Freitod in Dahlem (1915): Unveröffentlichte Briefe von Edith Hahn und Lise Meitner über Dr. Clara Haber geb. Immerwahr

The present contribution contains previously unpublished letters by Clara Haber's contemporaries Edith Hahn and Lise Meitner that were written within two weeks of Clara Haber′s tragic suicide. It also contains a commentary about the circumstances of obtaining these letters as well as notes concerning their interpretation.     

Non-adiabaticity in surface chemical reactions

Chemical reactions at surface may dissipate energy exciting electron-hole pairs in the metal substrate. Direct detection of the chemically induced hot charge carriers may be achieved by measuring the tunnel current in Ta–TaOx–Au tunnel junctions when the Au top electrode is exposed to an atomic hydrogen beam. A current of 1 nA cm^?2 was observed during a hydrogen exposure with a flux of 0.1 ML s^?1. The transient is related to the reaction kinetics and allows us to identify the elementary reaction steps causing the electronic excitations which are monitored by the observed current. Using Pt as top electrode material a markedly different transient is observed. Applying a bias voltage to the sensor allows spectroscopy of the electronic excitations. The experiments provide detailed insights into the non-adiabaticity of various reaction steps at a surface.     

Ligand exchange and ligand migration reactions involving dicyclopentadienylniobium(III) carbonyl derivatives

The methylniobocene carbonyl (C₅H₅)₂Nb(CH₃)(CO) shows an unexpected lack of reactivity with respect to ligand migration. Whereas (C₅H₅)₂V(CH₃) has been reported to react with CO to yield the acetyl derivative (C₅H₅)₂V(OC-CH₃)(CO) immediately, we find that the niobocene analogue (C₅H₅)₂Nb(CH₃) reacts with CO only to regenerate (C₅H₅)₂Nb(CH₃)(CO), from which it was obtained by photolysis. This resistance of the methylniobocene carbonyl derivative towards ligand migration is interpreted in terms of the bonding properties of the acetyl intermediate (C₅H₅)₂Nb(OCCH₃).     

Characterization of peptide–protein interactions using photoaffinity labeling and LC/MS

The combination of photoaffinity labeling (PAL) with modern mass spectrometric techniques is a powerful approach for the characterization of peptide–protein interactions. Depending on the analytical strategy applied, a PAL experiment can provide different levels of information ranging from the identification of interaction partners to the structural characterization of ligand-binding sites. On the basis of LC/MS data generated in the framework of the identification of the binding site of the neuropeptide corticotropin-releasing factor (CRF) on its binding protein (CRFBP), the key role of LC/MS in the characterization of photoadducts on different structural levels was demonstrated. Covalent photoadducts of rat CRFBP (rCRFBP) were obtained by PAL with different mono- and bifunctional benzophenone photoprobes designed on the basis of the sequence of the synthetic CRF fragment human/rat CRF^6–33 which binds to CRFBP with high affinity. In view of the stoichiometry, LC/MS analysis revealed that the photoadducts consisted of one molecule of photoprobe and one molecule of rCRFBP. For a further characterization of the photoadducts on the oligopeptide level, enzymatic digests of unlabeled rCRFBP and of the respective photoadduct were compared by peptide mapping monitored with LC/MS. Thereby, it was found that the photoprobe that contained the photophore at its N-terminus labeled the amino acid sequence rCRFBP(34–38), whereas the photoprobe that contained the photophore at its C-terminus labeled rCRFBP(12–26). On the basis of the characterization of the photoadduct formed by rCRFBP and the bifunctional photoprobe that contained photophores on both termini, semiquantitative comparison of different enzymatic digests was accomplished by application of the mass-selective multiple ion chromatogram strategy.     

Gravitational radiation generated by the gravitational scattering of two stars

Within the framework of general relativity, the gravitational scattering of two stars is considered with regard to the gravitational radiation effects. The angular and frequency dependence of the generated gravitational radiation is investigated by Fourier's analysis of the gravitational field in the radiation zone. The results of the numerical calculations show a strong directional dependence of the radiation in the plane of movement of the stars.     

Electrospray ionization mass spectrometry of biotin binding to streptavidin

Stepwise binding of biotin to streptavidin via several intermediates was monitored with electrospray ionization mass spectrometry (ESIMS). Protein ligand interactions that result in conformational changes could be recognized with ESIMS by a mass shift and a change of the average multiple charge state of this protein. In addition, mass spectrometry for the ions in the gas phase revealed a much greater strength of the noncovalent bonds between the streptavidin subunits in the tetrameric complex than between the streptavidin and biotin molecules and remarkable differences in stability for the different charge states of the biotin-streptavidin noncovalent complex.     

Kinetics study of the binding of multivalent ligands on size-selected gold nanoparticles

The effect of ligand multivalency and nanoparticle size on the binding kinetics of thiol ligands on gold nanoparticles is investigated by exchanging monovalently bound pyrene on gold nanoparticles against flexible mono- and multivalent thiol ligands. Variable-sized gold nanoparticles of 2.2 ± 0.4, 3.2 ± 0.7, and 4.4 ± 0.9 nm diameter are used as substrates. The particles are coated by thiol functionalized pyrene ligands and the binding kinetics of the thiol ligands is studied by time-resolved fluorescence spectroscopy. The effect of multivalency on the binding kinetics is evaluated by comparing the rate constants of ligands of different valency. This comparison reveals that the multivalent ligands are exchanging substantially more rapidly than the monovalent ones. A particle size dependence of the rate constants is also observed, which is used to derive structural information on the binding of the mono- and multivalent ligands to the nanoparticle surface.