Enhancing NMR Sensitivity of Natural‐Abundance Low‐γ Nuclei by Ultrafast Magic‐Angle‐Spinning Solid‐State NMR Spectroscopy

Zhang, Rongchun; Chen, Yitian; Rodrı́guez-Hornedo, Naı́r; Ramamoorthy, Ayyalusamy

doi:10.1002/cphc.201600637

Cited by 33 publications

(33 citation statements)

References 92 publications

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“…However, as we recently demonstrated, an incorporation of multiple-contact CP could significantly enhance the sensitivity of 2D proton-detected 13 C/ 1 H HETCOR experiment; the achieved signal enhancement is more impressive when natural-abundance 13 C spectrum is directly recorded. 52 …”

Section: D Experiments For Higher Resolution and Spectral Editingmentioning

confidence: 99%

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

2017

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CONSPECTUS Protons are vastly abundant in a wide range of exciting macromolecules and thus can be a powerful probe to investigate the structure and dynamics at atomic resolution using solid-state NMR (ssNMR) spectroscopy. Unfortunately, the high signal sensitivity, afforded by the high natural-abundance and high gyromagnetic ratio of protons, is greatly compromised by severe line broadening due to the very strong 1H–1H dipolar couplings. As a result, protons are rarely used, in spite of the desperate need for enhancing the sensitivity of ssNMR to study a variety of systems that are not amenable for high resolution investigation using other techniques including X-ray crystallography, cryo-electron microscopy, and solution NMR spectroscopy. Thanks to the remarkable improvement in proton spectral resolution afforded by the significant advances in magic-angle-spinning (MAS) probe technology, 1H ssNMR spectroscopy has recently attracted considerable attention in the structural and dynamics studies of various molecular systems. However, it still remains a challenge to obtain narrow 1H spectral lines, especially from proteins, without resorting to deuteration. In this Account, we review recent proton-based ssNMR strategies that have been developed in our laboratory to further improve proton spectral resolution without resorting to chemical deuteration for the purposes of gaining atomistic-level insights into molecular structures of various crystalline solid systems, using small molecules and peptides as illustrative examples. The proton spectral resolution enhancement afforded by the ultrafast MAS frequencies up to 120 kHz is initially discussed, followed by a description of an ensemble of multidimensional NMR pulse sequences, all based on proton detection, that have been developed to obtain in-depth information from dipolar couplings and chemical shift anisotropy (CSA). Simple single channel multidimensional proton NMR experiments could be performed to probe the proximity of protons for structure determination using 1H–1H dipolar couplings and to evaluate the changes in chemical environments as well as the relative orientation to the external magnetic field using proton CSA. Due to the boost in signal sensitivity enabled by proton detection under ultrafast MAS, by virtue of high proton natural abundance and gyromagnetic ratio, proton-detected multidimensional experiments involving low-γ nuclei can now be accomplished within a reasonable time, while the higher dimension also offers additional resolution enhancement. In addition, the application of proton-based ssNMR spectroscopy under ultrafast MAS in various challenging and crystalline systems is also presented. Finally, we briefly discuss the limitations and challenges pertaining to proton-based ssNMR spectroscopy under ultrafast MAS conditions, such as the presence of high-order dipolar couplings, friction-induced sample heating, and limited sample volume. Although there are still a number of challenges that must be circumvented by further developments in radio freq...

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Section: D Experiments For Higher Resolution and Spectral Editingmentioning

confidence: 99%

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

2017

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“…Therefore, we used the recently introduced technique of cross-polarization by multiple contact periods (multiCP) 31 to obtain quantitative 13 C NMR spectra with good sensitivity and which are independent of T 1ρH . This technique has already been applied with success to pharmaceuticals 32 and wood materials. 33 It has also been used to measure the crystallinity index of cellulose in bagasse samples by using spectral editing to remove lignin signals.…”

Section: ■ Introductionmentioning

confidence: 99%

Measuring the Purity of Chitin with a Clean, Quantitative Solid-State NMR Method

King

Stein

Shamshina

et al. 2017

ACS Sustainable Chem. Eng.

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Chitin is a versatile biopolymer which can be extracted directly from biomass and used for the preparation of high value materials, but such materials often require high-purity chitin. However, complete removal of proteinaceous material from chitin, which is obtained from biomass sources, can be difficult to determine. Here we report a quick, nondestructive method to measure chitin content using solid-state multiCP 13C NMR, which requires only 105 min and allows for recovery of the sample. A calibration curve was constructed from spectra of mass-based mixtures of commercial chitin and bovine serum albumin protein. This allowed for the quantification of chitin content (and therefore purity) in both chitinous biomass and extracted chitin samples in a quick, clean, nondestructive manner that agreed with measurements made by the method of Black and Schwartz, within the error of each of the methods.

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“…However, the use of residual proton magnetization is much more challenging due to its short T1 and T1r, but greatly beneficial for the signal enhancement of low-g nuclei as demonstrated by our work here and previous studies. [55,77]…”

Section: Resultsmentioning

confidence: 99%

Exploiting heterogeneous time scale of dynamics to enhance 2D HETCOR solid-state NMR sensitivity

Zhang

Nishiyama

Ramamoorthy

2019

Journal of Magnetic Resonance

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Multidimensional solid-state NMR spectroscopy plays a significant role in offering atomic-level insights into molecular systems. In particular, heteronuclear chemical shift correlation (HETCOR) experiments could provide local chemical and structural information in terms of spatial heteronuclear proximity and through-bond connectivity. In solid state, the transfer of magnetization between heteronuclei, a key step in HETCOR experiments, is usually achieved using cross-polarization (CP) or INEPT (insensitive nuclei enhanced by polarization transfer) depending on the sample characteristics and magic-angle-spinning (MAS) frequency. But, for a multiphase system constituting molecular components that differ in their time scales of mobilities, CP efficiency is pretty low for mobile components because of the averaging of heteronuclear dipolar couplings whereas INEPT is inefficient due to the short T2 of immobile components and can be non-selective due to strong proton spin diffusion for immobile components especially under moderate spinning speeds. Herein, in this study we present two 2D pulse sequences that enable the sequential acquisition of 13 C/ 1 H HETCOR NMR spectra for the rigid and mobile components by taking full advantage of the abundant proton magnetization in a single experiment with barely increasing the overall experimental time. In particular, the 13 C-detected HETCOR experiment could be applied under slow MAS conditions, where a multiple-pulse sequence is typically employed to enhance 1 H spectral resolution in the indirect dimension. In contrast, the 1 H-detected HETCOR experiment should be applied under ultrafast MAS, where CP and transient heteronuclear nuclear Overhauser effect (NOE) polarization transfer are combined to enhance 13 C signal intensities for mobile components. These pulse sequences are experimentally demonstrated on two model systems .

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Enhancing NMR Sensitivity of Natural‐Abundance Low‐γ Nuclei by Ultrafast Magic‐Angle‐Spinning Solid‐State NMR Spectroscopy

Cited by 33 publications

References 92 publications

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

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

Measuring the Purity of Chitin with a Clean, Quantitative Solid-State NMR Method

Exploiting heterogeneous time scale of dynamics to enhance 2D HETCOR solid-state NMR sensitivity

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