Effect of strain on surface diffusion in semiconductor heteroepitaxy

We present a first-principles analysis of the strain renormalization of the cation diffusivity on the GaAs(001) surface. For the example of In/GaAs(001)-c(4x4) it is shown that the binding of In is increased when the substrate lattice is expanded. The diffusion barrier \Delta E(e) has a non-monotonic strain dependence with a maximum at compressive strain values (e 0) studied. We discuss the consequences of spatial variations of both the binding energy and the diffusion barrier of an adatom caused by the strain field around a heteroepitaxial island. For a simplified geometry, we evaluate the speed of growth of two coherently strained islands on the GaAs(001) surface and identify a growth regime where island sizes tend to equalize during growth due to the strain dependence of surface diffusion.Comment: 10 pages, 8 figures, LaTeX2e, to appear in Phys. Rev. B (2001). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge (001) surfaces

First-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) surfaces. Our calculations reveal that the binding and activation energies on a strained Ge(001) surface increase and decrease, respectively, by 0.21 eV and 0.12 eV per percent compressive strain. For a growth temperature of 600 degrees C, these strain-dependencies give rise to a 16-fold increase in adatom density and a 5-fold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm.Comment: 4 pages, 4 figure

Niebla homalea Rundel & Bowler

<i>3.3. Extraction and isolation of secondary metabolites of Niebla homalea</i> <p> The lichen <i>Niebla homalea</i> (Ach.) Rundel & Bowler (62 g) was macerated for 1 week with 3 L of ethyl acetate. The extract was filtered and concentrated <i>in vacuo</i> to yield 4 g of a brown residue. This ethyl acetate residue was subjected to passage over a silica gel column [SiliaFlash® P60 (230–400 mesh)], and eluted sequentially with hexane containing increasing amounts of ethyl acetate (1:0, 20:1, 10:1, 5:1, 2:1, 1:1, and 0:1), to afford ten major fractions labeled N1 to N10. Fraction N2 (20 mg) yielded compound <b>6</b> (5 mg) by precipitation in chloroform (CHCl 3). Fractions N3 (6 mg) and N4 were washed with chloroform to afford compounds <b>4</b> (1 mg) and <b>7</b> (6 mg), respectively. Fraction N5 (40 mg) was purified using a C 18 column (CH 3 CN–H 2 O, 7:3) to give <b>5</b> (3 mg). Fraction N6 (40 mg) was purified also via a C 18 column (CH 3 CN–H 2 O, 3:2) to yield compound <b>9</b> (3 mg). Fraction N7 (120 mg) was chromatographed over a Sephadex LH-20 column with hexane-CHCl 3 -MeOH (5:5:1) as solvent and washed with hexanes-CHCl 3 -MeOH (5:5:1) to afford <b>11</b> (6 mg). Fraction N8 (170 mg) was chromatographed over a Sephadex LH-20 column, eluted with hexanes-CHCl 3 -MeOH (5:5:1), and further purified via silica gel column chromatography (hexanes-EtOAc, 5:1) to yield <b>12</b> (4 mg) and <b>8</b> (4 mg). Fraction N9 (130 mg) was chromatographed over a Sephadex LH-20 column with hexanes-CHCl 3 - MeOH (5:5:1) and further purified via a C 18 column (CH 3 CN–H 2 O, 7:3) to yield compounds <b>2</b> (2 mg) and <b>3</b> (2 mg). Fraction N10 (70 mg) was chromatographed over a Sephadex LH-20 column with hexanes-CHCl 3 - MeOH (5:5:1) and washed with hexanes-CHCl 3 -MeOH (5:5:1) to yield 3 mg of <b>1</b> and 4 mg of <b>10</b>.</p> <p> Anaya-Eugenio, G.D., Tan, C.Y., Rakotondraibe, L.H., Carcache de Blanco, E.J., 2020. Tumor suppressor p53 independent apoptosis in HT-29 cells by auransterol from <i>Penicillium aurantiacobrunneum</i>. Biomed. Pharmacother. 