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We report counter‐intuitive axial preferences in non‐stereochemically biased, selectively fluorinated methoxycyclohexanes. These pseudo‐anomeric effects are apparent when electronegative CF2 groups are placed at the C‐2, C‐4 and C‐6 positions of the cyclohexane ring to render the C‐3/5 axial hydrogen atoms electropositive. The electrostatic interaction between these axial hydrogen atoms and the ‐OMe oxygen is stabilising. The effect is explored using high‐level ab initio and DFT calculations in the framework of NBO, QTAIM and NCI analysis across a range of derivatives, and experimentally (19F{1H}‐NMR at −80 °C) for some illustrative examples. The effect is significant in energy terms for a weak interaction, and illustrates a new stereoelectronic aspect attributed to selective fluorine substitution in organic chemistry., Fluorine chemistry: Selective fluorination in methoxycyclohexanes induces an electrostatic 1,3‐diaxial interaction favouring a counter‐intuitive axial preference.

In this minireview, weak interactions that occur in supramolecular polymers are discussed. Combination of weak and strong interactions plays an important role in the construction of supramolecular polymers. It is beneficial to separate the contributions of the weak interactions, as well as each solvent effect on the weak interactions. However, it is generally difficult to observe each solvent effect separately at work in each interaction. Small molecular probes are useful to estimate the contributions of the weak interaction. But, the results should be treated with caution when applied to supramolecular polymer systems. To overcome the problems, a new solvent parameter, solvation ability (SA), is introduced, which was determined on the balance point of extended and stacked forms of porphyrin-based interconvertible supramolecular polymers.

Food web theory suggests that the placement of a weak interaction is critical such that under some conditions even one well-placed weak interaction can stabilise multiple strong interactions. This theory suggests that complex stable webs may be built from pivotal weak interactions such that the removal of even one to a few keystone interactions can have significant cascading impacts on whole system diversity and structure. However, the connection between weak interactions, derived from the theory of modular food web components, and keystone species, derived from empirical results, is not yet well understood. Here, we develop numerical techniques to detect potential oscillators hidden in complex food webs, and show that, both in random and real food webs, keystone consumer-resource interactions often operate to stabilise them. Alarmingly, this result suggests that nature frequently may be dangerously close to precipitous change with even the loss of one or a few weakly interacting species.

Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO8 Pd12 (SeO3 )8 ]6- (M=Zn2+ or Ni2+ ) and monovalent cations (Na+ , K+ , Rb+ , Cs+ ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr2+ , Ba2+ ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y3+ ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

The first quantum-mechanical calculations of all relevant potential constants in both the iron-molybdenum cofactor and the iron-vanadium cofactor of nitrogenase suggest that the carbide is bound to the center of the enzyme much more strongly than hitherto assumed. Previous studies seemed to indicate a dummy function of the interstitial carbon, with a weak force constant (ca. 0.32 N cm−1). Our new investigations confirm a different picture: the central carbon atom binds the iron-sulfur cluster through six covalent C−Fe bonds. With a potential constant of more than 1.3 N cm−1, the interstitial carbon also appears to be dynamically persistent. According to our investigations, the values for the elasticity within the iron-sulfur cluster have to be corrected too. These new details on the mechano-chemical properties of the FeMo cofactor will be important for elucidating the catalytic cycle of nitrogen fixation. By implementing our new algorithm in the freely available COMPLIANCE program, the dependence on the coordinates during the calculation of Hesse matrices is eliminated completely.

Theoretical treatments of electrochemical reactions at semiconductors are usually based on theories that presume a weak interaction between the reactant and the electrode. Herein a theory is developed that is valid for arbitrary interaction strengths, and its consequences are explored within a simple coupling scheme. This model can be used as a framework for the investigation of specific catalytic reactions including photoelectrocatalysis.

Overlapping peaks interfere in ion mobility spectrometry (IMS), but they are separated introducing mobility shift reagents (SR) in the buffer gas forming adducts with different collision cross-sections (size). IMS separations using SR depend on the ion mobility shifts which are governed by adduct's size and interaction energies (stabilities). Mobility shifts of valinol and ethanolamine ions were measured by electrospray-ionization ion mobility-mass spectrometry (MS). Methyl-chloro propionate (M) was used as SR; 2-butanol (B) and nitrobenzene (N) were used for comparison. Density functional theory was used for calculations. B produced the smallest mobility shifts because of its small size. M and N have two strong interaction sites (oxygen atoms) and similar molecular mass, and they should produce similar shifts. For both ethanolamine and valinol ions, stabilities were larger for N adducts than those of M. With ethanolamine, M produced a 68% shift, large compared to that using N, 61%, because M has a third weak interaction site on the chlorine atom and, therefore, M has more interaction possibilities than N. This third site overrode the oxygen atoms' interaction energy that favored the adduction of ethanolamine with N over that with M. On the contrary, with valinol mobility shifts were larger with N than with M (21 vs 18%) because interaction energy favored even more adduction of valinol with N than with M; that is, the interaction energy difference between adducts of valinol with M and N was larger than that between those adducts with ethanolamine, and the third M interaction could not override this larger difference. Mobility shifts were explained based on the number of SR's interaction sites, size of ions and SR, and SR-ion interaction energies. This is the first time that the number of interaction sites is used to explain mobility shifts in SR-assisted IMS. Copyright © 2016 John Wiley & Sons, Ltd.

