117 research outputs found
Autobiographical Sketches (2021)
Klaus Möbius gives a selection of his biographical experiences which have shaped his academic and personal life
Das Umweltproblem aus wirtschaftlicher Sicht
Die menschliche zivilisatorische TĂ€tigkeit war immer mit negativen Folgen fĂŒr die Umwelt verbunden. Erst die Kumulierung der Umweltbelastungen, vor allem in BallungsrĂ€umen, ĂŒbertrifft das natĂŒrliche Reinigungsvermögen. Das Umweltproblem beruht ganz ĂŒberwiegend darauf, daĂ nicht alle Auswirkungen wirtschaftlicher Entscheidungen kostenmĂ€Ăig berĂŒcksichtigt werden (Konzept der externen Effekte). Es ist nicht zwischen sauberer und verschmutzter Umwelt zu entscheiden, sondern es muĂ das noch vertretbare MaĂ der Umweltbelastung festgestellt werden. Es genĂŒgt nicht, Standards fĂŒr die Umweltbelastung festzusetzen, sondern neue Produkte und Produktionsprozesse mĂŒssen vorbeugend ĂŒberprĂŒft werden. Das Prinzip der Verursachung darf nicht nur bejaht, es muĂ auch durchgesetzt werden. Umweltschutz ist eine Frage der Reallokation der Ressourcen; sie kann auf sehr unterschiedliche Weise beeinfluĂt werden. Das Umweltproblem besitzt globale Aspekte, und seine konsequente Lösung wird mit einer Reallokation der Produktion verbunden sein. Das Umweltproblem kann mit den Mitteln einer Marktwirtschaft gelöst werden. Dazu bedarf es eines makroökonomischen Ansatzes, der Produktion und Umweltbelastungen --
High-field/high-frequency EPR spectroscopy in protein research: principles and examples
During the last decades, the combined efforts of biologists, chemists, and physicists in developing high-field/high-frequency EPR techniques and applying them to functional proteins have demonstrated that this type of magnetic resonance spectroscopy is particularly powerful for characterizing the structure and dynamics of stable and transient states of proteins in action on biologically relevant time scales ranging from nanoseconds to hours. The review article describes how high-field EPR methodology, in conjunction with site-specific isotope and spin-labeling strategies, is capable of providing new insights into fundamental biological processes. Specifically, we discuss the theoretical and instrumental background of continuous-wave and pulse high-field EPR and the multiple-resonance extensions EDNMR, ENDOR, TRIPLE, ESEEM, PELDOR, and RIDME. Some emphasis is placed on a balanced description of both the historical spadework and the achieved performance of advanced EPR at 95 GHz and 360 GHz. This culminates in a coherent treatment of state-of-the-art research of high-field EPR in terms of both instrumentation development and application to representative protein complexes such as cofactor binding sites in photosynthesis
High-field/High-frequency EPR Spectroscopy in Protein Research: Principles and Examples
During the last decades, the combined efforts of biologists, chemists, and physicists in developing high-field/high-frequency EPR techniques and applying them to functional proteins have demonstrated that this type of magnetic resonance spectroscopy is particularly powerful for characterizing the structure and dynamics of stable and transient states of proteins in action on biologically relevant time scales ranging from nanoseconds to hours. The review article describes how high-field EPR methodology, in conjunction with site-specific isotope and spin-labeling strategies, is capable of providing new insights into fundamental biological processes. Specifically, we discuss the theoretical and instrumental background of continuous-wave and pulse high-field EPR and the multiple-resonance extensions EDNMR, ENDOR, TRIPLE, ESEEM, PELDOR, and RIDME. Some emphasis is placed on a balanced description of both the historical spadework and the achieved performance of advanced EPR at 95 GHz and 360 GHz. This culminates in a coherent treatment of state-of-the-art research of high-field EPR in terms of both instrumentation development and application to representative protein complexes such as cofactor binding sites in photosynthesis
A Personal Account
In this minireview, we report on our year-long EPR work, such as
electronânuclear double resonance (ENDOR), pulse electron double resonance
(PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave
frequencies and magnetic fields. This report is dedicated to James S. Hyde and
honors his pioneering contributions to the measurement of spin interactions in
large (bio)molecules. From these interactions, detailed information is
revealed on structure and dynamics of macromolecules embedded in liquid-
