%0 Journal Article %1 lu_mechanism_2014 %A Lu, George J %A Opella, Stanley J %D 2014 %J J Chem Phys %K Bacteriophage Isotopes,Protons,Reference M13,Magnetic Proteins Resonance Spectroscopy,Nitrogen Standards,Viral %N 12 %P 124201 %R 10.1063/1.4869345 %T Mechanism of dilute-spin-exchange in solid-state \NMR\ %V 140 %X 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.

@article{lu_mechanism_2014, 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.}, added-at = {2017-03-14T02:48:56.000+0100}, author = {Lu, George J and Opella, Stanley J}, biburl = {https://www.bibsonomy.org/bibtex/2ffd5c431acebcc6f4fbf023af0a33f36/nmrresource}, doi = {10.1063/1.4869345}, interhash = {b3f944f44fe68bb5612f88dbb5d2729a}, intrahash = {ffd5c431acebcc6f4fbf023af0a33f36}, issn = {1089-7690}, journal = {J Chem Phys}, keywords = {Bacteriophage Isotopes,Protons,Reference M13,Magnetic Proteins Resonance Spectroscopy,Nitrogen Standards,Viral}, month = mar, number = 12, pages = 124201, pmid = {24697432}, timestamp = {2017-03-14T02:49:21.000+0100}, title = {{Mechanism of dilute-spin-exchange in solid-state {\{}NMR{\}}}}, volume = 140, year = 2014 }