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D Baran, T Kirchartz, S Wheeler, S Dimitrov, M Abdelsamie, J Gorman, R S Ashraf, S Holliday, A Wadsworth, N Gasparini, P Kaienburg, H Yan, A Amassian, C J Brabec, J R Durrant, I McCulloch
Optimization of the energy levels at the donor-acceptor interface of organic solar cells has driven their efficiencies to above 10%. However, further improvements towards efficiencies comparable with inorganic solar cells remain challenging because of high recombination losses, which empirically limit the open-circuit voltage (Voc) to typically less than 1 V. Here we show that this empirical limit can be overcome using non-fullerene acceptors blended with the low band gap polymer PffBT4T-2DT leading to efficiencies approaching 10% (9...
December 1, 2016: Energy & Environmental Science
Airi Kawasaki, Osamu Sugino
We extend the Coleman's antisymmetrized geminal power (AGP) to develop a wave function theory that can incorporate up to four-body correlation in a region of strong correlation. To facilitate the variational determination of the wave function, the total energy is rewritten in terms of the traces of geminals. This novel trace formula is applied to a simple model system consisting of one dimensional Hubbard ring with a site of strong correlation. Our scheme significantly improves the result obtained by the AGP-configuration interaction scheme of Uemura et al...
December 28, 2016: Journal of Chemical Physics
Qiongnan Gu, Meijuan Chen, Junbin Huang, Y D Wei, Tom Hsiang, Lu Zheng
The infection process of Colletotrichum higginsianum, which causes a disease of crucifers, involves several key steps: conidial germination, appressorial formation, appressorial penetration, and invasive growth in host tissues. In this study, the ChRgf gene encoding a Ras guanine-nucleotide exchange factor protein was identified by screening T-DNA insertion mutants generated from Agrobacterium tumefaciens-mediated transformation (AtMT) that were unable to cause disease on the host Arabidopsis thaliana. Targeted gene deletion of ChRgf resulted in a null mutant (ΔChrgf-42) with defects in vegetative growth, hyphal morphology and conidiation, and poor surface attachment and low germination on hydrophobic surfaces, but there were no apparent differences in appressorial turgor pressure between the wild-type and the mutant...
December 27, 2016: Phytopathology
Mary Mensah, Evans Elikem Amepetey, Richard Tia, Evans Adei
BACKGROUND: 1,3-Dipolar [3 + 2]-cycloaddition of nitrones to the carbon-carbon double bonds of methylenecyclopropanes yields a mixture of regioisomeric 4- and 5-isoxazolidines. The mechanisms of the reactions of N,C,C-trisubstituted nitrones with ring acceptor substituted dimethyl methylenecyclopropanes-1,2-dicarboxylate and aryl methylidene cyclopropanes-1,1-dicarboxylate have been investigated with the Becke 3-Parameter Lee-Yang-Par exchange-correlation functional, a Hartree-Fock DFT hybrid functional, to delineate the factors responsible for the regioselectivity of these class of reactions...
2016: SpringerPlus
Jakub P Piwowarski, Sebastian Granica, Joanna Stefańska, Anna K Kiss
Ellagitannin-rich plant materials are used as popular remedies in the treatment of various inflammatory diseases. Urolithins are gut microbiota metabolites of ellagitannins and are considered responsible for in vivo health effects. Various natural products have been studied that are known sources of urolithins. However, few studies have focused on the metabolism of ellagitannin molecules. The aim of the study was to examine the metabolic fate of select ellagitannins using ex vivo cultures of human gut microbiota...
December 23, 2016: Journal of Natural Products
Jennifer L Thweatt, Bryan H Ferlez, John H Golbeck, Donald A Bryant
Green bacteria are chlorophotorophs that synthesize bacteriochlorophyll (BChl) c, d, or e, which assemble into supramolecular, nanotubular structures in large light-harvesting structures called chlorosomes. The biosynthetic pathways of these chlorophylls are known except for one reaction. Null mutants of bciD, which encodes a putative radical-SAM protein, are unable to synthesize BChl e but accumulate BChl c; however, it is unknown whether BciD is sufficient to convert BChl c (or its precursor, bacteriochlorophyllide (BChlide) c into BChl e (or BChlide e)...