solution or solid-state environments. New developments in pulsed microwave and
sweepable cryomagnet technology as well as ultra-fast electronics for signal
data handling and processing have pushed the limits of EPR spectroscopy and
its multi-frequency extensions to new horizons concerning sensitivity of
detection, selectivity of molecular interactions and time resolution. Among
the most important advances is the upgrading of EPR to high magnetic fields,
very much in analogy to what happened in NMR. The ongoing progress in EPR
spectroscopy is exemplified by reviewing various multi-frequency
electronânuclear double-resonance experiments on organic radicals, light-
generated donorâacceptor radical pairs in photosynthesis, and site-
specifically nitroxide spin-labeled bacteriorhodopsin, the light-driven proton
pump, as well as EDNMR and ENDOR on nitroxides. Signal and resolution
enhancements are particularly spectacular for ENDOR, EDNMR and PELDOR on
frozen-solution samples at high Zeeman fields. They provide orientation
selection for disordered samples approaching single-crystal resolution at
canonical g-tensor orientationsâeven for molecules with small g-anisotropies.
Dramatic improvements of EPR detection sensitivity could be achieved, even for
short-lived paramagnetic reaction intermediates. Thus, unique structural and
dynamic information is revealed that can hardly be obtained by other
analytical techniques. Micromolar concentrations of sample molecules have
become sufficient to characterize stable and transient reaction intermediates
of complex molecular systemsâoffering exciting applications for physicists,
chemists, biochemists and molecular biologists
Möbius-Strip Topology of Expanded Porphyrins: A Minireview on EPR, ENDOR and DFT MO Studies
The one-sided Möbius strip with its characteristic 180° twist in the loop has inspired philosophers, artists and scientists since hundreds of years and continues to do so. On the molecular level, only in the last 15 years have some groups succeeded in synthesizing new expanded porphyrin compounds large enough to adopt Möbius-strip topology and Möbius aromaticity, the first being LechosĆaw Latos-GraĆŒyĆski and collaborators in Wroclaw (2007) and Atsuhiro Osuka and collaborators in Kyoto (2008). We report on new studies of expanded porphyrins with either Möbius topology or HĂŒckel topology that were synthesized in these laboratories. In this minireview, we focus on recent continuous-wave and time-resolved EPR, ENDOR and DFT MO studies on open-shell states of di-p-benzi[28]hexaphyrin(1.1.1.1.1.1), specifically, on the ground-state radical cation doublet state (total electron spin Sâ=â1/2) and the first excited triplet state (Sâ=â1). The review is largely based on the results and discussions of two previous publications: Möbius et al. (Appl Magn Reson 47:757â780, 2016) and Ema et al. (J Phys Chem Lett 9:2685â2690, 2018). In the open-shell systems, besides the electron-nuclear hyperfine couplings also the zero-field interaction tensor turned out to be a viable sensor for electronic structure changes between Möbius and HĂŒckel topologies. In the Outlook section, we address the cyclotides, a new class of natural circular mini-proteins, usually less than 100 amino acids long. They are distinguished by exceptional chemical and biological stability. This is due to topological constraints imposed by threefoil knot and Möbius-strip formation. As a result, their physical qualities are âtopologically protectedâ. This makes them highly interesting for medical or agricultural applications, for example as novel active ingredients against autoimmune diseases, viral infections, or as agents against insect damage to crops
Biomolecular EPR Meets NMR at High Magnetic Fields
In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 ÎŒL (S-band), 150 ÎŒL (X-band), 10 ÎŒL (Q-band) and 1 ÎŒL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electronânuclear and electronâelectron double-resonance techniques such as electronânuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Ă
. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientationsâeven for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electronânuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth. View Full-Tex
Hydrogen-Bonded Complexes of Neutral Nitroxide Radicals with 2-Propanol Studied by Multifrequency EPR/ENDOR