This brief review describes a class of uniquely crafted particle physics experiments that typically each tackle just one investigation—and they do that very well. The aim of these experiments is to both establish Standard Model parameters and also to provide unique tests in search of new physics. I provide a brief snapshot of many of the current activities, selected with a bias toward low-energy and high precision. These include searches for permanent electric dipole moments, charged lepton flavor violation, tests of the weak interaction, and other broad searches for deviations from very precise Standard Model predictions, such as the muon’s anomalous magnetic moment. I highlight what drives these efforts and how they might impact a new Standard Model.

The electronic structure of Ta4Pd3Te16 was analyzed by tight-binding band calculations based on the given structure. The compound electronically showed quasi-one-dimensional behavior even though it comprised a two-dimensional layered structure. A strong orbital interaction was found only along the crystallographic b-direction of the compound. Fermi surface nesting disappeared in Ta4Pd3Te16 because of the weak interaction between Ta–Te and Pd–Te polyhedra. It was found, therefore, that this compound could be a superconductor through suppression of the charge-density wave state via disappearance of Fermi surface nesting.

Ionic liquids (ILs), vary strongly in their interaction with CO2. We suggest simple theoretical approach to predict the CO2 absorption behavior of ILs. Strong interaction of the CO2 with the IL anions corresponds to chemical absorption whereas weak interaction indicates physical absorption. A predictive estimate with a clear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of a solvation model instead of optimizing it only in gas phase as has been done to date. The resulting Gibbs free energies compare very well with experimental values and the energies were correlated with experimental capacities. Promising anions, for ionic liquids with reversible CO2 absorption properties can be defined by a reaction Gibbs free energy of absorption in the range of -30 to 16 kJ mol(-1).

Attachment of Li(+) ion on graphene surface to realize Li(+)-ion conductor is a real challenge because of the weak interaction between the ions and the functional groups of graphene oxide; although, a large number of theoretical results are already available in the literature. To overcome this problem, graphene oxide is functionalized by 1-aza-15-crown-5, the cage-like structure containing four oxygens that can bind Li(+) ion through electrostatic interaction. Li(+) migration on graphene surface has been investigated using ac relaxation mechanism. Perfect Debye-type relaxation behavior with β (relaxation exponent) value ≈1 resulting from single ion is observed. The activation energy of Li(+) migration arising due to cation-π interaction is found to be 0.37 eV, which agrees well with recently reported theoretical value. It is believed that this study will help to design isolated ion conductors for Li(+)-ion battery.

In this paper, a surface enhanced Raman spectra (SERS) detection platform for the widely used pesticide of triadimefon (TDF) is described. TDF is difficult to connect to the gold/silver SERS substrate, but the optical properties of the probe molecule 4-mercaptobenzoic acid (4-MBA), including the peak intensity and the peak position, are easily altered by the multiple weak interaction-assisted SERS detection platform. The limit of detection (LOD) of this method is 1.0 × 10-9 M, and the linear range is from 1.0 × 10-6 M to 1.0 × 10-9 M. The linear region is from 1.0 × 10-6 M to 1.0 × 10-9 M, described by the equation y = 884.01x + 2.24 with a correlation coefficient (R2) of 0.9990. Interference of foreign metal ions with higher concentrations than common mineral water is too weak to the determination. Furthermore, physical insights into the phenomena and the detection mechanism were obtained and investigated theoretically. The preferential conformation of the complex and reduced density gradient (RDG) calculation results indicated that the interactions between TDF and 4-MBA consisted of multiple weak interactions through two hydrogen bonds and one van der Waals interaction. The intermolecular interaction was negative for the charge transfer from the SERS substrate to the probe molecule; thus, the peak intensity decreased. TDF interacts directly with the carboxyl of the probe molecule and consequently has an effect on the ring vibrations. Copyright © 2014 John Wiley & Sons, Ltd.

Driven by the association of chemical weak forces and solvent effects, zero- to two-dimensional nanostructures of thiophene-substituted perylene bisimide such as spheres and blocky structures were obtained. Light-controlled intramolecular charge transfer from the trithiophene unit to the perylene bisimide in the solid state can induce a hypochromatic shift and enhanced fluorescent emission.

