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Pierre Regenass, Damien Bosc, Stéphanie Riché, Patrick Gizzi, Marcel Hibert, Lydia Brelot, A Ganesan, Dominique Bonnet
Aza-diketopiperazines (Aza-DKP) represent an underprivileged motif obtained by scaffold hopping of 2,5-diketopiperazines (2,5-DKP). Herein, we compare the synthesis but also the structural and the physicochemical properties of aza-DKP 4 vs 2,5-DKP 7. Thus, X-ray and 1H NMR studies show that aza-DKP 4 is a rigid and non-flat scaffold like the 2,5-DKP 7. Moreover, the replacement of one Calpha-stereogenic center by a nitrogen atom results in a significant improvement of both the water solubility and the microsomal stability...
February 23, 2017: Journal of Organic Chemistry
Oriol Lamiel-Garcia, Kyoung Chul Ko, Jin Yong Lee, Stefan T Bromley, Francesc Illas
All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic and electronic structure of a series of stoichiometric TiO2 anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1- 6 nm size range. Initial structures were obtained from a Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces...
February 23, 2017: Journal of Chemical Theory and Computation
Lichao Sun, Qingfeng Zhang, Guangfang Grace Li, Esteban Villarreal, Xiaoqi Fu, Hui Wang
Kinetically controlled, seed-mediated coreduction provides a robust and versatile synthetic approach to multimetallic nanoparticles with precisely controlled geometries and compositions. Here we demonstrate that single-crystalline cylindrical Au nanorods selectively transform into a series of structurally distinct Au@Au-Pd alloy core-shell bimetallic nanorods with exotic multifaceted geometries enclosed by specific types of facets upon seed-mediated Au-Pd coreduction under diffusion controlled conditions. By adjusting several key synthetic parameters, such as the Pd/Au precursor ratio, the reducing agent concentration, the capping surfactant concentration, and foreign metal ion additives, we have been able to simultaneously fine-tailor the atomic-level surface structures and fine-tune the compositional stoichiometries of the multifaceted Au-Pd bimetallic nanorods...
February 23, 2017: ACS Nano
Meiling Xu, Sen Shao, Bo Gao, Jian Lv, Quan Li, Yanchao Wang, Hui Wang, Lijun Zhang, Yanming Ma
Titanium dioxide has been widely used as efficient transition metal oxide photocatalyst. However, its photocatalytic activity is limited to ultraviolet spectrum range due to the deficient large bandgap beyond 3 eV. Efforts towards to reduce the bandgap for achieving a broader spectrum range of light absorption are attempted with a success on the experimental synthesis of dopant-free metastable surface structure of rutile-type TiO2 (011) 21. This new surface phase possesses a much reduced bandgap of ~2.1 eV, showing a great potential for an excellent photocatalyst covering a wide range of visible light...
February 23, 2017: ACS Applied Materials & Interfaces
Maryam Yousaf, Huan Huang, Ping Li, Chen Wang, Yanlian Yang
Fibrillar deposits of the human islet amyloid polypeptide (hIAPP) is considered as a root of Type II diabetes mellitus. Fluorinated graphene quantum dots (FGQDs) are new carbon nanomaterials with unique physicochemical properties containing highly electronegative F atoms. Herein we report a single step synthesis method of FGQDs with an inhibitory effect on aggregation and cytotoxicity of hIAPP in vitro. Highly fluorescent and water dispersible FGQDs, less than 3 nm in size were synthesized by the microwave-assisted hydrothermal method...
February 23, 2017: ACS Chemical Neuroscience
Dejiong Zhang, Chuanhong Jin, He Tian, Yalin Xiong, Hui Zhang, Peisheng Qiao, Jie Fan, Ze Zhang, Z Y Li, Jixue Li
The surface oxidation of palladium nanocrystals plays an important role in changing the active sites and subsequently influencing the catalytic reactivity. Such a microscopy study on surface oxidation, down to the atomic scale, is essential for understanding the structure-property correlations of palladium nanocrystal based catalysts. Herein, we present an in situ atomic scale study on the surface oxidation behavior of palladium nanocrystals, which is induced by electron beam irradiation under low oxygen partial pressure and at room temperature inside an environmental transmission electron microscope...
February 23, 2017: Nanoscale
Sean R Tachibana, Longteng Tang, Yanli Wang, Liangdong Zhu, Weimin Liu, Chong Fang
Fluorescent protein biosensors are popular reporters for biological processes and life sciences, but their fundamental working mechanisms remain unclear. To characterize the functional fluorescence events on their native timescales, we implemented wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS) to shed light on a blue-green emission-ratiometric fluorescent protein based Ca(2+) biosensor with a single Pro377Arg mutation. The transient Raman modes of the embedded chromophore from ca. 1000-1650 cm(-1) exhibit characteristic intensity and frequency dynamics which infer the underlying atomic motions and photochemical reaction stages...
