15 research outputs found

    Tuning the Rotation Rate of Light-Driven Molecular Motors

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    Overcrowded alkenes are among the most promising artificial molecular motors because of their ability to undergo repetitive light-driven unidirectional rotary motion around the central Cī—»C bond. The exceptional features of these molecules render them highly useful for a number of applications in nanotechnology. Many of these applications, however, would benefit from higher rotation rates. To this end, a new molecular motor was designed, and the isomerization processes were studied in detail. The new motor comprises a fluorene lower half and a five-membered-ring upper half; the upper-half ring is fused to a <i>p</i>-xylyl moiety and bears a <i>tert</i>-butyl group at the stereogenic center. The kinetics of the thermal isomerization was studied by low-temperature UVā€“vis spectroscopy as well as by transient absorption spectroscopy at room temperature. These studies revealed that the <i>tert</i>-butyl and <i>p</i>-xylyl groups in the five-membered-ring upper half may be introduced simultaneously in the molecular design to achieve an acceleration of the rotation rate of the molecular motor that is larger than the acceleration obtained by using either one of the two groups individually. Furthermore, the new molecular motor retains unidirectional rotation while showing remarkably high photostationary states

    Optically Switchable NIR Photoluminescence of PbS Semiconducting Nanocrystals using Diarylethene Photoswitches

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    Precisely modulated photoluminescence (PL) with external control is highly demanded in material and biological sciences. However, it is challenging to switch the PL on and off in the NIR region with a high modulation contrast. Here, we demonstrate that reversible on and off switching of the PL in the NIR region can be achieved in a bicomponent system comprised of PbS semiconducting nanocrystals (NCs) and diarylethene (DAE) photoswitches. Photoisomerization of DAE to the ring-closed form upon UV light irradiation causes substantial quenching of the NIR PL of PbS NCs due to efficient triplet energy transfer. The NIR PL fully recovers to an on state upon reversing the photoisomerization of DAE to the ring-open form with green light irradiation. Importantly, fully reversible switching occurs without obvious fatigue, and the high PL on/off ratio (>100) outperforms all previously reported assemblies of NCs and photoswitches

    Driving Unidirectional Molecular Rotary Motors with Visible Light by Intra- And Intermolecular Energy Transfer from Palladium Porphyrin

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    Driving molecular rotary motors using visible light (530ā€“550 nm) instead of UV light was achieved using palladium tetraphenylporphyrin as a triplet sensitizer. Visible light driven rotation was confirmed by UV/vis absorption, circular dichroism and <sup>1</sup>H NMR spectroscopy and the rotation was confirmed to be unidirectional and with similar photostationary states, despite proceeding via a triplet instead of a singlet excited state of the molecular motor. Energy transfer proceeds in both inter- and intramolecular fashion from the triplet state of the porphyrin to the motor. Stern Volmer plots show that the rate of intermolecular quenching of the porphyrin excited state by the molecular motor is diffusion-controlled

    Global Identification of Genes Specific for Rice Meiosis

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    <div><p>The leptotene-zygotene transition is a major step in meiotic progression during which pairing between homologous chromosomes is initiated and double strand breaks occur. <i>OsAM1</i>, a homologue of maize <i>AM1</i> and <i>Arabidopsis SWI1</i>, encodes a protein with a coiled-coil domain in its central region that is required for the leptotene-zygotene transition during rice meiosis. To gain more insight into the role of OsAM1 in rice meiosis and identify additional meiosis-specific genes, we characterized the transcriptomes of young panicles of <i>Osam1</i> mutant and wild-type rice plants using RNA-Seq combined with bioinformatic and statistical analyses. As a result, a total of 25,750 and 28,455 genes were expressed in young panicles of wild-type and <i>Osam1</i> mutant plants, respectively, and 4,400 differentially expressed genes (DEGs; log<sub>2</sub> Ratio ā‰„ 1, FDR ā‰¤ 0.05) were identified. Of these DEGs, four known rice meiosis-specific genes were detected, and 22 new putative meiosis-related genes were found by mapping these DEGs to reference biological pathways in the KEGG database. We identified eight additional well-conserved OsAM1<i>-</i>responsive rice meiotic genes by comparing our RNA-Seq data with known meiotic genes in <i>Arabidopsis</i> and fission yeast.</p></div

    Comparison of expression levels of selected genes estimated by RNA-seq and RT-PCR.

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    <p>Y-axis: log<sub>2</sub> of estimated fold change between <i>Osam1</i> and wild type. X- axis: tested genes, 1, Os07g05630; 2, Os03g58600; 3, Os04g58630; 4, Os08g02380; 5, Os01g49010; 6, Os03g44760; 7, Os02g04080; 8, Os01g50616; 9, Os05g05720; 10, Os09g07510; 11, Os02g53120; 12, Os02g07240; 13, Os03g57310.</p

    Heatmap of differential expression genes between wild type and <i>Osam1</i> plants.

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    <p>Green represents low expression, red represents high expression, each row represents a differentially expressed gene and each column represents a sample. Changes in expression levels are shown in the color scales.</p

    Classification of all DEGs based on KEGG categorization.

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    <p>The top 10 most highly represented categories and the number of transcripts predicted to belong to each category are shown.</p