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Luning Zhao, Eric Neuscamman
We present a modification to variational Monte Carlo's linear method optimization scheme that addresses a critical memory bottleneck while maintaining compatibility with both the traditional ground state variational principle and our recently-introduced variational principle for excited states. For wave function ansatzes with tens of thousands of variables, our modification reduces the required memory per parallel process from tens of gigabytes to hundreds of megabytes, making the methodology a much better fit for modern supercomputer architectures in which data communication and per-process memory consumption are primary concerns...
May 17, 2017: Journal of Chemical Theory and Computation
Bene Bassetti
Second languages (L2s) are often learned through spoken and written input, and L2 orthographic forms (spellings) can lead to non-native-like pronunciation. The present study investigated whether orthography can lead experienced learners of EnglishL2 to make a phonological contrast in their speech production that does not exist in English. Double consonants represent geminate (long) consonants in Italian but not in English. In Experiment 1, native English speakers and EnglishL2 speakers (Italians) were asked to read aloud English words spelled with a single or double target consonant letter, and consonant duration was compared...
May 15, 2017: Journal of Experimental Psychology. Learning, Memory, and Cognition
Karina R Gaisina, Alexander F Khlebnikov, Mikhail S Novikov
The cycloaddition of arenecarbaldehydes and α,α,α-trifluoroacetophenones with gem-difluoro-substituted azomethine ylides, generated from N-benzhydrylideneamines and difluorocarbene, occurs regioselectively to give, after hydrolysis, oxazolidin-4-ones. The primary cycloadducts of trifluoroacetophenones, 4,4-difluoro-5-trifluoromethyloxazolidine derivatives, are sufficiently stable to be isolated in reasonable to excellent yields. The results of correlation analysis and DFT calculations reveal a non-pericyclic step-wise mechanism of the reaction...
May 12, 2017: Organic & Biomolecular Chemistry
Olga Konevtsova, Vladimir Pimonov, Vladimir Lorman, Sergey B Rochal
Like metal alloys and micellar systems in soft matter, the viral capsid structures can be of crystalline and quasicrystalline types. We reveal the local quasicrystalline order of proteins in small spherical viral capsids using their nets of dodecahedral type. We show that the structure of some of the viral shells is well described in terms of a chiral pentagonal tiling, whose nodes coincide with centers of mass of protein molecules. The chiral protein packing found in these capsids originates from the pentagonal Penrose tiling (PPT) due to a specific phason reconstruction needed to fit the protein order at the adjacent dodecahedron faces...
May 10, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Christine E Thacker
BACKGROUND: The Pleistocene closure of Isthmus of Panama, separating the basins of the Eastern Pacific and the Caribbean Sea, created a unique natural experiment that reveals how marine faunas respond to environmental change. To explore how fishes have been affected by this tectonic event, I compare transisthmian patterns in phylogeny and morphology for geminate lineages in two families, Eleotridae (sleepers) and Apogonidae (cardinalfishes). RESULTS: Time-calibrated phylogenies for these families show different diversification patterns...
May 10, 2017: BMC Evolutionary Biology
Marco Eli Reinhard, Gerald Auböck, Nicholas A Besley, Ian P Clark, Gregory M Greetham, Magnus W D Hanson-Heine, Raphael Horvath, Thomas S Murphy, Thomas James Penfold, Michael Towrie, Michael W George, Majed Chergui
Ferrous iron(II) hexacyanide in aqueous solutions is known to undergo photoionization and photoaquation reactions depending on the excitation wavelength. To investigate this wavelength dependence, we implemented ultrafast two-dimensional UV transient absorption spectroscopy, covering a range from 280 to 370 nm in both excitation and probing, along with UV pump/visible probe or time-resolved infrared (TRIR) transient absorption spectroscopy and density functional theory (DFT) calculations. As far as photoaquation is concerned, we find that excitation of the molecule leads to ultrafast intramolecular relaxation to the lowest triplet state of the [Fe(CN)6]4- complex, followed by its dissociation into CN- and [Fe(CN)5]3- fragments and partial geminate recombination, all within <0...
May 9, 2017: Journal of the American Chemical Society
Zilong Zheng, Naga Rajesh Tummala, Yao-Tsung Fu, Veaceslav Coropceanu, Jean-Luc Brédas
We investigate the impact of electronic polarization, charge delocalization, and energetic disorder on the charge-transfer (CT) states formed at a planar C60/pentacene interface. The ability to examine large complexes containing up to seven pentacene molecules and three C60 molecules allows us to take explicitly into account the electronic polarization effects. These complexes are extracted from a bilayer architecture modeled by molecular dynamics simulations and evaluated by means of electronic-structure calculations based on long-range-separated functionals (ωB97XD and BNL) with optimized range-separation parameters...
