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Molecular simulations for dynamic nuclear polarization in liquids: a case study of TEMPOL in acetone and DMSO

Küçük, Sami Emre and Neugebauer, Petr and Prisner, Thomas F. and Sezer, Deniz (2015) Molecular simulations for dynamic nuclear polarization in liquids: a case study of TEMPOL in acetone and DMSO. Physical Chemistry Chemical Physics, 17 (9). pp. 6618-6628. ISSN 1463-9076 (Print) 1463-9084 (Online)

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Official URL: http://dx.doi.org/10.1039/c4cp05832a

Abstract

A computational strategy for calibrating, validating and analyzing molecular dynamics (MD) simulations to predict dynamic nuclear polarization (DNP) coupling factors and relaxivities of proton spins is presented. Simulations of the polarizing agent TEMPOL in liquid acetone and DMSO are conducted at low (infinite dilution) and high (1 M) concentrations of the free radical. Because DNP coupling factors and relaxivities are sensitive to the time scales of the molecular motions, the MD simulations are calibrated to reproduce the bulk translational diffusion coefficients of the pure solvents. The simulations are then validated by comparing with experimental dielectric relaxation spectra, which report on the rotational dynamics of the molecular electric dipole moments. The analysis consists of calculating spectral density functions (SDFs) of the magnetic dipole–dipole interaction between the electron spin of TEMPOL and nuclear spins of the solvent protons. Here, MD simulations are used in combination with an analytically tractable model of molecular motion. While the former provide detailed information at relatively short spin–spin distances, the latter includes contributions at large separations, all the way to infinity. The relaxivities calculated from the SDFs of acetone and DMSO are in excellent agreement with experiments at 9.2 T. For DMSO we calculate a coupling factor in agreement with experiment while for acetone we predict a value that is larger by almost 50%, suggesting a possibility for experimental improvement.

Item Type:Article
Subjects:Q Science > QD Chemistry > QD450-801 Physical and theoretical chemistry
ID Code:27995
Deposited By:Deniz Sezer
Deposited On:19 Dec 2015 21:18
Last Modified:19 Dec 2015 21:18

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