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Rö,nsberg, David,Debbab, Abdessamad,Má,ndi, Attila,Vasylyeva, Vera,Bö,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>
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Sobanska, Sophie,Hwang, HeeJin,Choë,l, Marie,Jung, Hae-Jin,Eom, Hyo-Jin,Kim, HyeKyeong,Barbillat, Jacques,Ro, Chul-Un American ChemicalSociety 2012 ANALYTICAL CHEMISTRY - Vol.84 No.7
<P>In this work, quantitative electron probe X-ray microanalysis (EPMA) and Raman microspectrometry (RMS) were applied in combination for the first time to characterize the complex internal structure and physicochemical properties of the same ensemble of Asian dust particles. The analytical methodology to obtain the chemical composition, mixing state, and spatial distribution of chemical species within single particles through the combined use of the two techniques is described. Asian dust aerosol particles collected in Incheon, Korea, during a moderate dust storm event were examined to assess the applicability of the methodology to resolve internal mixtures within single particles. Among 92 individual analyzed particles, EPMA and RMS identified 53% of the particles to be internally mixed with two or more chemical species. Information on the spatial distribution of chemical compounds within internally mixed individual particles can be useful for deciphering the particle aging mechanisms and sources. This study demonstrates that the characterization of individual particles, including chemical speciation and mixing state analysis, can be performed more in detail using EPMA and RMS in combination than with the two single-particle techniques alone.</P>
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Enhanced Multiple Exciton Generation in PbS|CdS Janus-like Heterostructured Nanocrystals
Kroupa, Daniel M.,Pach, Gregory F.,Vö,rö,s, Má,rton,Giberti, Federico,Chernomordik, Boris D.,Crisp, Ryan W.,Nozik, Arthur J.,Johnson, Justin C.,Singh, Rohan,Klimov, Victor I.,Galli, American Chemical Society 2018 ACS NANO Vol.12 No.10
<P>Generating multiple excitons by a single high-energy photon is a promising third-generation solar energy conversion strategy. We demonstrate that multiple exciton generation (MEG) in PbS|CdS Janus-like heteronanostructures is enhanced over that of single-component and core/shell nanocrystal architectures, with an onset close to two times the PbS band gap. We attribute the enhanced MEG to the asymmetric nature of the heteronanostructure that results in an increase in the effective Coulomb interaction that drives MEG and a reduction of the competing hot exciton cooling rate. Slowed cooling occurs through effective trapping of hot-holes by a manifold of valence band interfacial states having both PbS and CdS character, as evidenced by photoluminescence studies and <I>ab initio</I> calculations. Using transient photocurrent spectroscopy, we find that the MEG characteristics of the individual nanostructures are maintained in conductive arrays and demonstrate that these quasi-spherical PbS|CdS nanocrystals can be incorporated as the main absorber layer in functional solid-state solar cell architectures. Finally, based upon our analysis, we provide design rules for the next generation of engineered nanocrystals to further improve the MEG characteristics.</P> [FIG OMISSION]</BR>
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Efficient Excitonic Photoluminescence in Direct and Indirect Band Gap Monolayer MoS<sub>2</sub>
Steinhoff, A.,Kim, J.-H.,Jahnke, F.,Rö,sner, M.,Kim, D.-S.,Lee, C.,Han, G. H.,Jeong, M. S.,Wehling, T. O.,Gies, C. American Chemical Society 2015 NANO LETTERS Vol.15 No.10
<P>We discuss the photoluminescence (PL) of semiconducting transition metal dichalcogenides on the basis of experiments and a microscopic theory. The latter connects ab initio calculations of the single-particle states and Coulomb matrix elements with a many-body description of optical emission spectra. For monolayer MoS<SUB>2</SUB>, we study the PL efficiency at the excitonic A and B transitions in terms of carrier populations in the band structure and provide a quantitative comparison to an (In)GaAs quantum well-structure. Suppression and enhancement of PL under biaxial strain is quantified in terms of changes in the local extrema of the conduction and valence bands. The large exciton binding energy in MoS<SUB>2</SUB> enables two distinctly different excitation methods: above-band gap excitation and quasi-resonant excitation of excitonic resonances below the single-particle band gap. The latter case creates a nonequilibrium distribution of carriers predominantly in the K-valleys, which leads to strong emission from the A-exciton transition and a visible B-peak even if the band gap is indirect. For above-band gap excitation, we predict a strongly reduced emission intensity at comparable carrier densities and the absence of B-exciton emission. The results agree well with PL measurements performed on monolayer MoS<SUB>2</SUB> at excitation wavelengths of 405 nm (above) and 532 nm (below the band gap).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-10/acs.nanolett.5b02719/production/images/medium/nl-2015-02719d_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02719'>ACS Electronic Supporting Info</A></P>
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Infinite Sidon Sets Contained in Sparse Random Sets of Integers
Kohayakawa, Yoshiharu,Lee, Sang June,Moreira, Carlos Gustavo,Rö,dl, Vojtě,ch Society for Industrial and Applied Mathematics 2018 SIAM Journal on Discrete Mathematics Vol.32 No.1
<P>A set <TEX>$S$</TEX> of natural numbers is a <italic toggle='yes'>Sidon</I> set if all the sums<TEX>$s_1+s_2$</TEX> with <TEX>$s_1$</TEX>, <TEX>$s_2\in S$</TEX> and <TEX>$s_1\leq s_2$</TEX> are distinct.Let constants <TEX>$\alpha>0$</TEX> and <TEX>$0<\delta<1$</TEX> be fixed, andlet <TEX>$p_m=\min\{1,\alpha m^{-1+\delta}\}$</TEX> for all positiveintegers <TEX>$m$</TEX>. Generate a random set <TEX>$R\subset {\mathbb N}$</TEX> by adding <TEX>$m$</TEX>to <TEX>$R$</TEX> with probability <TEX>$p_m$</TEX>, independently for each <TEX>$m$</TEX>. Weinvestigate how dense a Sidon set <TEX>$S$</TEX> contained in <TEX>$R$</TEX> can be. Ourresults show that the answer is qualitatively very different in atleast three ranges of <TEX>$\delta$</TEX>. We prove quite accurate results forthe range <TEX>$0<\delta\leq2/3$</TEX>, but only obtain partial results forthe range <TEX>$2/3<\delta\leq1$</TEX>.</P>
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