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Title: Mechanism of dilute-spin-exchange in solid-state NMR

Abstract

In the stationary, aligned samples used in oriented sample (OS) solid-state NMR, {sup 1}H-{sup 1}H homonuclear dipolar couplings are not attenuated as they are in magic angle spinning solid-state NMR; consequently, they are available for participation in dipolar coupling-based spin-exchange processes. Here we describe analytically the pathways of {sup 15}N-{sup 15}N spin-exchange mediated by {sup 1}H-{sup 1}H homonuclear dipolar couplings. The mixed-order proton-relay mechanism can be differentiated from the third spin assisted recoupling mechanism by setting the {sup 1}H to an off-resonance frequency so that it is at the “magic angle” during the spin-exchange interval in the experiment, since the “magic angle” irradiation nearly quenches the former but only slightly attenuates the latter. Experimental spectra from a single crystal of N-acetyl leucine confirm that this proton-relay mechanism plays the dominant role in {sup 15}N-{sup 15}N dilute-spin-exchange in OS solid-state NMR in crystalline samples. Remarkably, the “forbidden” spin-exchange condition under “magic angle” irradiation results in {sup 15}N-{sup 15}N cross-peaks intensities that are comparable to those observed with on-resonance irradiation in applications to proteins. The mechanism of the proton relay in dilute-spin-exchange is crucial for the design of polarization transfer experiments.

Authors:
Publication Date:
OSTI Identifier:
22253381
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 140; Journal Issue: 12; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COUPLINGS; IRRADIATION; LEUCINE; MONOCRYSTALS; NUCLEAR MAGNETIC RESONANCE; POLARIZATION; SOLIDS; SPECTRA; SPIN EXCHANGE

Citation Formats

Lu, George J., and Opella, Stanley J., E-mail: sopella@ucsd.edu. Mechanism of dilute-spin-exchange in solid-state NMR. United States: N. p., 2014. Web. doi:10.1063/1.4869345.
Lu, George J., & Opella, Stanley J., E-mail: sopella@ucsd.edu. Mechanism of dilute-spin-exchange in solid-state NMR. United States. https://doi.org/10.1063/1.4869345
Lu, George J., and Opella, Stanley J., E-mail: sopella@ucsd.edu. 2014. "Mechanism of dilute-spin-exchange in solid-state NMR". United States. https://doi.org/10.1063/1.4869345.
@article{osti_22253381,
title = {Mechanism of dilute-spin-exchange in solid-state NMR},
author = {Lu, George J. and Opella, Stanley J., E-mail: sopella@ucsd.edu},
abstractNote = {In the stationary, aligned samples used in oriented sample (OS) solid-state NMR, {sup 1}H-{sup 1}H homonuclear dipolar couplings are not attenuated as they are in magic angle spinning solid-state NMR; consequently, they are available for participation in dipolar coupling-based spin-exchange processes. Here we describe analytically the pathways of {sup 15}N-{sup 15}N spin-exchange mediated by {sup 1}H-{sup 1}H homonuclear dipolar couplings. The mixed-order proton-relay mechanism can be differentiated from the third spin assisted recoupling mechanism by setting the {sup 1}H to an off-resonance frequency so that it is at the “magic angle” during the spin-exchange interval in the experiment, since the “magic angle” irradiation nearly quenches the former but only slightly attenuates the latter. Experimental spectra from a single crystal of N-acetyl leucine confirm that this proton-relay mechanism plays the dominant role in {sup 15}N-{sup 15}N dilute-spin-exchange in OS solid-state NMR in crystalline samples. Remarkably, the “forbidden” spin-exchange condition under “magic angle” irradiation results in {sup 15}N-{sup 15}N cross-peaks intensities that are comparable to those observed with on-resonance irradiation in applications to proteins. The mechanism of the proton relay in dilute-spin-exchange is crucial for the design of polarization transfer experiments.},
doi = {10.1063/1.4869345},
url = {https://www.osti.gov/biblio/22253381}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 12,
volume = 140,
place = {United States},
year = {Fri Mar 28 00:00:00 EDT 2014},
month = {Fri Mar 28 00:00:00 EDT 2014}
}