C 13 – 1 H dipolar-driven C13–13C recoupling without C13 rf irradiation in nuclear magnetic resonance of rotating solids

Abstract

Two recently proposed 13 C-13 C recoupling methods under magic angle spinning ͑MAS͒, resonant interference recoupling ͑RIR͒, and 13 C-1 H dipolar-assisted rotational resonance ͑DARR͒, are examined on a common theoretical foundation using the average Hamiltonian theory. In both methods, a rf field is applied on not 13 C but 1 H to recouple the 13 C-1 H dipolar interactions, and spectral overlap necessary to conserve energy for 13 C-13 C polarization transfer is achieved by the 13 C-1 H dipolar line broadening. While DARR employs time-independent 13 C-1 H interactions recoupled by suitable rf irradiation to 1 H spins, RIR uses time-dependent 13 C-1 H interactions modulated appropriately by 1 H rf irradiation. There are two distinct cases where 13 C-1 H line broadening realizes 13 C-13 C spectral overlap. For a pair of a carbonyl or aromatic carbon and an aliphatic carbon, spectral overlap can be achieved between one of the spinning sidebands of the former 13 C resonance and the 13 C-1 H dipolar powder pattern of the latter. On the other hand for a pair of spins with a small chemical shift difference, the two center bands are overlapped with each other due to 13 C-1 H dipolar broadening. For the former, we show that both RIR and DARR occur in the first order, while for the latter, DARR recoupling is appreciable for time-independent 13 C-1 H interactions. We refer to the former DARR as the first-order DARR recoupling and the latter as the second-order DARR. Experimentally, we examined the following 13 C-1 H recoupling methods for DARR: 1 H CW irradiation fulfilling a rotary-resonance condition or a modulatory-resonance condition, and 1 H pulses applied synchronously to MAS. For RIR, the FSLG-m2mm sequence is applied to 1 H. Several one-dimensional DARR and RIR experiments were done for N-acetyl͓1,2-13 C, 15 N͔ DL-valine, and ͓2,3-13 C͔ L-alanine. It was found that the polarization transfer rate for RIR is larger than that for DARR except for fast spinning, while the rate for DARR is less sensitive to the spinning speed. Further, we showed that the efficiency of the second-order DARR recoupling is not significantly less than that of the first-order DARR. Among the 13 C-1 H recoupling methods examined, CW irradiation at the nϭ1 rotary-resonance condition is superior for DARR because it gives a larger 13 C-1 H dipolar broadening, leading to broadband recoupling. We showed that a broadband-recoupling experiment with the first and the second-order DARR by CW irradiation at the nϭ1 rotary-resonance condition is applicable to signal assignment as well as structural determination of a multiply/uniformly 13 C labeled molecule as demonstrated by two-dimensional 13 C-13 C DARR polarization-transfer experiments of uniformly 13 C, 15 N-labeled glycylisoleucine.

Atomic-resolution structure of a disease-relevant Aβ(1–42) amyloid fibril

“…In a first trial, 13 C, 15 N-labeled Aβ(1-42) was fibrillized in phosphate buffer (condition 0, SI Appendix, Table S1). Many more cross-peaks than expected were observed in a 2D [ 13 C, 13 C] dipolar-assisted rotational resonance (DARR) NMR spectrum (32,33) as highlighted in Fig. 1A and SI Appendix, Fig.…”

Dipolar truncation in magic-angle spinning NMR recoupling experiments

“…2 69 We restricted our investigation to zeroth-order dipolar recoupling sequences that produce a zeroth-order recoupled dipolar Hamiltonian, which are the ones typically used to obtain accurate internuclear distance measurements. We specifically avoided the treatment of proton-driven spin diffusion, [70][71][72] DARR/RAD, [73][74][75] homonuclear TSAR 22,23 techniques and MIRROR 25 recoupling, which perform polarization transfer via higher-order mechanisms that are more tolerant to dipolar truncation effects in multiple-spin systems, as shown previously, 22,51 but typically yield ambiguous distance constraints due to the complexity of the mechanisms.…”

Statistical approach for solid-state NMR spectra of cellulose derived from a series of variable parameters

“…Dipolar-assisted rotational resonance (DARR) [10][11][12] 13 was performed with an echo time of 3.6 ms, a recycle delay of 3 s and a MAS frequency of 8 kHz. A total of 256 t 1 increments were collected for an f1 spectral width of 597.82 p.p.m.…”