116 research outputs found

    DFT and SERS Study of l‑Cysteine Adsorption on the Surface of Gold Nanoparticles

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    Both surface enhanced Raman spectroscopy (SERS) experiments and density functional theory (DFT) calculations have been carried out to investigate the adsorption of cysteine on gold nanoparticle surface. Cysteine is one of the amino acids that have a rotating dihedral angle and several possible adsorption sites, so there could be many possible adsorption conformations. At present, the adsorption conformation of cysteine on the gold surface has not been solved, although previous work had explored the conformations based on DFT method, but no explicit experimental evidence was provided. Nevertheless, the previous work had indicated that the adsorption conformations of some simple rigid molecules on the surface of metal nanoparticles could be identified through SERS experimental data. Therefore, in this work, we attempted to figure out the conformation and adsorption sites of the flexible typical amino acid cysteine on gold nanoparticle surface by combining both DFT and SERS methods. We found that the adsorption of cysteine on the surface gold nanoparticle adopted the most predominant configuration in which cysteine chemically interacted with Au cluster through both S and O sites, with cysteine taking the configuration of a gauche position for the protonated amino group and an antiposition for the carboxylate group in the molecule

    Histone Acetylation Induced Transformation of B‑DNA to Z‑DNA in Cells Probed through FT-IR Spectroscopy

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    A nucleosome is made up of DNA and histones, and acetylation of histones perturbs the interaction of DNA and histones and thus affects the chromatin conformation and function. However, whether or how acetylation induces DNA conformation changes is still elusive. In this work, we applied FT-IR spectroscopy to monitor the DNA signals in cells as the histone acetylation was regulated by trichostatin A (TSA), a reversible inhibitor to histone deacetylases (HDACs). Our results unambiguously demonstrate the significant transformation of B-DNA to Z-DNA upon histone acetylation in the TSA treated HeLa cells. This is the first report providing the explicit experimental evidence for such a B-Z transformation of DNA in the epigenetic states of cells

    Novel oxidative aromatic alkene cleavage with sodium nitrite under mild conditions

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    <p>We have developed a simple and practical process for the oxidation of aromatic alkene to the corresponding carbonyl compounds using NaNO<sub>2</sub> as an oxidant. The practical utility of this oxidative process has been demonstrated in the gram-scale oxidation of 1-(<i>tert</i>-butyl)-4-vinylbenzene.</p

    Late-Stage C–H Nitration of Unactivated Arenes by Fe(NO<sub>3</sub>)<sub>3</sub>·9H<sub>2</sub>O in Hexafluoroisopropanol

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    Operationally simple and generally applicable arene nitration with cheap and easily accessible chemicals has been a long-sought transformation in the synthetic organic community. In this work, we realized this goal with nontoxic and inexpensive Fe(NO3)3·9H2O as the nitro source and easily recyclable solvent hexafluoroisopropanol as the promotor via a network of hydrogen-bonding interactions. As a result of the relative mildness and high reliability of this protocol, late-stage nitration of various highly functionalized natural products and commercially available drugs was realized

    Spectroscopic probe to contribution of physicochemical transformations in the toxicity of aged ZnO NPs to <i>Chlorella vulgaris</i>: new insight into the variation of toxicity of ZnO NPs under aging process

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    <p>Zinc oxide nanoparticles (ZnO NPs) are one of the most abundantly applied nanomaterials in nanotechnology-based industries and they may cause unexpected environmental and health risks with their physicochemical transformations in the environment. Currently, there is still a lack of the in-depth understanding of the toxicity of aged ZnO NPs to aquatic organisms, particularly demanding quantitative analysis of the physicochemical transformations to distinguish their contributions in the toxicity assessment. For this purpose, therefore, we initiated the study of the toxicity of aged ZnO NPs to the model aquatic microalga, i.e. <i>Chlorella vulgaris</i>, and with the aid of spectroscopic tools for characterization and quantification of the physicochemical transformations, we scrutinized the toxicity variations for ZnO NPs with different aging times. As a result, we found that the toxicity altered in an abnormal manner with the aging time, i.e. the toxicity of aged ZnO NPs for 30 days showed the higher toxicity to the green alga than the fresh ZnO NPs or the ZnO NPs aged for longer time (e.g. 120 and 210 days). Through spectroscopic tools such as XRD, FTIR and Raman spectroscopy, we made both the qualitative and quantitative assessments of the physicochemical changes of the ZnO NPs, and confirmed that in the early stage, the toxicity mainly stemmed from the release of zinc ions, but with longer aging time, the neoformation of the nanoparticles played the critical role, leading to the overall reduced toxicity due to the less toxic hydrozincite and zinc hydroxide in the transformed compounds.</p

