title: Rotational resonance NMR: separation of dipolar coupling and zero quantum relaxation.
abstract: The solid state NMR technique of rotational resonance (R2) has been used extensively to measure distances approaching 5-6 A between 13C nuclei in a variety of compounds including amyloidogenic peptides and membrane proteins. The accuracy of the distance information extracted from the time-dependent spin dynamics at R2 is often limited by the accuracy with which the relevant zero-quantum lineshape parameters are estimated. Here we demonstrate that measurement of spinning frequency dependent magnetization exchange dynamics provides data from which both distance and zero-quantum relaxation parameters can be extracted independently. In addition to providing more accurate distance information, this technique allows examination of the zero-quantum lineshape, which can indicate the presence of correlated relaxation or chemical shift distributions between dipolar-coupled sites. With this approach we have separated the contribution of dipolar couplings and zero quantum relaxation to R2 exchange curves. Thus, we have significantly improved the accuracy of the measurement of the intramolecular, internuclear distances between a pair of 13C's in two model compounds (N-acetyl-D,L-valine and glycylglycine.HCl) that lie in the distance range 4.6-4.7 A.
authors.affiliation: Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 01239-4307, USA.
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Costa
authors.forename: Boqin
authors.initials: B
authors.lastname: Sun
authors.forename: Robert G
authors.initials: RG
authors.lastname: Griffin
mesh_terms: D002247:Carbon Isotopes; D003198:Computer Simulation; D006033:Glycylglycine / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011786:Quality Control; D011789:Quantum Theory; D012996:Solutions / Q000737:chemistry; D013113:Spin Labels; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D012996:Solutions; D013113:Spin Labels; D006033:Glycylglycine; D014633:Valine; C055589:N-acetylvaline