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Yoon G.,Korea University | Kab Kim Y.,Korea University | Eom K.,Yonsei University | Eom K.,Institute for Molecular Science | Na S.,Korea University
Applied Physics Letters | Year: 2013

It has recently been reported that the mechanical behavior of prion nanofibrils may play a critical role in expression of neurodegenerative diseases. In this work, we have studied the mechanical behavior of HET-s prion nanofibrils using an elastic network model. We have shown that the mechanical properties of prion nanofibrils formed as left-handed β-helices are different from those of non-prion nanofibrils formed as right-handed β-helices. In particular, the bending behavior of prion nanofibrils depends on the length of the nanofibril and that the bending rigidity of the prion nanofibril is larger than that of the non-prion nanofibril. © 2013 American Institute of Physics. Source


Yoon G.,Korea University | Na S.,Korea University | Eom K.,Yonsei University | Eom K.,Institute for Molecular Science
Journal of Chemical Physics | Year: 2012

Single-molecule mechanical manipulation has enabled quantitative understanding of not only the kinetics of both bond rupture and protein unfolding, but also the free energy landscape of chemical bond andor protein folding. Despite recent studies reporting the role of loading device in bond rupture, a loading device effect on protein unfolding mechanics has not been well studied. In this work, we have studied the effect of loading-device stiffness on the kinetics of both bond rupture and protein unfolding mechanics using Brownian dynamics simulations. It is shown that bond rupture forces are dependent on not only loading rate but also the stiffness of loading device, and that protein unfolding mechanics is highly correlated with the stiffness of loading device. Our study sheds light on the importance of loading device effect on the mechanically induced bond ruptures and protein unfolding. © 2012 American Institute of Physics. Source


News Article
Site: http://phys.org/chemistry-news/

Ionic transport has been studied extensively over the years for energy devices such as fuel cells and batteries using Li+, H+, Ag+, Cu+, F–, and O2–. Yet as Genki Kobayashi and Ryoji Kanno point out in a recent report, hydride ions (H-) may be particularly useful for high-energy-density storage devices. Using an oxyhydride solid state cell they have now demonstrated pure H- conduction in an oxide for the first time. Metal hydrides tend to have an inflexible lattice, which makes H– transport difficult, so the researchers turned to oxyhydrides where oxygen and hydrogen share the same lattice sites. Another challenge is the high electron-donating properties of H-, which means that the electrons will dissociate from the H- to produce protons and electrons, giving rise to electron rather than hydride-ion transport. As a result the team sought a system containing cations that were more electron-donating than the H-. Kobayashi and Kanno collaborated with colleagues from the Institute for Molecular Science, Japan Science and Technology Agency, Tokyo Institute of Technology, Kyoto University and High Energy Accelerator Research Organization (KEK) in Japan. They examined how the structure of their oxyhydride compounds changed with composition and synthesis conditions. They also studied characteristics of the electronic structure that suggested an ionic Li-H bond in the compound, namely the existence of H– in the oxides. They then used La LiHO in an orthorhombic structural phase (o- La LiHO ) as an electrolyte in a cell with titanium anode and titanium hydride cathodes. Phase changes at the electrodes by the discharge were consistent with a Ti-H phase diagram suggesting hydride-ion transport. They conclude: "The present success in the construction of an all-solid-state electrochemical cell exhibiting H– diffusion confirms not only the capability of the oxyhydride to act as an H– solid electrolyte but also the possibility of developing electrochemical solid devices based on H– conduction." Batteries and fuel cells are electrochemical devices. In lithium ion batteries, for example, lithium ions move from a positive to a negative electrode during use, and back again during charging. They are now used ubiquitously for energy storage in mobile devices but improvements to the energy density, performance and environmental sustainability of these batteries is still sought to extend their use to other devices, such as cars. The ions move between electrodes through an electrolyte. Solid-state electrolytes have safety and stability advantages over liquids as they are less prone to leak and short circuit. In other types of electrochemical device different types of ion move back and forth, such as positive hydrogen ions in fuel cells. The charge and size of the ions affects its transport. Ions are described by the number of additional (negative ions) or absent (positive ions) electrons in the outside or 'valence' electronic orbital. Oxygen readily accepts electrons to form doubly negative ions (O2-). As a result when an ion is oxidised it loses electrons, increasing the positivity of its oxidation state. When an ion is reduced, it accepts electrons, reducing the positivity of its electron valence state. In batteries atoms can be oxidised to form positive ions that are attracted to the negative electrode where they are reduced or vice versa. These reduction and oxidation reactions are described as redox reactions. Although hydride-ion conduction has not been used in batteries, there are potential advantages for using these ions. They are similar in size to oxide and fluoride ions and have strong reducing properties. The standard redox potential of H-/H is -2.3 V - close to Mg/Mg2+ (-2.4 V) which has already attracted interest for batteries. Hydride ion conductors may therefore be applied in energy storage or conversion devices with high energy densities. To overcome some of the challenges inhibiting hydride-ion conduction—hydride-ion diffusion in oxide crystal lattices and the high tendency for hydride-ion dissociation to electrons and protons—the researchers studied oxyhydrides that have structures similar to K NiF . These included La LiHO (x = y = 0), Sr LiH O (x = 0, y = 2), La SrxLiH O (0 ≤ x ≤ 1, y = 0), and La Sr LiH O (0 ≤ x ≤ 1, y = 1). They found that La LiHO exists in two chemical phases—orthorhombic (o) and tetragonal (t) depending on the ratio of the starting chemicals and synthesis conditions. Studies of the conductivity of the compounds showed that the compound compositions that led to more vacancies were more conductive, indicating a relationship between vacancies and ionic diffusion. They also showed that the conductivity could be increased by increasing the number of vacancies. Explore further: Beyond the lithium ion—a significant step toward a better performing battery More information: G. Kobayashi et al. Pure H- conduction in oxyhydrides, Science (2016). DOI: 10.1126/science.aac9185


