Search

A general formulation for constructing addressable atomic clusters is introduced, based on one or more reference structures. By modifying the well depths in a given interatomic potential in favour of nearest-neighbour interactions that are defined in the reference(s), the potential energy landscape can be biased to make a particular permutational isomer the global minimum. The magnitude of the bias changes the resulting potential energy landscape systematically, providing a framework to produce clusters that should self-organise efficiently into the target structure. These features are illustrated for small systems, where all the relevant local minima and transition states can be identified, and for the low-energy regions of the landscape for larger clusters. For a 55-particle cluster, it is possible to design a target structure from a transition state of the original potential and to retain this structure in a doubly addressable landscape. Disconnectivity graphs based on local minima that have no direct connections to a lower minimum provide a helpful way to visualise the larger databases. These minima correspond to the termini of monotonic sequences, which always proceed downhill in terms of potential energy, and we identify them as a class of biminimum. Multiple copies of the target cluster are treated by adding a repulsive term between particles with the same address to maintain distinguishable targets upon aggregation. By tuning the magnitude of this term, it is possible to create assemblies of the target cluster corresponding to a variety of structures, including rings and chains. [ABSTRACT FROM AUTHOR]

A full-dimensional, global ab initio potential energy surface (PES) for the Ar-HOCO system is presented. The PES consists of a previous intramolecular ab initio PES for HOCO [J. Li, C. Xie, J. Ma, Y. Wang, R. Dawes, D. Xie, J. M. Bowman, and H. Guo, J. Phys. Chem. A 116, 5057 (2012)], plus a new permutationally invariant interaction potential based on fitting 12 432 UCCSD(T)-F12a/aVDZ counterpoise-corrected energies. The latter has a total rms fitting error of about 25 cm-1 for fitted interaction energies up to roughly 12 000 cm-1. Two additional fits are presented. One is a novel very compact permutational invariant representation, which contains terms only involving the Ar-atom distances. The rms fitting error for this fit is 193 cm-1. The other fit is the widely used pairwise one. The pairwise fit to the entire data set has an rms fitting error of 427 cm-1. All of these potentials are used in preliminary classical trajectory calculations of energy transfer with a focus on comparisons with the results using the benchmark potential. [ABSTRACT FROM AUTHOR]

Fifty indolocarbazole series as cyclin-dependent kinase inhibitors (CDKs) are used to establish a threedimensional quantitative structure-activity relationship (3D QSAR) model based on docking conformations resulting from the Topomer comparative molecular field analysis (Topomer CoMFA). The statistic parameters show that the cross-validation (q2), the multiple correlation coefficient of fitting (r2), and external validation statistic (Qext2) are 0.953, 0.968, and 0.954, respectively. It is demonstrated that this Topomer CoMFA model has good stability and prediction ability. The methodology of the fragment-based drug design (FBDD) was also used to virtually screen new CDKs by the Topomer Search technology. Four similar substitutional groups selected from the ZINC database were added to the basic scaffold. As a result, 18 new CDKs with high activities were obtained. The template molecule and new designed compounds are used to study the binding relationship between the ligands and the receptor protein with Surflex-Dock. The docking results suggest good binding interactions of the designed compounds with protein. There are several hydrogen bondings between CDKs with amino acid residues of LYS33, LYS89, ASP86, LEU83, GLU81. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The transition state geometry for the automerization of cyclobutadiene is an isosceles trapezium. • Enhanced π-π dynamic electron correlation is responsible. • The calculated energy barrier is 9.62 kcal/mol (0.417 eV). Abstract The application of the Restricted Active Space Self Consistent Field (RASSCF) quantum chemical method using an extended active space and including σ-σ, π-σ and π-π dynamical electron correlation shows that the transition state structure for the automerization reaction of cyclobutadiene is an isosceles trapezium. This transition state is obtained without any symmetry constraints. The calculated energy barrier height involving the zero point vibrational energy corrections is 9.62 kcal∙mol−1 (0.417 eV), with the corresponding rate constant being equal to 0.18 × 109 s−1 (or 7.1 × 1010 s−1 in case of using the vibrational energy splitting tunneling method). [ABSTRACT FROM AUTHOR]