The hydrogen bond plays a key role in weak directional intermolecular interactions. It is operative in determining molecular conformation and aggregation, and controls the function of many chemical systems, ranging from inorganic, organic to biological molecules. Although an enormous amount of spectroscopic information has been collected about hydrogen-bond formation between molecules with closed-shell electronic configuration, the details of such interactions between open-shell radicals and closed-shell molecules are still rare. Here we report on an investigation of hydrogen-bonded complexes between pyrroline-type as well as piperidine-type neutral nitroxide radicals and an alcohol, i.e., 2-propanol. These nitroxide radicals are commonly used as EPR spin labels and probes. To obtain information on the geometry of the complexes and their electronic structure, multi-resonance EPR techniques at various microwave frequencies (X-, Q-, W-band, 244 GHz) have been employed in conjunction with DFT calculations. The planar five-membered ring system of the pyrroline-type nitroxide radical was found to form exclusively well-defined in-plane Ï-type hydrogen-bonded complexes with one 2-propanol molecule in the first solvation shell in frozen solution. The measured hyperfine parameters of the hydrogen-bridge proton and the internal magnetic parameters describing the electron Zeeman and the electron-nuclear hyperfine and nuclear quadrupole interactions are in good agreement with values predicted by state-of-the-art DFT calculations. In contrast, multi-resonance EPR on the non-planar six-membered ring system of the piperidine-type nitroxide radical (TEMPOL) reveals a more complex situation, i.e., a mixture of a Ï-type with, presumably, an out-of-plane Ï-type complex, both present in comparable fraction in frozen solution. For TEMPOL, the DFT calculations failed to predict magnetic interaction parameters that are in good agreement with experiment, apparently due to the considerable flexibility of the nitroxide and hydrogen-bonded complex. The detailed information about nitroxide/solvent complexes is of particular importance for Dynamic Nuclear Polarization (DNP) and site-directed spin-labeling EPR studies that employ nitroxides as polarizing agents or spin labels, respectively
The axon-myelin unit in development and degenerative disease
Axons are electrically excitable, cable-like neuronal processes that relay information between neurons within the nervous system and between neurons and peripheral target tissues. In the central and peripheral nervous systems, most axons over a critical diameter are enwrapped by myelin, which reduces internodal membrane capacitance and facilitates rapid conduction of electrical impulses. The spirally wrapped myelin sheath, which is an evolutionary specialisation of vertebrates, is produced by oligodendrocytes and Schwann cells; in most mammals myelination occurs during postnatal development and after axons have established connection with their targets. Myelin covers the vast majority of the axonal surface, influencing the axon's physical shape, the localisation of molecules on its membrane and the composition of the extracellular fluid (in the periaxonal space) that immerses it. Moreover, myelinating cells play a fundamental role in axonal support, at least in part by providing metabolic substrates to the underlying axon to fuel its energy requirements. The unique architecture of the myelinated axon, which is crucial to its function as a conduit over long distances, renders it particularly susceptible to injury and confers specific survival and maintenance requirements. In this review we will describe the normal morphology, ultrastructure and function of myelinated axons, and discuss how these change following disease, injury or experimental perturbation, with a particular focus on the role the myelinating cell plays in shaping and supporting the axon
Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem I
The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pumpâprobe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of Aââ1A/Aââ1BâFX by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary Pâ+700Aââ0 and the secondary Pâ+700Aââ1 ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the Pâ+700Aââ1 was decreased by ~20%. Forward ET from the phylloquinone molecules in the Aââ1A and Aââ1B sites to the ironâsulfur cluster FX slowed from ~220 ns and ~20 ns in solution to ~13 ÎŒs and ~80 ns, respectively. However, as shown by EPR spectroscopy, the ~15 ÎŒs kinetic phase also contains a small contribution from the recombination between Aââ1B and Pâ+700. These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A- and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix
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