Simplical volume of closed locally symmetric spaces of non-compact type

We show that closed, locally symmetric spaces of non-compact type have positive simplicial volume. This gives a positive answer to a question that was first raised by (Gromov in Inst Hautes études Sci Publ Math 56:5, 1982).     

A note on the characteristic classes of non-positively curved manifolds

In this expository note, we give a simple conceptual proof of the Hirzebruch proportionality principle for Pontrjagin numbers of non-positively curved locally symmetric spaces. We also establish (non)-vanishing results for Stiefel–Whitney and Pontrjagin numbers of (finite covers of) the Gromov–Thurston examples of compact negatively curved manifolds. A byproduct of our argument gives a constructive proof of a well-known result of Rohlin: every closed orientable 3-manifold bounds orientably. We mention some geometric corollaries: a lower bound for degrees of covers having tangential maps to the non-negatively curved duals and estimates for the complexity of some representations of certain uniform lattices.     

Polygraphic resolutions and homology of monoids

We prove that for any monoid M, the homology defined by the second author by means of polygraphic resolutions coincides with the homology classically defined by means of resolutions by free ZM-modules.     

Syntheses of N-Acyl and N-Alkoxycarbonyl Derivatives of 2-Alkoxycarbonylamino-2-deoxy-D-glucose

Abstract

N-Acyl and N-alkoxycarbonyl derivatives of l, 3, 4, 6-tetra-O-acetyl-2-alkoxy-carbonylamino-2-deoxy-β-D-glucopyranose have been synthesized using mixed anhydrides and symmetrical or disymetrical pyrocarbonates. These derivatives have been used as donors in 1, 2-trans-glycosylation reactions promoted by Lewis acids. Besides the expected (β-D-glycosides, cyclisation and rearrangement side-products were often encountered in such glycosylations.     

A folk model structure on omega-cat

The primary aim of this work is an intrinsic homotopy theory of strict ω-categories. We establish a model structure on ωCat, the category of strict ω-categories. The constructions leading to the model structure in question are expressed entirely within the scope of ωCat, building on a set of generating cofibrations and a class of weak equivalences as basic items. All objects are fibrant while free objects are cofibrant. We further exhibit model structures of this type on n-categories for arbitrary n∈N, as specializations of the ω-categorical one along right adjoints. In particular, known cases for n=1 and n=2 nicely fit into the scheme.     

Spectroscopic characterisation and identification of ecdysteroids using high-performance liquid chromatography combined with on-line UV--diode array, FT-infrared and 1H-nuclear magnetic resonance spectroscopy and time of flight mass spectrometry

A prototype multiply hyphenated reversed-phase HPLC system has been applied to the analysis of a mixture of pure ecdysteroids and an ecdysteroid-containing plant extract. Characterisation was achieved via a combination of diode array UV, ¹H NMR, FT-IR spectroscopy and time of flight (TOF) mass spectrometry. This combination of spectrometers allowed the collection of UV, ¹H NMR, IR and mass spectra for a mixture of pure standards enabling almost complete structural characterisation to be performed. The technique was then applied to a partially purified plant extract in which 20-hydroxyecdysone and polypodine B were identified despite incomplete chromatographic resolution and the presence of co-chromatographing interferents. The experimental difficulties in the use of such a systems for these analytes are described.     

Improvement of a biomimetic porphyrin catalytic system by addition of acids

The conditions of the use of the manganese/porphyrin/imidazole system needed to be improved in order to obtain larger amounts of models of metabolites. An increase of the oxidation yields and a better preservation of this catalytic system have been obtained on the examples of various alkanes, by an acid addition in the reaction mixture. Three manganoporphyrins were checked for evaluation of the reaction. These results were extended to molecules of therapeutical interest such as ibuprofen and phenylbutazone.     

Self-organizing properties of natural and related synthetic glycolipids

In this article we report on the syntheses, self-organizing properties, and structures of a variety of cerebrosides and related synthetic glycolipids. The thermotropic and lyotropic liquid crystalline properties of the materials were evaluated in detail. All of the families of materials studied exhibited columnar mesophases. In the dry state the aliphatic chains were found to be located on the exterior of the columns, whereas in the wet state the reverse was the case with the polar headgroups on the exterior. Thus, the aliphatic chains act almost like hydrocarbon solvents in the dry state.     

Is Regioselectivity in the Enzyme‐Catalyzed Hydroperoxidation of Arachidonic Acid Necessarily Determined by Hydrogen Abstraction? The Case of Rabbit Leu597Ala/Ile663Ala ALOX15 Mutant

Molecular dynamics simulations and quantum mechanics/molecular mechanics calculations were performed on the in silico Leu597Ala/Ile663Ala double mutant of rabbit ALOX15 (12/15 lipoxygenase). The computational results suggested that subtle steric hindrance by the conserved Leu597 and C‐terminal Ile663 residues disturbed H10 abstractions in wildtype ALOX15 (which abstracts H13), but if these two bulky residues were mutated to smaller ones, H10 abstraction was no longer impeded and the regioselectivity of the initial H‐abstraction step was changed. However, site‐directed mutagenesis with HPLC analysis of the products of the whole oxidation process showed that the regioselectivity of the hydroperoxidation was not altered. This disagreement may be explained by the conformational reorganization of the system needed to rotate the ?OO^. group from an antarafacial to a suprafacial arrangement prior to back‐hydrogen transfer. After H10 abstraction and O₂ insertion, the evolution of the peroxy radical at C12 was sterically impeded, whereas peroxyl group rotation at C15 (after H13 abstraction) could easily evolve to a suprafacial arrangement, which thus led to the final product. For this reason, the global regiospecificity was not affected in the mutant. These findings exemplify that the regioselectivity of initial hydrogen abstraction and the regioselectivity of the final product do not necessarily coincide (in fact, they can be opposite) for the hydroperoxidation of arachidonic acid catalyzed by a lipoxygenase.     

Rapid determination of chlorogenic acid and related compounds in sunflower seeds by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

High-performance liquid chromatography (HPLC) in combination with atmospheric pressure chemical ionization mass spectrometry (APcI-MS) was applied to the determination of the phenolic fraction found in methanolic extracts of sunflower seeds (mainly chlorogenic acid and derived compounds). These extracts were directly separated by HPLC and detected by both negative and positive APcI-MS. Abundant structural information about these compounds can be obtained even at low extraction cone voltages. This method has been shown to be a rapid and effective method for the analysis of crude extracts from sunflower seeds.