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Rox308,nsberg, David,Debbab, Abdessamad,Max301,ndi, Attila,Vasylyeva, Vera,Box308,hler, Philip,Stork, Bjö,rn,Engelke, Laura,Hamacher, Alexandra,Sawadogo, Richard,Diederich, Marc,Wray, Vict American Chemical Society 2013 Journal of organic chemistry Vol.78 No.24
<P>Four tetrahydroxanthone dimers (<B>1</B>–<B>4</B>) and four biogenetically related monomers (<B>5</B>–<B>8</B>), including the new derivatives <B>4</B>–<B>6</B>, were isolated from the endophyte Phomopsis longicolla. The absolute configurations of <B>2</B>–<B>4</B> were established for the first time by TDDFT electronic circular dichroism calculations, and that of phomoxanthone A (<B>1</B>) was revised by X-ray crystallography. Phomoxanthone A (<B>1</B>) showed the strongest pro-apoptotic activity when tested against a panel of human cancer cell lines, including cisplatin-resistant cells, whereas it was up to 100-fold less active against healthy blood cells. It was also the most potent activator of murine T lymphocytes, NK cells, and macrophages, suggesting an activation of the immune system in parallel to its pro-apoptotic activity. This dual effect in combating cancer cells could help in fighting resistance during chemotherapy. Preliminary structure–activity studies of isolated compounds and derivatives obtained by semisynthesis (<B>9a</B>–<B>11</B>) hinted at the location of the biaryl axis and the presence of acetyl groups as important structural elements for the biological activity of the studied tetrahydroxanthones.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2013/joceah.2013.78.issue-24/jo402066b/production/images/medium/jo-2013-02066b_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo402066b'>ACS Electronic Supporting Info</A></P>
Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials
Kleemann, Hans,Gutierrez, Rafael,Lindner, Frank,Avdoshenko, Stanislav,Manrique, Pedro D.,Lux308,ssem, Bjö,rn,Cuniberti, Gianaurelio,Leo, Karl American Chemical Society 2010 Nano letters Vol.10 No.12
<P>Organic Zener diodes with a precisely adjustable reverse breakdown from −3 to −15 V without any influence on the forward current−voltage curve are realized. This is accomplished by controlling the width of the charge depletion zone in a pin-diode with an accuracy of one nanometer independently of the doping concentration and the thickness of the intrinsic layer. The breakdown effect with its exponential current voltage behavior and a weak temperature dependence is explained by a tunneling mechanism across the highest occupied molecular orbital−lowest unoccupied molecular orbital gap of neighboring molecules. The experimental data are confirmed by a minimal Hamiltonian model approach, including coherent tunneling and incoherent hopping processes as possible charge transport pathways through the effective device region.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-12/nl102916n/production/images/medium/nl-2010-02916n_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl102916n'>ACS Electronic Supporting Info</A></P>