A Study of Homonuclear Dipolar Recoupling Pulse Sequences in Solid-State Nuclear Magnetic Resonance

Abstract

Dipolar recoupling pulse sequences are of great importance in magic angle spinning solid-state NMR. Recoupling sequences are used for excitation of double-quantum coherence, which, in turn, is employed in experiments to estimate internuclear distances and molecular torsion angles. Much effort is spent on the design of recoupling sequences that are able to produce double-quantum coherence with high efficiency in demanding spin systems, i.e., spin systems with small dipole-dipole couplings and large chemical-shift anisotropies (CSAs). The sequence should perform robustly under a variety of experimental conditions. This paper presents experiments and computer calculations that extend the theory of double-quantum coherence preparation from the strong coupling/small CSA limit to the weak coupling limit. The performance of several popular dipole-dipole recoupling sequences-DRAWS, POST-C7, SPC-5, R1, and R2-are compared. It is found that the optimum performance for several of these sequences, in the weak coupling/large CSA limit, varies dramatically, with respect to the sample spinning speed, the magnitude and orientation of the CSAs, and the magnitude of dipole-dipole couplings. It is found that the efficiency of double-quantum coherence preparation by gamma-encoded sequences departs from the predictions of first-order theory. The discussion is supported by density-matrix calculations.

Theory and applications of supercycled symmetry-based recoupling sequences in solid-state nuclear magnetic resonance

“…3͑b͒. Similar problems with symmetry-based recouping sequences for the case of weak dipole-dipole couplings and large chemical shift terms were identified by Karlsson et al 43 Euler angles ͑degrees͒ relating the principal axis system of the CSA to the molecular reference frame. Table I, with a magnetic field of 9.4 T, a spinning frequency of 7 kHz, and a rf nutation frequency of 45.5 kHz.…”

“…23, 43 The work described in this paper shows that these disadvantages may be avoided by the con-struction of supercycles. Supercycles of the form S 0 S 0 ЈS Ј S are particularly useful.…”

Structure Determination of Membrane Proteins by NMR Spectroscopy

“…[165][166][167] A wide variety of pulse sequences that recouple the dipolar interactions that are averaged out by magic angle sample spinning are being implemented on proteins. 117,168,169 As described for solution NMR studies of membrane-associated peptides and proteins, 111,112 electron spin labels incorporated into specific sites, for example, on Cys side chains, enable distance-dependent line broadening to be used as a constraint for structure determination that is complementary to the orientation constraints available from the nuclear spin interactions alone.…”

Dipolar truncation in magic-angle spinning NMR recoupling experiments

“…In spite of the advances in pulse sequence design, the successful application of recoupling methods to the accurate measurement of 13 C- 13 C distance in macromolecules has typically been possible only when employing either specifically labeled spin-pair samples [26][27][28][29][30][31][32][33][34][35][36][37] or frequency-selective recoupling methods, [38][39][40][41][42][43][44][45][46][47] experiments in which a single internuclear distance is measured at a time. Although highly accurate ͑Ϯ5% is not difficult to achieve͒, both of these approaches are of limited practical utility in protein structure determinations that benefit from the availability of hundreds of constraints even for small proteins.…”