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- 저자 : Smith III, Milton R. (검색결과 6 건)
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Catalytic borylation of methane
Smith, Kyle T.,Berritt, Simon,Gonzá,lez-Moreiras, Mariano,Ahn, Seihwan,Smith III, Milton R.,Baik, Mu-Hyun,Mindiola, Daniel J. American Association for the Advancement of Scienc 2016 Science Vol.351 No.6280
<P>Despite steady progress in catalytic methods for the borylation of hydrocarbons, methane has not yet been subject to this transformation. Here we report the iridium-catalyzed borylation of methane using bis(pinacolborane) in cyclohexane solvent. Initially, trace amounts of borylated products were detected with phenanthroline-coordinated Ir complexes. A combination of experimental high-pressure and high-throughput screening, and computational mechanism discovery techniques helped to rationalize the foundation of the catalysis and identify improved phosphine-coordinated catalytic complexes. Optimized conditions of 150 degrees C and 3500-kilopascal pressure led to yields as high as similar to 52%, turnover numbers of 100, and improved chemoselectivity for monoborylated versus diborylated methane.</P>
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Mechanistic study of styrene aziridination by iron( <small>IV</small> ) nitrides
Crandell, Douglas ,W.,Muñ,oz III, Salvador B.,Smith, Jeremy M.,Baik, Mu-Hyun Royal Society of Chemistry 2018 Chemical Science Vol.9 No.45
<▼1><P>A combined experimental and computational investigation reveals that styrene aziridination by an iron(<SMALL>IV</SMALL>) nitride occurs by a stepwise mechanism involving multistate character.</P></▼1><▼2><P>A combined experimental and computational investigation was undertaken to investigate the mechanism of aziridination of styrene by the tris(carbene)borate iron(<SMALL>IV</SMALL>) nitride complex, PhB(<SUP><I>t</I></SUP>BuIm)<SUB>3</SUB>Fe 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 N. While mechanistic investigations suggest that aziridination occurs <I>via</I> a reversible, stepwise pathway, it was not possible to confirm the mechanism using only experimental techniques. Density functional theory calculations support a stepwise radical addition mechanism, but suggest that a low-lying triplet (<I>S</I> = 1) state provides the lowest energy path for C–N bond formation (24.6 kcal mol<SUP>–1</SUP>) and not the singlet ground (<I>S</I> = 0) state. A second spin flip may take place in order to facilitate ring closure and the formation of the quintet (<I>S</I> = 2) aziridino product. A Hammett analysis shows that electron-withdrawing groups increase the rate of reaction <I>σ</I><SUB>p</SUB> (<I>ρ</I> = 1.2 ± 0.2). This finding is supported by the computational results, which show that the rate-determining step drops from 24.6 kcal mol<SUP>–1</SUP> to 18.3 kcal mol<SUP>–1</SUP> when (<I>p</I>-NO<SUB>2</SUB>C<SUB>6</SUB>H<SUB>4</SUB>)CH 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CH<SUB>2</SUB> is used and slightly increases to 25.5 kcal mol<SUP>–1</SUP> using (<I>p</I>-NMe<SUB>2</SUB>C<SUB>6</SUB>H<SUB>4</SUB>)CH 00000000000
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Chakravorty, Soumitesh,Lee, Jong Seok,Cho, Eun Jin,Roh, Sandy S.,Smith, Laura E.,Lee, Jiim,Kim, Cheon Tae,Via, Laura E.,Cho, Sang-Nae,Barry III, Clifton E.,Alland, David American Society for Microbiology 2015 Journal of clinical microbiology Vol.53 No.1