Abstract: This article presents a system capable of performing isodynamic I/V and S‐parameter measurements. It is focused on the necessary characterization signals, laboratory equipment, and pulser (power head). Proper biasing waveforms are developed and used to extract accurate nonlinear measurements that take into account the frequency dispersive phenomena, namely, the drain lag and temperature rise observed in GaN HEMTs. The pulser can drive high power devices (120 V and 45 A) for very fast and accurate pulses (widths between 300 and 800 ns). As validation, a commercial 15 W GaN device (CGH27015P) from Wolfspeed was characterized using this setup. The consistency between the obtained pulsed I/V curves and others obtained by the integration of the small signal transcondutance (gm) and output conductance (gds) proves that the presented system is capable of performing isodynamic characterization of power transistors. [ABSTRACT FROM AUTHOR]

Let K be an arbitrary permutation group on a finite set Ω. Let G = H≀K be the corresponding permutational wreath product of a group H by K. It is proved that every Coleman automorphism of G is inner whenever H is either an almost simple group or a p-constrained group with for some prime p. In particular, the normalizer conjecture holds for such groups G. Other positive results regarding the normalizer conjecture are also obtained. Our results extend some known ones. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic ability of H2O and HCOOH to facilitate the tautomerism of KA to KIt isomer has been studied. It is shown that the direct tautomerism (path A) is unlikely because of the high activation free energy, whereas the presence of H2O and HCOOH (paths B and C) significantly contributes to decreasing the activation free energy. Meanwhile, the conventional transition state theory followed by Wigner tunneling correction is applied to estimate the rate constants. The rate constant with Wigner tunneling correction for direct tautomerization is obviously smaller than that of HCOOH‐mediated tautomerization, which is the most plausible mechanism. Finally, another important finding is that the ratio of reaction rates between direct tautomerism reaction and catalyst‐induced tautomerism increases with the increase of the catalyst concentration at a given temperature. The results of the present study demonstrate the feasibility of acid catalysis for DNA bases isomerization reaction that would otherwise be forbidden. [ABSTRACT FROM AUTHOR]

By assuming well defined magnetic surfaces we examine the characteristics of special three dimensional equilibria with incompressible flows such that any two out of the vectors of velocity, vorticity, magnetic field and current density are parallel one another. In the majority of the equilibria considered, it turns out that the only isodynamic equilibrium configuration, defined so that the magnetic field modulus be uniform on magnetic surfaces, is the axisymmetric Palumbo one. Also, except for equilibria with the velocity parallel to the current density in the other five of the above mentioned special axisymmetric (non-isodynamic) equilibria the velocity should be parallel to the magnetic field. In addition, isodynamicity is removed by the non parallel component of the flow associated with the electric field in axisymmetric equilibria with either complex lamellar generalised velocity, ρ V where ρ is the density, or complex lamellar magnetic field. [ABSTRACT FROM AUTHOR]

tBuCH=C(Li)S(O)( NSO2Tol)Ph ⋅L (L=2THF, TMEDA) ( 1⋅L) in THF solution is a monomer with a C−Li bond according to NMR spectroscopy and cryoscopy. It was identified as CIP through the scalar 13C,6Li coupling and 6Li,{1H} NOE experiments. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure. 6Li,1H FUCOUP and 6Li,1H HMQC NMR experiments of 1⋅TMEDA revealed a scalar 6Li,1H coupling across the Li−C=C−H bonds. According to the NMR data the π-bond of 1⋅L is polarized by the negative charge of the anionic C atom. tBuCH=C(Li)S(O)( NMe)Ph ( 2⋅L) is most likely also a monomer with a C−Li bond. According to 6Li,{1H} NOE experiments it has a four-membered C-Li-N-S chelate ring structure. 13C NMR spectroscopy showed the C−Li bonds of 1⋅L and 2⋅L to be fluxional. 1H NMR spectroscopy and 1D TOCSY experiments of Ph2C=C(Li)S(O)( NSO2Tol)Ph revealed topomerization of the phenyl groups, which is attributed to a fast positional exchange of the Li atom and the sulfonimidoyl group. The fluxionality of the C−Li bond and the interchange of the Li atom and the sulfonimidoyl group at the anionic C atom of sulfonimidoyl vinyllithiums, which result in a low configurational stability, most likely involve the formation of O, Li and N, Li CIPs through heterolysis of the C−Li bond. Ab initio calculation of MeCH=C(Li)S(O)( NMe)Ph yielded an energy minimum structure with a C−Li bond, a four-membered C-Li-N-S chelate ring and a strongly expanded C=C−Li bond angle. According to calculation of MeCH=C(Li)S(O)( NMe)Ph, [MeCH=CS(O)( NMe)Ph]− and MeCH=C(H)S(O)( NMe)Ph deprotonation is not accompanied by a shortening of the C−S bond. Ab initio calculation of MeCH=C(Li)S(O)( NSO2Me)Ph gave a structure with a C−Li bond and a six-membered C-Li-O-S-N-S chelate ring. 6Li,1H NOE experiments and cryoscopy of LiCH2S(O)( NSO2Tol)Ph ( 3) revealed a monomeric CIP with a C−Li bond. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure found in polymeric 3 in the crystal. [ABSTRACT FROM AUTHOR]