Density functional calculations on “catch and release” complexes of C60 with corannulene derived molecular bowls show that computationally obtained 1H nuclear magnetic resonance (NMR) chemical shifts can be used as a reliable predictor of binding constants. A wide range of functionals was benchmarked against accurate ab initio calculations to ensure a credible representation of the weak forces that dominate the interactions in these systems. The most reliable density functional theory (DFT) results were then calibrated using experimentally observed NMR data. Careful analysis and comparison of a wide range of commonly used density functionals shows that the explicit inclusion of dispersion corrections is currently the only reliable way to accurately describe the systems investigated in our study. Moreover, we are able to show that the B97-D and ωB97X-D functionals are not only able to reproduce ab initio benchmark calculations, but they do so accurately with a moderately sized basis sets and without the problems of numerical integration we encountered with other functionals in this study. © 2013 Wiley Periodicals, Inc.

Lorentz invariance in the weak interaction has been tested rather poorly compared to the electromagnetic interaction. In this work we show which tests on the weak interaction should be considered. We focus on one particular test that explores the spin degree of freedom in {\beta} decay. To connect various phenomenological tests of Lorentz invariance in the weak interaction, we exploit a new theoretical model that may provide a framework that relates the different tests.

1099-0682; A strictly heterodinuclear MnIII-Gd complex was prepared from a tripodal ligand and characterized by positive fast-atom bombardment mass spectrometry, which evidenced replacement of a nitrato counterion by a monoethylcarbonato anion. Variable-temperature direct current and alternating current studies confirm that the MnIII-Gd magnetic interaction is antiferromagnetic. Fitting of the magnetic susceptibility data yields an extremely weak interaction parameter JMnGd equal to -0.04 cm-1, along with a weak axial zero-field splitting parameter DMn = 0.1 cm-1. This result confirms that a change in the manganese oxidation state, from MnII to MnIII, corresponds to a radical transformation of the magnetic behavior of Mn-Gd, from a ferromagnetic to an antiferromagnetic interaction. In accordance with the magnetic behavior of CoII-Gd complexes previously studied (high-spin and low-spin CoII ions), the observed magnetic behavior change may be explained by the difference in the electronic occupancy of the Mn 3d x 2-y 2 orbital, which is singly occupied for MnII and vacant for MnIII.

The experimental achievements and the current program with the LPCTrap device installed at the LIRAT beam line of the SPIRAL1-GANIL facility are presented. The device is dedicated to the study of the weak interaction at low energy by means of precise measurements of the {\beta}-{\nu} angular correlation parameter. Technical aspects as well as the main results are reviewed. The future program with new available beams is briefly discussed.

A series of reports in the literature indicated symmetry breaking in assemblies of chiral molecules of opposite handedness. These unexpected observations could be accounted for as being generated by the “parity violation” of the nuclear weak force, combined with an autocatalytic amplification process. However, in many such cases, in particular of chiral fluids, this putative mechanism is far from providing a reasonable explanation for such discrimination. In this article it is suggested that space may have deviated a priori from absolute symmetry, a possibility which complies with observations in atoms and molecules and may even be implicated in the asymmetrical configuration of spiral galaxies. Space asymmetry can be extrapolated to a difference between the relative statistical weights of the “right” versus the “left” directions with respect to Euclidian coordinates or, analogously, to a difference between the clockwise and anticlockwise orientations in polar coordinates. The difference in weights of these directions in space is estimated to be around 1%, based on the differences observed in density values of chiral fluids and chiral crystals of NaClO3. The implied asymmetry of time, as the conjugated fourth dimension, suggests a similar difference in magnitude of the time coordinate in a right-handed versus left-handed space, which is feasible for experimental verification. Chirality 25:308–311, 2013. © 2013 Wiley Periodicals, Inc.

The stress relaxation behaviors of soft and bread-type wheat kernels were studied using the generalized Maxwell model. The data showed two phases, a fast phase at short times of about 1.52–16.88 sec (τ1 and τ2) and a slow phase with longer times of about 81.28–793.81 sec (τ3 and τ4). The shorter decay of σ1 can be explained by very weak forces that affect mainly the rheological properties. The slow decay (σ4) located at longer relaxation times resulted from strong forces. The first derivative obtained from the stress relaxation curve of intact wheat kernels was quite similar in shape to the dough farinograms. The stress relaxation parameters showed differences in springs, relaxation times, and viscosities of bread wheat compared with soft-type wheat kernels. The stresses σ1 and σ4 were correlated with wheat kernel, flour, rheological, and breadmaking properties; so especially were the elasticity of the spring (σ0) and viscosity of the fourth Maxwell element (η4), which were significantly correlat...