February 23, 2017: Physical Chemistry Chemical Physics: PCCP
Stephanie Oerum, Clément Dégut, Pierre Barraud, Carine Tisné
To date, about 90 post-transcriptional modifications have been reported in tRNA expanding their chemical and functional diversity. Methylation is the most frequent post-transcriptional tRNA modification that can occur on almost all nitrogen sites of the nucleobases, on the C5 atom of pyrimidines, on the C2 and C8 atoms of adenosine and, additionally, on the oxygen of the ribose 2'-OH. The methylation on the N1 atom of adenosine to form 1-methyladenosine (m1A) has been identified at nucleotide position 9, 14, 22, 57, and 58 in different tRNAs...
February 21, 2017: Biomolecules
Matija Uršič, Tanja Lipec, Anton Meden, Iztok Turel
Four novel ruthenium organometallic complexes: [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)Cl] (1), [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)pta]PF₆ (2), [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)Cl] (3) and [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)pta]PF₆ (4) were synthesized and characterized by elemental analysis, infrared (IR), UV-Vis, NMR and mass spectroscopy and single-crystal X-ray diffraction...
February 20, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Max Medina-Ramírez, Rogier W Sanders, Quentin J Sattentau
PURPOSE OF REVIEW: To provide an update on the latest developments in the field of HIV-1 antibody-based soluble envelope glycoprotein (Env) trimer design for vaccine use. RECENT FINDINGS: The development of soluble native-like HIV-1 Env trimer immunogens has moved the field of antibody-based vaccine design forward dramatically over the past few years with refinement of various stabilizing approaches. However, despite this progress, significant challenges remain...
February 21, 2017: Current Opinion in HIV and AIDS
Keka R Chakraborty, Barnita Paul, Rakesh Shukla, Psr Krishna, Amit Kumar, Mayuresh Mukadam, Balaji Mandal, Anushree Roy, Avesh Tyagi, S Yusuf
The structural and magnetic properties of the Y1-xTbxMnO3(0.1x0.3)compoundswere investigated.Neutron diffraction patterns for all three samples,recorded at room temperature (RT),were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K,for the x = 0.1 sample magnetic moments of the Tb3+ionic as well as Mn3+ionic were ordered.At 5 K for the x = 0.2 sample only the Mn3+ionic magnetic moments were ordered. Therewere six sites for Mn atoms. Three on the z = 0 plane and three on the z = 0...
February 23, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Wei Shi, Haitao Zhao, Bingan Lu
In this paper, ZnCo2O4 nanowall arrays were firstly obtained through self-assembly followed by calcination. Then atomic layer deposition was used to fabricate core-shell ZnCo2O4@TiO2 nanowall arrays (NWAs) as anode materials for lithium ion batteries (LIBs). The hierarchical nanowall array nanostructure with fast ion diffusion and electron transport at electrode/electrolyte interface, while the shell of TiO2 with excellent chemical stability can protect the ZnCo2O4 nanowall arrays from volume expansion during charge and discharge processes...
February 23, 2017: Nanotechnology
Soroosh Sharifi-Asl, Fernando A Soto, Anmin Nie, Yifei Yuan, Hasti Asayesh-Ardakani, Tara Foroozan, Vitaliy Yurkiv, Boao Song, Farzad Mashayek, Robert F Klie, Khalil Amine, Jun Lu, Perla B Balbuena, Reza Shahbazian-Yassar
Thermal runaways triggered by the oxygen release from oxide cathode materials pose a major safety concern for widespread application of lithium ion batteries. Utilizing in-situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at high temperatures, we show that oxygen release from LixCoO2 cathode crystals is occurring at the surface of particles. We correlated this local oxygen evolution from the LixCoO2 structure with local phase transitions spanning from layered to spinel and then to rock salt structure upon exposure to elevated temperatures...
February 23, 2017: Nano Letters
Maria E Fuentes-Pérez, Rafael Núñez-Ramírez, Alejandro Martín-González, David Juan-Rodríguez, Oscar Llorca, Fernando Moreno-Herrero, Maria A Oliva
Cytomotive filaments are essential for the spatial organization in cells, showing a dynamic behavior based on nucleotide hydrolysis. TubZ is a tubulin-like protein that functions in extrachromosomal DNA movement within bacteria. TubZ filaments grow in a helical fashion following treadmilling or dynamic instability, although the underlying mechanism is unclear. We have unraveled the molecular basis for filament assembly and dynamics combining electron and atomic force microscopy and biochemical analyses. Our findings suggest that GTP caps retain the filament helical structure and hydrolysis triggers filament stiffening upon disassembly...
