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Tomi F Nano, Terenz Escartin, Elina Ismailova, Karim S Karim, Jan Lindstrȍm, Ho Kyung Kim, Ian A Cunningham
PURPOSE: Acquisition of high-quality x-ray images using low patient exposures requires detectors with high detective quantum efficiency (DQE). We describe a novel apodized-aperture pixel (AAP) design that increases high-frequency modulation transfer function (MTF) and DQE values. The AAP design makes a separation of physical sensor elements from image pixels by using very small sensor elements (e.g. 0.010-0.025 mm) to synthesize desired larger image pixels (e.g. 0.1-0.2 mm). METHODS: A cascaded systems model of signal and noise propagation is developed to describe the benefits of the AAP approach in terms of the MTF, Wiener noise power spectrum (NPS) and DQE...
June 21, 2017: Medical Physics
Woon Yong Sohn, Sana Habka, Eric Gloaguen, Michel Mons
The presence in crystallized proteins of a local anchoring between the side chain of a His residue, located in the central position of a γ- or β-turn, and its local main chain environment, was assessed by the comparison of protein structures with relevant isolated model peptides. Gas phase laser spectroscopy, combined with relevant quantum chemistry methods, was used to characterize the γ- and β-turn structures in these model peptides. A conformer-selective NH stretch infrared study provided evidence for the formation in vacuo of two types of short-range H-bonded motifs, labelled ε-6(δ) and δ-(δ)7/π(H), bridging the His side chain (in its gauche+ rotamer) to the neighbouring NH(i) and CO(i) sites of the backbone; each side chain-backbone motif was found to be specific of the tautomer (ε or δ) adopted by the His side chain in its neutral form...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Chengfei Zhao, Kangying Wang, Qihong Cai, Haijian Tu, Linghong Pan, Liumin Yu
Nitrogen-doped carbon quantum dots (N-CQDs) with citric acid and ethylenediamine as raw materials were synthesized by an efficient one-step strategy. The N-CQDs showed a special property that the fluorescence was quenched by Fe(3+). The quenched fluorescence of N-CQDs could be recovered by glutathione (GSH). Therefore, a "signal-on" fluorescent sensor was developed to detect GSH. The fluorescent sensor could favorably avoid the interference of ascorbic acid, dopamine, glucose, oxidized glutathione and other amino acids in the detecting process of GSH...
June 21, 2017: Preparative Biochemistry & Biotechnology
Bin He, Ren Liu, Jiabin Ren, Caijian Tang, Yijun Zhong, Yong Hu
Metal ion doping and nanocoating to CdS photocatalyst have been proved to be effective strategies to inhibit photocorrosion and improve photocatalytic performance. In this study, carbon-coated Cu+-doped CdS nanocomposites (C-Cu-CdS) with a stable petalous structure and highly uniform size distribution were successfully synthesized via a facile one-step solvothermal method. Both Cu+ doping and carbon coating to the CdS photocatalyst are realized in this one-step strategy. Benefiting from the unique core-shell structure and metal ion doping, the as-prepared C-Cu-CdS catalyst exhibits significantly enhanced photostability and visible-light-driven photocatalytic efficiency...
June 21, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Francesca Nunzi, Diego Cesario, Fernando Pirani, Leonardo Belpassi, Gernot Frenking, Felice Grandinetti, Francesco Tarantelli
We studied the puzzling stability and short distances predicted by theory for helium adducts with some highly polar molecules, such as BeO or AuF. On the basis of high-level quantum-chemical calculations, we carried out a detailed analysis of the charge displacement occurring upon adduct formation. For the first time we have unambiguously ascertained that helium is able not only to donate electron density, but also, unexpectedly, to accept electron density in the formation of weakly bound adducts with highly polar substrates...
June 21, 2017: Journal of Physical Chemistry Letters
Ankit Jain, Oleksandr Voznyy, Marek Korkusinski, Pawel Hawrylak, Edward H Sargent
It has previously been found that Auger processes can lead to femtosec- ond carrier trapping in quantum dots, limiting their performance in opto- electronic applications that rely on radiative recombination. Here, using atomistic simulations, we investigate whether a shell can protect carriers from Auger-assisted trapping. For these studies we investigate CdSe/CdS core-shell quantum dots having total diameters reaching up to 10 nm. We find trapping lifetimes as fast as 1 ps for 2 nm shells, and we report that shells as thick as 6 nm are required to suppress trapping fully...
June 21, 2017: Journal of Physical Chemistry Letters
Jörg Kussmann, Christian Ochsenfeld
We present a parallel integral algorithm for two-electron contributions occurring in Hartree-Fock and hybrid density functional theory that allows for a strong scaling parallelization on inhomogeneous compute clusters. With a particular focus on graphic processing units, we show that our approach allows an efficient use of CPUs and graphics processing units (GPUs) simultaneously, although the different architectures demand conflictive strategies in order to ensure efficient program execution. Furthermore, we present a general strategy to use large basis sets like quadruple-ζ split valence on GPUs and investigate the balance between CPUs and GPUs depending on l-quantum numbers of the corresponding basis functions...