December 19, 2016: Journal of Biological Chemistry
Russell J Perkins, Richard K Shoemaker, Barry K Carpenter, Veronica Vaida
The chemistry of pyruvic acid is of great interest due to its essential role in metabolism for all life and its role in atmospheric chemistry. Pyruvic acid under a wide range of conditions, including normal storage conditions, will spontaneously dimerize to form zymonic acid. We isolated zymonic acid and, using a variety of 1D and 2D NMR techniques, identified it as a single structure as a solid or dissolved in DMSO. When in aqueous solution, however, we identified a mixture of five different tautomers and hydrates in equilibrium with each other with no single dominant form...
December 29, 2016: Journal of Physical Chemistry. A
Hellmuth Erhardt, Kevin A Kunz, Stefan F Kirsch
An operationally simple protocol for the rapid and efficient construction of highly substituted 3-hydroxypyridines is presented. The thermally induced cyclization of easily constructed geminal diazides derived from β-ketoesters having an additional olefin moiety affords the title compounds in yields up to 97% under reagent-free conditions. The new method allows for the synthesis of preparative quantities of material. Additionally, the synthetic utility of the pyridine products for the synthesis of valuable heterocycles is described...
December 16, 2016: Organic Letters
Ron Simkovitch, Dina Pines, Noam Agmon, Ehud Pines, Dan Huppert
About three decades ago, Pines and Huppert found that the excited-state proton transfer to water from a photoacid (8-hydroxy-1,3,6-pyrene trisulfonate (HPTS)) is followed by an efficient diffusion-assisted reversible geminate-recombination of the proton. To model the reaction, Pines, Huppert, and Agmon used the Debye-Smoluchowski equation with boundary conditions appropriate for reversible contact reaction kinetics. This reaction model has been used successfully to quantitatively fit the experimental data of the time-resolved fluorescence of HPTS and several commonly used photoacids...
December 15, 2016: Journal of Physical Chemistry. B
Jan Wallbaum, Lennart K B Garve, Peter G Jones, Daniel B Werz
Donor-acceptor cyclopropanes with two geminal carboxylic esters are reacted with chalcogenyl chlorides and bromides to afford ring-opened products bearing the halogen atoms in the 1-position, adjacent to the donor, and the chalcogenyl residue in the 3-position next to the two acceptor groups. A variety of different donors (e.g., aryl, N, and O) are used. The stereospecificity of the reaction is demonstrated by using a chiral starting material.
December 14, 2016: Organic Letters
Mei Qu, Shuai Chen, Wenbao Ma, Jiangang Chen, Kang Kong, Fengwei Zhang, Huan Li, Zhenshan Hou, Xian-Ming Zhang
The phase transfer of nanoparticles (NPs) from water to organic solvents by an amphiphilic room-temperature ionic liquid (IL) was reported. The geminal IL modified with Pluronic P123 stabilizes a variety of NPs of different size and nature, such as Pd, Au, Ag, and SiO2 NPs. Their phase transfer into a hydrophobic environment was realized by raising the temperature and adding salts (such as NaCl and KBr), both of which have a common effect of breaking the hydrogen bonds of the IL with H2O. A more straightforward method of using an organic solvent working as a hydrogen bond donor (such as butyl alcohol) was then proposed...
December 27, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Horabail S Venkatagiri, Nuggehalli P Nataraja, M Deepthi
The present study investigated the effect of certain unique morphophonemic features of Kannada words on the rate of stutters in a group of 22 adolescent and adult persons who stuttered in an oral reading task. A linear regression analysis showed that word length ranging from 1 to 8 syllables was a potent variable in the occurrence of stutters accounting for 25.3% of stutters. A composite index of morphophonemic complexity with points assigned for sandhi, geminates, consonant clusters, and number of morphemes accounted for a small 7...
December 12, 2016: Clinical Linguistics & Phonetics
Biying Zhou, Taishan Yan, Xiao-Song Xue, Jin-Pei Cheng
Fluorination mediated by the cyclic hypervalent fluoroiodane reagent (1) often requires an exogenous Lewis acid. The widely accepted Lewis-acid-activation model is that a given Lewis acid binds to the oxygen atom of 1 (O-coordination) to polarize the I-O bond. Computational studies of silver-mediated geminal difluorination of styrenes with 1 reveal a new "F-coordination" model that is energetically much preferred over the commonly accepted "O-coordination" model. The calculations rationalize the regioselective formation of the geminal difluorination product...