127, 110124. https://doi. org/10.1016/j.biopha.2020.110124.</p> <p>*Assignments based on HSQC and HMBC spectra.</p> <p> Carpentier, C., Queiroz, E.F., Marcourt, L., Wolfender, J.-L., Azelmat, J., Grenier, D., Boudreau, S., Voyer, N., 2017. Dibenzofurans and pseudodepsidones from the lichen <i>Stereocaulon paschale</i> collected in northern Quebec. J. Nat. Prod. 80, 210–214.</p> <p> Chin, W.J., Corbett, R.E., Heng, C.K., Wilkins, A.L., 1973. Lichens and fungi. XI. Isolation and structural elucidation of a new group of triterpenes from <i>Sticta coronata, S. colensoi</i>, and <i>S. flavicans</i>. J. Chem. Soc., Perkin Trans. 1, 1437–1446.</p> <p>Connolly, J.D., 1977. Triterpenoids. In: Terpenoids and Steroids, Vol. 7. Royal Society of Chemistry, Cambridge, UK, pp. 130–154.</p> <p> <i>Nieblastictane A (8S,9S,10R,14S,17R,18S,21R, 22R)-22α- hydroxystictan-3-on-30-oic acid, 1)</i>: white amorphous powder; [<i>α</i>] 20 D +66.0 (<i>c</i> 0.001, MeOH); IR (KBr) <i>ν</i> max: 3465, 2956, 2875, 1699, 1471, 1385, 1241, 754, 667 cm 1; 1 H NMR (400 MHz, CDCl 3) and 13 C NMR (100 MHz, CDCl 3) data, see Table 1; HRESIMS <i>m</i> / <i>z</i> 495.3447 [M + Na] + (calcd. for C 30 H 48 O 4 Na +: 495.3445).</p> <p> Connolly, J.D., Freer, A.A., Kalb, K., Huneck, S., 1984. Lichen substances. Part 141. Eriodermin, a dichlorodepsidone from the lichen <i>Erioderma physcioides</i> - crystal structure analysis. Phytochemistry 23, 857–858.</p> <p>Corbett, R.E., Wilkins, A.L., 1976a. Lichens and fungi. Part XII. Dehydration and isomerization of stictane triterpenoids. J. Chem. Soc., Perkin Trans. 1, 857–863.</p> <p>Corbett, R.E., Wilkins, A.L., 1976b. Lichens and fungi. Part XIII. Comparison of the nuclear magnetic resonance and mass spectra of 17,21-secohopane and 17,21- secoflavicane derivatives. J. Chem. Soc., Perkin Trans. 1, 1316–1320.</p> <p> <i>Nieblastictane B (8S,9S,10R,14S,17R,18S,21S,22R)-22α- Hydroxysticta-3-on-29 oic acid, 2)</i>: white amorphous powder; [<i>α</i>] 20 D +24.0 (<i>c</i> 0.001, MeOH); IR (KBr) <i>ν</i> max 3390, 2956, 2873, 1702, 1457, 1385, 1230, 1057, 755 cm 1; 1 H NMR (400 MHz, CDCl 3) and 13 C NMR (100 MHz, CDCl 3) data, see Table 1; HRESIMS <i>m</i> / <i>z</i> 495.3440 [M +Na] + (calcd. for C 30 H 48 O 4 Na +: 495.3445).</p> <p>Corbett, R.E., Heng, C.K., Wilkins, A.L., 1976. Lichens and fungi. XIV. A revised structure for retigerane triterpenoids. Aust. J. Chem. 29, 2567–2570.</p> <p>Culberson, C.F., 1969. Chemical and Botanical Guide to Lichen Products. Univ. North Carolina Press.</p> <p>Eastwood, A., 1924. Archibald Menzies’ Journal of the Vancouver Expedition. California Historical Society Quarterly 2 (4), 265–340.</p> <p> <i>Nieblastictane C (2R,8S,9S,10R,12S,13S,14S,17R,18S,21R,22R)-2- chloro-12, 22-dihydroxystictan-3-one (3)</i>: white amorphous powder; [<i>α</i>] 20 D 1.00 (<i>c</i> 0.001, MeOH); IR (KBr) <i>ν</i> max 3411, 2945, 2873, 1709, 1458, 1386, 1217, 1059, 1022, 755 cm 1; 1 H NMR (400 MHz, CDCl 3) and 13 C NMR (100 MHz, CDCl 3) data, see Table 1; HRESIMS <i>m</i> / <i>z</i> 515.3268 [M + Na] + (calcd. for C 30 H 49 O 3 ClNa, 515.3262).</p> <p> Elix, J.A., Whitton, A.A., Jones, A.J., 1982. Triterpenes from the lichen genus <i>Physcia</i>. Aust. J. Chem. 35, 641–647.</p> <p>Gollapudi, S.R., Telikepalli, H., Jampani, H.B., Mirhom, Y.W., Drake, S.D.,</p> <p> Bhattiprolu, K.R., Vander Velde, D., Mitscher, L.A., 1994. Alectosarmentin, a new antimicrobial dibenzofuranoid lactol from the lichen, <i>Alectoria sarmentosa</i>. J. Nat. Prod. 57, 934–938.