Mirror symmetry breaking is ubiquitous in our visible universe taking place in elementary particles, atoms, and molecules. Molecular chirality is not biogenic in itself, although its detection is often considered a biosignature, a conjecture inferred from the fact that we do not know life devoid of homochirality. The question of whether there is a connection between the cosmic preference for one enantiomer, as imposed by the weak force, and the single chirality displayed on Earth is vividly debated. This article gives a glimpse on the origin of asymmetry from a cosmological perspective and on physical transformations that lead to an enantiomeric imbalance, leaving chemical reactions essentially aside. These processes are more plausible as sources of prebiotic chirality than asymmetric amplifications requiring unnatural substrates and conditions and fighting against racemization. The latter may actually be a friend, not foe, and a driving force for enantioselection. Chirality 24:894–908, 2012. © 2012 Wiley Periodicals, Inc

Improvement in rubber-filler interaction is desirable for rubber technologists due to its influence on numerous properties of rubber compounds and vulcani- zates. In practice, there are coupling agents commercially available for the improvement of silica-rubber interaction. Surprisingly, only a limited number of works have been focused on interaction enhancement between carbon black (CB) and rubber. Thus, in the research presented in this article, attempts to improve interaction between ethylene- propylene rubber (EPM) and carbon black (CB) have been made by the use of either p-phenylene diamine (p-PDA) or N-tert-butyl-2-benzothiazole sulfenamide (TBBS) as an interaction modifier. Bound rubber content (BRC), used as an indicator for rubber-filler interaction and viscoelastic behavior of CB masterbatches and CB-filled EPM com- pounds were investigated and correlated. Results from the measurement of BRC in the CB masterbatches revealed that p-PDA was more effective in the enhancement of rub- ber-CB interaction than TBBS. Such improved interaction led to a decrease in magnitude of CB percolation (Payne effect). In respect of viscoelastic behavior, the interaction modifiers affected G 0 only in the small strain region (

Molecular and dissociative adsorption of O2 on Au atoms supported on the regular and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is shown that even weak interaction of Au with the defect-free h-BN support has an unusually strong influence on the binding and catalytic activation of the molecular oxygen. The strong interaction of Au with vacancy point defects on the h-BN surface is accompanied by the large charge transfer to/from the adsorbate which can considerably affect the catalytic activity of the supported Au. It is demonstrated that activation of the molecular O2 and barriers for O2 dissociation on the supported Au atom can be affected by the interaction of Au with the pristine or defected h-BN support. Therefore, the h-BN surface cannot be considered as an absolutely inert support for Au. © 2012 Wiley Periodicals, Inc.

In this work, we present a theoretical study of interaction of benzene with kaolinite and an analysis of the vibrational spectra, electrostatic potential maps, and self consistent field (SCF) orbitals. B3LYP and MP2 benzene–kaolinite results indicate a preferential interaction of benzene on kaolinite octahedral surface. Population analysis indicates that the atoms modified their charges when the monoaromatic molecule and clay mineral are close to tetrahedral and octahedral surface of kaolinite, which suggests that the adsorbed molecule becomes slightly positive. Infrared vibrational data show the reduction in the band frequencies related to the kaolinite external hydroxyls, indicating a weak interaction of benzene with clay mineral. It also was verified, from the potential electrostatic maps, a change in electron density in both benzene and kaolinite. Electron localization function analysis was also carried out for this interaction. © 2011 Wiley Periodicals, Inc.

The density functional calculation is performed to determine the structure of the grown GaN film on graphite substrate for comparison with experimental results using pulsed laser deposition method. The predicted result for polarity of the grown GaN is the nitrogen-terminated face, (0001) and it agrees with experiment. Since graphite is the 2 dimensional material having very weak interaction between layers, graphite is considered to be an ideal lattice mismatch free substrate for heteroepitaxial growth. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We evaluate the performance of ten functionals (B3LYP, M05, M05-2X, M06, M06-2X, B2PLYP, B2PLYPD, X3LYP, B97D, and MPWB1K) in combination with 16 basis sets ranging in complexity from 6-31G(d) to aug-cc-pV5Z for the calculation of the H-bonded water dimer with the goal of defining which combinations of functionals and basis sets provide a combination of economy and accuracy for H-bonded systems. We have compared the results to the best non-density functional theory (non-DFT) molecular orbital (MO) calculations and to experimental results. Several of the smaller basis sets lead to qualitatively incorrect geometries when optimized on a normal potential energy surface (PES). This problem disappears when the optimization is performed on a counterpoise (CP) corrected PES. The calculated interaction energies (ΔEs) with the largest basis sets vary from -4.42 (B97D) to -5.19 (B2PLYPD) kcal/mol for the different functionals. Small basis sets generally predict stronger interactions than the large ones. We found that, because of error compensation, the smaller basis sets gave the best results (in comparison to experimental and high-level non-DFT MO calculations) when combined with a functional that predicts a weak interaction with the largest basis set. As many applications are complex systems and require economical calculations, we suggest the following functional/basis set combinations in order of increasing complexity and cost: (1) D95(d,p) with B3LYP, B97D, M06, or MPWB1k; (2) 6-311G(d,p) with B3LYP; (3) D95++(d,p) with B3LYP, B97D, or MPWB1K; (4) 6-311++G(d,p) with B3LYP or B97D; and (5) aug-cc-pVDZ with M05-2X, M06-2X, or X3LYP.

