Since the first pioneering studies on small deuterated peptides dating more than 20 years ago, 1H detection has evolved into the most efficient approach for investigation of biomolecular structure, dynamics, and interactions by solid-state NMR. The development of faster and faster magic-angle spinning (MAS) rates (up to 150 kHz today) at ultrahigh magnetic fields has triggered a real revolution in the field. This new spinning regime reduces the 1H–1H dipolar couplings, so that a direct detection of 1H signals, for long impossible without proton dilution, has become possible at high resolution. The switch from the traditional MAS NMR approaches with 13C and 15N detection to 1H boosts the signal by more than an order of magnitude, accelerating the site-specific analysis and opening the way to more complex immobilized biological systems of higher molecular weight and available in limited amounts. This paper reviews the concepts underlying this recent leap forward in sensitivity and resolution, presents a detailed description of the experimental aspects of acquisition of multidimensional correlation spectra with fast MAS, and summarizes the most successful strategies for the assignment of the resonances and for the elucidation of protein structure and conformational dynamics. It finally outlines the many examples where 1H-detected MAS NMR has contributed to the detailed characterization of a variety of crystalline and noncrystalline biomolecular targets involved in biological processes ranging from catalysis through drug binding, viral infectivity, amyloid fibril formation, to transport across lipid membranes.

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In this work, we compared two methods (incipient wetness and melting) for the encapsulation of ibuprofen in the pores of Mobil Crystalline Material 41 (MCM-41) through NMR (nuclear magnetic resonance) spectroscopy. (1)H NMR spectra were recorded under very fast MAS (sample spinning 60 kHz) conditions in both 1D and 2D mode (NOESY sequence). We also performed (13)C cross-polarization magic angle spinning (CP/MAS) experiments, (13)C single pulse experiments (SPE), and (1)H-(13)C HSQC HR/MAS (heteronuclear single quantum coherence high resolution) HR/MAS correlations. Evaluation of the encapsulation methods included an analysis of the filling factor of the drug into the pores. The stability of Ibu/MCM in an environment of ethanol or water vapor was tested. Our study showed that melting a mixture of Ibu and MCM is a much more efficient method of confining the drug in the pores compared to incipient wetness. The optimal experiments for the former method achieved a filling factor of approximately 60%. We concluded that the major limitation to the applicability of the incipient wetness method (filling factor ca. 20%) is the high affinity of solvent (typically ethanol) for MCM-41. We found that even ethanol vapor can remove Ibu from the pores. When a sample of Ibu/MCM was stored for a few hours in a closed vessel with ethanol vapor, Ibu was transported from the pores to the outer walls of MCM. We observed a similar phenomenon with water vapor, although this process is slower compared to the analogous procedure using ethanol. Our study clearly demonstrates that existing methods used to encapsulate drugs in mesoporous silica nanoparticles (MSNs) require reevaluation.

Thanks to magic-angle spinning (MAS) probes with frequencies of 60-100 kHz, the benefit of high sensitivity 1 H detection can now be broadly realized in biomolecular solid-state NMR for the analysis of microcrystalline, sedimented, or lipid-embedded preparations. Nonetheless, performing the assignment of all resonances remains a rate-limiting step in protein structural studies, and even the latest optimized protocols fail to perform this step when the protein size exceeds ~20 kDa. Here we leverage the benefits of fast (100 kHz) MAS and high (800 MHz) magnetic fields to design an approach that lifts this limitation. Through the creation, conservation and acquisition of independent magnetization pathways within a single triple-resonance MAS NMR experiment, a single self-consistent dataset can be acquired, providing enhanced sensitivity, reduced vulnerability to machine or sample instabilities, and highly redundant linking that supports fully-automated peak picking and resonance assignment. The method, dubbed RAVASSA (Redundant Assignment Via A Single Simultaneous Acquisition), is demonstrated with the assignment of the largest protein to date in the solid state, the 42.5 kDa maltose binding protein, using a single fully protonated microcrystalline sample and one week of spectrometer time.

