Effect of the Steric Molecular Structure of Azobenzene on the Formation of Self-Assembled Monolayers with a Photoswitchable Surface Morphology

The growth processes of self-assembled monolayers (SAMs) of two azobenzene disulfides formed on flat gold surfaces were studied to confirm the effect of the intermolecular interactions between azobenzene molecules on the light-triggered surface morphologies of the SAMs. Scanning tunneling microscopy (STM), atomic force microscopy (AFM), thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–vis) absorption spectroscopy were employed to study the SAMs and their growth processes. The SAMs studied were of bulky-substituted azobenzene disulfide (Et-2S), and nonsubstituted azobenzene disulfide (Me-2S), formed on a gold-covered substrate, and had a twisted and a planar structure, respectively. STM-based imaging of the initial stage of the self-assembly of the Et-2S molecules revealed that cleavage of the disulfide bond occurred on the gold surface, and phase-separated domains composed of azobenzenethiolate and dodecanethiolate were formed. Time-dependent AFM-based imaging illustrated the mechanism through which the Et-2S SAM grewit was through the formation of dendritic aggregates and islandseventually resulting in phase-separated domains with a wormlike structure. This wormlike structure showed noticeable changes in its surface morphology upon irradiation with UV and visible light. On the other hand, while the growth process for the Me-2S SAM was similar to that of the Et-2S SAM, the final Me-2S SAM had smooth domains whose morphology did not exhibit photoswitchability. The TD and XP spectra of the SAMs showed that the number of adsorbed Et-2S molecules reached a point of saturation after a 24 h long immersion while the number of Me-2S molecules increased even after a 336 h long immersion. Furthermore, the area occupied by the azobenzene moiety in the Et-2S SAM was constant regardless of the immersion time, whereas that in the Me-2S SAM decreased with the immersion time. These results indicated that the strength of the interactions between the azobenzene molecules significantly influenced the aggregate-forming ability in SAMs

Universal Two-Component Dynamics in Supercritical Fluids

Despite the technological importance of supercritical fluids, controversy remains about the details of their microscopic dynamics. In this work, we study four supercritical fluid systemswater, Si, Te, and Lennard-Jones fluidvia classical molecular dynamics simulations. A universal two-component behavior is observed in the intermolecular dynamics of these systems, and the changing ratio between the two components leads to a crossover from liquidlike to gaslike dynamics, most rapidly around the Widom line. We find evidence to connect the liquidlike component dominating at lower temperatures with intermolecular bonding and the component prominent at higher temperatures with free-particle, gaslike dynamics. The ratio between the components can be used to describe important properties of the fluid, such as its self-diffusion coefficient, in the transition region. Our results provide an insight into the fundamental mechanism controlling the dynamics of supercritical fluids and highlight the role of spatiotemporally inhomogeneous dynamics even in thermodynamic states where no large-scale fluctuations exist in the fluid

Analysis of split-chromosomes in the mutants by CHEF gel electrophoresis and Southern hybridization (A–C)

<p><b>Copyright information:</b></p><p>Taken from "Chromosome XII context is important for rDNA function in yeast"</p><p>Nucleic Acids Research 2006;34(10):2914-2924.</p><p>Published online 31 May 2006</p><p>PMCID:PMC1474064.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> Chromosomal DNA was isolated from the following strains: () ID-11, () ID-12 and () ID-13. () Analysis of rDNA copy numbers. Genomic DNA was digested at a unique KpnI site in the rDNA unit and subjected to electrophoresis followed by Southern hybridization using 5S rDNA as a probe. A single copy gene was used as an internal control for normalization. Because the normalization factor for the 5S rDNA probe was found to be 15 relative to the single copy gene, rDNA copy numbers were determined by multiplying by 15. () Relative quantification of 18S rRNA using real-time RT–PCR. The 18S rRNA amount is divided by the ACT1 amount to obtain a normalized 18S rRNA value and the normalized amount of 18S rRNA in FY833 (WT) was used to compare the relative amount of 18S rRNA in different strains

MS-based identification of acetylcytidines in <i>S. pombe</i> 18S rRNA.

<p>A. Extracted ion monitoring of RNase T1 fragments of 18S rRNA containing acetylcytidine (AcC) and cytidine (C)-1297 (upper panel) and AcC and C-1815 (lower panel). The 18S rRNAs were purified from strain SP6 or Nat10_G285D grown at 30°C in YE medium, digested by RNase T1 and applied to the LC-MS system (50 fmol each). The sequences and m/z values of AcC and C-containing nucleotides are indicated. A mass window of 3 ppm was used for the extractions. Y axis indicates the peak intensity relative to the most intensive peak in each panel. Note that the MS signals of AcC-containing nucleotides were completely lost in the Nat10_G285D mutant strain (indicated by arrows). B. MS/MS spectra of AcC-containing fragments. The acetylated RNA ions [C(AcC)Gp¹⁻, m/z 1014.14; UUUC(AcC)Gp²⁻, m/z 965.60, in A) were analyzed by collision-induced dissociation. The position of acetylcytidine residues was identified by manual interpretation of the a-, c-, w- and y-type series ions and other specific product ions as indicated in the figure. The series ions assigned are indicated on the RNA sequence in the inset.</p

Analysis of the Nat10_G285D temperature-sensitive strain.

