Synthesis and Reactivity of Organometallic Intermediates Relevant to Cobalt-Catalyzed Hydroformylation

Intermediates relevant to cobalt-catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18-electron (R,R)-(^iPrDuPhos)Co(CO)₂H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H₂/CO gas (1:1) at 100 °C. Deuterium-labeling studies established reversible 2,1-insertion of styrene into the Co−D bond of (R,R)-(^iPrDuPhos)Co(CO)₂D. Whereas rapid β-hydrogen elimination from cobalt alkyls occurred under an N₂ atmosphere, alkylation of (R,R)-(^iPrDuPhos)Co(CO)₂Cl in the presence of CO enabled the interception of (R,R)-(^iPrDuPhos)Co(CO)₂C(O)CH₂CH₂Ph, which upon hydrogenolysis under 4 atm H₂ produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H⁻, Cl⁻), underwent exchange with free ¹³CO. Under reduced pressure, (R,R)-(^iPrDuPhos)Co(CO)₂Cl underwent CO dissociation to form (R,R)-(^iPrDuPhos)Co(CO)Cl.     

Chemically induced shifts of 235U and 234U neutron resonances

Transmission spectra were measured with the time-of-flight technique at the Dubna pulsed reactor for samples of metallic U, UO₂, U₃O₈, and UO₃ enriched in ²³⁵U, and were compared in the regions of nine low-energy resonances to observe chemically induced shifts. After elimination of contributions caused by different Doppler broadenings, the shifts are interpreted as changes of the mean-square charge radius for nuclei capturing neutrons. The 〈r²〉 of the compound-nucleus states show on average a weak diminution as compared with the ground-state value.     

Tackling the chemical diversity of microbial nonulosonic acids – a universal large-scale survey approach

Nonulosonic acids, commonly referred to as sialic acids, are a highly important group of nine-carbon sugars common to all domains of life. They all share biosynthetic and structural features, but otherwise display a remarkable chemical diversity. In humans, sialic acids cover all cells which makes them important for processes such as cellular protection, immunity and brain development. On the other hand, sialic acids and other nonulosonic acids have been associated with pathological processes including cancer and viral infections. In prokaryotes, nonulosonic acids are commonly associated with pathogens, which developed through molecular mimicry a strategy to circumvent the host''s immune response. However, the remarkably large chemical diversity of prokaryotic nonulosonic acids challenges their discovery, and research on molecular characteristics essential for medical applications are often not feasible. Here, we demonstrate a novel, universal large-scale discovery approach that tackles the unmapped diversity of prokaryotic nonulosonic acids. Thereby, we utilize selective chemical labelling combined with a newly established mass spectrometric all-ion-reaction scanning approach to identify nonulosonic acids and other ulosonic acid-like sugars. In doing so, we provide a first molecular-level comparative study on the frequency and diversity across different phyla. We not only illustrate their surprisingly wide-spread occurrence in non-pathogenic species, but also provide evidence of potential higher carbon variants. Many biomedical studies rely on synthetic routes for sialic acids, which are highly demanding and often of low product yields. Our approach enables large-scale exploration for alternative sources of these highly important compounds.

A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a first molecular level comparative study is presented.     

On N1-free modules with trivial dual

In this paper we generalize the notion of Fountain-Gould order to the context of associative pairs. We give theorems about the existence and uniqueness of the left quotient pair and we obtain a Goldie-like haracterization which describes left orders in semiprime pairs coinciding with their socle.     

Ueber die Absorptionsspectren verschiedener Farbstoffe

Ohne Zusammenfassung     

Comparison of agarose and dextran-grafted agarose strong ion exchangers for the separation of protein aggregates

The control of aggregate levels in recombinant protein based drugs is a primary concern during process development and manufacture. In recent years, a novel class of dextran-grafted ion exchange matrices has gained popularity for process scale protein purification due to increased mass transfer rates and higher dynamic binding capacity compared to conventional matrices. Using bovine serum albumin and a monoclonal antibody as model proteins, we studied Sepharose FF and Sepharose XL ion exchangers for the separation of protein aggregates. Experimental results comparing linear gradient elution, stepwise elution, and flow-through chromatography for aggregate separation are described. Differences in performance for the various ion exchangers are discussed and modeled. Strategies for the optimization of protein aggregate separation are provided.