Transient Receptor Potential Vanilloid, member 1 (TRPV1), is a non-selective cation channel belonging to the transient receptor potential (TRP) family of ion channels. It occurs in the peripheral and central nervous system, activated by a variety of exogenous and endogenous stimuli, thus playing a key role in transmission of pain. This has been a target for chronic pain since more than a decade and a number of antagonists that progressed into clinical trials have failed due to the unexpected side effect of core body temperature rise, thus halting progress in this field. Of late, there has been an upsurge in research on this target, with the rat TRPV1 structure being determined, many new antagonists discovered that are temperature-neutral and many new therapeutic avenues being discovered for TRPV1, including diseases of respiratory and digestive systems, skin and bladder. Towards identifying diverse compounds to decipher the role of this target in various indications, here we report a 3D-QSAR model built using the new topomer-CoMFA methodology on a series of piperazinyl-aryl TRPV1 antagonists and the use of this model, along with a pharmacophore model and the shape of one of the potent compounds of this series, to virtually screen a subset of the ZINC database to find novel and diverse hits. These can serve as starting points to develop modality-selective antagonists for chronic pain and to elucidate the critical role of TRPV1 in the various new therapeutic areas. [ABSTRACT FROM AUTHOR]

In the 1960s, many years prior to the advent of personal computers and mainstream cultural accessibility to them, Emmett Williams devised a method that he felt reflected the expressive potential of algorithmic processes within a printed page's confines. Williams' "IBM" method serves as a "muse's assistant," in which a user-contrived vocabulary is employed to construct poems in which letters of words in one line are used to create subsequent lines. This article introduces the imposed conditions of Williams' invention, comparing and placing them within a range of digital writings that appear during subsequent decades. [ABSTRACT FROM AUTHOR]

Recently Vaughan Jones showed that the R. Thompson group F encodes in a natural way all knots and links in R 3 , and a certain subgroup F → of F encodes all oriented knots and links. We answer several questions of Jones about F → . In particular we prove that the subgroup F → is generated by x 0 x 1 , x 1 x 2 , x 2 x 3 (where x i , i ∈ N are the standard generators of F ) and is isomorphic to F 3 , the analog of F where all slopes are powers of 3 and break points are 3-adic rationals. We also show that F → coincides with its commensurator. Hence the linearization of the permutational representation of F on F / F → is irreducible. We show how to replace 3 in the above results by an arbitrary n , and to construct a series of irreducible representations of F defined in a similar way. Finally we analyze Jones' construction and deduce that the Thompson index of a link is linearly bounded in terms of the number of crossings in a link diagram. [ABSTRACT FROM AUTHOR]