In the present contribution, we report a theoretical investigation of the magnetic properties of the dihydrogen-evolving enzyme [FeFe]-hydrogenase, based on both DFT models of the active site (the H-cluster, a Fe6S 6 assembly including a binuclear portion directly involved in substrates binding), and QM/MM models of the whole enzyme. Antiferromagnetic coupling within the H-cluster has been treated using the broken-symmetry approach, along with the use of different density functionals. Results of g value calculations turned out to vary as a function of the level of theory and of the extension of the model. The choice of the broken-symmetry coupling scheme also had a significant influence on the calculated g values, for both the active-ready (Hox) and the CO-inhibited (Hox-CO) enzyme forms. However, hyperfine coupling-constant calculations were found to provide more consistent results. This allowed us to show that the experimentally detected delocalization of an unpaired electron at the binuclear subcluster in Desulfovibrio desulfuricans Hox is compatible with a weak interaction between the catalytic centre and a low-weight exogenous ligand like a water molecule. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA.

We present theoretical evidence that the two types of interactions exist in the complexes formed between methylenecyclopropane (MECP) and XY (X, Y = H, F, Cl, and Br). Two seats of XY interacted with MECP are located: (a) is via the pseudo-π bonding electron pair associated with a CC bond of the cyclopropane ring and (b) is via the typical-π bonding of electron pair of the CC bond of MECP. These two types of weak interactions are compared based on the calculated geometries, interaction energies, frequency changes, and topological properties of electron density. The integration of electron density over the interatomic surface is found to be a good measure for the strength of weak interaction. Furthermore, the total electron density and separated σ and π electron densities are also computed and discussed in this article. The separated electron density shows σ electron density determined the strength and π electron density influenced the direction of the hydrogen/halogen bond. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Flame propagation velocities and temperatures in composite stoichiometric mixtures H2/CH4/O2 at different compositions and dilution have been investigated. The experimental results show a weak interaction in the sense of a weak inhibition of hydrogen combustion by methane and a weak promotion of the methane combustion by hydrogen. The activation energy of the branching process in these composite mixtures lies between the values derived from experiments on the separate binary mixtures H2/O2 and CH4/O2.

We present a DFT analysis of the interactions between chemisorbed oxygen on the unreconstructed (1x1)-Pt(100) surface. These interactions control ordering of O not just for single-species adsorption, but also within O domains during coadsorption and reaction with other species such as CO. The calculations indicate that O prefers bridge sites, as deduced previously. In addition, we find a large difference in the interactions between O at different types of bridge site pairs separated by one lattice constant. There is strong repulsion for pairs separated by a Pt atom, but only a weak interaction for pairs separated by a fourfold hollow site. This finding elucidates the tendency for striped (nx1)-O ordering often observed in chemisorption and reaction studies.

Grid-based energy density analysis (EDA), in which numerical integration is performed for two-electron integrals by the pseudospectral method (Imamura et al., J. Chem. Phys. 2007, 126, 034103), is extended to correlated methods: second-order Moller-Plesset (MP2) perturbation and coupled-cluster singles and doubles (CCSD). Using EDA for MP2 and CCSD, we estimate atomic correlation energy differences and correlation energy density difference maps for C2H4CH4 complexes. The analyses confirm that polarization and diffuse functions essentially contribute to the descriptions of weak interaction around the nuclei and in the area between C2H4 and CH4, respectively. © 2008 Wiley Periodicals, Inc. J Comput Chem 29: 1555–1563, 2008

In this paper, some new results on the selective weak interaction between N-alpha-4-tosyl-L-arginine methyl ester hydrochloride (TAME) and adenosine-5'-triphosphate (ATP) have been reported. Fluorescence spectrophotometry and Fourier transform infrared (FT-IR) spectroscopy were used to investigate this kind of weak interaction. In fluorescence experiments, obvious fluorescence quenching phenomena were observed when TAME was added, Which indicated the weak interactions between TAME and ATP. It has been identified by fluorescence titration experiments that TAME exhibited high selectivity to ATP over ADP and AMP. FT-IR spectral results showed that an ATP-TAME adduct was formed. The experimental results indicated that the interaction sites were the guanidinium group of TAME main-chain and the gamma-phosphate group of ATP, and the interaction took place through hydrogen bonding and electrostatic force. In addition, the effects of metal ions on the weak interaction between ATP and TAME, or between ATP and analogues of L-arginine were studied.

