Biomedical subjects
Publications and source records attributed to Stefan Steuernagel.
The first experimental evidence for the formation of ordered three-dimensional structures in solutions of organometallic complexes in a thin film of supported ionic liquid was obtained. The ordering effect leads to drastically reduced mobility of ionic liquid and complex molecules.
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.
A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid organic solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond (1)H-(13)C INEPT transfer for crystalline organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 x 10.4 kDa).
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The sensitivity of high-resolution 17O (I = 5/2) NMR spectroscopy of solids has advanced significantly in recent years. Here, we show that excellent results are now obtainable from milligram quantities of 17O-enriched materials, thereby allowing the technique to be applied to silicate phases synthesized under very high pressures in a multiple-anvil apparatus. We report the first 17O NMR study of beta-Mg2SiO4 (9.6 mg of 35% 17O-enriched material, synthesized at p = 16 GPa and T = 1873 K), a dense phase believed to have a significant role in the Earth's mantle. Using STMAS at magnetic fields of B0 = 9.4 and 11.7 T and MQMAS at B0 = 18.8 T, we have resolved and assigned all four crystallographically distinct O sites and determined their chemical shift and quadrupolar parameters.
In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state.
In this paper we demonstrate experimentally that the continuously phase-modulated homonuclear decoupling sequence DUMBO-1 is suitable for high-resolution proton NMR spectroscopy of rigid solids. Over a wide range of experimental conditions, we show on the model sample L-alanine as well as on small peptides that proton linewidths of less than 0.5 ppm can be obtained under DUMBO-1 decoupling. In particular the DUMBO-1 sequence yields well resolved proton spectra both at slow and fast MAS. The DUMBO-1 decoupling scheme can in principle be inserted in any multi-nuclear or multi-dimensional solid-state NMR experiment which requires a high-resolution 1H dimension. An example is provided with the 13C-1H MAS-J-HMQC experiment.
Sporopollenin from the pollen of Typha angustifolia L. was exposed to a series of 36 subsequent acidic methanolysis procedures. The remaining decomposition products were investigated using several spectroscopic methods including Fourier transform infrared spectroscopy (FT-IR), solid state 13C nuclear magnetic resonance spectroscopy (13C-CPMAS-NMR) and X-ray photoelectron spectrometry (XPS). Substantial weight losses of the sporopollenin material occur after each acidic methanolysis step, while FT-IR and 13C-CPMAS-NMR spectra display no noticeable differences after 12, 24 and 36 steps. These findings are interpreted as a hint that the sporopollenin polymer has a uniform composition, i.e. relatively small monomer moieties of similar primary structure are present. Moreover, the weight losses account for the presence of substantial amounts of ether linkages in the sporopollenin polymer.