Effect of Guest–Host Hydrogen Bonding on Thermodynamic Stability of Clathrate Hydrates: Diazine Isomers

Guest–host hydrogen bonding strongly affects the physical properties of clathrate hydrate, such as the thermodynamic stability, water dynamics, and dielectric properties, but attempts to quantify the effects of hydrogen bonding on these properties are rare thus far. As a preliminary work, this study investigates methane clathrate hydrates with three diazine isomers, pyrazine, pyrimidine, and pyridazine, which expect nearly the same van der Waals volumes due to their similar molecular shapes and sizes, and their guest–host hydrogen-bonding behaviors. The crystal structures of all three binary diazine + CH₄ hydrate phases were identified as a cubic <i>Fd</i>3̅<i>m</i> structure, including diazine molecules in the 5¹²6⁴ cavity, commonly termed as structure II hydrate, by a high-resolution powder diffraction pattern analysis. The phase equilibrium curves of their clathrate hydrates were obtained by the <i>P–T</i> trajectory of the hydrate formation and dissociation process, and the thermodynamic stability trend was well-explained by the guest–host hydrogen bonding behavior as evaluated by the molecular polarities, proton affinities, and ring-breathing vibration frequencies of the three diazine isomers obtained from Raman spectroscopy. This study provides useful information that contributes to the realization of the expansion of the thermodynamics of clathrate hydrates to include guest–host hydrogen-bonding interactions

Metastability of Ethane Clathrate Hydrate Induced by [Co(NH₃)₆]³⁺ Complex

The metal complex of [Co(NH3)6]3+ is introduced to C2H6 hydrate to confirm its possible inclusion in hydrogen-bonded water cages and the occurrence of metastable structure. The 13C NMR spectra of C2H6 + ([Co(NH3)6]Cl3 + 6NaOH in D2O) hydrate confirmed a new peak at 6.5 ppm matching with C2H6 in sII-L cages. The retarded appearance of metastable sII phase is due to brine rejection of the cobalt complex occurring during solution freezing. The anions of OH− and F− were found to be incorporated in the host water cage framework, providing proton-deficient sites. The ionic conductivity of the frozen [Co(NH3)6]3+ solution increased up to 20-fold after ethane hydrate formation, implying the incorporation of F− into the host lattice. A notable finding of this work is that the metastability occurs only when the cobalt complex is in the presence of anions such as OH− and F−

Water-Soluble Structure H Clathrate Hydrate Formers

Hexamethyleneimine, 1-methylpiperidine, 2-methylpiperidine, 3-methylpiperidine, and 4-methylpiperidine as isomers of C6H13N were revealed as new sH clathrate hydrate forming molecules. They show fully soluble characteristics to water, whereas already known sH formers such as methylcyclohexane and 2,2-dimethylbutane (neohexane) are immiscible or very slightly soluble to water. The L–H–V equilibrium P–T behavior of these new sH clathrate hydrates shows a tendency to shift to much milder conditions than already known ones. We particularly note that 1-methylpiperidine appears to be the best for promotion. To verify the distribution of CH4 molecules and crystal structure of clathrate hydrates, 600 MHz solid-state NMR, Raman spectroscopy, and XRD pattern analysis were conducted. These noticeable properties of new formers are expected to open new research fields to the hydrate community and contribute to hydrate-based technological applications with high energy efficiency

MXene-Integrated Metal Oxide Transparent Photovoltaics and Self-Powered Photodetectors

MXene-integrated photovoltaic devices can be used to create optically transparent systems to produce electrical energy. MXenes, an emerging family of two-dimensional materials, have attracted a tremendous amount of interest for their use in various applications. In particular, their optical transparency, metallic conductivity, and large-scale processing make MXenes highly applicable in transparent photovoltaic devices (TPVDs). Here we propose a Ti3C2Tx MXene-based inorganic TPVD. Reducing the sheet resistance of MXene and improving its contact with the metal oxide (NiO/TiO2) heterojunction enables the generation of electric power (30 μW cm–2) from ultraviolet light while selectively passing visible light for high-transparency (39.73%). Moreover, the photovoltaic effect induces a high photovoltage of 0.45 V to enable the TPVD to work in self-powered mode. The MXene-embedded transparent photodetector works in photovoltaic mode and has a fast response speed of 80 μs and high detectivity of 1.6 × 1010 Jones. The spacing of the MXene-transparent devices at color-neutral coordinates in color maps indicates the invisibility of the device. This work demonstrates the large-scale application of MXene as a seamless platform for transparent electronics of photovoltaics and photodetectors. Transparent photoelectric interfaces can be used for energy generation; in bioelectronics; and in windows of building, vehicles, and displays

Palm-sized, vibration-insensitive and vacuum-free all-fiber-photonic module for 10-14-level stabilization of CW lasers and frequency combs

Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency comb to a vibration-insensitive optical fiber delay-line. We could achieve a thermal-noise-limited frequency noise level in the 10 Hz - 1 kHz offset frequency range for both the continuous-wave laser and the optical frequency comb with the minimal frequency instability of 2.7x10-14 at 0.03-s and 2.6x10-14 at 0.01-s averaging time, respectively, in non-vacuum condition. The optical fiber spool, working as a delay reference, is designed to be insensitive to external vibration, with a vibration sensitivity of sub-10-10 [1/g] and volume of 32 mL. Finally, the ring-resonator setup is packaged in a palm-sized aluminum case with 171-mL volume with a vibration-insensitive spool, as well as an even smaller 97-mL-volume case with an ultra-compact 9-mL miniaturized fiber spool