<P>Resistance to amikacin (AMK) and kanamycin (KAN) in clinical <I>Mycobacterium tuberculosis</I> strains is largely determined by specific mutations in the <I>rrs</I> gene and <I>eis</I> gene promoter. We developed a rapid, multiplexed sloppy molecular beacon (SMB) assay to identify these mutations and then evaluated assay performance on 603 clinical <I>M. tuberculosis</I> DNA samples collected in South Korea. Assay performance was compared to gold-standard phenotypic drug susceptibility tests, including Lowenstein-Jensen (LJ) absolute concentration, mycobacterial growth indicator tubes (MGIT), and TREK Sensititre MycoTB MIC plate (MycoTB) methods. Target amplicons were also tested for mutations by Sanger sequencing. The SMB assay correctly detected 115/116 mutant and mixed sequences and 487/487 wild-type sequences (sensitivity and specificity of 99.1 and 100%, respectively). Using the LJ method as the reference, sensitivity and specificity for AMK resistance were 92.2% and 100%, respectively, and sensitivity and specificity for KAN resistance were 87.7% and 95.6%, respectively. Mutations in the <I>rrs</I> gene were unequivocally associated with high-level cross-resistance to AMK and KAN in all three conventional drug susceptibility testing methods. However, <I>eis</I> promoter mutations were associated with KAN resistance using the MGIT or MycoTB methods but not the LJ method. No testing method associated <I>eis</I> promoter mutations with AMK resistance. Among the discordant samples with AMK and/or KAN resistance but wild-type sequence at the target genes, we discovered four new mutations in the <I>whiB7</I> 5′ untranslated region (UTR) in 6/22 samples. All six samples were resistant only to KAN, suggesting the possible role of these <I>whiB7</I> 5′ UTR mutations in KAN resistance.</P>
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THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 5253
Calzetti, D.,Johnson, K. E.,Adamo, A.,Gallagher III, J. S.,Andrews, J. E.,Smith, L. J.,Clayton, G. C.,Lee, J. C.,Sabbi, E.,Ubeda, L.,Kim, H.,Ryon, J. E.,Thilker, D.,Bright, S. N.,Zackrisson, E.,Kennic IOP Publishing 2015 The Astrophysical journal Vol.811 No.2
<P>The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the 'radio nebula'). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 angstrom 1.9 mu m in 13 filters. These include H alpha, P beta, and P alpha, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (M-V < -8.8) and the two young radio nebula clusters. The clusters have ages similar to 1-15 Myr and masses similar to 1 x 10(4)-2.5 x 10(5) M-circle dot. The clusters' spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last similar to 15 Myr. The most massive cluster is in the radio nebula; with a mass similar to 2.5 x 10(5) M-circle dot and an age similar to 1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV similar to 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also similar to 1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.</P>
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Chintharlapalli, Sudhakar,Papineni, Sabitha,Abdelrahim, Maen,Abudayyeh, Ala,Jutooru, Indira,Chadalapaka, Gayathri,Wu, Fei,Mertens-Talcott, Susanne,Vanderlaag, Kathy,Cho, Sung Dae,Smith III, Roger,Safe Wiley Subscription Services, Inc., A Wiley Company 2009 International journal of cancer: Journal internati Vol.125 No.8
<P>Methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) is a synthetic derivative of glycyrrhetinic acid, a triterpenoid phytochemical found in licorice extracts. CDODA-Me inhibited growth of RKO and SW480 colon cancer cells and this was accompanied by decreased expression of Sp1, Sp3 and Sp4 protein and mRNA and several Sp-dependent genes including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1 or Flt-1). CDODA-Me also induced apoptosis, arrested RKO and SW480 cells at G<SUB>2</SUB>/M, and inhibited tumor growth in athymic nude mice bearing RKO cells as xenografts. CDODA-Me decreased expression of microRNA-27a (miR-27a), and this was accompanied by increased expression of 2 miR-27a-regulated mRNAs, namely ZBTB10 (an Sp repressor) and Myt-1 which catalyzes phosphorylation of cdc2 to inhibit progression of cells through G<SUB>2</SUB>/M. Both CDODA-Me and antisense miR-27a induced comparable responses in RKO and SW480 cells, suggesting that the potent anticarcinogenic activity of CDODA-Me is due to repression of oncogenic miR-27a. © 2009 UICC</P>
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