Abnormal grain growth in AI 2 O 3 compositions containing MgO in a solid solution was studied at temperatures between 1700° and 1950°C in H 2 gas. The amounts of normal grain growth (NGG) observed for AI 2 O 3 compositions with MgO solute concentration (C MgO ) > 70 and 75 ppm at 1880°C and explained by the solute drag theory. The abrupt transition from low-velocity (low-V) to high-V boundary migration was observed when the C mgo decreased to a critical concentration (C MgO-crit .) ≈60 ppm. This abrupt transition was not affected by C3 +r or Ti 3+ concentration in the AI 2 O 3 solid solution or the temperature between about 1700° and 1950°C. There were no marked changes in grain-boundary mobility at the solubility limits. The apparent mobilities of high-V boundaries ranged between 1 and 16 x 10 -11 m 3 /Ns and agreed well with "near-intrinsic" boundary mobilities for "pure" AI 2 O 3 estimated in the literature. The breakaway of high-V boundaries from the MgO solute "cloud" at C MgO-crit. was explained by the weak interaction energy between the boundary and the MgO solute. It is speculated that Mg AI defects are charge compensated with an equimolar amount of Si AI impurity defects, resulting in neutral defect complexes of [Mg AI - Si AI ] x with a low segregation at grain boundaries.

Two different types of instabilities of equilibrium stripe and ring solutions are studied for the singularly perturbed two-component Gray-Scott (GS) model in a two-dimensional domain. The analysis is performed in the semi-strong interaction limit where the ratio O(e -2 ) of the two diffusion coefficients is asymptotically large. For e → 0, an equilibrium stripe solution is constructed where the singularly perturbed component concentrates along the mid-line of a rectangular domain. An equilibrium ring solution occurs when this component concentrates on some circle that lies concentrically within a circular cylindrical domain. For both the stripe and the ring, the spectrum of the linearized problem is studied with respect to transverse (zigzag) and varicose (breakup) instabilities. Zigzag instabilities are associated with eigenvalues that are asymptotically small as e → 0. Breakup instabilities, associated with eigenvalues that are O(1) as e → 0, are shown to lead to the disintegration of a stripe or a ring into spots. For both the stripe and the ring, a combination of asymptotic and numerical methods are used to determine precise instability bands of wavenumbers for both types of instabilities. The instability bands depend on the relative magnitude, with respect to e, of a nondimensional feed-rate parameter A of the GS model. Both the high feed-rate regime A = O(1), where self-replication phenomena occurs, and the intermediate regime O(e 1/2 ) « A « O(1) are studied. In both regimes, it is shown that the instability bands for zigzag and breakup instabilities overlap, but that a zigzag instability is always accompanied by a breakup instability. The stability results are confirmed by full numerical simulations. Finally, in the weak interaction regime, where both components of the GS model are singularly perturbed, it is shown from a numerical computation of an eigenvalue problem that there is a parameter set where a zigzag instability can occur with no breakup instability. From full-scale numerical computations of the GS, it is shown that this instability leads to a large-scale labyrinthine pattern.

In the (Z) isomer, but not in the (E) isomer of title compound 1, moderate 19F,19F spin–spin coupling across the “cove” is observed [J(F,F) = 11.0 Hz], which is deemed to obey a through-space mechanism. The coupling between the isochronous fluorine nuclei of 1Z causes second-order effects in the 1H, 13C and 19F NMR spectra of this compound and allows its easy distinction from the (E) isomer. A B3LYP/6-31+G(d) calculation of 1Z as an isolated molecule was carried out which gave a non-bonded F,F distance d(F,F) of 2.711 A and an angle between the two C–F bond vectors of 34.1°. The computed F···F compliance constant of 6.96 A/mdyn points to a very weak interaction. According to our previous correlation between d(F,F) and through-space J(F,F), the F,F distance in 1Z would be expected to go along with a coupling constant of ca. 46 Hz. This discrepancy between prediction and experiment gives support to our earlier presumption that a simple d(F,F)/J(F,F) correlation may not sufficiently describe through-space couplings and that an angular factor should also be taken into account. An X-ray diffraction study of 1Z resulted in an F,F distance of 2.638 A and an angle between the C–F bonds of 36.4°, in fair agreement with the MO calculation. The rigidity of the (Z) isomer was studied using theoretical compliance constants. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

We compare magneto-photoluminescence spectra of individual semimagnetic quantum dots (QDs) with different strengths of exchange interaction between a localized exciton and surrounding magnetic ions. The spectra of individual QDs with strong magnetic exchange interaction show a single line corresponding to a ground-state exciton. In QDs with weak interaction, exciton and biexciton spectra are identified, both showing a fine structure due to electron-hole exchange interaction. The anticrossing of dark and bright exciton states in low-symmetry QDs is demonstrated in magnetic fields in the Faraday geometry.