June 21, 2017: Journal of Chemical Theory and Computation
Ryan J Stoddard, Felix T Eickemeyer, John K Katahara, Hugh W Hillhouse
High bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a Ligand-Assisted Crystallization (LAC) technique that introduces additives in-situ during the solvent wash and developed a new method to dynamically measure the absolute-intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation...
June 21, 2017: Journal of Physical Chemistry Letters
Olga V Dorofeeva, Oxana N Ryzhova, Taisiya A Suchkova
Enthalpies of formation, ∆_f H_298^°, both in the gas and condensed phase, and enthalpies of sublimation or vaporization have been estimated for hydrazine, NH2NH2, and its 36 various derivatives using quantum chemical calculations. The composite G4 method has been used along with isodesmic reaction schemes to derive a set of self-consistent high accuracy gas-phase enthalpies of formation. To estimate the enthalpies of sublimation and vaporization with reasonable accuracy (5-20 kJ/mol), the method of molecular electrostatic potential (MEP) has been used...
June 21, 2017: Journal of Physical Chemistry. A
Fengrui Qu, Seungjo Park, Kristina Martinez, Jessica L Gray, Fathima Shazna Thowfeik, John A Lundeen, Ashley E Kuhn, David J Charboneau, Deidra L Gerlach, Molly M Lockart, James A Law, Katherine L Jernigan, Nicole Chambers, Matthias Zeller, Nicholas A Piro, W Scott Kassel, Russell H Schmehl, Jared J Paul, Edward J Merino, Yonghyun Kim, Elizabeth T Papish
Metallo prodrugs that take advantage of the inherent acidity surrounding cancer cells have yet to be developed. We report a new class of pH-activated metallo prodrugs (pHAMPs) that are activated by light- and pH-triggered ligand dissociation. These ruthenium complexes take advantage of a key characteristic of cancer cells and hypoxic solid tumors (acidity) that can be exploited to lessen the side effects of chemotherapy. Five ruthenium complexes of the type [(N,N)2Ru(PL)](2+) were synthesized, fully characterized, and tested for cytotoxicity in cell culture (1A: N,N = 2,2'-bipyridine (bipy) and PL, the photolabile ligand, = 6,6'-dihydroxybipyridine (6,6'-dhbp); 2A: N,N = 1,10-phenanthroline (phen) and PL = 6,6'-dhbp; 3A: N,N = 2,3-dihydro-[1,4]dioxino[2,3-f][1,10]phenanthroline (dop) and PL = 6,6'-dhbp; 4A: N,N = bipy and PL = 4,4'-dimethyl-6,6'-dihydroxybipyridine (dmdhbp); 5A: N,N = 1,10-phenanthroline (phen) and PL = 4,4'-dihydroxybipyridine (4,4'-dhbp)...
June 21, 2017: Inorganic Chemistry
Christian Espinosa-Bustos, Diego Cortés-Arriagada, Marco A Soto-Arriaza, José Robinson-Duggon, Nancy Pizarro, Alan R Cabrera, Denis Fuentealba, Cristian O Salas
In this paper, we explored the fluorescence properties of eight aurone derivatives bearing methoxy groups and bromine atoms as substituents in the benzene rings. All derivatives showed strong solvatochromic absorption and emission properties in solvents of different polarities. Some of them showed high fluorescence quantum yields, which make them potential compounds for sensing applications. The position of the methoxy groups in the benzofuranone moiety and the presence of bromine atoms in the benzene ring had a strong influence on the fluorescence behaviour of the aurones...
June 21, 2017: Photochemical & Photobiological Sciences
Jiří Černý, Bohdan Schneider, Lada Biedermannová
Water molecules represent an integral part of proteins and a key determinant of protein structure, dynamics and function. WatAA is a newly developed, web-based atlas of amino-acid hydration in proteins. The atlas provides information about the ordered first hydration shell of the most populated amino-acid conformers in proteins. The data presented in the atlas are drawn from two sources: experimental data and ab initio quantum-mechanics calculations. The experimental part is based on a data-mining study of a large set of high-resolution protein crystal structures...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Alejandro Morales-Bayuelo
Mycobacterium tuberculosis remains one of the world's most devastating pathogens. For this reason, we developed a study involving 3D pharmacophore searching, selectivity analysis and database screening for a series of anti-tuberculosis compounds, associated with the protein kinases A, B, and G. This theoretical study is expected to shed some light onto some molecular aspects that could contribute to the knowledge of the molecular mechanics behind interactions of these compounds, with anti-tuberculosis activity...
