Biomedical subjects

Günter Hempel

Publications and source records attributed to Günter Hempel.

3 recordsLinked to original sources

PubMed2006

Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei.

In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403-410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW1/tau-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SWtau-FAM). For static spectra of 27Al (I=5/2), better signal-enhancement performance is found for the SW1/tau-FAM sequence, as demonstrated both by experiments and numerical simulations.

Journal Article↗

PubMed2004

Protonated nucleobase ligands: synthesis, structure and characterization of 9-methyladeninium hexachloroplatinate and pentachloro(9-methyladeninium)platinum(IV).

Na(2)[PtCl(6)] was found to react with (9-MeAH)Cl(.)H(2)O (2) (9-MeA=9-methyladenine) in aqueous solution yielding (9-MeAH)(2)[PtCl(6)](.)2H(2)O (3). The same compound was obtained from hexachloroplatinic acid and 9-methyladenine. Performing this reaction at 60 degrees C, complex formation took place yielding the 9-methyladeninium complex [PtCl(5)(9-MeAH)](.)2H(2)O (4a). An analogous complex, [PtCl(5)(9-MeAH)](.)1/2(18C6)(.)H(2)O (4b, 18C6=crown ether 18-crown-6), was formed in the reaction of aquapentachloroplatinic acid (H(3)O)[PtCl(5)(H(2)O)](.)2(18C6)(.)6H(2)O (1) with 9-methyladenine in 1:1 ratio. All complexes were isolated in moderate to good yields as yellow powder (4b) and crystals (3, 4a), respectively. They were fully characterized by microanalysis, IR and NMR ((1)H, (13)C, (195)Pt) spectroscopies, and in part (2, 3, 4a) also by single-crystal X-ray diffraction analysis. Molecular structure of complex 4a exhibited that the 9-methyladeninium ligand is N1 protonated and coordinated through N7 to platinum(IV).

Adenine↗

PubMed2003

Simultaneous processing of solid-state NMR relaxation and 1D-MAS exchange data: the backbone dynamics of free vs. binase-bound barstar.

Two types of dynamic solid-state NMR experiments-relaxation and 1D-MAS exchange-were combined for the investigation of the backbone dynamics of a 15% randomly 15N-enriched protein barstar in both free and binase-bound states. The main novelty of this work is a simultaneous quantitative processing of the results of these two types of experiments that we call Simultaneous Relaxation and Exchange Data Analysis (SREDA) approach. It extends the well-known model-free approach such that it permits to discriminate between various motional models (jumps between different sites, wobbling in a cone, etc.). This objective cannot be achieved by analyzing the relaxation or exchange data separately. The SREDA approach was applied to probe a modification of the average backbone dynamics of barstar upon forming a complex with another protein binase. T(1) and off-resonance T(1rho) relaxation times of 15N backbone nuclei were measured at three temperatures between 0 and 45 degrees C, 1D-MAS exchange (CODEX) data were obtained at room temperature within the mixing time range from 0.3 to 200 ms. It has been found that the barstar backbone participates in two molecular processes with correlation times in the 10(-9)-10(-7) and 10(-3)-10(-2) s ranges. Forming the complex with binase results in a significant decrease of the amplitudes of both motions, suggesting that the complex is a more rigid and stable structure than free barstar.

Bacillus↗