    Highly Sensitive and Selective Surface-Enhanced Raman Spectroscopy Label-free Detection of 3,3′,4,4′-Tetrachlorobiphenyl Using DNA Aptamer-Modified Ag-Nanorod Arrays

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    An improved label-free approach for highly sensitive and selective detection of 3,3′,4,4′-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio <i>I</i>(656 cm<sup>–1</sup>)/<i>I</i>(733 cm<sup>–1</sup>) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10<sup>–8</sup> M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment

    Diastereoselective Construction of Tetrahydropyridine Fused Bicyclic Structures via Three-Component Domino Reaction

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    The three-component reactions of enals, electron-deficient alkynes, and hydroxyl-functionalized primary amines for the highly diastereoselective construction of dihydro-3<i>H</i>-benzo­[4,5]­oxazolo­[3,2-<i>a</i>]­pyridines, hexahydropyrido­[2,1-<i>b</i>]­[1,3]­oxazines, and tetrahydro-2<i>H</i>-oxazolo­[3,2-<i>a</i>]­pyridines have been achieved. Domino formation of one C–C, two C–N, and one C–O bonds are furnished in these reactions. This bis-annulation protocol allows for the synthesis of fused heterocyclic products of high structural diversity with variation not only of appended fragments but also the ring size of the central backbone

    Mono-, di-, and trinuclear phosphonate oxygen-bridged copper(II) complexes: syntheses, structures, and properties

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    <p>Reactions of copper salts, zoledronic acid, and 2,2′-bipyridine/1,10-phenanthroline in aqueous ethanolic solutions afforded four phosphonate oxygen-bridged copper complexes, Cu(bipy)(H<sub>4</sub>zdn)(HSO<sub>4</sub>) (<b>1</b>), [Cu<sub>2</sub>(bipy)<sub>2</sub>(H<sub>2</sub>zdn)(H<sub>2</sub>O)(Cl)]·4H<sub>2</sub>O (<b>2</b>), [Cu<sub>2</sub>(phen)<sub>2</sub>(H<sub>2</sub>zdn)(H<sub>2</sub>O)(Cl)]·2.5H<sub>2</sub>O (<b>3</b>), and [Cu<sub>3</sub>(bipy)<sub>3</sub>(H<sub>4</sub>zdn)(H<sub>2</sub>zdn)(SO<sub>4</sub>)]·5H<sub>2</sub>O (<b>4</b>) (H<sub>5</sub>zdn = zoledronic acid, bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline). The copper centers of <b>1</b>–<b>4</b> have square pyramidal coordination geometries. The Cu(II) ions are coordinated to bipy/phen, zoledronate, and HSO<sub>4</sub><sup>−</sup>/Cl<sup>−</sup> forming mononuclear units for <b>1</b>, dinuclear for <b>2</b> and <b>3</b>, and trinuclear for <b>4</b>. These building units are further extended into 3-D supramolecular networks via multiple hydrogen bond interactions. Temperature-dependent magnetic properties of <b>2</b> and <b>4</b> suggest weak antiferromagnetic coupling (<i>J</i> = −4.53(8) cm<sup>−1</sup> for <b>2</b>, <i>J</i> = −1.69(4) cm<sup>−1</sup> for <b>4</b>). The antitumor activity of <b>2</b> was evaluated against the human lung cancer cell line and indicates effective time- and dose-dependent cytotoxic effects.</p

    Cell viability of ARPE-19 cells.

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    <p>The viability of ARPE-19 cells was assessed by WST-1 assay. ARPE-19 cells were subjected to a single dose of 400μM H<sub>2</sub>O<sub>2</sub> treatment for 24h and the untreated cells served as controls. The data showed that there was no significant difference in the cell viability between H<sub>2</sub>O<sub>2</sub> treated and control cells (defined as 100%) (P > 0.05). The experiment was performed three times independently with triplicate in each group.</p
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