AP205 is a single-stranded RNA bacteriophage that has a coat protein sequence not similar to any other known single-stranded RNA phage. Here, we report an atomic-resolution model of the AP205 virus-like particle based on a crystal structure of an unassembled coat protein dimer and a cryo-electron microscopy reconstruction of the assembled particle, together with secondary structure information from site-specific solid-state NMR data. The AP205 coat protein dimer adopts the conserved Leviviridae coat protein fold except for the N-terminal region, which forms a beta-hairpin in the other known single-stranded RNA phages. AP205 has a similar structure at the same location formed by N- and C-terminal beta-strands, making it a circular permutant compared to the other coat proteins. The permutation moves the coat protein termini to the most surface-exposed part of the assembled particle, which explains its increased tolerance to long N- and C-terminal fusions. [ABSTRACT FROM AUTHOR]

We study sharp permutation groups of type {0,k} and observe that, once the isomorphism type of a point stabilizer is fixed, there are only finitely many possibilities for such a permutation group. We then show that a sharp permutation group of type {0,k} in which a point stabilizer is isomorphic to the alternating group on 5 letters must be a geometric group. There is, up to permutation isomorphism, one such permutation group. [ABSTRACT FROM PUBLISHER]

Several di-substituted diimines ( 3a – 3f ) and heteroatom-substituted unsaturated secondary phosphine oxides (HASPO, 6a – 6f ) were prepared and characterized. Compounds 6a – 6f are regarded as pre-ligands because of their ability of tautomerization to heteroatom-substituted phosphinous acid (HAPA, 7a – 7f ). An unexpected 3e -coordinated palladium dibromide 8e was observed from the reaction of compound 6e with PdBr 2 . Molecular structures of pre-ligands 6a , 6c , and 6e , as well as palladium complexes 8e were determined by single crystal X-ray diffraction methods. When pre-ligand 6a was applied to palladium-catalyzed Suzuki-Miyaura cross-coupling reactions, satisfactory yields were obtained. Density functional theory were employed to examine the electronic properties of HASPO 6a–6f pre-ligands, their corresponding 1,3-di- N -substituted tautomers 7a–7f , and the saturated counterpart 7as of 7a . Compound 7a is the most effective and genuine ligand in Suzuki-Miyaura reaction that is confirmed by its higher-lying lone-pair (LP) molecular orbital (HOMO-1). The LP orbital of 7c – 7f is lower-lying HOMO-5. For each 7c – 7f , two conformational rotamers with minute energy difference were located. Hirshfeld charge and population analysis of 7c – 7f were also calculated in order to comprehend the electronic properties for these two rotamers for each HAPAs. Besides, the steric effect of HAPAs was estimated in terms of the Percent Buried Volume (% V bur ). This model has shown that 7a has similar steric property to that of PCy 3 , which is an effective ligand in Suzuki-coupling reactions. [ABSTRACT FROM AUTHOR]

Cyclobutadiene has a four-membered carbon ring with two double bonds, but this highly strained molecular configuration is almost square and, via a coordinated motion, the nuclei quantum mechanically tunnels through the high-energy square state to a configuration equivalent to the initial configuration under a 90° rotation. This results in a square ground state, comprising a superposition of two molecular configurations, that is driven by quantum tunneling. Using a quantum mechanical model, and an effective nuclear potential from density functional theory, we calculate the vibrational energy spectrum and the accompanying wavefunctions. We use the wavefunctions to identify the motions of the molecule and detail how different motions can enhance or suppress the tunneling rate. This is relevant for kinematics of tunneling-driven reactions, and we discuss these implications. We are also able to provide a qualitative account of how the molecule will respond to an external perturbation and how this may enhance or suppress infra-red-active vibrational transitions. [ABSTRACT FROM AUTHOR]

In this short paper we consider the effect of the presence of conducting sidewalls of finite thickness on the onset of convection in a two-dimensional porous cavity. Two cases are considered where the outer boundaries of the sidewalls are either perfectly insulating or perfectly conducting. A unified theory is presented which combines both these cases, and the stability properties of the overall system is found to undergo a full transition from that of the classical Darcy-Bénard problem to that of the degenerate system studied in detail by Rees and Tyvand (J Eng Math 49:181-193, ). [ABSTRACT FROM AUTHOR]

In this paper, we present several necessary conditions for the reversed Dickson polynomial E n ( 1 , x ) of the second kind to be a permutation of F q . In particular, we give explicit evaluation of the sum ∑ a ∈ F q E n ( 1 , a ) . [ABSTRACT FROM AUTHOR]