« DOE announces $3M for 2nd round of HPC4Mfg for industry access to high performance computing | Main | IEEE publishes three updated standards to support connected vehicle development » Scientists at Tokyo Institute of Technology, in collaboration with colleagues in Japan, have demonstrated the first electrochemical reaction based on hydride ions in an oxide-based solid-state cell for potential next-generation batteries. A paper on their work is published in the journal Science. Ionic transport has been studied extensively over the years for energy devices such as fuel cells and batteries using Li+, H+, Ag+, Cu+, F–, and O2– as ionic charge carriers. The conduction of hydride ions, H–, is also attractive, the team notes in their paper. In contrast to proton conduction that takes place widely in oxides and other systems, pure H– conduction has been verified only for a few hydrides of alkaline earth metals such as BaH . Unfortunately, utilization of the hydrides is difficult because of their structural inflexibility, which makes control of the lattice structure to create smooth transport pathways and control of the conducting hydride ion content difficult. Using an oxyhydride solid state cell, the researchers have now demonstrated pure H- conduction in an oxide for the first time. Metal hydrides tend to have an inflexible lattice, which makes H– transport difficult, so the researchers turned to oxyhydrides where oxygen and hydrogen share the same lattice sites. Another challenge is the high electron-donating properties of H-, which means that the electrons will dissociate from the H- to produce protons and electrons, giving rise to electron rather than hydride-ion transport. As a result the team sought a system containing cations that were more electron-donating than the H-. Genki Kobayashi and Ryoji Kanno from Tokyo Tech collaborated with colleagues from the Institute for Molecular Science, Japan Science and Technology Agency, Tokyo Institute of Technology, Kyoto University and High Energy Accelerator Research Organization (KEK) in Japan. They examined how the structure of their oxyhydride compounds changed with composition and synthesis conditions. They also studied characteristics of the electronic structure that suggested an ionic Li-H bond in the compound—the existence of H– in the oxides. They then used La LiHO in an orthorhombic structural phase (o-La LiHO ) as an electrolyte in a cell with titanium anode and titanium hydride cathodes. Phase changes at the electrodes by the discharge were consistent with a Ti-H phase diagram suggesting hydride-ion transport. In a Perspective on the work by Kobayashi et al., published in the same issue of Science, Shu Yamaguchi of The University of Tokyo observed that: Kobayashi et al. report a material with pure H− conductivity (and yet an electronic insulator) in an oxyhydride system, which has been a “last frontier” in solid state ionics. … The result … is just the beginning of a new materials science of H− conductivity in oxyhydride systems that will require further elaboration of the underlying mechanisms, as well as potential applications of the extremely reducing H− ion in chemical synthesis. A drawback of the current material is its chemical reactivity in oxidizing atmospheres, but this disadvantage may be overcome by various techniques, like surface protection coatings. These explorations of H− conductors now leave the question of what will be the next last frontier for solid state ionics. This research was supported by Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology (PRESTO), and Grant-in-Aid for Scientific Research on Innovative Areas from the Japan Society for the Promotion of Science (JSPS).


Dai M.D.,Konkuk University | Kim C.-W.,Konkuk University | Kim C.-W.,Institute for Molecular Science | Eom K.,Yonsei University | Eom K.,Institute for Molecular Science
Nanoscale Research Letters | Year: 2012

Graphene has received significant attention due to its excellent mechanical properties, which has resulted in the emergence of graphene-based nano-electro-mechanical system such as nanoresonators. The nonlinear vibration of a graphene resonator and its application to mass sensing (based on nonlinear oscillation) have been poorly studied, although a graphene resonator is able to easily reach the nonlinear vibration. In this work, we have studied the nonlinear vibration of a graphene resonator driven by a geometric nonlinear effect due to an edge-clamped boundary condition using a continuum elastic model such as a plate model. We have shown that an in-plane tension can play a role in modulating the nonlinearity of a resonance for a graphene. It has been found that the detection sensitivity of a graphene resonator can be improved by using nonlinear vibration induced by an actuation force-driven geometric nonlinear effect. It is also shown that an in-plane tension can control the detection sensitivity of a graphene resonator that operates both harmonic and nonlinear oscillation regimes. Our study suggests the design principles of a graphene resonator as a mass sensor for developing a novel detection scheme using graphene-based nonlinear oscillators. © 2012 Dai et al. Source

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