The structural properties of two BrOH2O (1 and 2) and three HOBrH2O complexes (3, 4 and 5) have been investigated using four methods at the 6-311++G(d,p) basis set level. In the two BrOH2O complexes, the complex 2 with 2A state, in which the interaction exists between Br atom of BrO and O atom of water, has a binding energies of about 11.37-13.92 J/mol and it is global minimum. As to HOBrH2O complexes, the binding energies of 3 and 4 are about 16.30-21.32 J/mol and the stability order of the three HOBrH2O complexes is: complex 3complex 4>complex 5.

Pulse-splitting, or self-replication, behavior is studied for some two-component singularly perturbed reaction-diffusion systems on a one-dimensional spatial domain. For the Gierer-Meinhardt model in the weak interaction regime, characterized by asymptotically small activator and inhibitor diffusivities, a numerical approach is used to verify the key bifurcation and spectral conditions of Ei et al. [Japan. J. Indust. Appl. Math., 18, (2001)] that are believed to be essential for the occurrence of pulse-splitting in a reaction-diffusion system. The pulse-splitting that is observed here is edge-splitting, where only the spikes that are closest to the boundary are able to replicate. For the Gray-Scott model, it is shown numerically that there are two types of pulse-splitting behavior depending on the parameter regime: edge-splitting in the weak interaction regime, and a simultaneous splitting in the semi-strong interaction regime. For the semi-strong spike interaction regime, where only one of the solution components is localized, we construct several model reaction-diffusion systems where all of the pulse-splitting conditions of Ei et al. can be verified analytically, yet no pulse-splitting is observed. These examples suggest that an extra condition, referred to here as the multi-bump transition condition, is also required for pulse-splitting behavior. This condition is in fact satisfied by the Gierer-Meinhardt and Gray-Scott systems in their pulse-splitting parameter regimes.

The equilibrium structures, the binding energies, and the second-order energy components of a series of hydrogen-bonded complexes involving acetylene are studied. The strength of the binding energy of the selected systems (H F... HCCH, HCl ... HCCH, HC N... HCCH, and HCC H... HCCH) was different, ranging from a very weak interaction to a strong interaction. Calculations have been carried out at both the Hartree-Fock and correlated (second-order Moller-Plesset perturbation theory) levels of theory, using several different basis sets (6-31G(d,p), 6-311G(d,p), 6- 31G(d,p), 6-311G(d,p), 6-31G(2d,2p) and 6-311G(2d,2p)). The widely used a posteriori Boys-Bernardi counterpoise (CP) correction scheme has been compared with the a priori CHA/CE, CHA-MP2, and CHA-PT2 methods, using the chemical Hamiltonian approach (CHA). The results show that at both levels the CP and the appropriate CHA results are very close to each other. Only the monomer-based CHA- PT2 theory gives slightly overcorrected results, reflecting that the charge transfer and polarization effects are not taken into account in this method up to second order. We have also applied our earlier developed energy decomposition scheme in order to decompose the second-order energy contribution into different physically meaningful components. The results show that at large and intermediate intermolecular distances

The energy of a disubstituted molecule has often been approximated by simple electrostatic formulas that represent the substituents as poles or dipoles. Herein, we test this approach on a new model system that is more direct and more efficient than testing on acid-base properties. The energies of 27 1,4-derivatives of bicyclo[2.2.2]octane were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level; interaction of the two substituents was evaluated in terms of isodesmic homodesmotic reactions. This interaction energy, checked previously on some experimental gas-phase acidities, was considered to be accurate and served as reference to test the electrostatic approximation. This approximation works well in the qualitative sense as far as the sign and the order of magnitude are concerned: beginning with the strongest interaction between two poles, a weaker interaction between pole and dipole, and the weakest between two dipoles. However, all the electrostatic calculations yield energies that are too small, particularly for weak interaction, and this fundamental defect is not remedied by some possible improvements. In particular, variation of the effective permittivity would require a physically impossible value less than unity. The explanation must lie in a more complex distribution of electron density than anticipated in the electrostatic model. It also follows that possible conclusions about the transmission of substituent effects "through space" have little validity.