The mechanism of the degenerated Z , E -isomerization (topomerization) and the electronic structure of the imines R 2 C NR′ (R = NMe 2 , CF 3 , CO 2 Me, SMe, Me, OMe, F, CN, COMe; R′ = Me, i -Pr, t -Bu) have been investigated with the DFT method (B3LYP/6-31+G(d,p)) in terms of NBO. It has been established that the topomerization of N-alkylimines passes through the inversion mechanism independently of C-substituent type (with the minor contribution of rotational component in individual cases). By means of the correlation analysis it was shown that interactions of the lone pair of the nitrogen atom with orbitals of C-substituents (nN → σ ∗ C R and nN ↔ σ C R ) have the main influence on the value of the inversion barrier (Δ E i ≠ ) in the ground state. The increase of the energies of nN → σ ∗ C R interactions or the difference between energies of nN → σ ∗ C R and nN ↔ σ C R interactions leads to reduction of the Δ E i ≠ value, shortening of the C N bond, and promotes the inversion mechanism of the topomerization. The charge on the nitrogen atom mainly depends on conjugation effect of C-substituents, whereas the charge on the imino-carbon atom depends on their electronegativity (inductive effect). The increase of electronegativity of groups of the 2nd period elements at the imino-carbon atom leads to the raise of the positive charge on the imino-carbon atom whereas the increase of electronegativity of carbon-containing groups leads to the decrease of the positive charge. At the same time, the positive charges on the imino-carbon atoms for the imines with the mentioned C-substituents correlate with the values of χ -, σ i -, σ R -, σ P -constants according to various linear dependences. These dependences differ in the sign and in the value of slope. [ABSTRACT FROM AUTHOR]

Coagulation factor Xa (Factor Xa, FXa) is a particularly promising target for novel anticoagulant therapy. The first oral factor Xa inhibitor has been approved in the EU and Canada in 2008. In this work, 38 [6,6,5] Tricyclic Fused Oxazolidinones were studied using a combination of molecular modeling techniques including three-dimensional quantitative structure–activity relationship (3D-QSAR), molecular docking, molecular dynamics and Topomer CoMFA (comparative molecular field analysis) were used to build 3D-QSAR models. The results show that the best CoMFA model has q 2 = 0.511 and r 2 = 0.984, the best CoMSIA (comparative molecular similarity indices analysis) model has q 2 = 0.700 and r 2 = 0.993 and the Topomer CoMFA analysis has q 2 = 0.377 and r 2 = 0.886. The results indicated the steric, hydrophobic, H-acceptor and electrostatic fields play key roles in models. Molecular docking and molecular dynamics explored the binding relationship of the ligand and the receptor protein. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of a fully discrete T-ψ finite element method based on H-decomposition to solve a nonlinear degenerate transient eddy current problem with ferromagnetic materials. Here, the ferromagnetic properties are linked by a power material law. We first design a nonlinear time-discrete scheme for approximation in suitable function spaces. We show the well-posedness of the semidiscrete problem and prove the convergence of the nonlinear scheme by the Minty-Browder technique. Finally, we suggest a fully discrete scheme, derive its error estimate and give some numerical experiments to validate the theoretical result. [ABSTRACT FROM AUTHOR]

In this paper, we study the spreading frontiers in the partially degenerate reaction–diffusion systems with a mobile and a stationary component, which are described by a class free boundary condition. The center of our investigation is to understand the effect of the dispersal rate D of the mobile component, the expansion capacity μ (the ratio of the expansion speed of the free boundary and the gradient of the mobile component at the spreading frontiers) and the initial numbers u 0 and v 0 on the long-run dynamics of the spreading frontiers. It is shown that a spreading–vanishing dichotomy holds, and the sharp criteria for the spreading and vanishing by choosing D , μ , u 0 and v 0 as variable factors are also obtained. In particular, our results still reveal that slow dispersal rate unconditionally favors the frontiers to spread, but the fast one, however, leads to a conditional vanishing of the frontiers. Moreover, as applications, we consider a man–environment–man epidemic model in physiology and a reaction–diffusion model with a quiescent stage in population dynamics. [ABSTRACT FROM AUTHOR]

