Cross-conjugated poly(selenylene vinylene)s

Poly(selenylene vinylene) (PSV) is a close analog to the extensively studied poly(thienylene vinylene) (PTV) polymers, and possesses unique properties originating from the larger, more polarizable Se atoms.

η^2 bonded Nickel(0) thiophene π-complexes - identifying the missing link in catalyst transfer polymerization

<p>We have structurally characterized a nickel(0) thiophene complex that represents a close analog to the proposed intermediates in the mechanism of catalyst transfer polycondensation (CTP) of thiophenes. Additional studies on this intermediate allow us to determine the bonding in such complexes using a combination of nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, and DFT-based computations. Our structure of the catalyst agrees with previous postulates but provides important new structural insights into the species. Furthermore, our studies explain why these complexes actually exist and are stable enough to support living CTP.</p>

η^2 bonded Nickel(0) thiophene π-complexes - identifying the missing link in catalyst transfer polymerization

<p>We have structurally characterized a nickel(0) thiophene complex that represents a close analog to the proposed intermediates in the mechanism of catalyst transfer polycondensation (CTP) of thiophenes. Additional studies on this intermediate allow us to determine the bonding in such complexes using a combination of nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, and DFT-based computations. Our structure of the catalyst agrees with previous postulates but provides important new structural insights into the species. Furthermore, our studies explain why these complexes actually exist and are stable enough to support living CTP.</p>

η^2 bonded Nickel(0) thiophene π-complexes - identifying the missing link in catalyst transfer polymerization

<p>We have structurally characterized a nickel(0) thiophene complex that represents a close analog to the proposed intermediates in the mechanism of catalyst transfer polycondensation (CTP) of thiophenes. Additional studies on this intermediate allow us to determine the bonding in such complexes using a combination of nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, and DFT-based computations. Our structure of the catalyst agrees with previous postulates but provides important new structural insights into the species. Furthermore, our studies explain why these complexes actually exist and are stable enough to support living CTP.</p>

Newly Seen Debris Disks from the HST NICMOS Archive

By reprocessing the NICMOS coronagraphic archive using improved PSF subtraction methods, we have obtained new images of 5 debris disks, all previously unseen using classical PSF subtractions. Three of the disks are edge on and two appear to be ring like, one of which is extremely asymmetric.Their stellar hosts are nearby, young F and G type stars (40-90 pc, 12–30 Myr), including one that is a close analog to the young sun at roughly the age at which terrestrial planets were assembling. This is a 25% increase in the sample of debris disks seen in scattered light. Analysis and modeling of the disk geometries is in process. Given these systems' youth, proximity, and brightness (V = 7.2 to 8.5), these will be superb targets for investigating planet formation, and are perfect targets for studies with GPI, SPHERE and JWST.

Biochemical and Chemical Characterization of Trifluoromethylglyoxal Bis(guanylhydrazone), a Close Analog of the Antileukemic Drug Mitoguazone

In order to study the structure-activity relationships of bis(guanylhydrazone) type polyamine antimetabolites, trifluoromethylglyoxal bis(guanylhydrazone) (CF3-GBG), a close analog of the antileukemic drug methylglyoxal bis(guanylhydrazone) (mitoguazone. MGBG) was synthesized according to a novel modification of previous methods, yielding single crystals. Single-crystal X-ray crystallography revealed the presence of an isomer different from the one detected in the case of MGBG and all other bis(guanylhydrazones) so far studied. In contrast to MGBG, CF3-GBG was shown to be a very weak inhibitor of yeast adenosylmethionine decarboxylase, being thus devoid of value as a polyamine antimetabolite. In addition, the compound did not have antiproliferative activity against mouse L1210 leukemia cells in vitro. As long as analogous isomers of the two compounds are not available, no conclusions can be drawn about the reasons lying behind the drastical differences between their biological properties.

The Rôle of the Lion in Chretien de Troyes' Yvain

Although the lion plays a considerable rôle in Chrétien de Troyes' Chevalier au Lion, his function in the poem has traditionally attracted relatively little attention on the part of Arthurian scholars. Gaston Paris, in one of his notable articles on Chrétien, relegated the story of the noble beast to a footnote in which he said: “cette historiette … ne sert à rien dans le récit où Chrétien a jugé bon de l'insérer.”1Naturally enough, scholars who regard Yvain as a Celtic otherworld tale dressed up in French clothing, finding no close analog to the lion in Celtic lore, have paid little attention to him. And those who have con-cerned themselves with demonstrating that the source of the lion story was Latin or Greek have been interested more in the relation between Yvain's lion and that of Androcles (or some other one) than in his function in the poem. Those who have studied particularly the structure of the poem have attached more importance to the lion,2 but so far as I know no one has pointed out what seems to me to be his symbolic significance. Since Chrétien repeatedly said that he was concerned both with the “matière” and the “sens” of his romances,3 and as he called Yvain the roman du Chevalier au Lion,4 it seems reasonable to examine the poem in some detail and try to see if he attached more significance to the lion than modern scholarship has pointed out.