Proton assisted insensitive nuclei cross polarization

This Communication presents a solid-state NMR N-15-C-13 polarization transfer scheme applicable at high B-0 and high MAS frequencies, requiring moderate rf powers and mixing time (1-6 ms). The sequence, PAIN-CP, involves the abundant nearby protons in the heteronuclear recoupling dynamics and provides a new tool for obtaining long distance N-15-C-13 contacts. It should be of major interest for biomolecular structural studies

Spin dynamics in the modulation frame : application to homonuclear recoupling in magic angle spinning solid-state NMR

We introduce a family of solid-state NMR pulse sequences that generalizes the concept of second averaging in the modulation frame and therefore provides a new approach to perform magic angle spinning dipolar recoupling experiments. Here, we focus on two particular recoupling mechanisms-cosine modulated rotary resonance (CMpRR) and cosine modulated recoupling with isotropic chemical shift reintroduction (COMICS). The first technique, CMpRR, is based on a cosine modulation of the rf phase and yields broadband double-quantum (DQ) (13)C recoupling using > 70 kHz omega(1,C)/2 pi rf field for the spinning frequency omega(r)/2=10-30 kHz and (1)H Larmor frequency omega(0,H)/2 pi up to 900 MHz. Importantly, for p >= 5, CMpRR recouples efficiently in the absence of (1)H decoupling. Extension to lower p values (3.5 <= p < 5) and higher spinning frequencies is possible using low power (1)H irradiation (<0.25 omega(r)/2 pi). This phenomenon is explained through higher order cross terms including a homonuclear third spin assisted recoupling mechanism among protons. CMpRR mitigates the heating effects of simultaneous high power (13)C recoupling and (1)H decoupling. The second technique, COMICS, involves low power (13)C irradiation that induces simultaneous recoupling of the (13)C DQ dipolar and isotropic chemical shift terms. In contrast to CMpRR, where the DQ bandwidth (similar to 30 kHz at omega(0,H)/2 pi=750 MHz) covers the entire (13)C spectral width, COMICS recoupling, through the reintroduction of the isotropic chemical shift, is selective with respect to the carrier frequency, having a typical bandwidth of similar to 100 Hz. This approach is intended as a general frequency selective method circumventing dipolar truncation (supplementary to R(2) experiments). These new gamma-encoded sequences with attenuated rf requirements extend the applicability of homonuclear recoupling techniques to new regimes-high spinning and Larmor frequencies-and therefore should be of major interest for high resolution biomolecular studies. (C) 2008 American Institute of Physics

Heteronuclear proton assisted recoupling

We describe a theoretical framework for understanding the heteronuclear version of the third spin assisted recoupling polarization transfer mechanism and demonstrate its potential for detecting long-distance intramolecular and intermolecular (15)N-(13)C contacts in biomolecular systems. The pulse sequence, proton assisted insensitive nuclei cross polarization (PAIN-CP) relies on a cross term between (1)H-(15)N and (1)H-(13)C dipolar couplings to mediate zero-and/or double-quantum (15)N-(13)C recoupling. In particular, using average Hamiltonian theory we derive effective Hamiltonians for PAIN-CP and show that the transfer is mediated by trilinear terms of the form N(+/-)C(-/+)H(z) (ZQ) or N(+/-)C(-/+)H(z) (DQ) depending on the rf field strengths employed. We use analytical and numerical simulations to explain the structure of the PAIN-CP optimization maps and to delineate the appropriate matching conditions. We also detail the dependence of the PAIN-CP polarization transfer with respect to local molecular geometry and explain the observed reduction in dipolar truncation. In addition, we demonstrate the utility of PAIN-CP in structural studies with (15)N-(13)C spectra of two uniformly (13)C, (15)N labeled model microcrystalline proteins-GB1, a 56 amino acid peptide, and Crh, a 85 amino acid domain swapped dimer (MW = 2 x 10.4 kDa). The spectra acquired at high magic angle spinning frequencies (omega(r)/2 pi > 20 kHz) and magnetic fields (omega(0H)/2 pi = 700-900 MHz) using moderate rf fields, yield multiple long-distance intramonomer and intermonomer (15)N-(13)C contacts. We use these distance restraints, in combination with the available x-ray structure as a homology model, to perform a calculation of the monomer subunit of the Crh protein. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3541251

High-resolution solid-state NMR structure of a 17.6 kDa protein

The use of pseudocontact shifts arising from paramagnetic metal ions in a microcrystalline protein sample is proposed as a strategy to obtain unambiguous signal assignments in solid-state NMR spectra enabling distance extraction for protein structure calculation. With this strategy, 777 unambiguous (281 sequential, 217 medium-range, and 279 long-range) distance restraints could be obtained from PDSD, DARR, CHHC, and the recently introduced PAR and PAIN-CP solid-state experiments for the cobalt(II)substituted catalytic domain of matrix metalloproteinase 12 (159 amino acids, 17.6 kDa). The obtained structure is a high resolution one, with backbone rmsd of 1.0 +/- 0.2 angstrom, and is in good agreement with the X-ray structure (rmsd to X-ray 1.3 angstrom). The proposed strategy, which may be generalized for nonmetalloproteins with the use of paramagnetic tags, represents a significant step ahead in protein structure determination using solid-state NMR