Endophytic mycobiota on leaves, twigs and cupules of Fagus crenata were investigated using a culture-dependent method over a growing season to test the hypothesis that endophytic fungi of cupule (a woody phyllome) share some components of the endophytic fungal assemblages with both leaves and twigs. A total of 14 fungal taxa were isolated, and the most frequent taxon was Phomopsis sp., followed by Xylaria sp., Ascochyta fagi and Geniculosporium sp. The compositions of fungal assemblages of leaf laminae and petioles were generally relatively dissimilar to those of current and first-year twigs when compared for each sampling month, and those of cupules and cupule stalks were intermediate between those of leaves and twigs. Permutational multivariate analysis of variance confirmed that month and organ were significant factors of the variation of the composition of endophytic fungal assemblages. Phomopsis sp., a common twig endophyte, and A. fagi , a common leaf endophyte, were common in cupules and cupule stalks. These results suggested that the endophytic fungal assemblages of cupules shared component taxa with those of both leaves and twigs. [ABSTRACT FROM AUTHOR]

Multi-particle-plus-triaxial-rotor (MPR) model calculations were performed for chiral partner bands associated with strongly asymmetric manyparticle nucleon configuration in the 190 mass region. Multiple chiral systems were found, but they may not necessarily form well defined pairs of near-degenerate bands. [ABSTRACT FROM AUTHOR]

Rates and energy barriers of degenerate halide substitution on tetracoordinate halophosphonium cations have been measured by NMR techniques (VT and EXSY) using a novel experimental design whereby a chiral substituent (sBu) lifts the degeneracy of the resultant salts. Concomitantly, a viable computational approach to the system was developed to gain mechanistic insights into the structure and relative stabilities of the species involved. Both approaches strongly suggest a two-step mechanism of formation of a pentacoordinate dihalophosphorane via backside attack followed by dissociation, resulting in inversion of configuration at phosphorus. The experimentally determined barriers range from <9 kcal mol-1 to nearly 20 kcal mol-1, ruling out a mechansm via Berry pseudorotation involving equatorial halides. In all cases studied, epimerization of chlorophosphonium chlorides has a lower energy barrier (by 2 kcal mol-1) than the analogous bromo salts. Calculations determined that this was due to the easier accessibility in solution of pentacoordinate dichlorophosphoranes when compared to analogous dibromophosphoranes. In line with the proposed associative mechanism, bulky substituents slow the reaction in the order Me < Et < iPr < 'Bu. Bulky substituents affect the shape of the reaction energy profile so that the pentacoordinate intermediate is destabilized eventually becoming a transition state. The magnitude of the steric effects is comparable to that of the same substituents on substitution at primary alkyl halides, which can be rationalized by the relatively longer P-C bonds. The reaction displays first-order kinetics due to the prevalence of tight- or solvent-separated ion pairs in solution. Three-dimensional reaction potential energy profiles (More O'Ferrall--Jencks plots) indicated a relatively shallow potential well corresponding to the trigonal bipyramid intermediate flanked by two transition states [ABSTRACT FROM AUTHOR]

In this paper, a specific design strategy targeting c-met kinase was reported based on docking modeling and topomer comparative molecular field analysis (Topomer CoMFA). A novel U-shape conformation which is distinct from the literature was demonstrated by molecular docking among 68 U-shape c-met inhibitors. According to the docking results, two Topomer CoMFA models with high predictive ability were established based on the two fragment rule. The results from both docking and topomer CoMFA showed that the π-π stacking interaction with Tyr1230 and the hydrogen bond with hinge region play an important role in inhibitory activity. Furthermore, the flexible linker and the adjacent solvent group would be favorable to stabilize the conformation and to enhance the two interactions mentioned above. Based on our patent, 14 new compounds were designed by our design strategy. The binding mode exhibited as expected and their activities were predicted by topomer CoMFA model. The preliminary biological tests showed most of them have potent activity to c-met kinase. Our study would provide guidelines to design some new U-shaped c-met inhibitors with new scaffolds and optimize the current molecules. [ABSTRACT FROM AUTHOR]

