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https://www.readbyqxmd.com/read/29334685/observation-of-a-phononic-quadrupole-topological-insulator
#1
Marc Serra-Garcia, Valerio Peri, Roman Süsstrunk, Osama R Bilal, Tom Larsen, Luis Guillermo Villanueva, Sebastian D Huber
The modern theory of charge polarization in solids is based on a generalization of Berry's phase. The possibility of the quantization of this phase arising from parallel transport in momentum space is essential to our understanding of systems with topological band structures. Although based on the concept of charge polarization, this same theory can also be used to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. The theory of this quantized polarization has recently been extended from the dipole moment to higher multipole moments...
January 15, 2018: Nature
https://www.readbyqxmd.com/read/29329285/a-direct-interaction-of-cholesterol-with-the-dopamine-transporter-prevents-its-out-to-inward-transition
#2
Talia Zeppelin, Lucy Kate Ladefoged, Steffen Sinning, Xavier Periole, Birgit Schiøtt
Monoamine transporters (MATs) carry out neurotransmitter reuptake from the synaptic cleft, a key step in neurotransmission, which is targeted in the treatment of neurological disorders. Cholesterol (CHOL), a major component of the synaptic plasma membrane, has been shown to exhibit a modulatory effect on MATs. Recent crystal structures of the dopamine transporter (DAT) revealed the presence of two conserved CHOL-like molecules, suggesting a functional protein-CHOL direct interaction. Here, we present extensive atomistic molecular dynamics (MD) simulations of DAT in an outward-facing conformation...
January 12, 2018: PLoS Computational Biology
https://www.readbyqxmd.com/read/29320481/architecture-of-a-channel-forming-o-antigen-polysaccharide-abc-transporter
#3
Yunchen Bi, Evan Mann, Chris Whitfield, Jochen Zimmer
O-antigens are cell surface polysaccharides of many Gram-negative pathogens that aid in escaping innate immune responses. A widespread O-antigen biosynthesis mechanism involves the synthesis of the lipid-anchored polymer on the cytosolic face of the inner membrane, followed by transport to the periplasmic side where it is ligated to the lipid A core to complete a lipopolysaccharide molecule. In this pathway, transport to the periplasm is mediated by an ATP-binding cassette (ABC) transporter, called Wzm-Wzt...
January 10, 2018: Nature
https://www.readbyqxmd.com/read/29318719/crystal-structures-of-mglb-2-tp0684-a-topologically-variant-d-glucose-binding-protein-from-treponema-pallidum-reveal-a-ligand-induced-conformational-change
#4
Chad A Brautigam, Ranjit K Deka, Wei Z Liu, Michael V Norgard
Previously, we determined the crystal structure of apo-TpMglB-2, a D-glucose-binding component of a putative ABC transporter from the syphilis spirochete Treponema pallidum. The protein had an unusual topology for this class of proteins, raising the question of whether the D-glucose-binding mode would be different in TpMglB-2. Here, we present the crystal structures of a variant of TpMglB-2 with and without D-glucose bound. The structures demonstrate that, despite its aberrant topology, the protein undergoes conformational changes and binds D-glucose similarly to other Mgl-type proteins, likely facilitating D-glucose uptake in T...
January 10, 2018: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/29318657/crystal-structure-of-tetrameric-human-rabin8-gef-domain
#5
Melanie Vetter, Niels Boegholm, Anni Christensen, Sagar Bhogaraju, Marie B Andersen, Anna Lorentzen, Esben Lorentzen
Rab GTPases and their effectors, activators and guanine nucleotide exchange factors (GEFs) are essential for vesicular transport. Rab8 and its GEF Rabin8 function in formation of the cilium organelle important for developmental signaling and sensory reception. Here we show by size exclusion chromatography and analytical ultracentrifugation that Rabin8 exists in equilibrium between dimers and tetramers. The crystal structure of tetrameric Rabin8 GEF domain reveals an occluded Rab8 binding site suggesting that this oligomer is enzymatically inactive, a notion we verify experimentally using Rabin8/Rab8 GEF assays...
