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Preparation of Fungal and Plant Materials for Structural Elucidation Using Dynamic Nuclear Polarization Solid-State NMR

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Dynamic Nuclear Polarization in the solid state: a transition between the cross effect and the solid effect.

Daphna Shimon¹, Yonatan Hovav, Akiva Feintuch

¹Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel.

Physical Chemistry Chemical Physics : PCCP

|March 16, 2012

Summary

This summary is machine-generated.

Proton Dynamic Nuclear Polarization (DNP) experiments reveal temperature-dependent contributions of the Solid Effect (SE) and Cross Effect (CE) mechanisms. Lowering temperatures below 20 K enhances SE-DNP while diminishing CE-DNP in TEMPOL-doped samples.

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Area of Science:

Magnetic Resonance Spectroscopy
Physical Chemistry

Background:

Dynamic Nuclear Polarization (DNP) enhances nuclear magnetic resonance (NMR) signals by transferring polarization from electron spins to nuclei.
In solid-state DNP, enhancement mechanisms include the Solid Effect (SE), Cross Effect (CE), and Thermal Mixing (TM).

Purpose of the Study:

To determine the dominant DNP mechanisms responsible for proton signal enhancement in TEMPOL-doped frozen solutions.
To investigate the influence of temperature and microwave power on SE-DNP and CE-DNP contributions.

Main Methods:

Proton DNP experiments were performed using a hybrid Electron Paramagnetic Resonance (EPR)-NMR spectrometer.
Measurements included electron and nuclear spin-lattice relaxation rates, enhancement buildup times, and microwave-swept DNP spectra.
A theoretical model was employed to analyze DNP spectra and quantify SE-DNP and CE-DNP contributions.

Main Results:

Observed variations in DNP spectral lineshapes indicated changes in the relative contributions of SE-DNP and CE-DNP with temperature and microwave power.
Analysis revealed that lowering the temperature below 20 K increased the SE-DNP contribution and decreased the CE-DNP contribution.
The Thermal Mixing (TM) mechanism was found to be negligible in this study.

Conclusions:

The study successfully quantified the contributions of SE-DNP and CE-DNP mechanisms to proton signal enhancement.
Temperature plays a critical role in modulating the balance between SE-DNP and CE-DNP, with implications for optimizing DNP experiments.