February 23, 2017: Scientific Reports
Lide Yao, Sampo Inkinen, Sebastiaan van Dijken
Resistive switching in transition metal oxides involves intricate physical and chemical behaviours with potential for non-volatile memory and memristive devices. Although oxygen vacancy migration is known to play a crucial role in resistive switching of oxides, an in-depth understanding of oxygen vacancy-driven effects requires direct imaging of atomic-scale dynamic processes and their real-time impact on resistance changes. Here we use in situ transmission electron microscopy to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films...
February 23, 2017: Nature Communications
Yong-Chao Liang, Rang-Su Liu, Quan Xie, Ze-An Tian, Yun-Fei Mo, Hai-Tao Zhang, Hai-Rong Liu, Zhao-Yang Hou, Li-Li Zhou, Ping Peng
To investigate the structural evolution and hereditary mechanism of icosahedral nano-clusters formed during rapid solidification, a molecular dynamics (MD) simulation study has been performed for a system consisting of 10(7) atoms of liquid Mg70Zn30 alloy. Adopting Honeycutt-Anderson (HA) bond-type index method and cluster type index method (CTIM-3) to analyse the microstructures in the system it is found that for all the nano-clusters including 2~8 icosahedral clusters in the system, there are 62 kinds of geometrical structures, and those can be classified, by the configurations of the central atoms of basic clusters they contained, into four types: chain-like, triangle-tailed, quadrilateral-tailed and pyramidal-tailed...
February 23, 2017: Scientific Reports
David L Cortie, Yury Khaydukov, Thomas Keller, David John Sprouster, Jacob S Hughes, James P Sullivan, Xiaolin Wang, Anton P Le Brun, Joel Bertinshaw, Sara J Callori, Robert D Aughterson, Michael James, Peter J Evans, Gerry Triani, Frank Klose
High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study we report a large magnetization formed by ion implantation of Co into amorphous TiO2-δ films producing an inhomogenous magnetic moment, with certain regions producing over 2.5 µB per Co, depending on the local dopant concentration...
February 23, 2017: ACS Applied Materials & Interfaces
Chunming Cui, Hailong Ren, Yu-Peng Zhou, Yun-Ping Bai, Matthias Driess
C-H Borylation of arenes has been a subject of great current interest because of its atom-economy and the wide applicability of borylated products in value-added synthesis. A new bis(silylene)cobalt(II) complex bearing a bis(N-heterocyclic silylene)-pyridine pincer ligand (SiNSi) has been synthesized and structurally characterized. It enabled the regioselective catalytic C-H borylation of pyridines, furans and fluorinated arenes. Notably, it exhibited the complementary regioselectivity for the borylation of fluorinated arenes compared to previously known catalytic systems, demonstrating that N-heterocyclic silylene donors have enormous potential in metal-catalyzed catalytic applications...
February 23, 2017: Chemistry: a European Journal
Yi Lai, Zhijian Zong, Yujie Tang, Weimin Mo, Nan Sun, Baoxiang Hu, Zhenlu Shen, Liqun Jin, Wen-Hua Sun, Xinquan Hu
A series of bulky geometry-constrained iminopyridylpalladium chlorides were developed. The steric environment adjacent to the nitrogen atom in the pyridine rings and diimine parts enhanced the thermal stability of the palladium species. Bulkier groups at the imino group stabilized the palladium species and the corresponding palladium chlorides showed high activities in the coupling reaction of aryl chlorides.
2017: Beilstein Journal of Organic Chemistry
Kun V Tian, Giulia Festa, Francesco Basoli, Giuseppina Laganà, Antonella Scherillo, Carla Andreani, Patrizio Bollero, Silvia Licoccia, Roberto Senesi, Paola Cozza
Quantitative metallurgical and phase analyses employing neutron diffraction technique were conducted on two as-received commercial rectangular austenitic stainless steel orthodontic archwires, G&H and Azdent, 0.43×0.64 mm (0.017×0.025 inch). Results showed a bi-phase structure containing martensitic phase (45.67% for G&H and 6.62% for Azdent) in addition to the expected metastable austenite. The former may be a strain-induced phase-transformation arising during the cold working process of wire fabrication...
February 22, 2017: Dental Materials Journal
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