10 research outputs found

    Site Occupation Engineering toward Giant Red-Shifted Photoluminescence in (Ba,Sr)<sub>2</sub>LaGaO<sub>5</sub>:Eu<sup>2+</sup> Phosphors

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    Exploring oxide-based red-emitting phosphors is essential for improving the color rendering index (Ra) and reducing the correlated color temperature (CCT) of white-light-emitting diode (LED) lighting sources. Especially, it is challenging to design Eu2+ red emission in inorganic solids. Here, the Eu2+-activated oxide phosphor Sr2LaGaO5:Eu2+ was synthesized with red emission peaking at 618 nm under 450 nm excitation. The crystal structure and spectral analysis indicate that Eu2+ tends to occupy [Sr1/LaO8] polyhedrons with a smaller coordination number, resulting in a large crystal field splitting at the 5d level and realizing the broadband 4f–5d red emission. When Sr is substituted by Ba atoms, density functional theory calculations verify that Ba tends to enter [Sr2O10] with a large coordination number, further giving rise to the lattice distortion and a giant spectral redshift (618–800 nm). The white LED device fabricated by mixing red Sr1.8Ba0.2GaO5:Eu2+ and green Lu3Al5O12:Ce3+ phosphors exhibits a high color rendering index (Ra = 92.1) and a low color-dependent temperature (CCT = 4570 K). This study will give guidance for exploring new Eu2+ activated oxide-based red phosphors as well as achieving tunable emission through cations’ substitution

    Mimicking Ribosomal Unfolding of RNA Pseudoknot in a Protein Channel

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    Pseudoknots are a fundamental RNA tertiary structure with important roles in regulation of mRNA translation. Molecular force spectroscopic approaches such as optical tweezers can track the pseudoknot’s unfolding intermediate states by pulling the RNA chain from both ends, but the kinetic unfolding pathway induced by this method may be different from that in vivo, which occurs during translation and proceeds from the 5′ to 3′ end. Here we developed a ribosome-mimicking, nanopore pulling assay for dissecting the vectorial unfolding mechanism of pseudoknots. The pseudoknot unfolding pathway in the nanopore, either from the 5′ to 3′ end or in the reverse direction, can be controlled by a DNA leader that is attached to the pseudoknot at the 5′ or 3′ ends. The different nanopore conductance between DNA and RNA translocation serves as a marker for the position and structure of the unfolding RNA in the pore. With this design, we provided evidence that the pseudoknot unfolding is a two-step, multistate, metal ion-regulated process depending on the pulling direction. Most notably, unfolding in both directions is rate-limited by the unzipping of the first helix domain (first step), which is Helix-1 in the 5′ → 3′ direction and Helix-2 in the 3′ → 5′ direction, suggesting that the initial unfolding step in either pulling direction needs to overcome an energy barrier contributed by the noncanonical triplex base-pairs and coaxial stacking interactions for the tertiary structure stabilization. These findings provide new insights into RNA vectorial unfolding mechanisms, which play an important role in biological functions including frameshifting

    Chemical Structure and Properties of Interstrand Cross-Links Formed by Reaction of Guanine Residues with Abasic Sites in Duplex DNA

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    A new type of interstrand cross-link resulting from the reaction of a DNA abasic site with a guanine residue on the opposing strand of the double helix was recently identified, but the chemical connectivity of the cross-link was not rigorously established. The work described here was designed to characterize the chemical structure and properties of dG–AP cross-links generated in duplex DNA. The approach involved characterization of the nucleoside cross-link “remnant” released by enzymatic digestion of DNA duplexes containing the dG–AP cross-link. We first carried out a chemical synthesis and complete spectroscopic structure determination of the putative cross-link remnant <b>9b</b> composed of a 2-deoxyribose adduct attached to the exocyclic <i>N</i><sup>2</sup>-amino group of dG. A reduced analogue of the cross-link remnant was also prepared (<b>11b</b>). Liquid chromatography–tandem mass spectrometric (LC-MS/MS) analysis revealed that the retention times and mass spectral properties of synthetic standards <b>9b</b> and <b>11b</b> matched those of the authentic cross-link remnants released by enzymatic digestion of duplexes containing the native and reduced dG–AP cross-link, respectively. These results establish the chemical connectivity of the dG–AP cross-link released from duplex DNA and provide a foundation for detection of this lesion in biological samples. The dG–AP cross-link in duplex DNA was remarkably stable, decomposing with a half-life of 22 days at pH 7 and 23 °C. The intrinsic chemical stability of the dG–AP cross-link suggests that this lesion in duplex DNA may have the power to block DNA-processing enzymes involved in transcription and replication

    Electrical Stimulation over Bilateral Occipito-Temporal Regions Reduces N170 in the Right Hemisphere and the Composite Face Effect

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    <div><p>Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that can modulate cortical excitability. Although the clinical value of tDCS has been advocated, the potential of tDCS in cognitive rehabilitation of face processing deficits is less understood. Face processing has been associated with the occipito-temporal cortex (OT). The present study investigated whether face processing in healthy adults can be modulated by applying tDCS over the OT. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115772#s2" target="_blank">Experiment 1</a> investigated whether tDCS can affect N170, a face-sensitive ERP component, with a face orientation judgment task. The N170 in the right hemisphere was reduced in active stimulation conditions compared with the sham stimulation condition for both upright faces and inverted faces. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115772#s3" target="_blank">Experiment 2</a> further demonstrated that tDCS can modulate the composite face effect, a type of holistic processing that reflects the obligatory attention to all parts of a face. The composite face effect was reduced in active stimulation conditions compared with the sham stimulation condition. Additionally, the current polarity did not modulate the effect of tDCS in the two experiments. The present study demonstrates that N170 can be causally manipulated by stimulating the OT with weak currents. Furthermore, our study provides evidence that obligatory attention to all parts of a face can be affected by the commonly used tDCS parameter setting.</p></div

    Single Locked Nucleic Acid-Enhanced Nanopore Genetic Discrimination of Pathogenic Serotypes and Cancer Driver Mutations

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    Accurate and rapid detection of single-nucleotide polymorphism (SNP) in pathogenic mutants is crucial for many fields such as food safety regulation and disease diagnostics. Current detection methods involve laborious sample preparations and expensive characterizations. Here, we investigated a single locked nucleic acid (LNA) approach, facilitated by a nanopore single-molecule sensor, to accurately determine SNPs for detection of Shiga toxin producing <i>Escherichia coli</i> (STEC) serotype O157:H7, and cancer-derived <i>EGFR</i> L858R and <i>KRAS</i> G12D driver mutations. Current LNA applications that require incorporation and optimization of multiple LNA nucleotides. But we found that in the nanopore system, a single LNA introduced in the probe is sufficient to enhance the SNP discrimination capability by over 10-fold, allowing accurate detection of the pathogenic mutant DNA mixed in a large amount of the wild-type DNA. Importantly, the molecular mechanistic study suggests that such a significant improvement is due to the effect of the single-LNA that both stabilizes the fully matched base-pair and destabilizes the mismatched base-pair. This sensitive method, with a simplified, low cost, easy-to-operate LNA design, could be generalized for various applications that need rapid and accurate identification of single-nucleotide variations