Solid-state NMR backbone chemical shift assignments of α-synuclein amyloid fibrils at fast MAS regime.

The α-synuclein (α-syn) amyloid fibrils are involved in various neurogenerative diseases. Solid-state NMR (ssNMR) has been showed as a powerful tool to study α-syn aggregates. Here, we report the H, C and N back-bone chemical shifts of a new α-syn polymorph obtained using proton-detected ssNMR spectroscopy under fast (95 kHz) magic-angle spinning conditions.

Development of in situ high resolution NMR: Proof-of-principle for a new (spinning) cylindrical mini-pellet approach applied to a Lithium ion battery.

Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is a powerful technique for characterizing the local structure and dynamics of battery and other materials. It has been widely used to investigate bulk electrode compounds, electrolytes, and interfaces. Beside common ex situ investigations, in situ and operando techniques have gained considerable importance for understanding the reaction mechanisms and cell degradation of electrochemical cells.

High and fast: NMR protein-proton side-chain assignments at 160 kHz and 1.2 GHz.

The NMR spectra of side-chain protons in proteins provide important information, not only about their structure and dynamics, but also about the mechanisms that regulate interactions between macromolecules. However, in the solid-state, these resonances are particularly difficult to resolve, even in relatively small proteins. We show that magic-angle-spinning (MAS) frequencies of 160 kHz, combined with a high magnetic field of 1200 MHz proton Larmor frequency, significantly improve their spectral resolution.

NMR Assignment of Methyl Groups in Immobilized Proteins Using Multiple-Bond C Homonuclear Transfers, Proton Detection, and Very Fast MAS.

In nuclear magnetic resonance spectroscopy of proteins, methyl protons play a particular role as extremely sensitive reporters on dynamics, allosteric effects, and protein-protein interactions, accessible even in high-molecular-weight systems approaching 1 MDa. The notorious issue of their chemical shift assignment is addressed here by a joint use of solid-state H-detected methods at very fast (nearly 100 kHz) magic-angle spinning, partial deuteration, and high-magnetic fields. The suitability of a series of RF schemes is evaluated for the efficient coherence transfer across entire C side chains of methyl-containing residues, which is key for establishing connection between methyl and backbone H resonances.

Faster magic angle spinning reveals cellulose conformations in woods.

We present a first report on the detection of three different C6 conformers of cellulose in spruce, as revealed by solid-state 1H-13C correlation spectra. The breakthrough in 1H resolution is achieved by magic-angle spinning in the regime of 150 kHz. The suppression of dense dipolar network of 1H provides inverse detected 13C spectra at a good sensitivity even in natural samples.

Selectively Enhanced H-H Correlations in Proton-Detected Solid-State NMR under Ultrafast MAS Conditions.

Proton-detected solid-state NMR has emerged as a powerful analytical technique in structural elucidation via H-H correlations, which are mostly established by broadband methods. We propose a new class of frequency-selective homonuclear recoupling methods to selectively enhance H-H correlations of interest under ultrafast magic-angle spinning (MAS). These methods, dubbed as selective phase-optimized recoupling (SPR), can provide a sensitivity enhancement by a factor of ∼3 over the widely used radio-frequency-driven recoupling (RFDR) to observe H-H contacts in a protonated tripeptide -formyl-Met-Leu-Phe (fMLF) under 150 kHz MAS and are successfully utilized to probe a long-range H-H contact in a pharmaceutical molecule, the hydrochloride form of pioglitazone (PIO-HCl).

Protein NMR Spectroscopy at 150 kHz Magic-Angle Spinning Continues To Improve Resolution and Mass Sensitivity.

Spectral resolution is the key to unleashing the structural and dynamic information contained in NMR spectra. Fast magic-angle spinning (MAS) has recently revolutionized the spectroscopy of biomolecular solids. Herein, we report a further remarkable improvement in the resolution of the spectra of four fully protonated proteins and a small drug molecule by pushing the MAS rotation frequency higher (150 kHz) than the more routinely used 100 kHz.

Screening of Nutraceuticals and Plant Extracts for Inhibition of Amyloid-β Fibrillation.

Fluorescence spectroscopy for in vitro amyloid-β (Aβ) fibrillation diagnosis and spectral fluorescence signature for the identification of bioactive compounds were applied to study traditional Ayurvedic nutraceuticals - Brahmi, Ashwagandha, Shanka pushpi, and Gotu kola - as well as their plant extracts for possible treatment of Alzheimer's disease. All samples manifest as inhibitors on three different variants of the Aβ peptide: methionine Aβ1-40, Aβ1-40, and Aβ1-42. The main compounds within the nutraceuticals were identified.

