4 research outputs found

    Hierarchically Driven IrO<sub>2</sub> Nanowire Electrocatalysts for Direct Sensing of Biomolecules

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    Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO<sub>2</sub>) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules

    Conformer-Specific and Diastereomer-Specific Spectroscopy of <i>αβα</i> Synthetic Foldamers: Ac–Ala−β<sub>ACHC</sub>–Ala–NHBn

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    The folding propensities of a capped, cyclically constrained, mixed <i>α/β</i> diastereomer pair, (<i>SRSS)</i> Ac–Ala−β<sub>ACHC</sub>–Ala–NHBn (hereafter <i>RS</i>) and (<i>SSRS)</i> Ac–Ala−β<sub>ACHC</sub>–Ala–NHBn (<i>SR</i>), have been studied in a molecular beam using single-conformation spectroscopic techniques. These <i>α/β</i>-tripeptides contain a cyclohexane ring across each C<sub>α</sub><i>–</i>C<sub>β</sub> bond, at which positions their stereochemistries differ. This cyclic constraint requires any stable species to adopt one of two ACHC configurations: equatorial CO/axial NH or equatorial NH/axial CO. Resonant two-photon ionization (R2PI) and infrared–ultraviolet hole-burning (IR–UV HB) spectroscopy were used in the S<sub>0</sub>–S<sub>1</sub> region of the UV chromophore, revealing the presence of three unique conformational isomers of <i>RS</i> and two of <i>SR</i>. Resonant ion-dip infrared spectra were recorded in both the NH stretch (3200–3500 cm<sup>–1</sup>) and the amide I (1600–1800 cm<sup>–1</sup>) regions. These experimental vibrational frequencies were compared with the scaled calculated normal-mode frequencies from density functional theory at the M05-2X/6-31+G­(d) level of theory, leading to structural assignments of the observed conformations. The <i>RS</i> diastereomer is known in crystalline form to preferentially form a C11/C9 mixed helix, in which alternating hydrogen bonds are arranged in near antiparallel orientation. This structure is preserved in one of the main conformers observed in the gas phase but is in competition with both a tightly folded C7<sub>eq</sub>/C12/C8/C7<sub>eq</sub> structure, in which all four amide NH groups and four CO groups are engaged in hydrogen bonding, as well as a cap influenced C7<sub>eq</sub>/NH···π/C11 structure. The <i>SR</i> diastereomer is destabilized by inducing backbone dihedral angles that lie outside the typical Ramachandran angles. This diastereomer also forms a C11/C9 mixed helix as well as a cap influenced bifurcated C7<sub>ax</sub>–C11/NH···π/C7<sub>eq</sub> structure as the global energy minimum. Assigned structures are compared with the reported crystal structure of analogous <i>α/β</i>-tripeptides, and disconnectivity graphs are presented to give an overview of the complicated potential energy surface of this tripeptide diastereomer pair

    Synthesis of Monoclinic Potassium Niobate Nanowires That Are Stable at Room Temperature

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    We report the synthesis of KNbO<sub>3</sub> nanowires (NWs) with a monoclinic phase, a phase not observed in bulk KNbO<sub>3</sub> materials. The monoclinic NWs can be synthesized via a hydrothermal method using metallic Nb as a precursor. The NWs are metastable, and thermal treatment at ∼450 °C changed the monoclinic phase into the orthorhombic phase, which is the most stable phase of KNbO<sub>3</sub> at room temperature. Furthermore, we fabricated energy-harvesting nanogenerators by vertically aligning the NWs on SrTiO<sub>3</sub> substrates. The monoclinic NWs showed significantly better energy conversion characteristics than orthorhombic NWs. Moreover, the frequency-doubling efficiency of the monoclinic NWs was ∼3 times higher than that of orthorhombic NWs. This work may contribute to the synthesis of materials with new crystalline structures and hence improve the properties of the materials for various applications
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