Ambient connections realising conformal Tractor holonomy

For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat ambient metric in the sense of Fefferman and Graham. Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse 9, 1090 Vienna, Austria Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany     

Recent developments in the maytansinoid antitumor agents

Maytansine and its congeners have been isolated from higher plants, mosses and from an Actinomycete, Actinosynnema pretiosum. Many of these compounds are antitumor agents of extraordinary potency, yet phase II clinical trials with maytansine proved disappointing. The chemistry and biology of maytansinoids has been reviewed repeatedly in the late 1970s and early 1980s; the present review covers new developments in this field during the last two decades. These include the use of maytansinoids as "warheads" in tumor-specific antibodies, preliminary metabolism studies, investigations of their biosynthesis at the biochemical and genetic level, and ecological issues related to the occurrence of such typical microbial metabolites in higher plants.     

Einfluß der Nachimpulse des Photosekundärelektronenvervielfachers bei Flüssigkeitsszintillationszählungen

Der Einfluβder Nachimpulse einiger Exemplare des Vervielfachertyps S 12 FS 35 vom VEB Carl Zeiss Jena auf die Flüssigkeitsszintillationszählung wurde in Abhängigkeit von verschiedenen Parametern untersucht. Daraus ergeben sich praktische Hinweise zur Vermeidung von Fehlmessungen durch Nachimpulse, die bei absoluten Aktivitätsbestimmungen mit dem Flüssigkeitsszintillationszähler (z. B. Meβkopf Nr. 25510 der Firma E. Zimmermann, Leipzig) unbedingt zu berücksichtigen sind.     

Fluorinated Azobenzenes Switchable with Red Light

Molecular photoswitches triggered with red or NIR light are optimal for photomodulation of complex biological systems, including efficient penetration of the human body for therapeutic purposes (“therapeutic window”). Yet, they are rarely reported, and even more rarely functional under aqueous conditions. In this work, fluorinated azobenzenes are shown to exhibit efficient E→Z photoisomerization with red light (PSS_660nm >75 % Z) upon conjugation with unsaturated substituents. Initially demonstrated for aldehyde groups, this effect was also observed in a more complex structure by incorporating the chromophore into a cyclic dipeptide with propensity for self-assembly. Under physiological conditions, the latter molecule formed a supramolecular material that reversibly changed its viscosity upon irradiation with red light. Our observation can lead to design of new photopharmacology agents or phototriggered materials for in vivo use.     

On the full holonomy group of Lorentzian manifolds

The classification of restricted holonomy groups of \(n\) -dimensional Lorentzian manifolds was obtained about ten years ago. However, up to now, not much is known about the structure of the full holonomy group. In this paper we study the full holonomy group of Lorentzian manifolds with a parallel null line bundle. Based on the classification of the restricted holonomy groups of such manifolds, we prove several structure results about the full holonomy. We establish a construction method for manifolds with disconnected holonomy starting from a Riemannian manifold and a properly discontinuous group of isometries. This leads to a variety of examples, most of them being quotients of pp-waves with disconnected holonomy, including a non-flat Lorentzian manifold with infinitely generated holonomy group. Furthermore, we classify the full holonomy groups of solvable Lorentzian symmetric spaces and of Lorentzian manifolds with a parallel null spinor. Finally, we construct examples of globally hyperbolic manifolds with complete spacelike Cauchy hypersurfaces, disconnected full holonomy and a parallel spinor.     

Composite cryogel with immobilized concanavalin A for affinity chromatography of glycoproteins

Composite cryogels containing porous adsorbent particles were prepared under cryogelation conditions. The composites with immobilized concanavalin A (Con A) were used for capturing glycoproteins. Adsorbent particles were introduced into the structure in order to improve the capacity and to facilitate the handling of the particles. The monolithic composite cryogels were produced from suspensions of polyvinyl alcohol particles and porous adsorbent particles and cross‐linked under acidic conditions at sub‐zero temperature. The cryogels were epoxy activated and Con A was immobilized as an affinity ligand. Binding and elution of horseradish peroxidase (HRP) was studied in batch experiment and in a chromatographic setup. Increasing adsorbent concentration in composite cryogels will increase ligand density, which therefore enhances the amount of bound HRP from 0.98 till 2.9 (milligram enzyme per milliliter of gel) in the chromatographic system. The material was evaluated in 10 cycles for binding and elution of HRP.     

The effects of a thiol-containing quinazolinedione derivative (MECH) on the lipid oxidation in bilayer liposomes

In order to investigate the radical chemistry of 3-(2-mercaptoethyl)quinazoline-2,4(1H, 3H)-dione (MECH) in homogeneous and liposomal solutions experiments were performed with pulse radiolysis, γ radiolysis and the chemical radical intiator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). It is shown that the thiol group represents the most sensitive group to radical attack. The thiyl radical originating from MECH is detected indirectly by product analysis and by pulse radiolysis. The thiyl radical can abstract bisallylic hydrogens from polyunsaturated fatty acids. This is shown by pulse radiolysis in homogeneous and liposomal solutions via the formation of the pentadienyl radical which has a strong and characteristic absorption band at 280 nm.     

Polyketides from the marine-derived fungus Ascochyta salicorniae and their potential to inhibit protein phosphatases

Chemical investigation of the marine fungus Ascochyta salicorniae led to the isolation of two new epimeric compounds, ascolactones A (1) and B (2), in addition to the structurally-related polyketides hyalopyrone (3), ascochitine (4), ascochital (5) and ascosalipyrone (6). The absolute configurations of the epimeric compounds 1 and 2 were assigned as (1R,9R) and (1S,9R), respectively, through simulation of the chiroptical properties using quantum-chemical CD calculations, and chiral GC-MS subsequent to oxidative cleavage (Baeyer-Villiger oxidation) of the side chain. In silico screening using the PASS software identified some of the A. salicorniae compounds (1-6) as potential inhibitors of protein phosphatases. Compound was found to inhibit the enzymatic activity of MPtpB with an IC(50) value of 11.5 microM.