Recent progress in solid-state (SS)NMR spectroscopic methods based on fast magic angle spinning (MAS) [1] has enabled new opportunities for the structural study of small quantities (< 5 mg) of natural abundance samples. Utilizing throughspace and through-bond polarization transfer, indirect detection of low-g nuclei, and suitable homo-and heteronuclear decoupling, one-and two-dimensional (1D and 2D) spectra of such samples can be measured with excellent sensitivity and resolution.[2] However, determination of the short-range intermolecular order often remains elusive. Such analyses can be well-served by studying heteronuclear correlations that take advantage of the large chemical shift range of most low-g nuclei (for example, 13 C or 15 N). Indeed, heteronuclear correlation (HETCOR) NMR spectroscopy and measurements of internuclear distances, often in concert with theoretical calculations, have provided structural details of complex hydrogen-bonded systems in chemistry and biology, blended materials, and host-guest pairs.[3] Still, intermolecular polarization transfers to low-g nuclei are often hampered by low sensitivity. A promising solution to this challenge is offered by homonuclear 1 H-1 H 2D correlation methods, such as double-quantum (DQ)MAS [4] or spin-diffusion (NOESYlike) experiments, [5] provided that sufficient resolution is achieved in both dimensions. One of the possible approaches is the use of 1 H CRAMPS decoupling in concert with fast MAS to boost resolution in these experiments.[6] The recent development of ultrafast MAS (at 100 kHz and more [7] ) provides access to appropriate 1 H resolution without RF decoupling.Herein, we report the first application of 1 H 2D SSNMR measurements under MAS at 100 kHz, which are used in combination with indirectly detected 1 H{ 13 C} and 1 H{ 15 N} HETCOR experiments and theoretical calculations to scrutinize the interactions within a host-guest (HG) system consisting of 5,10,15-tris(pentafluorophenyl)corrole 1, and toluene (Scheme 1).Corroles are aromatic macrocycles composed of four pyrrolic rings connected by three meso carbons and bearing one direct pyrrole-pyrrole link. The first synthesis of these materials was a multi-step process with low overall yield.[8] As synthetic methods have improved, there has been increased interest in potential applications of corroles in catalysis, sensors, imaging, and medicinal chemistry.[9] The coordination chemistry of corroles has attracted particular attention, and new metal-corrole systems possessing intriguing properties are being continuously reported.[10] Studies of solid-state structures of corroles and their interactions with other aromatic compounds pose challenges for diffraction and spectroscopic methods. Owing to the difficulties involved in growing X-ray quality crystals of the corroles, which tend to form disordered host(corrole)-guest(solvent) systems, only a few X-ray structures of unsubstituted metal-free corrole have been published to date, including that of corrole 1.[11]Herein, we present the results ...

We report a new multidimensional magic angle spinning NMR methodology, which provides an accurate and detailed probe of molecular motions occurring on timescales of nano- to microseconds, in sidechains of proteins. The approach is based on a 3D CPVC-RFDR correlation experiment recorded under fast MAS conditions (νR = 62 kHz), where 13C-1H CPVC dipolar lineshapes are recorded in a chemical shift resolved manner. The power of the technique is demonstrated in model tripeptide Tyr-(D)Ala-Phe and two nanocrystalline proteins, GB1 and LC8. We demonstrate that, through numerical simulations of dipolar lineshapes of aromatic sidechains, their detailed dynamic profile, i.e., the motional modes, is obtained. In GB1 and LC8 the results unequivocally indicate that a number of aromatic residues are dynamic, and using quantum mechanical calculations, we correlate the molecular motions of aromatic groups to their local environment in the crystal lattice. The approach presented here is general and can be readily extended to other biological systems.

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Layered hybrid organic–inorganic perovskites such as the lead halide Ruddlesden–Popper (RP) series are solution-processable two-dimensional (2D) materials with tunable optoelectronic properties. Dynamic interactions between the ionic perovskite substructure and organic spacer cations impact optoelectronic properties relevant for device applications. Here, the static and dynamic structures of linear alkylammonium and aromatic spacers in lead iodide RP phases (n = 1) are characterized at ambient temperatures using solid-state NMR (ssNMR) spectroscopy and compared with previously reported crystal structures derived from X-ray diffraction. Rigid and flexible sites of spacers are distinguished by examining 13C­{1H} and 15N­{1H} cross-polarization magic-angle spinning (CP-MAS) signal intensity build-up. Different trends in site-specific rigidity are observed for short and long alkylammonium spacers. Short spacers (e.g., butylammonium) are attached by strong affinity interactions to lead iodide octahedra, whereas longer spacers (e.g., dodecylammonium) are more rigid within the RP interlayer than near the octahedral surface. Phenethylammonium and butylammonium spacers are similarly rigid, and we estimate that the local reorientation time scale of phenyl rings is 10–100 μs by 2D 13C CP-variable contact (CP-VC) experiments. These ssNMR results indicate that the interplay between spacer interactions with lead iodide octahedra (Coulombic and hydrogen-bonding) and van der Waals forces between spacers is responsible for a variety of site-specific dynamics and local structural distortions at intermediate time scales (microsecond to millisecond). This study demonstrates a general method to characterize nanoscale structures and site-specific dynamics that contribute to structural and electronic disorder in functional optoelectronic RP phases.