The interactions of rare gas atoms (Rg = Ar, Kr, and Xe) with small neutral and cationic silver clusters have been investigated by density functional methods and the effect of these weak interactions on the resonance Raman spectra of the complexes has been evaluated. The resonance Raman technique that depends on the properties of ground and excited state, seems deeply sensitive to the weak rare gas–metal cluster interactions, and the use of inert gases has been proven to be an excellent approach to recognize the ability of this technique to detect extremely weak interactions. In this work, for Ag4,6−Rg, and Ag3,5+−Rg complexes the IR, normal and resonance Raman spectra have been calculated and the effect of rare gas–cluster stretching vibration ( vAgn−Rgst) on the pattern and the relative intensities of different spectra have been investigated. The resonance Raman spectra for the weakly interacted complexes (with the interaction energies less than −2.0 kcal/mol) exhibit the vAgn−Rgst vibration with the detectable intensity that its intensity increases by going from Ag6–Ar to Ag6–Xe complex. Moreover, the resonance Raman spectra (based on the excited state gradient approximation) for high intensity nearly degenerate excited states, proved the effect of accumulation of the excited state charge density on the relative intensity of vAgn−Rgstvibration.

A small matter-antimatter asymmetry of the weak force was experimentally established. This CP violation may be related to the small excess of matter from the big bang. The nature of CP violation in the K0 system has been clarified after 35 years of experimentation: it is due to a small part of the weak interaction (“milliweak interaction”). A non-trivial phase in the weak quark mixing matrix generates “direct CP violation” in the weak Hamiltonian. The experiments demonstrating direct CP violation are discussed.

We introduce the topic of fundamental symmetries of physics in relation to molecular chirality by a brief review of the development and current status of the theory of parity violation in chiral molecules. We then discuss in some detail CHBrClF (bromochlorofluoromethane) as a test case, to which the work of André Collet has contributed importantly. For this molecule and its isotopomers, we report here the first detailed theoretical calculations of the influence of parity violation on statistical thermodynamic properties. High-quality ab initio calculations (RPA, random phase approximation, and CASSCF, complete-active-space self-consistent-field) were performed to determine the small energy difference between R- and S-enantiomers of H and D isotopomers of bromochlorofluoromethane (CHBrClF, CDBrClF), and fluorooxirane ((1)H(3)C(2)OF) introduced by the parity-violating weak interaction. Together with vibrational and rotational frequency shifts caused by parity violation, these were used to determine the statistical thermodynamic quantities from the corresponding partition functions within the separable harmonic and in part also anharmonic adiabatic approximation. Temperature-dependent equilibrium constants for the stereomutation were calculated and are discussed in relation to biochemical homochirality.

Single-electron tunneling devices were made by self-assembly of colloidal ligand-stabilized gold clusters in the small gap between two gold electrodes, which were covered with a self-assembled monolayer of 1,8-octanedithiol. With this method we control the size of the active part of the device which is smaller than the traditional lithographic resolution, with chemical methods and use self-positioning of the particle by weak forces between the substrate and the particle. The current voltage characteristic of the devices exhibit a Coulomb staircase and gate effect at 4.2 K, and a prominent Coulomb blockade at room temperature.

International audience; We study theoretically the pull-out of polymer chains from an adsorbed polymer layer by sticking of the chain ends on an opposing surface using scaling arguments and a mean field theory. When only one chain is pulled out from the layer, we extend previous results obtained for a single adsorbed chain and calculate the force necessary to extract the chain from the layer. We then discuss end adsorption from an adsorbed layer of polymers bearing specific end groups onto a second surface. Two bridging regimes are predicted: a diffuse layer regime at weak separations (or/and weak interaction) and a large separation strong interaction regime where the bridges stretch into a brush like structure. Bridging fractions and force profiles are displayed that could be compared to atomic force microscope or surface force apparatus experiments.

The neurotoxicity of beta-amyloid protein (beta AP) fragments may be a result of their solution conformation, which is very sensitive to solution conditions. In this work we describe NMR and CD studies of the conformation of beta AP(12-28) in lipid (micelle) environments as a function of pH and lipid type. The interaction of beta AP(12-28) with zwitterionic dodecylphosphocholine (DPC) micelles is weak and alters the conformation when compared to water solution alone. By contrast, the interaction of the peptide with anionic sodium dodecylsulfate (SDS) micelles is strong: beta AP(12-28) is mostly bound, is alpha-helical from K16 to V24, and aggregates slowly. The pH-dependent conformation changes of beta AP(12-28) in solution occur in the pH range at which the side-chain groups of E22, D23, H13, and H14 are deprotonated (pKas ca. 4 and 6.5); the interaction of beta AP(12-28) with SDS micelles alters the pH-dependent conformational transitions of the peptide whereas the weak interaction with DPC micelles causes little change.