with outstanding sensitivity, yet have limited use for the enhancement of abundant species like 1H nuclei. Small‐ and intermediate‐sized molecules, however, show strong heteronuclear cross‐relaxation effects: spontaneous processes with an inherent isotopic selectivity, whereby only the 13C‐bonded protons receive a polarization enhancement. These effects are here combined with a recently developed method that delivers homonuclear‐decoupled 1H spectra in natural abundance samples based on heteronuclear couplings to these same, 13C‐bonded nuclei. This results in the HyperBIRD methodology; a single‐shot combination of these two effects that can simultaneously simplify and resolve complex, congested 1H NMR spectra with many overlapping spin multiplets, while achieving 50–100 times sensitivity enhancements over conventional thermal counterparts. 相似文献
Chemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO ( 1 ) or Et3N ( 2 ) with a wide range of electron acceptors support the involvement of amine radical‐cations (e.g., 1. + or 2. + ) as key intermediates. Radical ions such as 2. + may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2. ). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene (1Naph*), the resulting pair 2. + /Naph.? reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state. 相似文献