Category Archives: e-Book

DNP Mechanisms #DNPNMR

Kundu, Krishnendu, Frédéric Mentink‐Vigier, Akiva Feintuch, and Shimon Vega. “DNP Mechanisms.” In EMagRes, 295–338. American Cancer Society, 2019.

This article presents a comprehensive description of the spin dynamics underlying the main DNP mechanisms leading to nuclear signal enhancements in glassy amorphous solids containing free radicals. The emphasis of the article to derive quantum mechanically based formalisms that enable us to analyze experimental DNP data. After a short review of the history of DNP, rate equations of the eigenstate populations of static coupled electron–nuclear spin systems are introduced, based on their spin-Hamiltonians and including spin-lattice and cross-relaxation mechanisms. They are used to simulate the dynamics of small spin systems under microwave (MW) irradiation and the basic Solid Effect (SE), Cross Effect (CE), and Overhauser DNP (O-DNP) enhancement mechanisms are presented. These calculations are then extended to systems containing up to 10 spins and are used to calculate EPR, ELDOR, and DNP spectra. Plots showing the population of the eigenstates vs energy are used to demonstrate the conditions for the thermal mixing mechanism and the corresponding EPR and ELDOR spectra are discussed. Following these calculations, the electron spectral diffusion (eSD) and the indirect Cross Effect (iCE) numerical models are introduced and used to analyze EPR and DNP spectra of real samples. In the last section, the basic theory of magic angle spinning (MAS) DNP on small spin systems is summarized and the influence of the rotor events on the quasiperiodic steady-state DNP enhancements discussed. The origins of depolarization effects occurring when no MW is applied are described. Finally, the nuclear spin diffusion process inside the diffusion barrier is studied using multielectron and multinuclear calculations.

Let’s start the new year with an article that is already a bit older. However, I just came across it recently and I don’t think I posted it already. It is a very nice overview about Dissolution DNP by Walther Koeckenberger.

Köckenberger, W., Dissolution Dynamic Nuclear Polarization, in eMagRes. 2007, John Wiley & Sons, Ltd.

Dissolution DNP (dissDNP) is an experimental strategy that can be used to substantially increase the nuclear spin polarization in liquid-state samples. The strategy is based on DNP carried out at cryogenic temperatures with a subsequent fast temperature rise of the sample that is achieved by dissolving the initially frozen sample in a hot solvent. The strategy has opened up novel avenues in medical diagnostic imaging, as 13C-labeled compounds can first be prepared with high-spin polarization by dissDNP before their administration to humans or animals, followed by their in vivo detection using MRI. The use of fast spectroscopic imaging acquisition schemes makes it possible to observe the in vivo spatial distribution of 13C-labeled compounds and monitor their in vivo metabolic turnover due to the high-spin polarization and the related increase in sensitivity. The strategy has also shown to be useful in measuring in vitro metabolism in cell cultures with high time resolution, and in enabling novel experimental protocols for in vitro molecular dynamics studies.

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