December 2, 2016: Organic Letters
Ashraf Alkhairy, Afshan Jafri
Heterophones pose challenges during training of automatic speech recognition (ASR) systems because they involve ambiguity in the pronunciation of an orthographic representation of a word. Heterophones are words that have the same spelling but different pronunciations. This paper addresses the problem of heterophonic languages by developing the concept of a Composite Phoneme (CP) as a basic pronunciation unit for speech recognition. A CP is a set of alternative sequences of phonemes. CP's are developed specifically in the context of Arabic by defining phonetic units that are consonant centric and absorb phonemically contrastive short vowels and gemination, not represented in the Arabic Modern Orthography (MO)...
2016: SpringerPlus
Silvia Primativo, Keir X X Yong, Timothy J Shakespeare, Sebastian J Crutch
Spelling is a complex cognitive task where central and peripheral components are involved in engaging resources from many different cognitive processes. The present paper aims to both characterize the oral spelling deficit in a population of patients affected by a neurodegenerative condition and to clarify the nature of the graphemic representation within the currently available spelling models. Indeed, the nature of graphemic representation as a linear or multi-componential structure is still debated. Different hypotheses have been raised about its nature in the orthographic lexicon, with one positing that graphemes are complex objects whereby quantity and identity are separately represented in orthographic representations and can thus be selectively impaired...
January 8, 2017: Neuropsychologia
Ge-Min Fang, Oliver Seitz
Fluorogenic probes that signal the presence of specific DNA or RNA sequences are key enabling tools for molecular disease diagnosis and imaging studies. Usually, at least one fluorophore is attached through covalent bonding to an oligonucleotide probe. However, the additional conjugation step increases costs. Here we introduce a method that avoids the requirement for the preparation of fluorescence-labelled oligonucleotides and provides the opportunity to alter the fluorogenic reporter dye without resynthesis...
November 24, 2016: Chembiochem: a European Journal of Chemical Biology
Wenxing Jin, Yi Wang, Chao-Pei Liu, Na Yang, Mingliang Jin, Yao Cong, Mingzhu Wang, Rui-Ming Xu
Assembly of the spliceosomal small nuclear ribonucleoparticle (snRNP) core requires the participation of the multisubunit SMN (survival of motor neuron) complex, which contains SMN and several Gemin proteins. The SMN and Gemin2 subunits directly bind Sm proteins, and Gemin5 is required for snRNP biogenesis and has been implicated in snRNA recognition. The RNA sequence required for snRNP assembly includes the Sm site and an adjacent 3' stem-loop, but a precise understanding of Gemin5's RNA-binding specificity is lacking...
November 1, 2016: Genes & Development
Peter A Limacher
A new truncation scheme for non-orthogonal antisymmetrized products of interacting geminals (APIG) is introduced based on antisymmetrized products of strongly orthogonal geminals (APSG). This wavefunction hierarchy of interacting geminals (IG) allows us to gradually increase the accuracy at which the ground state of a seniority-zero Hamiltonian can be estimated, ranging from APSG up to approximation-free APIG. Mathematical expressions for the lowest four orders (IG0, IG1, IG2, and IG3) are given explicitly and the computational cost to evaluate their transition density matrix is verified to scale only cubically with system size...
November 21, 2016: Journal of Chemical Physics
Diana Yepes, Pablo Jaque, Israel Fernández
H2 activation mediated by geminal aminoborane-based frustrated Lewis pairs (FLPs; R2 N-CH2 -BR'2 ) has been computationally explored within the density functional theory framework. It is found that the activation barrier of this process as well as the geometry of the corresponding transition states strongly depend on the nature of the substituents directly attached either to the acidic or the basic centers of the FLPs. The physical factors controlling the whole activation path are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method...
December 23, 2016: Chemistry: a European Journal
Giuseppina Turco, Bettina Braun
The present study investigates non-local temporal adjustments before an upcoming length contrast in Italian minimal pairs that differ only in the length of the medial consonant (e.g., geminate word palla "ball" vs singleton word pala "shovel"). This contrast is reportedly signaled by the duration of the singleton/geminate consonant and of the preceding vowel. Here, it is shown that the duration adjustment extends further to the word-initial consonant, e.g., the [p] in palla is significantly longer than that in pala (experiment 1)...
October 2016: Journal of the Acoustical Society of America
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