Spin-projected spin polarized Møller-Plesset and spin polarized coupled clusters calculations have been made to estimate the cyclobutadiene automerization, the ethylene torsion barriers in their ground state, and the gap between the singlet and triplet states of ethylene. The results have been obtained optimizing the geometries at MP4 and/or CCSD levels, by an extensive Gaussian basis set. A comparative analysis with more complex calculations, up to MP5 and CCSDTQP, together with others from the literature, have also been made, showing the efficacy of using spin-polarized wave functions as a reference wave function for Møller-Plesset and coupled clusters calculations, in such problems. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The quantum yield for the release of leaving groups from o-nitrobenzyl 'caged' compounds varies greatly with the nature of these leaving groups, for reasons that have never been well understood. We found that the barriers for the primary hydrogen-atom transfer step and the efficient nonradiative processes on the excited singlet and triplet surfaces determine the quantum yields. The excited-state barriers decrease when the exothermicity of the photoreaction increases, in accord with Bell-Evans-Polanyi principle, a tool that has never been applied to a nonadiabatic photoreaction. We further introduce a simple ground-state predictor, the radical-stabilization energy, which correlates with the computed excited-state barriers and reaction energies, and that might be used to design new and more efficient photochemical processes. [ABSTRACT FROM AUTHOR]

For a series of [2] rotaxane molecular shuttles possessing linear rigid rod-like axles of varying lengths between degenerate recognition sites, the activation barrier for shuttling motion was clearly shown to be constant. Moreover, dynamic NMR studies have revealed that both the entropie and enthalpic contributions to the shuttling motion remain constant regardless of the actual length of the rigid rod-like axles employed herein. [ABSTRACT FROM AUTHOR]

In the present work we report the spectral and photophysical properties of 3-hydroxyisoquinoline in various protic/aprotic solvents. Our steady state and time resolved fluorescence data indicates that in the monomer form of 3HIQ phototautomerization can take place in the excited state through excited state intramolecular proton, while as per earlier suggestions phototautomerization in 3HIQ occurs in dimer or complex (in the presence of acetic acid) form. Moreover, we find rather slow tautomerization (occurring on the nanosecond scale). It is found that proton transfer occurs both in the ground as well as excited states and is controlled by the polarity of the solvent. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence steady-state and decay measurements of the azaaromatic derivative norharmane were obtained in solvents with different polarities: dichloromethane (DCM) and acetonitrile (ACN), at different temperatures, in the absence and the presence of a donor/acceptor hydrogen bond such as acetic acid. 2D NOESY experiments confirmed that this compound forms a hydrogen-bonding cyclic complex with acetic acid in the ground state. This complex induced a phototautomeric equilibrium, which produced new emission bands at 400 and 500nm. This tautomeric process was established only in the first excited state via a concerted proton–electron transfer. Indeed, the cyclic complex formed in the ground state evolved to a like-cation upon cooling from room temperature to 225K, and a new emission band at 450nm is observed. The fluorescence decay times confirmed these results. [Copyright &y& Elsevier]

Whereas standard strong bases (n-BuLi, s-BuLi/TMEDA, n-BuLi/t-BuOK, TMPMgCl·LiCl, and LDA) reduce the N=N bond of the parent azobenzene (Y = H), aromatic H→Li permutation occurs with LTMP when a suitable director of lithiation (Y = OMe, CONEt2, F) is present in the benzene residue of the azo compound. The method allows direct access to new substituted azobenzenes. [ABSTRACT FROM AUTHOR]

It is shown that the condition of stationary second adiabatic invariant at the magnetic axis of a stellarator configuration can be satisfied to good accuracy for all reflected particles. [ABSTRACT FROM AUTHOR]

This paper reports incorporation of the perturbative triples correction within the explicitly correlated Mukherjee’s multireference coupled cluster method using the SP ansatz. In accord with the standard approximation, these corrections are not directly entered by the correlation factor amplitudes, but the explicitly correlated part of the effective Hamiltonian is included in full. The performance of the new method is tested on singlet methylene, potential curve of fluorine molecule and automerisation barrier of cyclobutadiene. It has been found that the convergence pattern of the MkCCSD(T)-F12 results with increasing basis set is improved by approximately one cardinal number, as compared to conventional MkCCSD(T). This improvement appears at the level of single and double excitations, whereas no significant impact of the explicit treatment of the electron correlation on the (T) correction has been observed, in analogy to a single-reference approach. [ABSTRACT FROM PUBLISHER]

