Nuclear magnetic resonance (NMR) is a fundamental spectroscopic technique for the study of biological systems and materials, molecular imaging and the analysis of small molecules. It detects interactions at very low energies and is thus non-invasive and applicable to a variety of targets, including animals and humans. However, one of its most severe limitations is its low sensitivity, which stems from the small interaction energies involved. Here, we report that dynamic nuclear polarization in liquid solution and at room temperature can enhance the NMR signal of C nuclei by up to three orders of magnitude at magnetic fields of ∼3 T. The experiment can be repeated within seconds for signal averaging, without interfering with the sample magnetic homogeneity. The method is therefore compatible with the conditions required for high-resolution NMR. Enhancement ofC signals on various organic compounds opens up new perspectives for dynamic nuclear polarization as a general tool to increase the sensitivity of liquid NMR.

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. However, the approach in liquids still faces several challenges. Herein we report the observation of room‐temperature, liquid DNP 13C signal enhancements in organic small molecules as high as 600 at 9.4 Tesla and 800 at 1.2 Tesla. A mechanistic investigation of the 13C‐DNP field dependence shows that DNP efficiency is raised by proper choice of the polarizing agent (paramagnetic center) and by halogen atoms as mediators of scalar hyperfine interaction. Observation of sizable DNP of 13CH2 and 13CH3 groups in organic molecules at 9.4 T opens perspective for a broader application of this method.

Polarization transfer efficiency in liquid-state dynamic nuclear polarization (DNP) depends on the interaction between polarizing agents (PAs) and target nuclei modulated by molecular motions. We show how translational and rotational diffusion differently affect the DNP efficiency. These contributions were disentangled by measuring 1 H-DNP enhancements of toluene and chloroform doped with nitroxide derivatives at 0.34 T as a function of either the temperature or the size of the PA. The results were employed to analyze 13

We report a large variation in liquid DNP performance of up to a factor of about five in coupling factors among organic radicals used commonly as polarizing agents. A comparative...

Large 31P-NMR enhancements are observed with DNP in PPh3 doped with BDPA radical, while they are reduced when a nitroxide radical or triphenylphosphine-oxide are used instead. This is due to different non-covalent radical/target molecule interactions.

A systematic review and analysis of the most stable spatial arrangements of n carbon, n oxygen, and 2n hydrogen atoms including vibrational zero-point energy up to n = 5 shows that small-molecule aggregates win, typically followed by thermally unstable molecules, before kinetically stable molecules and finally carbohydrates are found. Near n ≈ 60 a crossover to carbon allotropes and ice as the global minimum structure is expected and the asymptotic limit is most likely graphite and ice. Implications for astrochemical and fermentation processes are discussed. Density functionals like B3LYPD3 are found to describe these energy sequences quite poorly, mostly due to an overestimated stability of carbon in high oxidation states.

Nuclear magnetic resonance (NMR) techniques play an essential role in natural science and medicine.Inspite 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), at echnique based on transfer of polarization from electron to nuclear spins,h as emerged as atool to enhance sensitivity of NMR. However,the approach in liquids still faces several challenges.H erein we report the observation of room-temperature,l iquid DNP 13 C signal enhancements in organic small molecules as high as 600 at 9.4 Tesla and 800 at 1.2 Tesla. Amechanistic investigation of the 13 C-DNP field dependence shows that DNP efficiency is raised by proper choice of the polarizing agent (paramagnetic center) and by halogen atoms as mediators of scalar hyperfine interaction. Observation of sizable DNP of 13 CH 2 and 13 CH 3 groups in organic molecules at 9.4 To pens perspective for abroader application of this method.Improving the sensitivity of NMR and magnetic resonance imaging (MRI) remains am ain target of research aiming to expand the scope of NMR applications.Besides technological developments in spectrometer construction, the most powerful approaches rely on hyperpolarization techniques that increase the population difference (or polarization) of nuclear spins far from the polarization at thermal equilibrium. [1] Dynamic nuclear polarization (DNP) takes advantage of the higher polarization of ap olarizing agent and transfers it to nuclear spins via their hyperfine interaction and microwave (MW) irradiation. [2] Themethod has historically worked well in solid-state NMR experiments but turned out to be much more challenging in liquids,b ecause of mechanistic and technical reasons.F irst, the mechanism in liquids requires electron-nuclear hyperfine interaction to be modulated at the time scale of the electron-spin resonance frequency. [3] At low magnetic fields ( 1T esla), molecular diffusion with correlation times on the order of tens of ps provides the suited time scale for this modulation, but it does not for resonance frequencies in the high field range (! 3T esla). [2,3b] Moreover, 13 C-DNP performed up to medium fields revealed an intriguing dependence of the signal enhancements on the 13 C chemical environment, which hampered quantitative mechanistic descriptions. [4] Secondly,i mplementing liquid DNP at high magnetic fields and ambient temperatures is aggravated by dielectric losses.T his effect can be reduced by using MW resonant structures where the sample is placed in aminimum of the electric field of the standing wave. [5] Progress in this direction has been shown in recent reports. [6] We have recently reported the observation of athousandfold 13 CD NP signal enhancement in the liquid state at 3.4 Te sla. [4f] Our report raised the question whether the method is compatible with magnetic fields and requirements used in high-resolution NMR spectroscopy. [7] Herein, we explore the capabilities of 13 Cl iquid DNP over...

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