Quantifying proton NMR coherent linewidth in proteins under fast MAS conditions: a second moment approach.

Proton detected solid-state NMR under fast magic-angle-spinning (MAS) conditions is currently redefining the applications of solid-state NMR, in particular in structural biology. Understanding the contributions to the spectral linewidth is thereby of paramount importance. When disregarding the sample-dependent inhomogeneous contributions, the NMR proton linewidth is defined by homogeneous broadening, which has incoherent and coherent contributions.

H-MAS.

We characterize a new generation of MAS probes, designed for 1H detection in solid and viscous structures. High top speed (currently 170 kHz), existence of a wide speed range and quick acceleration enable numerous new experiment categories. Most notably, massive biomolecular structures become amenable to a detailed structural and dynamics studies.

Spinning faster: protein NMR at MAS frequencies up to 126 kHz.

We report linewidth and proton T, T and T' relaxation data of the model protein ubiquitin acquired at MAS frequencies up to 126 kHz. We find a predominantly linear improvement in linewidths and coherence decay times of protons with increasing spinning frequency in the range from 93 to 126 kHz. We further attempt to gain insight into the different contributions to the linewidth at fast MAS using site-specific analysis of proton relaxation parameters and present bulk relaxation times as a function of the MAS frequency.

Medical Plants and Nutraceuticals for Amyloid-β Fibrillation Inhibition.

Plaque formation due to amyloid-β oligomerization and fibrillation is a key issue for its deposition in the brains of dementia and Alzheimer's disease patients. Related drugs preventing this peptide fibril accumulation bear the potential of considerable medical and social value. In this study, we performed fibrillation inhibition tests with eight different medical plant extracts and nutraceuticals using fluorescence spectroscopy.

Preparation of fibril nuclei of beta-amyloid peptides in reverse micelles.

We report the preparation of protofibrils from oligomeric Aβ40 aggregates, which have been incubated under spatially constrained conditions. The molecular structure of the resultant protofibrils is highly homogeneous, suggesting that the phenomenon of structural polymorphism commonly observed in Aβ40 fibrils may be largely due to multiple nucleation events.

H line width dependence on MAS speed in solid state NMR - Comparison of experiment and simulation.

Recent developments in magic angle spinning (MAS) technology permit spinning frequencies of ≥100 kHz. We examine the effect of such fast MAS rates upon nuclear magnetic resonance proton line widths in the multi-spin system of β-Asp-Ala crystal. We perform powder pattern simulations employing Fokker-Plank approach with periodic boundary conditions and H-chemical shift tensors calculated using the bond polarization theory.

Characterization of Protein-Protein Interfaces in Large Complexes by Solid-State NMR Solvent Paramagnetic Relaxation Enhancements.

Solid-state NMR is becoming a viable alternative for obtaining information about structures and dynamics of large biomolecular complexes, including ones that are not accessible to other high-resolution biophysical techniques. In this context, methods for probing protein-protein interfaces at atomic resolution are highly desirable. Solvent paramagnetic relaxation enhancements (sPREs) proved to be a powerful method for probing protein-protein interfaces in large complexes in solution but have not been employed toward this goal in the solid state.

Protein resonance assignment at MAS frequencies approaching 100 kHz: a quantitative comparison of J-coupling and dipolar-coupling-based transfer methods.

We discuss the optimum experimental conditions to obtain assignment spectra for solid proteins at magic-angle spinning (MAS) frequencies around 100 kHz. We present a systematic examination of the MAS dependence of the amide proton T 2' times and a site-specific comparison of T 2' at 93 kHz versus 60 kHz MAS frequency. A quantitative analysis of transfer efficiencies of building blocks, as they are used for typical 3D experiments, was performed.

Solid-state NMR of a protein in a precipitated complex with a full-length antibody.

NMR spectroscopy is a prime technique for characterizing atomic-resolution structures and dynamics of biomolecular complexes but for such systems faces challenges of sensitivity and spectral resolution. We demonstrate that the application of (1)H-detected experiments at magic-angle spinning frequencies of >50 kHz enables the recording, in a matter of minutes to hours, of solid-state NMR spectra suitable for quantitative analysis of protein complexes present in quantities as small as a few nanomoles (tens of micrograms for the observed component). This approach enables direct structure determination and quantitative dynamics measurements in domains of protein complexes with masses of hundreds of kilodaltons.

