C-S Bond Cleavage Reactions of Sulfonediimines

Abstract

Nucleophilic C-S bond cleavage of Sulfonediimines to Sulfinamidine-type Structures is discussed     

Structural and magneto-transport characterization of Co2CrxFe1-xAl Heusler alloy films

We investigate the structure and magneto-transport properties of thin films of the Co₂Cr_0.6Fe_0.4Al full-Heusler compound, which is predicted to be a half-metal by first-principles theoretical calculations. Thin films are deposited by magnetron sputtering at room temperature on various substrates in order to tune the growth from polycrystalline on thermally oxidized Si substrates to highly textured and even epitaxial on MgO(001) substrates, respectively. Our Heusler films are magnetically very soft and ferromagnetic with Curie temperatures up to 630 K. The total magnetic moment is reduced compared to the theoretical bulk value, but still comparable to values reported for films grown at elevated temperature. Polycrystalline Heusler films combined with MgO barriers are incorporated into magnetic tunnel junctions and yield 37% magnetoresistance at room temperature.     

Recent advances in scanning tunneling microscopy involving magnetic probes and samples

We report on recent developments in the field of STM performed with magnetic probes and samples. The choice of appropriate magnetic sensors and their in situ preparation will be described. We further focus on the information obtained in spin-polarized scanning tunneling microscopy (SPSTM) as well as on possible modes of operation for simultaneous acquisition of topographic and magnetic data. The prospects for SPSTM and related magnetic sensitive SXM techniques will be discussed.Permanent address: Forschungszentrum Jülich, ISI, W-5170 Jülich 1, Fed. Rep. Germany     

The surface structure of icosahedral Al68Pd23Mn9 measured by STM and LEED

For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al₆₈Pd₂₃Mn₉ sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive step heights show quasiperiodic order according to the Fibonacci chain. The normals of these terraces are parallel to a five-fold axis as revealed by highly resolved STM images. On the terraces five-fold stars and pentagonal holes are observed. Their orientation is the same on all terraces investigated. Additionally to this long-range orientational order, a high degree of quasiperiodic order is found for the pentagonal holes. This indicates that the quasiperiodic order of this highly ordered and thermodynamically stable quasicrystal extends even up to the surface. Both the step heights and the distances between the pentagonal holes well agree with the values derived from a structural model of this material. Five-fold symmetric LEED patterns can be analysed by means of the Fourier transform of a Fibonacci pentagrid as suggested by the STM data. The analysis yields the same line separations within the pentagrid as deduced from the STM experiments.     

Riemann-Roch-Transformationen und Kobordismen

Ohne Zusammenfassung     

Enantioselective High-Throughput Assay Showcased for the Identification of (R)- as well as (S)-Selective Unspecific Peroxygenases for C−H Oxidation

Identifying (bio)catalysts displaying high enantio-/stereoselectivity is a fundamental prerequisite for the advancement of asymmetric catalysis. Herein, a high-throughput, stereoselective screening assay is reported that gives information on enantioselectivity, stereopreference and activity as showcased for peroxygenase-catalyzed hydroxylation. The assay is based on spectrophotometric analysis of the simultaneous formation of NAD(P)H from the alcohol dehydrogenase catalyzed enantioselective oxidation of the sec-alcohol product formed in the peroxygenase reaction. The assay was applied to investigate a library comprising 44 unspecific peroxygenases (UPOs) containing 25 UPOs not reported yet. Thereby, previously non-described wild-type UPOs displaying (S)- as well as (R)-stereoselectivity for the hydroxylation of representative model substrates were identified, reaching up to 98 % ee for the (R)- and 94 % ee for the (S)-enantiomer. Homology models with concomitant docking studies indicated the structural reason for the observed complementary stereopreference.     

Über Kohomologietheorien mit formaler Gruppe der Charakteristikp

Ohne Zusammenfassung     

A splitting theorem for certain cohomology theories associated to BP* (−)

Let P(n)^*(–) be Brown-Peterson cohomology modulo I_n and put B(n)^*(–)=P(n)^*(–)[1/v_n]. In this note we construct a canonical multiplicative and idempotent operation _n in a suitable completion (n)^*(–) of B(n)^*(–) which has the property that its image is canonically isomorphic to the n-th Morava K-theory K(n)^*(–). In particular, the ring theory K(n)^*(–) is contained as a direct summand in the theory (n)^*(–). A similar result is not true before completing. pleting. Because the completion map B (n)^*(–) (n)^*(–) is injective, the above splitting theorem contains also information about B(n)^*(–). The proof of the theorem depends on a result about the behaviour of formal groups of finite height over complete graded F_p.