</p> <p> Gonzalez, A.G., Barrera, J.B., Rodriguez Perez, E.M., 1991. Chemical constituents of the lichen <i>Cladina macaronesica</i>. Z. Naturforsch., C: Biosci. 46, 12–18.</p> <p> <i>Nieblaflavicane A</i> (<i>8S,9S,10R,14S,17R,18S,21S)-30-nor-21βH-flavican-3,22-dione, 4)</i>: thin white needles (CH 2 Cl 2 – CH 3 OH); [<i>α</i>] 20 D 127.2 (<i>c</i> 0.001, MeOH); IR (KBr) <i>ν</i> max 2928, 1704, 1383 cm 1; 1 H NMR (400 MHz, CDCl 3) and 13 C NMR (100 MHz, CDCl 3) data, see Table 2; HRESIMS <i>m</i> / <i>z</i> 449.3394 [M +Na] + (calcd. for 449.3396, C 29 H 46 O 2 Na).</p> <p> <i>Nieblaflavicane B (8S,9S,10R,14S,17R,18S)</i> -22,29,30- <i>trinor-flavican-3,21-dione, 5)</i>: white needles (CH 2 Cl 2 – CH 3 OH); [<i>α</i>] 20 D +3.0 (<i>c</i> 0.001, MeOH); IR (KBr) <i>ν</i> max 2928, 2869, 1734, 1705, 1461, 1384, 1110 cm 1; 1 H NMR (400 MHz, CDCl 3) and 13 C NMR (100 MHz, CDCl 3) data, see Table 2; HRESIMS <i>m</i> / <i>z</i> 421.3088 [M + Na] + (calcd. for 421.3083, C 27 H 42 O 2 Na).</p> <i>3.4. Cytotoxicity assay</i> <p>The cytotoxic activities of the isolates were evaluated against human hormone-dependent breast (MCF-7) and ovarian (A2780) cancer cell lines, according to a previously described protocol and paclitaxel and camptothecin were used as positive controls (Tan et al., 2019).</p> <p> <b>Funding</b></p> <p>This project was supported by supplement 3P01CA125066-09/10S1 of a NIH / NCI program grant (P01CA125066). We thank the College of Pharmacy and the Campus Chemical Instrument Center (CCIC) instrumentation facilities for access to NMR and MS equipment.</p> Declaration of competing interest <p>The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.</p> Appendix A. Supplementary data <p>Supplementary data to this article can be found online at https://doi. org/10.1016/j.phytochem.2020.112521.</p> References <p> Gonzalez Gonzalez, A., Delgado Martin, J., Perez, C., 1974. Three new triterpenes from the lichen <i>Xanthoria resendei</i>. Phytochemistry 13, 1547–1549.</p> <p> Huneck, S., 1984. Lichen substances. Part 142. <i>tert</i> -Butanolysis of lichen depsides. Phytochemistry 23, 2697–2698.</p> <p>Jachens, R.C., Wentworth, C.M., McLaughlin, R.J., 1998. Pre-San Andreas location of the Gualala block inferred from magnetic and gravity anomalies. In: Elder, W.P. (Ed.),</p> <p>Geology and Tectonics of the Gualala Block, Northern California. Society of Economic Paleontologists and Mineralologists, Pacific Section, Book 84, pp. 27–36.</p> <p>Kirk, D.N., Klyne, W., 1976. Chiroptical studies. Part LXXXIX. An empirical analysis of the circular dichroism of hexahydroindanones, bicyclo[4.2.0]octan-7-ones, and their polycyclic analogs. J. Chem. 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A one- and two-dimensional carbon-13 and proton NMR study of some triterpenes of the hopane, stictane and flavicene groups. Aust. J. Chem. 42, 243–257.</p> <p> Yu, X., Guo, Q., Su, G., Yang, A., Hu, Z., Qu, C., Wan, Z., Li, R., Tu, P., Chai, X., 2016. Usnic acid derivatives with cytotoxic and antifungal activities from the lichen <i>Usnea longissima</i>. J. Nat. Prod. 79, 1373–1380.</p>Published as part of <i>Zhang, Yan, Tan, Choon Yong, Spjut, Richard W., Fuchs, James R., Kinghorn, A. Douglas & Rakotondraibe, Liva Harinantenaina, 2020, Specialized metabolites of the United States lichen Niebla homalea and their antiproliferative activities, pp. 1-7 in Phytochemistry (112521) (112521) 180</i> on pages 5-7, DOI: 10.1016/j.phytochem.2020.112521, <a href="http://zenodo.org/record/8301840">http://zenodo.org/record/8301840</a&gt