Weak Interaction Effects Research Articles

Comparison of Relative Activation Energies Obtained by Density Functional Theory and the Random Phase Approximation for Several Claisen Rearrangements.

We investigate several representative density functional theory approaches for the calculation of relative activation energies and free energies of a set of model pericyclic reactions, some of which have been studied experimentally. In particular, we use a standard hybrid functional (B3LYP), the same hybrid functional augmented with a basis set superposition error and dispersion correction, a meta-hybrid functional developed to treat transition states and weak interactions (M06-2X), and the recently implemented random phase approximation (RPA) based on Kohn-Sham orbitals from conventional density functional theory by Furche and co-workers. We apply these methods to calculate relative activation energies and estimated free energies for the amide acetal Claisen rearrangement. We focus on relative activation energies to assess the effects of steric and weak interactions in the various methods and compare with experiment where possible. We also discuss the advantages of using this set of reactions as a test bed for the comparison of treatments of weak interactions. We conclude that all methods yield similar trends in relative reactivity, but the RPA yields results in best agreement with the experimental values.

The effect of weak interactions on the shape of cadmium(II) coordination polymers with pyridine-based hydrazines

Coordination polymers are infinite systems build up from metal ions and organic ligands (linkers) as the main units assembled via coordination bonds and weak interactions (hydrogen bonds, π–π interactions, metal-metal interactions, metal-aromatic interactions). Coordination polymers can extend in one, two or three dimensions. The 1D motif can be represented by linear, zigzag, double, ladder-like chains or helices. 2D and 3D coordination polymers are often called metal-organic frameworks (MOF). These materials have been used in crystal engineering due to their structural diversity and their applications as porous materials, in catalysis, ion exchange and gas storage. Coordination polymers can also have other interesting properties e. g. nonlinear optics, luminescence and magnetism. We have prepared a series of cadmium(II) coordination polymers with isoniazid and niazid and various counterions (chloride, bromide, iodide, thiocyanate). Isonicotinylhydrazine (isoniazid) and nicotinylhydrazine (niazid) are suitable linkers for construction of coordination polymers as they are multidentate ligands - N, O-bidentate and N-bridging. They are capable of satisfying cadmium(II) coordination number (usually 5-7) by acting as N, O-bidentate ligands and they bridge the metal ions at the same time (via pyridine N atom). The aim of our study was to determine the effect of the counterions size, shape and their involvement in weak interactions on dimensionality of cadmium(II) polymers with isoniazid and niazid. In case of chloride and bromide use, we obtained 1D polymers with double chains, linked via chloride/bromide bridging atoms, while in case of iodide use, a 1D polymer with zigzag chain was formed, containing terminal iodide ions only. A 2D polymer was obtained by using thiocyanate ion, as it is an ambidentate ligand with N and S donor atoms, enabling the formation of a network. The polymers were also studied by IR spectroscopy, PXRD and thermal methods (TG/DTA, DSC) and various crystallization techniques were employed to get suitable single crystals for X-ray structure analysis.

Instanton theory for bosons in a disordered speckle potential

We study the tail of the spectrum for non-interacting bosons in a blue-detuned random speckle potential. Using an instanton approach we derive the asymptotic behavior of the density of states in d dimensions. The leading corrections resulting from fluctuations around the saddle point solution are obtained by means of the Gel'fand-Yaglom method generalized to functional determinants with zero modes. We find a good agreement with the results of numerical simulations in one dimension. The effect of weak repulsive interactions in the Lifshitz tail is also discussed.

Impact of Temporality and Identifiability in Online Deliberations on Discussion Quality: An Experimental Study

There is a perception that citizen deliberation brings about higher-quality discussions than discussions where deliberative norms are not used. Often, deliberations are realised in mini-publics in which certain contextual features ensure, a priori, that the discussions are likely to be of a high quality. However, few studies have as yet explored the boundaries of deliberation; that is, contemplated what happens to discussion quality if the ideal-speech situation is strayed away from. To address this point, this article reports on an online experiment in which the discursive setting of citizen deliberations is manipulated. The experiment (n = 50 participants) was carried out online in Finland in November 2013 in order to test the impact on discussion quality related to two factors: the temporality (asynchronous or synchronous discussions) and identifiability of participants (known or anonymous) in an online deliberation. The findings clearly indicate that asynchronous discussions have the most positive influence on discussion quality. Moreover, the identifiability factor only had a small weak influence on discussion quality, and there was only one weak interaction effect between the two factors.

Stressor experience negatively affects life satisfaction in adolescents: the positive role of sense of coherence.