May 17, 2017: ACS Applied Materials & Interfaces
Daisuke Koyama, Paul M Donaldson, Andrew J Orr-Ewing
The mechanism of the thiol-ene reaction induced by 330 nm ultraviolet excitation of 1,2-di(quinolin-2-yl)disulfide (QSSQ) in the presence of methyl methacrylate (MMA) is investigated by sub-picosecond to microsecond transient absorption spectroscopy. The measurements, spanning more than seven orders of magnitude of time, directly reveal multiple radical reaction steps. The ground state quinoliene-2-thiyl radical (QS) is formed with a time constant of ∼200 fs by photolysis of QSSQ, followed by (64 ± 1)% decay of the initially formed QS radical because of solvent cage induced geminate recombination and QS dimer formation with a rate coefficient of (3...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
Xiao Cai, Amir Keshavarz, Justin D Omaque, Benjamin J Stokes
Using triphenylmethylium tetrakis(pentafluorophenyl)borate as a convenient Brønsted acid precatalyst, β-(α,α-dimethylbenzyl)styrenes are shown to cyclize efficiently to afford a variety of new indanes that possess a benzylic quaternary center. The geminal dimethyl-containing quaternary center is proposed to be necessary to arm the substrate for cyclization through steric biasing.
May 5, 2017: Organic Letters
Yun-Lin Liu, Gerald Kehr, Constantin G Daniliuc, Gerhard Erker
Cyclopropylacetylene reacts with two molar equivalents of Piers' borane [HB(C6F5)2] under mild conditions by an addition/rearrangement sequence with cyclopropyl ring opening to give a mixture of two α-B(C6F5)2 substituted tetrahydroboroles. This compound forms an active frustrated Lewis pair with P (t) Bu3 that heterolytically splits dihydrogen and adds carbon dioxide as a geminal chelate bis-boryl component. The respective reactions of the two-fold HB(C6F5)2 addition to Ph-CH2CH2C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CH were studied as a geminal Lewis acid reference...
February 1, 2017: Chemical Science
Gerhard Erker, Yun-Lin Liu, Gerald Kehr, Constantin G Daniliuc
The geminal chelate bis-borylalkanes 4 and 5 featuring strongly electrophilic B(C6F5)2 and B(C6F5) groups, respectively, serve as efficient catalysts for the borylation of arenes and heteroarenes. The borylation reactions proceed under mild conditions with liberation of dihydrogen.
April 27, 2017: Chemistry: a European Journal
Zhi-Shan Tu, Qi Wang, Dan-Dan Sun, Fang Dai, Bo Zhou
Activation of nuclear factor erythroid-2-related factor 2 (Nrf2) has been proven to be an effective means to prevent the development of cancer, and natural curcumin stands out as a potent Nrf2 activator and cancer chemopreventive agent. In this study, we synthesized a series of curcumin analogs by introducing the geminal dimethyl substituents on the active methylene group to find more potent Nrf2 activators and cytoprotectors against oxidative death. The geminally dimethylated and catechol-type curcumin analog (compound 3) was identified as a promising lead molecule in terms of its increased stability and cytoprotective activity against the tert-butyl hydroperoxide (t-BHP)-induced death of HepG2 cells...
April 5, 2017: European Journal of Medicinal Chemistry
Ulric B le Paige, Bauke Smits, Peter 't Hart, Fons Lefeber, Nathaniel I Martin, Hugo van Ingen
Magnetic inequivalence of nuclear spins is well known to cause additional splittings that complicate spectral analysis. Here, we present an extraordinary case of magnetic inequivalence, manifested in the 13-spin system of a (13)C,(15)N-labeled trimethylated amine. All methyl group protons are chemically equivalent due to the molecular symmetry, but not all are magnetically equivalent as they have different (1)JCH and (3)JCH couplings. In general, spectra of such a large spin system can be expected to be extremely complicated by the presence of hundreds if not thousands of extra lines, caused by the strong coupling between inequivalent nuclei...
