Natural abundance solution 13C NMR studies of a phototropin with photoinduced polarization

Strongly spin-polarized 13C NMR lines have been observed upon photoexcitation of FMN-binding LOV domains from the blue-light receptor phototropin. Their origin can be rationalized in terms of intermediate radical-pair spin chemistry. Due to hyperfine-selective branching into singlet and triplet products of different lifetime, nuclear spin polarization builds up on nuclei that possess high electron-spin density in the radical state. By examining point-mutated LOV domains of phototropin, spin-polarized 13C NMR signals in emission arising from 13C nuclei at natural abundance in the apoprotein can be unambiguously assigned to a tryptophan residue that is located at a distance of about 14 A from the FMN cofactor and that undergoes photoinduced electron transfer to the flavin. This demonstrates the potential of photo-CIDNP in unraveling reactive intermediates in protein function.     

Expanding Reaction Horizons: Evidence of the 5-Deazaflavin Radical Through Photochemically Induced Dynamic Nuclear Polarization

Deazaflavins are important analogues of the naturally occurring flavins: riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). The use of 5-deazaflavin as a replacement coenzyme in a number of flavoproteins has proven particularly valuable in unraveling and manipulating their reaction mechanisms. It was frequently reported that one-electron-transfer reactions in flavoproteins are impeded with 5-deazaflavin as the cofactor. Based on these findings, it was concluded that the 5-deazaflavin radical is significantly less stable compared to the respective flavin semiquinone and quickly re-oxidizes or undergoes disproportionation. The long-standing paradigm of 5-deazaflavin being solely a two-electron/hydride acceptor/donor—“a nicotinamide in flavin clothing”—needs to be re-evaluated now with the indirect observation of a one-electron-reduced (paramagnetic) species using photochemically induced dynamic nuclear polarization (photo-CIDNP) ¹H nuclear magnetic resonance (NMR) under biologically relevant conditions.     

Average site perimeter of directed animals on the two-dimensional lattices

We introduce new combinatorial (bijective) methods that enable us to compute the average value of three parameters of directed animals of a given area, including the site perimeter. Our results cover directed animals of any one-line source on the square lattice and its bounded variants, and we give counterparts for most of them in the triangular lattices. We thus prove conjectures by Conway and Le Borgne. The techniques used are based on Viennot’s correspondence between directed animals and heaps of pieces (or elements of a partially commutative monoid).     

Modern Trends in Organic Light-Emitting Devices (OLEDs)

Summary. Synthesis of crosslinkable small and large organic molecules having OLED properties will be presented. Three strategies for the construction of multilayer devices will be described. In the first case small, well-defined OLED-molecules are functionalized with oxetanes as crosslinker. The second case deals with polymers having OLED active units in the main chain and pendant crosslinkers and finally it was shown that styrene polymers with pendant OLED functions and crosslinkers can be applied for the construction of such multilayer and multicolour devices.     

High resolution dissociative electron attachment to gas phase adenine

The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6 eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0 to 15 eV with an electron energy resolution of about 100 meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed.     

Luteapyrone,a Novel ƴ-Pyrone Isolated from the Filamentous Fungus Metapochonia lutea

In the process of screening for new bioactive microbial metabolites we found a novel ƴ-pyrone derivative for which we propose the trivial name luteapyrone, in a recently described microscopic filamentous fungus, Metapochonia lutea BiMM-F96/DF4. The compound was isolated from the culture extract of the fungus grown on modified yeast extract sucrose medium by means of flash chromatography followed by preparative HPLC. The chemical structure was elucidated by NMR and LC-MS. The new compound was found to be non-cytotoxic against three mammalian cell lines (HEK 263, KB-3.1 and Caco-2). Similarly, no antimicrobial activity was observed in tested microorganisms (gram positive and negative bacteria, yeast and fungi).     

Molding plateable micropatterns of electrically insulating and electrically conducting poly(methyl methacrylate)s by the LIGA technique

A new process of molding directly plateable molded plastic pieces has been developed for the mass fabrication of metal micropatterns of any shape by the LIGA-technique. In this process, electrically insulating micropatterns of poly(methyl methacrylate) are molded on the surface of an electrically conducting poly(methyl methacrylate) composite. The composite is made of a methyl methacrylate casting resin. In the development process, the polymerization of casting resins was studied for various fillers and initiators. In addition, poly(methyl methacrylate)s filled with silver were subjected to studies of the electrical, thermal, and mechanical behavior of the composites as a function of the filler content.