January 10, 2018: Proteins
https://www.readbyqxmd.com/read/29313668/high-thermoelectric-performance-of-in4se3-based-materials-and-the-influencing-factors
#6
Xin Yin, Jing-Yuan Liu, Ling Chen, Li-Ming Wu
Materials that can directly convert electricity into heat, i.e., thermoelectric materials, have attracted renewed attention globally for sustainable energy applications. As one of the state-of-the-art thermoelectric materials, In4Se3 features an interesting crystal structure of quasi-two-dimensional sheets comprising In/Se chains that provide a platform to achieve a Peierls distortion and support a charge density wave instability. Single-crystal In4Se3-δ (δ = 0.65) shows strong anisotropy in its thermoelectric properties with a very high ZT of 1...
January 9, 2018: Accounts of Chemical Research
https://www.readbyqxmd.com/read/29311332/single-crystal-metal-growth-on-amorphous-insulating-substrates
#7
Kai Zhang, Xue Bai Pitner, Rui Yang, William D Nix, James D Plummer, Jonathan A Fan
Metal structures on insulators are essential components in advanced electronic and nanooptical systems. Their electronic and optical properties are closely tied to their crystal quality, due to the strong dependence of carrier transport and band structure on defects and grain boundaries. Here we report a method for creating patterned single-crystal metal microstructures on amorphous insulating substrates, using liquid phase epitaxy. In this process, the patterned metal microstructures are encapsulated in an insulating crucible, together with a small seed of a differing material...
January 8, 2018: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/29311076/crystal-structure-of-nisi-in-a-lipid-free-form-the-nisin-immunity-protein-from-lactococcus-lactis
#8
Jin Hee Jeong, Sung Chul Ha
Nisin is a lantibiotic, a family of polypeptides containing lanthionine with antimicrobial activity. Nisin-producing microorganisms require immunity proteins for self-protection from nisin itself. Lactococcus lactis, a microorganism that synthesizes nisin, has an integral NisFEG ABC transporter and NisI lipoprotein that function in the nisin immunity. Here, we present the crystal structure of the full length of NisI22-C, a lipid-free form of NisI, determined at 1.9 Å resolution. Similar to the NMR structures of N- and C-terminal domain of NisI, NisI22-C is composed of N- and C-terminal domains, both of which display a fold similar to that found in SpaI, a lipoprotein with immunity against subtilin in Bacillus subtilis The full length structure of NisI22-c reveals a large and deep cleft by the interdomain association, one side of which is occupied by the residues important for immunity...
January 8, 2018: Antimicrobial Agents and Chemotherapy
https://www.readbyqxmd.com/read/29300483/unexpected-diffusion-anisotropy-of-carbon-dioxide-in-the-metal-organic-framework-zn2-dobpdc
#9
Alexander C Forse, Miguel I Gonzalez, Rebecca L Siegelman, Velencia J Witherspoon, Sudi Jawahery, Rocio Mercado, Phillip J Milner, Jeffrey D Martell, Berend Smit, Bernhard Blümich, Jeffrey R Long, Jeffrey A Reimer
Metal-organic frameworks are promising materials for energy-efficient gas separations, but little is known about the diffusion of adsorbates in materials featuring one-dimensional porosity at the nanoscale. An understanding of the interplay between framework structure and gas diffusion is crucial for the practical application of these materials as adsorbents or in mixed-matrix membranes, since the rate of gas diffusion within the adsorbent pores impacts the required size (and therefore cost) of the adsorbent column or membrane...
January 4, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29300012/one-pot-growth-of-two-dimensional-lateral-heterostructures-via-sequential-edge-epitaxy
#10
Prasana K Sahoo, Shahriar Memaran, Yan Xin, Luis Balicas, Humberto R Gutiérrez
Two-dimensional heterojunctions of transition-metal dichalcogenides have great potential for application in low-power, high-performance and flexible electro-optical devices, such as tunnelling transistors, light-emitting diodes, photodetectors and photovoltaic cells. Although complex heterostructures have been fabricated via the van der Waals stacking of different two-dimensional materials, the in situ fabrication of high-quality lateral heterostructures with multiple junctions remains a challenge. Transition-metal-dichalcogenide lateral heterostructures have been synthesized via single-step, two-step or multi-step growth processes...