<p>A. Effects of <i>Nat10</i> on the temperature sensitivity of the Nat10_G285D mutant. The Nat10_G285D strain (deficient in <i>leu1</i> gene) was supplemented with <i>Nat10</i> cDNA in pREP1 vector containing the nmt1 promoter and an auxotrophic marker, <i>leu2</i> gene, and incubated for 3 days on an SD plate without leucine at 30°C or 37°C. The cDNAs used were: 1) mock vector; 2) Nat10_G285D cDNA in the vector; 3) wild-type Nat10 cDNA in the vector; and 4) no vector and cDNA. Note that the temperature-sensitive mutant grows at 37°C with the expression of <i>Nat10</i> cDNA. B. Effects of <i>Nat10</i> on the growth rate of Nat10_G285D mutant. Doubling time during the logarithmic growth phase (5.0×10⁶ to 2.5×10⁷ cells/ml) at 30°C was measured in SD medium without leucine. The strains used were Nat10_G285D supplemented with pREP1-Nat10_wt or the mock vector. Each value represents the mean ± standard deviation of three independent assays. The arrow indicates a significant difference as determined by the Student's t test (p<0.05). Note that the growth rate of the Nat10_G285D mutant was recovered upon expression of <i>Nat10</i> cDNA.</p

The <i>Nat10</i> null mutant is inviable.

<p>Tetrad dissection experiments were carried out using segregates shown below the panel. The four spores from each given tetrad are grouped horizontally. The dissected spores were grown at 30°C for 3 days on YE medium. Parental strain: <i>h+/h– leu1-32/+ his3-D1/+ ura4-D18/ura4-D18 nat10::ura4/+</i>.</p

Effect of <i>Nat10</i> on the acetylation of cytidines 1297 and 1815 in 18S rRNA.

<p>Extracted ion monitoring of RNase T1 fragments of 18S rRNA containing AcC-1297 (upper panel) and AcC-1815 (lower panel) is shown. The analysis was performed for 18S rRNAs purified from strain SP6 supplemented with the mock vector, strain Nat10_G285D supplemented with the mock vector, or strain Nat10_G285D supplemented with pREP1-Nat10_wt, respectively, as indicated. Each yeast strain was grown at 30°C in EMMmedium without leucine. The rRNA was digested by RNase T1 and applied to the LC-MS system (50 fmol each). The sequences and m/z values of AcC-containing nucleotides are indicated. A mass window of 3 ppm was used for the extractions. Y axis indicates the peak intensity relative to the most intensive peak in each panel. Note that the MS signals of AcC-containing nucleotides at the positions indicated by arrows appear in the Nat10_G285D mutant strain upon expression of <i>Nat10</i> cDNA.</p

Effect of <i>Nat10</i> on ribosome assembly.

<p>A. Ultracentrifugation analysis of ribosome assembly in the Nat10_G285D mutant. Ribosomal and polysomal fractions prepared from strain SP6 (upper panel) or Nat10_G285D mutant (lower panel), grown at 30°C in YE medium were analyzed with 15–50% sucrose density gradient centrifugation. The UV profiles (A₂₅₄) of the separation are depicted. The scales under each UV profile denote individual fractions, and the electrophoretograms shown below the UV profile are the results of agarose gel electrophoresis of each fraction. B. Effect of <i>Nat10</i> on ribosome assembly of the Nat10_G285D mutant. Ribosomal and polysomal fractions derived from strain Nat10_G285D supplemented with the mock vector (upper panel) or with pREP1-Nat10_wt (lower panel) grown at 30°C in EMM medium without leucine were analyzed with 15–50% sucrose density gradient centrifugation under the conditions as in A. Note that the apparently aberrant phenotype in ribosome assembly of the Nat10_G285D mutant was rescued upon expression of <i>Nat10</i>, as indicated by the decrease in free large subunit (LSU) and increase in SSU and monosomes.</p

Crizotinib overcomes HGF triggered resistance to mutant-selective EGFR-TKIs in EGFR-TKI resistant lung cancer cells harboring EGFR mutation.

<p>Tumor cells (2×10³ cells per well) were incubated with various concentrations of WZ4002, with or without crizotinib (300 nmol/L) and/or HGF (10 ng/mL), for 72 hours. Cell growth was determined by the MTT assay. The percentage of growth is shown relative to untreated controls. Each sample was assayed in triplicate, with each experiment repeated at least 3 times independently.</p