May 2017: Journal of Magnetic Resonance
Ye Xu, Kalin Vetsigian
A case can be made for stochastic germination and interactions among germinating spores as beneficial germination strategies in uncertain environments. However, there is little data on how widespread, species-specific or diverse such phenomena are. Focusing on Streptomycetes, a platform was developed for quantification of germination and early growth within communities of spores. We found that the germination process is stochastic at three levels: spores vary in their germination times, mycelium networks grow at different rates, and a fraction of germlings stall their growth shortly after germination...
April 6, 2017: Scientific Reports
Santosh Hunasgi, Anila Koneru, Vardendra Manvikar, M Vanishree, Rudraraju Amrutha
Twinning is referred to the development of two separate teeth that arose from the complete separation of one tooth bud. To the best of our knowledge very few cases of twinning in primary or permanent dentition have been previously reported. Here, we report an additional case of twinning involving primary maxillary left lateral incisor and a literature review of clinical and radiographic findings of previous reported cases of gemination and twinning is also discussed. A six-year-old male patient reported to the dental clinic with the complaint of decay in the left front teeth region of the upper jaw...
February 2017: Journal of Clinical and Diagnostic Research: JCDR
Brett Van Der Goetz, Eric Neuscamman
We demonstrate that four-body real-space Jastrow factors are, with the right type of Jastrow basis function, capable of performing successful wave function stenciling to remove unwanted ionic terms from an overabundant Fermionic reference without unduly modifying the remaining components. In addition to greatly improving size consistency (restoring it exactly in the case of a geminal power), real-space wave function stenciling is, unlike its Hilbert-space predecessors, immediately compatible with diffusion Monte Carlo, allowing it to be used in the pursuit of compact, strongly correlated trial functions with reliable nodal surfaces...
May 9, 2017: Journal of Chemical Theory and Computation
Martin Pieper, Jan-Hendrik Lamm, Beate Neumann, Hans-Georg Stammler, Norbert W Mitzel
New geminally bonded intramolecular donor-acceptor systems, Cp2LnCH2PR2 (Ln = Y, Ho, Er, R = CHMe2, CMe3), were prepared by salt elimination reactions between the dicyclopentadienyl-element chlorides (Cp2LnCl, Ln = Y, Ho, Er) and diorganylphosphinomethanides (R2PCH2Li; R = CHMe2, CMe3). These compounds, 1-6, were characterized by elemental analyses, mass spectrometry and X-ray diffraction experiments and the yttrium species additionally by NMR spectroscopy. In the solid state the molecular structures differ from each other, depending on the steric demand of the phosphorus substituents...
April 19, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Vera P Tuguldurova, Alexander V Fateev, Victor S Malkov, Oleg Kh Poleshchuk, Olga V Vodyankina
The product of acetaldehyde and ammonia reaction, namely, 2,4,6-trimethyl-1,3,5-hexahydrotriazine trihydrate, was synthesized and identified using a combination of experimental (NMR spectroscopy, IR spectroscopy, melting point determination) and DFT-based theoretical approaches. A reaction mechanism was proposed. The reaction was shown to proceed via the formation of aminoalcohol, imine, and geminal diamine intermediates accompanied by cyclization of these species. The calculation results allowed us to build a potential energy surface of the acetaldehyde and ammonia interaction and determine the most energetically favorable pathway to yield acetaldehyde ammonia trimer...
April 13, 2017: Journal of Physical Chemistry. A
Laetitia Dalstein, Elizaveta Potapova, Eric Tyrode
It has been long recognized that the surface chemistry of silica, and in particular the type and relative amount of surface bound silanol groups, plays a critical role in many of the properties associated with the material, where a typical example is the discrepant adsorption behavior observed depending on the pretreatment history of the surface. However, in spite of its importance, the direct probing of specific surface silanol groups under water has been hampered by instrumental limitations. Here we make use of vibrational sum frequency spectroscopy (VSFS) to first, identify under water the OH stretch of isolated surface silanols, and second, explore its acid/base behavior and dependence on the surface pretreatment method...
April 19, 2017: Physical Chemistry Chemical Physics: PCCP
Takayuki Arai, Eri Iwagami, Emi Yanagisawa
This study tests the perception of geminate consonants for native speakers of Japanese using audio and visual information. A previous study showed that formant transitions associated with the closing gesture of articulators at the end of a preceding vowel are crucial for perception of stop geminate consonants in Japanese. In addition, this study further focuses on visual cues, to test if seeing the closing gesture affects perception of geminate consonants. Based on a perceptual experiment, it is observed that visual information can compensate for a deficiency in geminate consonant auditory information, such as formant transitions...
March 2017: Journal of the Acoustical Society of America
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