Dynamic nuclear polarization sensitivity enhancement

Key Words Dynamic nuclear polarization, DNP, Overhauser effect, Hyperpolarization, Sensitivity enhancement,... 

An extremely sensitive technique able to detect the nature of radical pairs in a photochemical reaction is called chemically induced dynamic nuclear polarization (CIDNP), which depends on the observation of an enhanced absorption in a nuclear magnetic resonance (NMR) spectrum of the sample, irradiated in situ, in the cavity of a NMR spectrometer. The background to and interpretation of CIDNP are discussed by Gilbert and Baggott (28). 

T. Kobayashi, O. Lafon, A.S.L. Thankamony, LI. Slowing, K. Kandel, D. Camevale, V. Vitzthum, H. Vezin, J.P. Amoureux, G. Bodenhausen, M. Pruski, Analysis of sensitivity enhancement by dynamic nuclear polarization in solid-state NMR a case study offunctionalizedmesoporous materials, Phys. Chem. Chem. Phys. 15 (2013) 5553-5562. 

Demonstrated a 100-fold sensitivity enhancement with dynamic nuclear polarization (DNP) of urea [42]... 

The recent renaissance of dynamic nuclear polarization (DNP) provides an extremely promising approach for sensitivity enhancement [87—89]. It borrows the large Boltzmann polarization from unpaired electron spins of free radicals to boost the NMR signal. DNP experiments have been performed on quadrupolar nuclei such as [90], " N [91], [92,93],... 

Le et al. show the utility of the overall sensitivity enhancements provided by dynamic nuclear polarization (DNP) for the CPNMR characterization of polymer samples doped with biradicals and prepared either by film casting, or by glass forming using 1,1,2,2-tetrachloroethane as the solvent. 

A major limitation for NMR spectroscopy is the intrinsically low sensitivity due to the rather unfavorable Boltzmann distribution for nuclear spins at thermal equilibrium. Thus, considerable effort in magnetic resonance spectroscopy is made towards sensitivity enhancement by hyperpolarization techniques, such as optical polarization, para-hydrogen-induced polarization enhancement, and dynamic nuclear polarization (DNP), a method which exploits the magnetization of unpaired electrons in stable radicals or transition metals to enhance nuclear polarization beyond the Boltzmann limit. In the chapter Dynamic Nuclear Hyperpolarization in Liquids, the fundamental theory for different polarization transfer... 

The enormous improvement in the nuclear spin polarization achievable by these optical approaches has great potential to impact conventional NMR smdies in a variety of ways. Besides simply increasing the detection sensitivity of NMR, the enhanced nuclear spin polarization may be useful for obtaining enhanced spectral selectivity (e.g., for some spatial, structural, or dynamical feature of a sample) enhanced contrast and resolution in MRI and improved density matrix purity (e.g., for NMR quantum computation). Finally, it is worth noting that the optical fields used in some of these methods can be gated, thereby permitting time-resolved studies that would not be possible with conventional NMR approaches. 

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