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Mobility of sodium ions in agarose gels probed through combined single- and triple-quantum NMR
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http://dx.doi.org/10.13039/501100001659
Deutsche Forschungsgemeinschaf
Pseudo rotary resonance relaxation dispersion effects in isotropic samples
Full text linkEnhanced transverse relaxation near rotary resonance conditions is a well-documented effect for anisotropic solid samples undergoing magic-angle spinning (MAS). We report transverse signal decay associated with rotary resonance conditions for rotating liquids, a surprising observation, since first-order anisotropic interactions are averaged at a much faster timescale compared with the spinning frequency. We report measurements of 13C and 1H signal intensities under spin lock for spinning samples of polybutadiene rubber, polyethylene glycol solution, and 99.96 % D2O. A drastic reduction in spin-lock signal intensities is observed when the spin-lock frequency matches 1 or 2 times the MAS rate. In addition, oscillations of the signal are observed, consistent with a coherent origin of the effect, a pseudo rotary resonance relaxation dispersion (pseudo-RRD). Through simulations, we qualitatively describe the appearance of pseudo-RRD, which can be explained by time dependence caused by sample rotation and an inhomogeneous field, the origin of which is an instrumental imperfection. Consideration of this effect is important for MAS experiments based on rotary resonance conditions and motivates the design of new MAS coils with improved radio frequency (RF)-field homogeneity
Windowed cross polarization at 55 kHz magic-angle spinning
Full text linkCross polarization (CP) transfers via Hartmann-Hahn matching conditions are one of the cornerstones of solid-state magic-angle spinning NMR experiments. Here we investigate a windowed sequence for cross polarization (wCP) at 55 kHz magic-angle spinning, placing one window (and one pulse) per rotor period on one or both rf channels. The wCP sequence is known to have additional matching conditions. We observe a striking similarity between wCP and CP transfer conditions when considering the flip angle of the pulse rather than the rf-field strength applied during the pulse. Using fictitious spin-1/2 formalism and average Hamiltonian theory, we derive an analytical approximation that matches these observed transfer conditions. We recorded data at spectrometers with different external magnetic fields up to 1200 MHz, for strong and weak heteronuclear dipolar couplings. These transfers, and even the selectivity of CP were again found to relate to flip angle (average nutation)
Great Offset Difference Internuclear Selective Transfer
Full text linkCarbon–carbon dipolar recoupling sequences are frequently used building blocks in routine magic-angle spinning NMR experiments. While broadband homonuclear first-order dipolar recoupling sequences mainly excite intra-residue correlations, selective methods can detect inter-residue transfers and long-range correlations. Here, we present the great offset difference internuclear selective transfer (GODIST) pulse sequence optimized for selective carbonyl or aliphatic recoupling at fast magic-angle spinning, here, 55 kHz. We observe a 3- to 5-fold increase in intensities compared with broadband RFDR recoupling for perdeuterated microcrystalline SH3 and for the membrane protein influenza A M2 in lipid bilayers. In 3D (H)COCO(N)H and (H)CO(CO)NH spectra, inter-residue carbonyl–carbonyl correlations up to about 5 Å are observed in uniformly 13C-labeled proteins
Backbone Torsion Angle Determination Using Proton Detected Magic-Angle Spinning Nuclear Magnetic Resonance
No full textSeeing double: the persistent dimer‐of‐dimers structure of drug resistant influenza A M2
No full textThe currently circulating S31N variant of the M2 proton channel of influenza A is resistant to antiviral drugs. Recently, there has been a growing concern regarding the impact of the lipid environment on the structural features of the S31N variant. The native symmetry of the M2 tetramer remains controversial. Here we show that S31N M2 persists in a dimer‐of‐dimers structure in different lipid preparations independent of the amount of solvating lipids up to at least 180 lipids per tetramer. NMR spectra clearly detect the characteristic resonances of the dimer‐of‐dimers of M2 (residues 18‐60 or 18‐62) reconstituted in lipids. NMR‐based distance measurements indicate that two isoleucine residues with upfield shifted alpha carbon resonances, typical of extended conformations, are compatible with a particular side‐chain rotameric state and helical backbone geometry. These chemical shifts are therefore compatible with the expected native transmembrane helical fold. Symmetry breaking at the pH sensing H37 residues, detected via peak doubling, is a stable feature of S31N M2 based on the reference strain Udorn/1972(H3N2). By contrast, the spectrum is dramatically altered for Columbia/2014/(H3N2) M2, which differs in sequence in the amphipathic helices. This highlights an allosteric coupling between the amphipathic helices and the pH sensing residues
Self-assembled cellulosic superstructures with unanticipated high quantum yields
No full textAbstract Nonconventional luminophores devoid of traditional, large π-conjugates often suffer from low solid-state fluorescence quantum yields (FLQYs). In parallel, self-assembled bowl-shaped and helical architectures at the micro- and macroscale are unusual (mostly reported at the nanoscale). Here, we report that surface-stearoylated cellulose nanocrystals and cellulose stearoyl esters co-assemble into macroscale helices (FLQY: 86%) with diameters of 32−104 μm. Meanwhile, surface-lauroylated cellulose nanocrystals and cellulose lauroyl esters co-assemble into porous bowl-shaped microparticles (FLQY: 91%) with diameters of 8−19 μm. The high FLQYs are ascribed to the synergism of the dense oxygen clusters and abundant van der Waals interactions and hydrogen bonds between side stearoyl or lauroyl groups, which can promote through-space electron delocalization, ultimately improving fluorescence performance. These results were rationalized by theoretical calculations. Such superstructures exhibit great potential for stable anti-counterfeiting materials due to the excellent regeneration ability as well as structural stability of the oxygen clusters.EU:‘NEuM’China Scholarship Council https://doi.org/10.13039/501100004543Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada https://doi.org/10.13039/501100000038Alexander von Humboldt-Stiftung https://doi.org/10.13039/10000515
Modest Offset Difference Internuclear Selective Transfer via Homonuclear Dipolar Coupling
No full textDynamically Tunable All-Weather Daytime Cellulose Aerogel Radiative Supercooler for Energy-Saving Building
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