January 3, 2018: Nature
https://www.readbyqxmd.com/read/29298979/defects-controlled-hole-doping-and-multivalley-transport-in-snse-single-crystals
#11
Zhen Wang, Congcong Fan, Zhixuan Shen, Chenqiang Hua, Qifeng Hu, Feng Sheng, Yunhao Lu, Hanyan Fang, Zhizhan Qiu, Jiong Lu, Zhengtai Liu, Wanling Liu, Yaobo Huang, Zhu-An Xu, D W Shen, Yi Zheng
SnSe is a promising thermoelectric material with record-breaking figure of merit. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping mechanism in SnSe is still absent. Here we report the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. We prove that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe2 microdomains via interfacial charge transferring...
January 3, 2018: Nature Communications
https://www.readbyqxmd.com/read/29298071/band-like-carrier-transport-at-the-single-crystal-contact-interfaces-between-2-5-difluoro-7-7-8-8-tetracyanoquinodimethane-and-electron-donors
#12
Takuro Shimada, Yukihiro Takahashi, Jun Harada, Hiroyuki Hasegawa, Tamotsu Inabe
Some heterojunction interfaces formed with molecular solids show metal-like transport behavior. In order to clarify the requirement, the interfaces were fabricated by lamination of single-crystal electron-accepting 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F2TCNQ) and electron-donating molecules with a wide range of ionization potentials. Carrier injection between the acceptor and donor crystals generated highly conducting interfaces, some of which exhibited band-like charge transport behaviors. Combinations with weak donors also resulted in interfaces with band-like transport properties...
January 3, 2018: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/29295993/structural-characterisation-reveals-insights-into-substrate-recognition-by-the-glutamine-transporter-asct2-slc1a5
#13
Amanda J Scopelliti, Josep Font, Robert J Vandenberg, Olga Boudker, Renae M Ryan
Cancer cells undergo a shift in metabolism where they become reliant on nutrients such as the amino-acid glutamine. Glutamine enters the cell via the alanine/serine/cysteine transporter 2 (ASCT2) that is upregulated in several cancers to maintain an increased supply of this nutrient and are therefore an attractive target in cancer therapeutic development. ASCT2 belongs to the glutamate transporter (SLC1A) family but is the only transporter in this family able to transport glutamine. The structural basis for glutamine selectivity of ASCT2 is unknown...
January 2, 2018: Nature Communications
https://www.readbyqxmd.com/read/29289195/a-high-resolution-combined-scanning-laser-and-widefield-polarizing-microscope-for-imaging-at-temperatures-from-4-k-to-300-k
#14
M Lange, S Guénon, F Lever, R Kleiner, D Koelle
Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as, for example, birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved...
December 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/29281173/high-crystalline-prussian-white-nanocubes-as-a-promising-cathode-for-sodium-ion-batteries
#15
Cong Li, Rui Zang, Pengxin Li, Zengming Man, Shijian Wang, Yuhan Wu, Shuaishuai Liu, Guoxiu Wang
Prussian blue and its analogues (PBAs) have been recognized as one of the most promising cathode materials for room temperature sodium-ion batteries (SIBs). Herein, we report highly crystalline and Na-rich Prussian white Na2CoFe(CN)6 nanocubes synthesized by an optimized and facile co-precipitation method. The influence of crystallinity and sodium content on the electrochemical properties was systematically investigated. The optimized Na2CoFe(CN)6 nanocubes exhibited an initial capacity of 151 mA h g-1, which is close to its theoretical capacity (170 mA h g-1)...