June 21, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Andrey Turlapov, Maxim Yu Kagan
Physics of many-body systems where particles are restricted to move in two spatial dimensions is challenging and even controversial: On one hand, neither long-range order nor Bose condensation may appear in infinite uniform 2D systems at finite temperature, on the other hand this does not prohibit superfluidity or superconductivity. Moreover, 2D superconductors, such as cuprates, are among the systems with highest critical temperatures. Ultracold atoms are a platform for studying 2D physics. Uniquely to other physical systems, quantum statistics may be completely changed in an ultracold gas: an atomic Fermi gas may be smoothly crossed over into a gas of Bose molecules (or dimers) by tuning interatomic interactions...
June 21, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Shin Nakamura, Takumi Noguchi
Photosynthetic water oxidation is performed at the Mn4CaO5 cluster in photosystem II (PSII). The protonation structures of amino acid residues and water molecules around the Mn4CaO5 cluster are crucial in water oxidation reactions. In this study, we determined the protonation state of a key His residue in water oxidation, D1-H337, which is directly hydrogen bonded with the oxygen atom of the Mn4CaO5 cluster, using polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Flash-induced polarized ATR-FTIR difference spectra upon the S1→S2 transition of oriented PSII membranes showed broad negative and positive features around 2600 and 2900 cm-1, respectively, with large dichroic ratios, accompanied with several minor peaks attributable to the Fermi resonance of a His NH vibration...
June 21, 2017: Journal of the American Chemical Society
Ashim Nandi, Dennis Gerbig, Peter R Schreiner, Weston Thatcher Borden, Sebastian Kozuch
Using the tunneling-controlled reactivity of cyclopropylmethylcar-bene, we demonstrate the viability of isotope-controlled selectivity (ICS), a novel non-classical control element of chemical reactivity where a molecular system with two conceivable products of tunneling exclusively produces one or the other, depending only on isotopic composition. Our multidimensional small-curvature tunneling (SCT) computations indicate that under cryogenic conditions, 1-methoxycyclopropylmethylcarbene shows rapid H-migration to 1-methoxy-1-vinylcyclopropane, whereas deuterium-substituted 1-methoxycyclopropyl-d3-methylcarbene undergoes ring expansion to 1-d3-methylcyclobutene...
June 21, 2017: Journal of the American Chemical Society
Vincent Morris Friebe, Diego Millo, David Swainsbury, Michael R Jones, Raoul N Frese
The high quantum efficiency of photosynthetic reaction centers make them attractive for bioelectronic and biophoto-voltaic applications. However, much of the native reaction center efficiency is lost in communication between surface bound reaction centers and electrode materials. State of the art biophotoelectrodes utilizing cytochrome c (cyt c) as a biological wiring agent have at best approached 32% retained RC quantum efficiency. However, bottlenecks in cyt c -mediated electron transfer have not been fully elucidated...
June 21, 2017: ACS Applied Materials & Interfaces
Hongmei Yang, Yan Zhang, Li Li, Lina Zhang, Feifei Lan, Jinghua Yu
This paper describes the design and construction of sudoku-like lab-on-paper platform, in which dual enhancement of reaction intermediates strategy was incorporated for multiplexed competitive electrochemiluminescence (ECL) cyto-assay. Benefit from the sudoku-like structure, integrated multifunction were obtained on such elaborately devised platform, including specific reagents storage, multiple samples immobilization, residual automatic washing, and signal collection. By utilizing semicarbazide (SE) and silver nanoparticles (AgNPs) as dual enhancers, more ECL intermediates could be obtained in the graphene quantum dots (GQDs) and peroxydisulfate system, resulting in the production of more excited state GQDs to emit light...
June 21, 2017: Analytical Chemistry
Jin Zhang, Junkai Ma, Fangdan Shi, Demei Tian, Haibing Li
How to convert the weak chiral-interaction into the macroscopic properties of materials remains a huge challenge. Here, this study develops highly fluorescent, selectively chiral-responsive liquid quantum dots (liquid QDs) based on the hydrophobic interaction between the chiral chains and the oleic acid-stabilized QDs, which have been designated as (S)-1810-QDs. The fluorescence spectrum and liquidity of thermal control demonstrate the fluorescence properties and the fluidic behavior of (S)-1810-QDs in the solvent-free state...
June 21, 2017: Advanced Materials
K T Law, Patrick A Lee
1T-TaS2 is unique among transition metal dichalcogenides in that it is understood to be a correlation-driven insulator, where the unpaired electron in a 13-site cluster experiences enough correlation to form a Mott insulator. We argue, based on existing data, that this well-known material should be considered as a quantum spin liquid, either a fully gapped [Formula: see text] spin liquid or a Dirac spin liquid. We discuss the exotic states that emerge upon doping and propose further experimental probes.
June 20, 2017: Proceedings of the National Academy of Sciences of the United States of America
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