Measurement of dipole-coupled lineshapes in a many-spin system by constant-time two-dimensional solid state NMR with high-speed magic-angle spinning

A two-dimensional solid state NMR technique for measurements of dipole-dipo le couplings in many-spin systems under high-speed magic-angle spinning (MA S) is described. The technique, called constant-time finite-pulse radiofreq uency-driven recoupling (fpRFDR-CT), uses the fpRFDR pulse sequence to gene rate non-zero effective homonuclear dipole-dipole couplings under high-spee d MAS that have the same operator symmetry as static dipole-dipole coupling s. By incorporating fpRFDR into a multiple-pulse cycle based on the Waugh-H uber-Haeberlen (WAHUHA) homonuclear decoupling cycle, a constant-time ti ev olution period is created. The constant-time tl period minimizes distortion s of the experimental data due to various pulse sequence imperfections. The fpRFDR-CT technique is demonstrated experimentally in C-13 NMR spectroscop y of carboxylate-labeled, polycrystalline L-alanine. 2D fpRFDRCT spectra co rrelate the dipole-coupled lineshape of the C-13 carboxylate groups with th eir isotropic chemical shift. Good agreement is obtained between the experi mental second and fourth moments of the dipole-coupled lineshapes and calcu lated moments based on the L-alanine crystal structure and an average Hamil tonian analysis of the fpRFDR sequence. Applications in structural investig ations of biologically relevant systems are anticipated. This technique ill ustrates many of the important concepts in modern multi-dimensional solid s tate NMR. (C) 2001 Elsevier Science B.V. All rights reserved.