Search

We discuss the optimum experimental conditions to obtain assignment spectra for solid proteins at magic-angle spinning (MAS) frequencies around 100kHz. 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 93kHz versus 60kHz MAS frequency. A quantitative analysis of transfer efficiencies of building blocks, as they are used for typical 3D experiments, was performed. To do this, we compared dipolar-coupling and J-coupling based transfer steps. The building blocks were then combined into 3D experiments for sequential resonance assignment, where we evaluated signal-to-noise ratio and information content of the different 3D spectra in order to identify the best assignment strategy. Based on this comparison, six experiments were selected to optimally assign the model protein ubiquitin, solely using spectra acquired at 93kHz MAS. Within 3days of instrument time, the required spectra were recorded from which the backbone resonances have been assigned to over 96%.

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)[subscript 3]Cl[subscript 3]][subscript 2]·NaCl·6H[subscript 2]O (en = ethylenediamine, C[subscript 2]H[subscript 8]N[subscript 2]) doped with Cr(III) in varying concentrations between 0.1 and 3 mol %. We demonstrate that [superscript 1]H, [superscript 13]C, and [superscript 59]Co can be polarized by irradiation of Cr(III) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(III) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins., National Institutes of Health (U.S.) (EB00280), National Institutes of Health (U.S.) (EB002026), German Science Foundation (DFG Research Fellowship CO 802/1-1), Natural Sciences and Engineering Research Council of Canada (Banting Postdoctoral Fellowship), European Molecular Biology Organization (ASTF-491/2013)

We demonstrate here that the [superscript 17]O NMR properties of bound water in a series of amino acids and dipeptides can be determined with a combination of nonspinning and magic-angle spinning experiments using a range of magnetic field strengths from 9.4 to 21.1 T. Furthermore, we propose a [superscript 17]O chemical shift fingerprint region for bound water molecules in biological solids that is well outside the previously determined ranges for carbonyl, carboxylic, and hydroxyl oxygens, thereby offering the ability to resolve multiple [superscript 17]O environments using rapid one-dimensional NMR techniques. Finally, we compare our experimental data against quantum chemical calculations using GIPAW and hybrid-DFT, finding intriguing discrepancies between the electric field gradients calculated from structures determined by X-ray and neutron diffraction., National Institute of Biomedical Imaging and Bioengineering (U.S.) (grant number: EB-003151), National Institute of Biomedical Imaging and Bioengineering (U.S.) (grant number: EB-001960), National Institute of Biomedical Imaging and Bioengineering (U.S.) (grant number: EB-002026)