De novo 3D structure determination from sub-milligram protein samples by solid-state 100 kHz MAS NMR spectroscopy.

Solid-state NMR spectroscopy is an emerging tool for structural studies of crystalline, membrane-associated, sedimented, and fibrillar proteins. A major limitation for many studies is still the large amount of sample needed for the experiments, typically several isotopically labeled samples of 10-20 mg each. Here we show that a new NMR probe, pushing magic-angle sample rotation to frequencies around 100 kHz, makes it possible to narrow the proton resonance lines sufficiently to provide the necessary sensitivity and spectral resolution for efficient and sensitive proton detection.

Correlations between lithium local structure and electrochemistry of layered LiCo(1-2x)Ni(x)Mn(x)O2 oxides: 7Li MAS NMR and EPR studies.

Advanced (7)Li MAS NMR technologies and high frequency EPR are combined to identify structural motifs and their relation to electrochemical properties of layered lithium-cobalt-nickel-manganese oxides LiCo1-2xNixMnxO2 (0 < x ≤ 0.5) used as cathode materials in lithium ion batteries. Structural-chemical shift regularities were established by systematic variation of the ratio of diamagnetic Co(3+) to paramagnetic Ni/Mn ions with variable valences.

Ultra-high resolution 17O solid-state NMR spectroscopy of biomolecules: a comprehensive spectral analysis of monosodium L-glutamate·monohydrate.

Monosodium L-glutamate monohydrate, a multiple oxygen site (eight) compound, is used to demonstrate that a combination of high-resolution solid-state NMR spectroscopic techniques opens up new possibilities for (17)O as a nuclear probe of biomolecules. Eight oxygen sites have been resolved by double rotation (DOR) and multiple quantum (MQ) NMR experiments, despite the (17)O chemical shifts lying within a narrow shift range of <50 ppm. (17)O DOR NMR not only provides high sensitivity and spectral resolution, but also allows a complete set of the NMR parameters (chemical shift anisotropy and electric-field gradient) to be determined from the DOR spinning-sideband manifold.

Spin diffusion driven by R-symmetry sequences: applications to homonuclear correlation spectroscopy in MAS NMR of biological and organic solids.

We present a family of homonuclear (13)C-(13)C magic angle spinning spin diffusion experiments, based on R2(n)(v) (n = 1 and 2, v = 1 and 2) symmetry sequences. These experiments are well suited for (13)C-(13)C correlation spectroscopy in biological and organic systems and are especially advantageous at very fast MAS conditions, where conventional PDSD and DARR experiments fail. At very fast MAS frequencies the R2(1)(1), R2(2)(1), and R2(2)(2) sequences result in excellent quality correlation spectra both in model compounds and in proteins.

Longer-range distances by spinning-angle-encoding solid-state NMR spectroscopy.

A new spinning-angle-encoding spin-echo solid-state NMR approach is used to accurately determine the dipolar coupling corresponding to a C-C distance over 4 Å in a fully labelled dipeptide. The dipolar coupling dependent spin-echo modulation was recorded off magic angle, switching back to the magic angle for the acquisition of the free-induction decay, so as to obtain optimum sensitivity. The retention of both ideal resolution and long-range distance sensitivity was achieved by redesigning a 600 MHz HX MAS NMR probe to provide fast angle switching during the NMR experiment: for 1.

High-resolution 17O double-rotation NMR characterization of ring and non-ring oxygen in vitreous B2O3.

The application of double rotation (DOR) NMR to crystalline materials (both inorganic and organic) has made tremendous strides in providing site-specific information about materials in recent years. However (17)O DOR has yet to demonstrate its potential in disordered materials such as glasses. In the present study, we have successfully recorded high resolution (17)O DOR spectra of vitreous B(2)O(3) (v-B(2)O(3)), a highly effective glass-forming oxide of considerable technological importance.

(17)O DOR and other solid-state NMR studies concerning the basic properties of zeolites LSX.

We demonstrate complementary (1)H, (17)O, (27)Al and (29)Si measurements for basic low-silica-X zeolites, which were unloaded and pyrrole and formic acid-loaded. It was found that the acid-base-system is not stabile, if the loading exceeds one pyrrole molecule or two formic acid molecules per supercage.(17)O DOR NMR spectra exhibit at least four lines, which are broadened by a distribution of chemical shifts in a similar extend as the (29)Si MAS NMR spectra are broadened by distribution of Si-O-Al angles.