Efficient dipolar recoupling in the NMR of rotating solids. A sevenfold symmetric radiofrequency pulse sequence

Symmetry‐Based Pulse Sequences in Magic‐Angle Spinning Solid‐State NMR

“…For example, C = 270 0 180 180 90 0 is an amplitude-modulated basic element, while R = 90 −45 90 45 90 −45 is a phase-modulated basic element. In the case of amplitude-modulated basic elements, the rf Euler angles are given by (36) where ω nut is the amplitude of the rf field, expressed as a nutation frequency (180 • phase shifts may be taken into account by reversing the sign of ω nut ). The calculation of the scaling factor is more difficult if the basic element is phase modulated.…”

“…The original version of the C7 pulse sequence used the locallycompensated element C = 360 0 360 180 in a C7 1 2 symmetry scheme. 36 In this case, each of the double-quantum 'hot spots' at β rf = 90 • and β rf = 270 • are traversed twice during each element. The scaling factor of |κ 2122 | = 0.155 is almost the same as for the simple element C = 360 0 , which has |κ 2122 | = 0.157.…”

“…39 For example, although the symmetry C7 1 2 is compensated for rf amplitude errors to first order (in the case of amplitude-modulated basic elements), geometrical arguments show that the second-order rf error terms are large. 39 As a result, C7 1 2 sequences must usually be based on elements which have a built-in rf error compensation, such as the original element C = 360 0 360 180 , 36 or the "POST" element C = 90 0 360 180 270 0 . 37 In Ref.…”

“…The isotropic chemical shift terms are symmetry-allowed so the scaling factors of these terms must be set to zero by a suitable choice of the basic element C. Table 5 includes the symmetry C7 1 2 , which was initially demonstrated with the basic element C = 360 0 360 180 . 36 The 'POST' element C = 90 0 360 180 270 0 is more robust with respect to chemical shift offsets and is now favored. 37 The symmetry C14 5 4 allows operation at high spinning frequencies, if it is stabilized by the use of supercycles.…”

Application of REDOR subtraction for filtered MAS observation of labeled backbone carbons of membrane-bound fusion peptides

“…In samples labeled with two nearby homonuclei (e.g., 13 C separated by <5 A A), double-quantum MAS methods based on the homonuclear dipolar coupling have been developed which can filter out the natural abundance signal [15,[21][22][23][24]. Because only nearby 13 C- 13 C pairs are observed with these techniques, 13 C natural abundance www.academicpress.com nuclei are typically filtered by a factor of up to $100 relative to the labels.…”