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Synthetic ion transporters can induce apoptosis by facilitating chloride anion transport into cells
Ko, Sung-Kyun,Kim, Sung Kuk,Share, Andrew,Lynch, Vincent M.,Park, Jinhong,Namkung, Wan,Van Rossom, Wim,Busschaert, Nathalie,Gale, Philip A.,Sessler, Jonathan L.,Shin, Injae Nature Publishing Group 2014 Nature chemistry Vol.6 No.10
Anion transporters based on small molecules have received attention as therapeutic agents because of their potential to disrupt cellular ion homeostasis. However, a direct correlation between a change in cellular chloride anion concentration and cytotoxicity has not been established for synthetic ion carriers. Here we show that two pyridine diamide-strapped calix[4]pyrroles induce coupled chloride anion and sodium cation transport in both liposomal models and cells, and promote cell death by increasing intracellular chloride and sodium ion concentrations. Removing either ion from the extracellular media or blocking natural sodium channels with amiloride prevents this effect. Cell experiments show that the ion transporters induce the sodium chloride influx, which leads to an increased concentration of reactive oxygen species, release of cytochrome c from the mitochondria and apoptosis via caspase activation. However, they do not activate the caspase-independent apoptotic pathway associated with the apoptosis-inducing factor. Ion transporters, therefore, represent an attractive approach for regulating cellular processes that are normally controlled tightly by homeostasis.
Fatigue Crack Growth Behavior of Corner Cracks under LBH Loading
Oh, Chung Seog,Park, Philip,Huh, Yong Hak,Ko, Soon Gyu,Hwang, Don Young,An, Hyeon Mo Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-
<P>This investigation aims at doing some durability and damage tolerant (DaDT) tests with 2124-T851 aluminum specimens having corner cracks under a random history, correlating with the simulation results from AFGROW and then drawing some conclusions from those comparisons. Two hydraulic actuators and a homemade Wood’s alloy grip are employed to do the test. The surface crack lengths are measured by a traveling microscope and used as a reference for the later fractography. The crack penetration and the total lives are about 17 and 27 blocks, respectively. The crack length and depth are evaluated by the fractography after completing each test and used to grasp the shape change. The Forman equation is used to simulate the fatigue crack growth behavior according to a bearing stress ratio extensively. The crack penetration life is decreased as the bearing stress ratio increases. The crack aspect ratio is very dependent on the bearing stress ratio. The LBH loading accelerates the fatigue crack growth in the crack depth direction but decelerates that in the length direction until crack penetration.</P>
Unraveling the Origin of Operational Instability of Quantum Dot Based Light-Emitting Diodes
Chang, Jun Hyuk,Park, Philip,Jung, Heeyoung,Jeong, Byeong Guk,Hahm, Donghyo,Nagamine, Gabriel,Ko, Jongkuk,Cho, Jinhan,Padilha, Lazaro A.,Lee, Doh C.,Lee, Changhee,Char, Kookheon,Bae, Wan Ki American Chemical Society 2018 ACS NANO Vol.12 No.10
<P>We investigate the operational instability of quantum dot (QD)-based light-emitting diodes (QLEDs). Spectroscopic analysis on the QD emissive layer within devices in chorus with the optoelectronic and electrical characteristics of devices discloses that the device efficiency of QLEDs under operation is indeed deteriorated by two main mechanisms. The first is the luminance efficiency drop of the QD emissive layer in the running devices owing to the accumulation of excess electrons in the QDs, which escalates the possibility of nonradiative Auger recombination processes in the QDs. The other is the electron leakage toward hole transport layers (HTLs) that accompanies irreversible physical damage to the HTL by creating nonradiative recombination centers. These processes are distinguishable in terms of the time scale and the reversibility, but both stem from a single origin, the discrepancy between electron <I>versus</I> hole injection rates into QDs. Based on experimental and calculation results, we propose mechanistic models for the operation of QLEDs in individual quantum dot levels and their degradation during operation and offer rational guidelines that promise the realization of high-performance QLEDs with proven operational stability.</P> [FIG OMISSION]</BR>
Inducing superconducting correlation in quantum Hall edge states
Lee, Gil-Ho,Huang, Ko-Fan,Efetov, Dmitri K.,Wei, Di S.,Hart, Sean,Taniguchi, Takashi,Watanabe, Kenji,Yacoby, Amir,Kim, Philip NATURE PUBLISHING GROUP 2017 NATURE PHYSICS Vol.13 No.7
The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states.
Water-Gated Charge Dopingof Graphene Induced by MicaSubstrates
Shim, Jihye,Lui, Chun Hung,Ko, Taeg Yeoung,Yu, Young-Jun,Kim, Philip,Heinz, Tony F.,Ryu, Sunmin American ChemicalSociety 2012 Nano letters Vol.12 No.2
<P>We report on the existence of water-gated charge dopingof graphenedeposited on atomically flat mica substrates. Molecular films of waterin units of ∼0.4 nm thick bilayers were found to be presentin regions of the interface of graphene/mica heterostacks preparedby micromechanical exfoliation of kish graphite. The spectral variationof the G and 2D bands, as visualized by Raman mapping, shows thatmica substrates induce strong p-type doping in graphene with holedensities of (9 ± 2) × 10<SUP>12</SUP> cm<SUP>–2</SUP>. The ultrathin water films, however, effectively block interfacialcharge transfer, rendering graphene significantly less hole-doped.Scanning Kelvin probe microscopy independently confirmed a water-gatedmodulation of the Fermi level by 0.35 eV, which is in agreement withthe optically determined hole density. The manipulation of the electronicproperties of graphene demonstrated in this study should serve asa useful tool in realizing future graphene applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-2/nl2034317/production/images/medium/nl-2011-034317_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl2034317'>ACS Electronic Supporting Info</A></P>