Proton assisted recoupling and protein structure determination

We introduce a homonuclear version of third spin assisted recoupling, a second-order mechanism that can be used for polarization transfer between (13)C or (15)N spins in magic angle spinning (MAS) NMR experiments, particularly at high spinning frequencies employed in contemporary high field MAS experiments. The resulting sequence, which we refer to as proton assisted recoupling (PAR), relies on a cross-term between (1)H-(13)C (or (1)H-(15)N) couplings to mediate zero quantum (13)C-(13)C (or (15)N-(15)N recoupling). In particular, using average Hamiltonian theory we derive an effective Hamiltonian for PAR and show that the transfer is mediated by trilinear terms of the form C(1)(+/-)C(2)(-/+)H(Z) for (13)C-(13)C recoupling experiments (or N(1)(+/-)N(2)(-/+)H(Z) for (15)N-(15)N). We use analytical and numerical simulations to explain the structure of the PAR optimization maps and to delineate the PAR matching conditions. We also detail the PAR polarization transfer dependence with respect to the local molecular geometry and explain the observed reduction in dipolar truncation. Finally, we demonstrate the utility of PAR in structural studies of proteins with (13)C-(13)C spectra of uniformly (13)C, (15)N labeled microcrystalline Crh, a 85 amino acid model protein that forms a domain swapped dimer (MW=2x10.4 kDa). The spectra, which were acquired at high MAS frequencies (omega(r)2 pi>20 kHz) and magnetic fields (750-900 MHz (1)H frequencies) using moderate rf fields, exhibit numerous cross peaks corresponding to long (up to 6-7 A) (13)C-(13)C distances which are particularly useful in protein structure determination. Using results from PAR spectra we calculate the structure of the Crh protein

Solvent-derived defects suppress adsorption in MOF-74

Acknowledgements: This work is financially supported by National Natural Science Foundation of China (21922410, 22072133, 22275159, X.K.); Zhejiang Provincial Natural Science Foundation (LR19B050001, X.K.); Leading Innovation and Entrepreneurship Team of Zhejiang Province (2020R01003, X.K.); CEA ECC program (Programme Economie Circulaire du Carbone-Projet HyperCool NMR, G.D.P.), the French National Research Agency (CBH-EUR-GS and ARCANE ANR-17-EURE-0003, G.D.P.), the “Investissements d’avenir” program (ANR-15-IDEX-02, CDP-DefiCO2, G.D.P.) and the European Research Council Grant ERC-CoG-2015 (No. 682895, G.D.P.). US Department of Energy (DoE), Office of Science, Office of Basic Energy Sciences under award number (DE-SC0019992, J.R.L. and J.A.R.).AbstractDefects in metal-organic frameworks (MOFs) have great impact on their nano-scale structure and physiochemical properties. However, isolated defects are easily concealed when the frameworks are interrogated by typical characterization methods. In this work, we unveil the presence of solvent-derived formate defects in MOF-74, an important class of MOFs with open metal sites. With multi-dimensional solid-state nuclear magnetic resonance (NMR) investigations, we uncover the ligand substitution role of formate and its chemical origin from decomposed N,N-dimethylformamide (DMF) solvent. The placement and coordination structure of formate defects are determined by 13C NMR and density functional theory (DFT) calculations. The extra metal-oxygen bonds with formates partially eliminate open metal sites and lead to a quantitative decrease of N2 and CO2 adsorption with respect to the defect concentration. In-situ NMR analysis and molecular simulations of CO2 dynamics elaborate the adsorption mechanisms in defective MOF-74. Our study establishes comprehensive strategies to search, elucidate and manipulate defects in MOFs.</jats:p

Proton assisted recoupling at high spinning frequencies

We demonstrate the successful application of (13)C-(13)C proton assisted recoupling (PAR) on [U-(13)C,(15)N] N-f-MLF-OH and [U-(13)C,(15)N] protein GBI at high magic angle spinning (MAS) frequencies (omega(r)/2 pi = 65 kHz). Specifically, by combining PAR mixing with low power heteronuclear decoupling (omega(1H)/2(pi) similar to 16 kHz) and high spinning frequencies, we obtain high resolution 2D spectra displaying long-range (13)C-(13)C contacts from which distance estimates call be extracted. These experiments therefore demonstrate the possibility of performing high resolution Structural studies in the limit of high spinning frequency and low power (1)H decoupling, a regime which optimizes the resolution of protein samples and preserves their integrity

Pushing NMR sensitivity limits using dynamic nuclear polarization with closed-loop cryogenic helium sample spinning

International audienceWe report a strategy to push the limits of solid-state NMR sensitivity far beyond its current state-of-the-art. The approach relies on the use of dynamic nuclear polarization and demonstrates unprecedented DNP enhancement factors for experiments performed at sample temperatures much lower than 100 K, and can translate into 6 orders of magnitude of experimental time-savings. This leap-forward was made possible thanks to the employment of cryogenic helium as the gas to power magic angle sample spinning (MAS) for dynamic nuclear polarization (DNP) enhanced NMR experiments. These experimental conditions far exceed what is currently possible and allows currently reaching sample temperatures down to 30 K while conducting experiments with improved resolution (thanks to faster spinning frequencies, up to 25 kHz) and highly polarized nuclear spins. The impressive associated gains were used to hyperpolarize the surface of an industrial catalyst as well as to hyperpolarize organic nano-assemblies (self-assembling peptides in our case), for whom structures cannot be solved using diffraction techniques. Sustainable cryogenic helium sample spinning significantly enlarges the realm and possibilities of the MAS-DNP technique and is the route to transform NMR into a versatile but also sensitive atomic-level characterization tool