December 27, 2017: Chemistry, An Asian Journal
https://www.readbyqxmd.com/read/29280163/theoretical-insights-into-the-1d-charge-transport-properties-in-a-series-of-hexaazatrinaphthylene-based-discotic-molecules
#16
Beibei An, Keke Wen, Songyan Feng, Xiao Pan, Wenpeng Wu, Xugeng Guo, Jinglai Zhang
Discotic liquid crystal (DLC) materials have attracted considerable attention mainly due to their high charge carrier mobilities in quasi-one-dimensional columns. In this article, five hexaazatrinaphthylene-based DLC molecules were investigated theoretically, and their frontier molecular orbital energy levels, crystal structures, and electron/hole drift mobilities were calculated by combination of density functional theory (DFT) and semiclassical Marcus charge transfer theory. The systems studied in this work include three experimentally reported molecules (1, 2, and 3) and two theoretically designed molecules (4 and 5)...
December 26, 2017: Journal of Computational Chemistry
https://www.readbyqxmd.com/read/29260845/hierarchically-porous-graphene-zif-8-hybrid-aerogel-preparation-co2-uptake-capacity-and-mechanical-property
#17
Min Jiang, Houzhi Li, Lijuan Zhou, Ruofei Xing, Jianming Zhang
Hierarchical zeolitic imidazole framework (ZIFs) combining micropore with mesoporous structure is desirable to enhance mass transport and give rise to novel applications. Here, hierarchically porous graphene/ZIF-8 hybrid aerogel (GZAn) materials were successfully prepared by a two-step reduction strategy and layer-by-layer assembly method. To avoid a tedious dry step and a use of energy-consuming freeze-drying technology, a reduced graphene oxide hydrogel with different reduction degree was chosen as template to in-situ grow ZIF-8 crystals...
December 20, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/29260732/thermoelectric-properties-of-nanocrystalline-sb-sub-2-sub-te-sub-3-sub-thin-films-experimental-evaluation-and-first-principles-calculation-addressing-effect-of-crystal-grain-size
#18
Satoshi Morikawa, Takuya Inamoto, Masayuki Takashiri
The effect of crystal grain size on the thermoelectric properties of nanocrystalline antimony telluride (Sb2Te3) thin films was investigated by experiment and first-principles studies using a developed relaxation time approximation. The Sb2Te3 thin films were deposited on glass substrates using radio-frequency magnetron sputtering. To change the crystal grain size of the Sb2Te3 thin films, thermal annealing was performed at different temperatures. The crystal grain size, lattice parameter, and crystal orientation of the thin films were estimated using XRD patterns...
December 20, 2017: Nanotechnology
https://www.readbyqxmd.com/read/29259089/peptide-uptake-is-essential-for-borrelia-burgdorferi-viability-and-involves-structural-and-regulatory-complexity-of-its-oligopeptide-transporter
#19
Ashley M Groshong, Abhishek Dey, Irina Bezsonova, Melissa J Caimano, Justin D Radolf
Borrelia burgdorferi is an extreme amino acid (AA) auxotroph whose genome encodes few free AA transporters and an elaborate oligopeptide transport system (B. burgdorferi Opp [BbOpp]). BbOpp consists of five oligopeptide-binding proteins (OBPs), two heterodimeric permeases, and a heterodimeric nucleotide-binding domain (NBD). Homology modeling based on the crystal structure of liganded BbOppA4 revealed that each OBP likely binds a distinct range of peptides. Transcriptional analyses demonstrated that the OBPs are differentially and independently regulated whereas the permeases and NBDs are constitutively expressed...
December 19, 2017: MBio
https://www.readbyqxmd.com/read/29258315/influence-of-structural-defects-on-biomineralized-zns-nanoparticle-dissolution-an-in-situ-electron-microscopy-study
#20
Jeremy R Eskelsen, Jie Xu, Michelle Y Chiu, Ji-Won Moon, Branford O Wilkins, David E Graham, Baohua Gu, Eric M Pierce
The dissolution of metal sulfides, such as ZnS, is an important biogeochemical process affecting fate and transport of trace metals in the environment. However, currently studies of in-situ dissolution of metal sulfides and the effects of structural defects on dissolution are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized via several abiotic and biological pathways. Specifically, the biogenic ZnS nanoparticles were produced by an anaerobic, metal-reducing bacterium Thermoanaerobacter sp...
December 19, 2017: Environmental Science & Technology
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