Abstract: By analogy with the Stone–Wales rearrangement in sp2-hybridized carbon allotropes that involves turning one CC bond by 90° in a graphene sheet and reconnecting it cross-wise with two carbon atoms, the similar rearrangement for the diamond lattice was called connected exchange. In this case one C–C bond in the diamond lattice involving sp3-hybridized atoms is switched such that two anti bonds exchange one of their endpoints. As a result of this connected exchhange one obtains a defect in the diamond lattice with four 5-membered and four 7-membered rings. For the hydrocarbon pyracyclene with sp2-hybridized atoms, the Stone–Wales rearrangement is degenerate (automerization). By analogy, one can imagine a hydrocarbon having sp3-hybridized atoms that could undergo a degenerate connected exchange. [Copyright &y& Elsevier]

A stellarator vacuum field is found in which, at a finite aspect ratio (A ≈ 40), the contours of the second adiabatic invariant of nearly all particles reflected inside that surface are poloidally closed. [ABSTRACT FROM AUTHOR]

Summary: The codon-equivalent multiple alignment suite begins conservational analysis for polymerase chain reaction primer design at the protein level, allowing the user to design consensus primers capable of detecting homologous coding sequences even when low-to-moderate sequence information is available. This package also condenses the wealth of information associated with multiple sequence alignments and presents them in an intuitive manner, allowing the user to quickly and effectively address degenerate primer design considerations. Availability and implementation: https://sourceforge.net/projects/cemasuite/. [ABSTRACT FROM AUTHOR]

Dynamic molecular motions resulting from the folding of a flexible macrocyclic component in a Cu(i)-complexed pseudorotaxane have been evidenced by variable temperature NMR experiments. The proposed conformational changes are also supported by the X-ray crystal structures of the compounds and computational studies. [ABSTRACT FROM AUTHOR]

The author discusses aspects of the article by biostatistician Nathan Mantel regarding the methodologic breakthrough in evaluating whether the occurrences of diseases are related to exposures by their spatiotemporal pattern of clusters. Topics include the aspects of the permutational approach to evaluate spatial and temporal clusters, the several scientific disciplines involve in Mantel's method, and the model in studying the influence of gene flow and distribution of genetic variability.

In this article, we compare optical light curves of two SN2002es-like Type Ia supernovae (SNe), iPTF14atg and iPTF14dpk, from the intermediate Palomar Transient Factory. Although the two light curves resemble each other around and after maximum, they show distinct early-phase rise behavior in the r-band. On the one hand, iPTF14atg revealed a slow and steady rise that lasted for 22 days with a mean rise rate of 0.2–0.3 mag day–1, before it reached the R-band peak (−18.05 mag). On the other hand, iPTF14dpk rose rapidly to −17 mag within a day of discovery with a rise rate , and then rose slowly to its peak (−18.19 mag) with a rise rate similar to iPTF14atg. The apparent total rise time of iPTF14dpk is therefore only 16 days. We show that emission from iPTF14atg before −17 days with respect to its maximum can be entirely attributed to radiation produced by collision between the SN and its companion star. Such emission is absent from iPTF14dpk probably because of an unfavored viewing angle, provided that SN2002es-like events arise from the same progenitor channel. We further show that an SN2002es-like SN may experience a dark phase after the explosion but before its radioactively powered light curve becomes visible. This dark phase may be lit by radiation from supernova–companion interaction. [ABSTRACT FROM AUTHOR]

The reaction of 2-methylpyridines (I) with B(C6F5)3 leads to borylated pyridinium derivatives (III), which are used for the Suzuki-Miyaura coupling to afford 2-benzylpyridines (V). [ABSTRACT FROM AUTHOR]

A new pseudo domino sequence allows the synthesis of the title compounds. [ABSTRACT FROM AUTHOR]