Constant-time 2D and 3D through-bond correlation NMR spectroscopy of solids under 60 kHz MAS

Abstract

Establishing connectivity and proximity of nuclei is an important step in elucidating the structure and dynamics of molecules in solids using magic angle spinning (MAS) NMR spectroscopy. Although recent studies have successfully demonstrated the feasibility of proton-detected multidimensional solid-state NMR experiments under ultrafast-MAS frequencies and obtaining high-resolution spectral lines of protons, assignment of proton resonances is a major challenge. In this study, we first re-visit and demonstrate the feasibility of 2D constant-time uniform-sign cross-peak correlation (CTUC-COSY) NMR experiment on rigid solids under ultrafast-MAS conditions, where the sensitivity of the experiment is enhanced by the reduced spin-spin relaxation rate and the use of low radio-frequency power for heteronuclear decoupling during the evolution intervals of the pulse sequence. In addition, we experimentally demonstrate the performance of a proton-detected pulse sequence to obtain a 3D 1 H/ 13 C/ 1 H chemical shift correlation spectrum by incorporating an additional cross-polarization period in the CTUC-COSY pulse sequence to enable proton chemical shift evolution and proton detection in the incrementable t 1 and t 3 periods, respectively. In addition to through-space and through-bond 13 C/ 1 H and 13 C/ 13 C chemical shift correlations, the 3D 1 H/ 13 C/ 1 H experiment also provides a COSY-type 1 H/ 1 H chemical shift correlation spectrum, where only the chemical shifts of those protons, which are bonded to two neighboring carbons, are correlated. By extracting 2D F1/F3 slices ( 1 H/ 1 H chemical shift correlation spectrum) at different 13 C chemical shift frequencies from the 3D 1 H/ 13 C/ 1 H spectrum, resonances of proton atoms located close to a specific carbon atom can be identified. Overall, the through-bond and through-space homonuclear/heteronuclear proximities determined from the 3D 1 H/ 13 C/ 1 H experiment would be useful to study the structure and dynamics of a variety of chemical and biological solids. C 2016 AIP Publishing LLC. [http://dx

Proton-Based Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy

“…In addition, by incorporating constant-time 13 C chemical shift evolution into the pulse sequence, 1 H/ 1 H correlation among protons bonded to two neighboring carbons could also be obtained for further improving proton spectral resolution as well as resonance assignments. 31 …”

Proton-detected solid-state NMR spectroscopy of spin-1/2 nuclei with large chemical shift anisotropy

“…49 The trade-off between sensitivity and resolution is observed in many constant-time solid-state NMR experiments. [51][52][53][54][55][56] To demonstrate that AID D-HMQC is applicable for the indirect detection of a wide range of nuclei, we have performed 1 H{ 35 Cl} population transfer (PT) TONE D-HMQC-3 experiments with L-histidine⋅HCl⋅H2O. The addition of the AID t1-incrementation protocol did not introduce distortions in the second-order quadrupolar lineshape and resulted in improved sensitivity as compared to a constant-time experiment (Figure S2).…”

Quadrupolar Isotope-Correlation Spectroscopy in Solid-State NMR

“…Pulse-width calibrations were performed on solid RbBr: directly for 87 Rb and indirectly for 85 Rb, which was calibrated via its cross-polarization (CP) to 87 Rb. All used sequences relied on such 85 Rb → 87 Rb CPs and included either a 1D CP 27 , 28 with Carr–Purcell–Meiboom–Gill (CPMG) acquisition 29 − 33 or 2D constant-time 34 − 36 CP-CPMG with whole-echo acquisition for an absorptive line shape. 37 , 38 The phase-cycling used for the 1D CP-CPMG was as follows: ϕ 1 = x ,– x , ϕ 3 = y , ϕ 4 = x , x ,– x ,– x , y , y ,– y ,– y , ϕ 4 = x ,– x , x ,– x , y ,– y , y ,– y , and ϕ rec = ϕ 1 + ϕ 4 = x ,– x ,– x , x , y ,– y ,– y , y .…”