Resolution and chiroptical properties of the neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo) and related compounds: quantum chemical CD calculations and X-ray diffraction analysis

Separation and stereochemical attribution of the two enantiomers of the neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo) has been achieved by applying chromatography on a chiral phase HPLC column in hyphenation with circular dichroism (CD) spectroscopy (LC-CD coupling). Assignment of the absolute configuration of TaClo and its N-methyl analog has been achieved by quantum chemical CD calculations and has finally been confirmed by single-crystal X-ray diffraction analyses of the two enantiomers of N-formyl-TaClo as obtained in enantiomerically pure form by crystallization.     

Incoherent switching between multistable cavity solitons in a semiconductor optical resonator

We demonstrate numerically a two-dimensional threefold storage scheme based on different types of solitary waves in the transmitted field of a semiconductor planar resonator. Switching between among different solitary waves can be achieved by use of a weak incoherent switching beam.     

Theodor Schmidt and Hans Kopfermann – Pioneers in Hyperfine Physics

Systematic optical hyperfine interaction studies in various isotope series gave first indications to the possibility of single-particle and collective motions of nucleons in atomic nuclei and the variation of the nuclear radius with the mass number and deformation (isotope shift). Indeed, the careful studies by Schmidt (1908–1986), which he performed together with Schüler in Potsdam, revealed the existence of both nuclear quadrupole deformation and single-particle magnetic moments (Schmidt lines). These findings were essential as a basis for the nuclear vibrational and rotational models and the single particle shell model, respectively. The talk reviews some of the achievements of Schmidt and Kopfermann (1895–1963) and sheds some light on their working conditions before, during and after World War II. This revised version was published online in September 2006 with corrections to the Cover Date.     

Activation of N-sulfonyl oxaziridines using copper(II) catalysts: aminohydroxylations of styrenes and 1,3-dienes

N-Sulfonyl oxaziridines are susceptible to electrophilic activation using copper(II) catalysts and react with styrenes under these conditions to provide 1,3-oxazolidines in a formal aminohydroxylation of the alkene. We propose a two-step mechanism involving a cationic intermediate to account for the rate differences and regioselectivities observed using a variety of styrenes. In accord with our hypothesis, aminohydroxylations of a range of substrates bearing electron-stabilizing groups are successful, and 1,3-dienes are particularly good substrates for copper(II)-catalyzed aminohydroxylation. Reactions of unsymmetrical dienes provide good to excellent olefin selectivity, the sense and magnitude of which can be rationalized upon consideration of the stability of the cationic intermediates suggested by our mechanism. Diastereoselective synthesis of a diverse range of densely functionalized structures can be achieved by polyfunctionalization of dienes using aminohydroxylation as a key complexity-increasing step.     

Diffusion of oriented single molecules with switchable mobility in networks of long unidimensional nanochannels

Single dye molecules incorporated into a mesoporous matrix can act as highly sensitive reporters of their environment. Here, we use single TDI molecules incorporated as guests into hexagonal mesoporous films containing highly structured domains. The dye molecules allow us to map the size of these domains which can extend to over 100 microm. Investigation of the translational and orientational dynamics via single molecule fluorescence techniques gives structural as well as dynamical information about the host material. In an air atmosphere, the guest molecules show no movement but perfect orientation along the pore direction. The diffusion of the TDI molecules can be induced by placing the mesoporous film in a saturated atmosphere of chloroform. In single molecule measurements with very high positioning accuracy (down to 2-3 nm) the movement of molecules could be observed even between neighboring channels. This reveals the presence of defects like dead ends closing the pores or small openings in the silica walls between neighboring channels, where molecules can change from one channel to the next. A statistical analysis demonstrates that the diffusion of TDI in the mesoporous film cannot be described with a 1D-random diffusion but is more complicated due to the presence of adsorption sites in which the TDI molecules can be occasionally trapped.