Photochemical preparation of highly functionalized 1-indanones

A series of o-alkylphenyl alkyl ketones 1 were synthesized by different methods. The presence of a leaving group X adjacent to the carbonyl group is the special peculiarity of these ketones. Upon irradiation the keto carbonyl group of these compounds undergoes an n-pi* excitation followed by a 1,5-hydrogen migration from the o-alkyl substituent to the carbonyl oxygen atom. The thus formed 1,4-diradicals are subject to a very rapid elimination of acid HX, giving 1,5-diradicals. We called this process spin center shift. After intersystem crossing these diradicals cyclize to 1-indanones 20 in good yields. Depending on the solvent and on substituents, o-alkoxyalkyl ketones 22 or benzo[c]furanes 21 are obtained as byproducts. The mechanism of the cyclization was elucidated by quantum chemical calculations and kinetic measurements.     

Photochemically induced dynamic nuclear polarization in photosystem I of plants observed by 13C magic-angle spinning NMR

Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in photosystem I of spinach by (13)C magic angle spinning solid-state NMR under continuous illumination with white light. An almost complete set of chemical shifts of the aromatic ring carbons of a single Chl a molecule has been obtained which is assigned to the P2-cofactor of the primary electron donor P700. Since all light-induced (13)C NMR signals appear to be emissive, a predominance of the three-spin mixing mechanism over the differential decay mechanism is proposed. The origin of the strong contribution of the three-spin mixing mechanism and the differences with photosystem II are discussed.     

Peak compression effects in capillary electrochromatography

Peak compression in CEC is a phenomenon that can generate very narrow peaks with extremely high efficiencies that defy current chromatographic theory. This review article summarises the content of publications in this area up to this date. Two main types of peak compression effects have been observed in the literature. First, an irreproducible and hard to control focusing effect of unclear origin, observed on strong cation exchangers. Second, a reproducible continuous stacking effect caused by sample composition induced system zones demonstrated on several types of stationary phases.     

Interaction of C60 with carbon nanotubes and graphite

The interaction of C60 with single-wall carbon nanotubes (SWNTs) and graphite is studied experimentally by thermal desorption spectroscopy and theoretically by molecular-mechanics and molecular-dynamics calculations. The van der Waals parameters and force field for C60-graphene and C60-SWNT interactions are derived from the low-coverage C60 binding energy to the graphite surface. We use these to compare the efficiency of different mechanisms by which C60 can be encapsulated into SWNTs.     

On the influence of the basis set superposition error on calculated vibrational frequencies

The relation between the so called basis set superposition error and intramolecular vibrational frequencies calculated at the Hartree Fock SCF level of approximation was investigated. A linear conformation of HF dimer was chosen as test system for the investigation. It was found that the direct basis set superposition error for the studied system is rather small. It was further found that the shifts are mainly determined by the geometry parameters of the system. AcknowledgementsJ. M. H.-R. wishes to thank the Ministerio de Educación, Cultura y Deporte for the award of a research grant.     

Gas chromatography with mass spectrometric,atomic emission and Fourier transform infrared spectroscopic detection as complementary analytical techniques for the identification of unknown impurities in pharmaceutical analysis

An example of the complementary use of GC-MS. GC-AED and GC-FT-IR is described for efficient structure elucidation of an unknown impurity in pharmaceutical analysis. None of the analytical techniques could solve the structure of the unknown impurity alone; identification was, however, straightforward by combining the available spectroscopic information. GC-MS provided information about structural fragments and molecular mass of the unknown compound. GC-AED was used for confirmation of the occurrence of the individual elements in the structure and to enable calculation of the empirical formula. GC-FT-IR gave valuable information regarding functional groups in the molecule.     

Sheaf cohomology and free resolutions over exterior algebras

We derive an explicit version of the Bernstein-Gel'fand-Gel'fand (BGG) correspondence between bounded complexes of coherent sheaves on projective space and minimal doubly infinite free resolutions over its ``Koszul dual' exterior algebra. Among the facts about the BGG correspondence that we derive is that taking homology of a complex of sheaves corresponds to taking the ``linear part' of a resolution over the exterior algebra.

We explore the structure of free resolutions over an exterior algebra. For example, we show that such resolutions are eventually dominated by their ``linear parts" in the sense that erasing all terms of degree 1$"> in the complex yields a new complex which is eventually exact.

As applications we give a construction of the Beilinson monad which expresses a sheaf on projective space in terms of its cohomology by using sheaves of differential forms. The explicitness of our version allows us to prove two conjectures about the morphisms in the monad, and we get an efficient method for machine computation of the cohomology of sheaves. We also construct all the monads for a sheaf that can be built from sums of line bundles, and show that they are often characterized by numerical data.

     

Zwei Beispiele ganzer Funktionen mit algebraischem Höchstindex einer Stellensorte

Ohne Zusammenfassung     

The Generation of Maximal Triangle-Free Graphs

In this paper we present an efficient algorithm for generating maximal triangle-free graphs. A program based on this algorithm has been used to check a conjecture of Erdo´´s about the local density of triangle-free graphs and turned out to be very powerful for the computation of triangle Ramsey numbers.