Improving a Sulfur-Tolerant Ruddlesden–Popper Catalyst by Fluorine Doping for CO₂ Electrolysis Reaction

We report a highly improved cathode catalyst by doping fluorine anions in oxygen sites of a Ruddlesden–Popper material for CO2 electrolysis to produce CO in solid oxide electrolysis cells (SOECs). The obtained fluorine-doped catalyst of La0.9Sr0.8Co0.4Mn0.6O3.9−δF0.1 (R.P.LSCoMnF) exhibited the higher electrochemical performance of 499 mA/cm2 at 1.3 V and 850 °C with the smaller polarization resistance of 0.853 Ω·cm2 than those of the undoped catalyst of La0.9Sr0.8Co0.4Mn0.6O4−δ (R.P.LSCoMn). Moreover, a high faradaic efficiency of 98.6% and a CO production rate of 135 μmol/cm2·min were achieved for CO2 electrolysis reaction in the single cell with the R.P.LSCoMnF cathode catalyst. These enhanced performances are mainly attributed to the improved properties of surface exchange of oxygen and bulk oxygen diffusion by fluorine doping. More importantly, a negligible sign of performance degradation was observed from the galvanostatic test under CO2 gas streams containing H2S gas, and its structure was maintained even after exposure to 100 ppm H2S in an N2 gas stream at 850 °C for 10 h, suggesting that R.P.LSCoMnF is highly robust against poisonous sulfur species. Therefore, this newly developed fluorine-doped Ruddlesden–Popper catalyst could be a promising cathode for the electrolysis of sulfur-containing CO2 gas stream, which is emitted from steel-making blast furnaces or power plants

Enhancing the Contact between a‑IGZO and Metal by Hydrogen Plasma Treatment for a High-Speed Varactor (>30 GHz)

We achieved the lowest contact resistance between a-IGZO and a metal electrode for >30 GHz operation of an oxide semiconductor device. For high-resolution display and high-speed electronic devices, both bulk and contact resistances need to be reduced. In this study, hydrogen plasma was used to lower the contact resistance significantly by modifying the surface of the a-IGZO thin film. The potential barrier width at the interface was decreased by increasing the carrier concentration, and weak M–OH bonds were sufficiently diffused out with optimized plasma process. The minimum contact resistance was measured to be 1.33 × 10–6 Ω·cm2 by the transfer line method, which is the lowest reported value to the best of our knowledge. Utilizing this enhanced contact property between a-IGZO and metal, the metal–insulator–semiconductor varactor was fabricated, and its operating frequency was measured to be higher than 30 GHz

Decoding the Parkinson’s Symphony: PARIS, Maestro of Transcriptional Regulation and Metal Coordination for Dopamine Release

Parkin interacting substrate (PARIS) is a pivotal transcriptional regulator in the brain that orchestrates the activity of various enzymes through its intricate interactions with biomolecules, including nucleic acids. Notably, the binding of PARIS to insulin response sequences (IRSs) triggers a cascade of events that results in the functional loss in the substantia nigra, which impairs dopamine release and, subsequently, exacerbates the relentless neurodegeneration. Here, we report the details of the interactions of PARIS with IRSs via classical zinc finger (ZF) domains in PARIS, namely, PARIS(ZF2–4). Our biophysical studies with purified PARIS(ZF2–4) elucidated the binding partner of PARIS, which generates specific interactions with the IRS1 (5′-TATTTTT, Kd = 38.9 ± 2.4 nM) that is positioned in the promoter region of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α). Mutational and metal-substitution studies demonstrated that Zn(II)–PARIS(ZF2–4) could recognize its binding partner selectively. Overall, our work provides submolecular details regarding PARIS and shows that it is a transcriptional factor that regulates dopamine release. Thus, PARIS could be a crucial target for therapeutic applications

Hematoporphyrin Photosensitizer-Linked Carbon Quantum Dots for Photodynamic Therapy of Cancer Cells

The direct use of conventional photosensitizers in photodynamic therapy (PDT) of cancer cells has been thwarted by their low solubility, poor photostability, and aggregation tendency. Hence, complex and hectic synthetic procedures, such as developing nanomaterials and subsequently loading them with photosensitizers, have become mandatory for the effective use of photosensitizers in PDT. In this study, we have avoided complex procedures and produce hematoporphyrin (HP) photosensitizer-encapsulated carbon quantum dots (CQDs) (HP-CQDs) facilely through a well-controlled one-step microwave reaction by using the HP monomer as one of the precursors. The as-synthesized HP-CQDs retained all intrinsic optical and chemical properties of HP, while displaying excellent solubility in water. Importantly, the excellent reactive oxygen species generation ability of HP-CQDs under the illumination of deep red light favored their applicability in PDT-assisted efficient eradication of human breast cancer cells (MCF-7). Compared to HP, HP-CQDs exhibited very high phototoxicity and low dark toxicity toward MCF-7 cells. Overall, this study offers a proof of concept that photosensitizer-implanted CQDs, having excellence in PDT-assisted cancer treatment, can be easily designed by strategically exploiting the diversity available in the selection of precursors and synthesis conditions to produce CQDs