View Single Post
  #1  
Unread 04-06-2014, 02:01 AM
nmrlearner's Avatar
nmrlearner nmrlearner is offline
Senior Member
 
Join Date: Jan 2005
Posts: 23,137
Points: 193,617, Level: 100
Points: 193,617, Level: 100 Points: 193,617, Level: 100 Points: 193,617, Level: 100
Level up: 0%, 0 Points needed
Level up: 0% Level up: 0% Level up: 0%
Activity: 50.7%
Activity: 50.7% Activity: 50.7% Activity: 50.7%
Last Achievements
Award-Showcase
NMR Credits: 0
NMR Points: 0
Downloads: 0
Uploads: 0
Default Mechanism of dilute-spin-exchange in solid-state NMR.

Mechanism of dilute-spin-exchange in solid-state NMR.

Mechanism of dilute-spin-exchange in solid-state NMR.

J Chem Phys. 2014 Mar 28;140(12):124201

Authors: Lu GJ, Opella SJ

Abstract
In the stationary, aligned samples used in oriented sample (OS) solid-state NMR, (1)H-(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 (15)N-(15)N spin-exchange mediated by (1)H-(1)H homonuclear dipolar couplings. The mixed-order proton-relay mechanism can be differentiated from the third spin assisted recoupling mechanism by setting the (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 (15)N-(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 (15)N-(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.


PMID: 24697432 [PubMed - in process]



More...
Reply With Quote


Did you find this post helpful? Yes | No