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Issue 22, 2010
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Optimization of dynamic nuclear polarization experiments in aqueous solution at 15 MHz/9.7 GHz: a comparative study with DNP at 140 MHz/94 GHz

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Abstract

Dynamic nuclear polarization is emerging as a potential tool to increase the sensitivity of NMR aiming at the detection of macromolecules in liquid solution. One possibility for such an experimental design is to perform the polarization step between electrons and nuclei at low magnetic fields and then transfer the sample to a higher field for NMR detection. In this case, an independent optimization of the polarizer and detection set ups is required. In the present paper we describe the optimization of a polarizer set up at 15 MHz 1H NMR/9.7 GHz EPR frequencies based on commercial hardware. The sample consists of the nitroxide radical TEMPONE-D,15N in water, for which the dimensions were systematically decreased to fit the homogeneous B1 region of a dielectric ENDOR resonator. With an available B1 microwave field up to 13 G we observe a maximum DNP enhancement of −170 at room temperature by irradiating on either one of the EPR lines. The DNP enhancement was saturated at all polarizer concentrations. Pulsed ELDOR experiments revealed that the saturation level of the two hyperfine lines is such that the DNP enhancements are well consistent with the coupling factors derived from NMRD data. By raising the polarizing field and frequencies 10-fold, i.e. to 140 MHz 1H/94 GHz EPR, we reach an enhancement of −43 at microwave field strengths (B1 ≈ 5 G). The results are discussed in view of an application for a DNP spectrometer.

Graphical abstract: Optimization of dynamic nuclear polarization experiments in aqueous solution at 15 MHz/9.7 GHz: a comparative study with DNP at 140 MHz/94 GHz

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Article information


Submitted
09 Feb 2010
Accepted
23 Apr 2010
First published
08 May 2010

Phys. Chem. Chem. Phys., 2010,12, 5893-5901
Article type
Paper

Optimization of dynamic nuclear polarization experiments in aqueous solution at 15 MHz/9.7 GHz: a comparative study with DNP at 140 MHz/94 GHz

M. Türke, I. Tkach, M. Reese, P. Höfer and M. Bennati, Phys. Chem. Chem. Phys., 2010, 12, 5893
DOI: 10.1039/C002814M

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