Accurate 1H-14N distance measurements by phase-modulated RESPDOR at ultra-fast MAS

t1-Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy

“…There is no appreciable gain in SNR with TONE when d aniso is 1 ppm or when s MAS is close to zero. However, the SNR with the TONE sequence is predicted to increase by a factor 2-8 when d aniso is 17 The TONE D-HMQC pulse sequences were experimentally tested for 1 H detection of a variety of NMR active nuclei including 35 Cl, 25 Mg, 13 C and 17 O. Fig.…”

“…3 shows experimental data acquired with the different D-HMQC pulse sequences on 35 Cl traces extracted from 2D 1 H{ 35 Cl} spectra at 1 H d iso = 12.7 ppm for the five pulse sequences in order (top to bottom). Sensitivity (S), defined as the SNR per square root of unit time, is provided for all 35 Cl traces in units of min À1/2 . The 2D spectra were processed with the same contour floor level to aid the visual comparison of signal and noise.…”

“…The relative intensity of the 1 H signals at 9.0 ppm and 12.7 ppm are indicated. The 35 Cl spectra shown in Fig. 3F-J were extracted from the most intense column (the ammonium signal at d iso = 9.0 ppm) of the corresponding 2D D-HMQC spectra (Fig.…”

“…27,28,30,31 Recently, random signal fluctuations observed in 1 H{ 14 N} RESPDOR experiments have also been attributed to MAS instability. 35 Generally, the strategies such as spin-lock trim pulses, 36 BIRD filters 37,38 or pulsed field gradients 39 often used to suppress t 1 -noise in HMQC solution NMR experiments are either incompatible with existing pulse sequences, or simply cannot be implemented with current SSNMR probes. A number of t 1 sampling and processing techniques have been proposed to reduce t 1 -noise in solution NMR experiments.…”

“…TONE D-HMQC sequences minimize t 1 -noise by refocusing 1 H CSA after each recoupling block to reduce the variation of the NMR signal intensity with MAS frequency fluctuations and by reducing (saturating) signals from uncorrelated magnetization. The TONE D-HMQC sequences are shown to provide enhanced sensitivity for proton detected D-HMQC experiments with a wide range of spin-1/2 and half-integer quadrupolar nuclei such as 13 C, 17 O, 25 Mg, 27 Al and 35 Cl.…”