Beyond prostaglandins--chemistry and biology of cyclic oxygenated metabolites formed by free-radical pathways from polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are important constituents in all organisms. They fulfil many functions, ranging from modulating the structure of membranes to acting as precursors of physiologically important molecules, such as the prostaglandins, which for a long time were the most prominent cyclic PUFA metabolites. However, since the beginning of the 1990s a large variety of cyclic metabolites have been discovered that form under autoxidative conditions in vivo to a much larger extent than do prostaglandins. These compounds--isoprostanes, neuroprostanes, phytoprostanes, and isofurans--proved subsequently to be ubiquitous in nature. They display a wide range of biological activities, and isoprostanes have become the currently most reliable indicators of oxidative stress in humans. In a relatively short time, the structural variety, properties, and applications of the autoxidatively formed cyclic PUFA derivatives have been uncovered.     

Stickstoffmonoxid,Superoxid und Peroxynitrit: Radikalchemie im Organismus

^˙NO is an arginine‐derived signal molecule which together with prostacyclin is involved in blood vessel relaxation. Superoxide (^˙O2‐) being a radical like ^˙NO, almost quantitatively traps ^˙NO under formation of peroxynitrite, which is able to oxidatively modify biomolecules. Already submicromolar concentrations of peroxynitrite selectively cause a tyrosine nitration and inactivation of prostacyclin synthase. The mechanism of this nitration could be explained by a heme‐thiolate‐catalyzed homolytic cleavage of peroxynitrite followed by the formation of a ferryl/^˙NO2 intermediate. By this nitration reaction the superoxide radical gains a new function as a signal molecule with antagonistic actions to ^˙NO. Inflammatory conditions upregulate ^˙NO and superoxide in many cells and by the generating higher levels of peroxynitrite cause pathophysiological effects. Such oxidative changes may be a future target for pharmacological interventions by suitable antioxidants.     

Dialkylcyclopentadithiophene Polymers and Copolymers

Poly(2,6‐(4,4‐dialkyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene) (PCPDT) homopolymers and poly[(2,7‐(9,9‐dialkyl)fluorene)‐co‐(2,6‐(4,4‐dialkyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene)] (PF/PCPDT) copolymers have been synthesized according to Yamamoto with Ni(COD)₂ (or NiCl₂/Zn in the case of the homopolymer). PCPDT is characterized by a red‐shifted long wavelength absorption maximum (565 nm) when compared to that of polyfluorene (PF, 378 nm). In contrast to PF, its heteroaromatic analogue PCPDT does not form thermotropic LC phases. The PF/PCPDT copolymers show clear indications for a block copolymer character (two separated π‐π* absorption maxima, two glass transitions).     

X‐ray Rotation‐Tilt‐Method — First Results of a new X‐ray Diffraction Technique

That from us as X‐ray Rotation‐Tilt Technique (XRT Method) designated procedure principle represents a world innovation and overcomes essential disadvantages of comparable diffraction techniques known up to now. Starting from the origin and the informational content of the XRT interferences a realization of a special equipment and selected examples of some first applications are presented.     

Persistence of nematic liquid crystalline phase in a polyfluorene‐based organic semiconductor: A high pressure study

The role of high pressure on a low molecular weight nematic liquid crystalline organic semiconductor, ethyl‐hexyl substituted polyfluorene (PF2/6) is investigated using photoluminescence (PL), Raman scattering, and X‐ray scattering studies at pressures from 1 to 8 GPa. The PL and the Raman data under pressure are consistent with each other with no abrupt changes in the pressure coefficients of PL or Raman peaks. The PL energies redshift and broaden, consistent with both enhanced intra‐ and interchain interactions. The Raman peak positions yield pressure coefficients similar to other phenyl based π‐conjugated polymers. The broadening of a doublet peak in the 1135 cm^?1 region indicates a more planar backbone conformation with increasing pressure. X‐ray scattering indicates that the torsion angle between adjacent repeats reduces with increasing pressure and reverts back with decompression. The intermolecular structure is weakly ordered (frozen nematic) and essentially maintained with increasing pressure, in contrast to a high molecular weight PF2/6. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1014–1023     

Direct Hydroboration of BB Bonds: A Mild Strategy for the Proliferation of BB Bonds

Synthetic access to electron‐precise boron chains is hampered by the preferential formation of nonclassical structures. The few existing strategies for this involve either strongly reducing reagents or transition‐metal catalysts, both with distinct disadvantages. The synthesis of new furyl‐ and thienyl‐substituted diborenes is presented, along with their direct hydroboration with catecholborane (CatBH) to form a new electron‐precise B? B bond and a B₃ chain. The reaction is diastereoselective and proceeds under mild conditions without the use of strong reducing agents or transition‐metal catalysts commonly used in B‐B coupling reactions.