The aim of the present study was to investigate the association between different normative stressors, sense of coherence and life satisfaction separately for gender in Norwegian adolescents. The interaction effect of stress by sense of coherence in relation to life satisfaction was also investigated. The data are based on a cross-sectional sample of 1239 adolescents (13-18 years) from public elementary and secondary schools in Central Norway. Hierarchical multiple regression analysis was used to evaluate the association between stressors, sense of coherence and life satisfaction, separately for gender. The results showed significant differences between genders, where boys reported higher scores than girls on sense of coherence and life satisfaction, whereas girls scored higher than boys on five of seven stressor domains. All stressors were significantly and inversely associated with life satisfaction in both genders; however, all associations were stronger for girls compared to boys. Sense of coherence showed a significant strong and positive association with life satisfaction, controlled for age and each individual stressor. A significant although weak interaction effect of stress related to romantic relationships by sense of coherence was found in association with life satisfaction for boys; the other interaction effects were nonsignificant in both genders. The results give support for a significant unique role of stressor experience and sense of coherence in relation to life satisfaction in both genders during adolescence, where the associations were especially strong in girls.

Effects of strong hydrogen bonds and weak intermolecular interactions on supramolecular assemblies of 4-fluorobenzylamine

A series of supramolecular salts have been obtained by the self-assembly of 4-fluorobenzylamine and halide ions or metal chloride with 18-crown-6 as the host in the hydrochloric acid medium, i.e. (C7H9FN)+⋅X− (X=Cl−, 1; Br−, 2), [(C7H9FN)2⋅(18-crown-6)2]2+⋅(MCl4)2− (M=Mn, 3; Co, 5; Zn, 7; Cd, 8), [(C7H9FN)⋅(18-crown-6)]+⋅(FeCl4)− (4) and [(C7H9FN)⋅(18-crown-6)]+⋅1/2(CuCl4)2− (6). Structural analyses indicate that 1–2 crystallize in the triclinic space group P−1, 4 in orthorhombic space group Pnma and 3, 5, 6–8 in the monoclinic space group P21/c or C2/c. In these compounds, extensive intermolecular interactions have been utilized for the self-assembly of diverse supramolecular architectures, ranging from strong N–H⋯X (X=O, Cl, Br) hydrogen bonds to weak C–H⋯Y (Y=F, Cl, π) interactions. N–H⋯Cl/Br hydrogen bonds offer the major driving force in the crystal packing of salts 1–2 while N–H⋯O hydrogen bonds are found in salts 3–8.

Higher order corrections to the hyperfine splitting of positronium

The positronium ground state hyperfine splitting (hfs) has long been of interest as a high-precision test of our understanding of binding in QED. The positronium hfs is particularly sensitive to recoil effects (because the ratio of masses is one) and to virtual electron-positron annihilation, but positronium is insensitive to strong and weak interaction effects. Consequently, the comparison between theory and experiment for the positronium hfs, and more generally the positronium spectrum, tests different aspects of the theory compared to comparisons in other exotic atoms. For the past fifteen years there has been a persistent discrepancy between predicted and measured values of the positronium hfs of about four standard deviations (although a new experimental result is consistent with present theory). Recent experimental work is leading to new high-precision measurements, and the calculation of order- α 3 corrections has begun. The status of the positronium hfs problem and a discussion of recent progress is the topic of this contribution.

Role of Noncovalent Interactions in Vanadium Tellurite Chain Connectivities

Structural differences in [V2Te2O10]n(2n-) chain metrics are directly ascribed to variations in noncovalent interactions in a series of organically templated vanadium tellurites, including [C6H17N3][V2Te2O10]·H2O, [C5H16N2][V2Te2O10], and [C4H14N2][V2Te2O10]. The noncovalent interaction (NCI) method was used to locate, quantify, and visualize intermolecular interactions in [C4H14N2][V2Te2O10] and [C5H16N2][V2Te2O10]. Variations in the van der Waals attractions between [1,4-diaminobutaneH2](2+) and [1,5-diaminopentaneH2](2+) result in divergent packing motifs for these cations, which causes a reorganization of N-H···O hydrogen bonding and variances in the [V2Te2O10]n(2n-) chain metrics. The application of the NCI method to this type of solid-state structure provides a direct method to elucidate the structural effects of weak noncovalent interactions.

Comparative study of multiwalled carbon nanotube/polyethylene composites produced via different techniques

A comparative study of multiwalled carbon nanotube/polyethylene (MWCNT/PE) composites produced by different methods (thermal mechanical mixing, coagulation precipitation technique and in situ ethylene polymerization with a Ziegler–Natta catalyst supported on MWCNTs) has been performed. The morphology and structure of the produced composites were investigated by optical, scanning and transmission electron microscopies. MWCNT incorporation into PE matrix results in the change of conductivity mechanism from conductivity typical of a system with local disorder and effects of weak interaction of electrons (quantum correction to conductivity) to conductivity that can be described within the theory of Coulomb blockade or quasi‐one‐dimensional variable‐range hopping conductivity with variable length of hops (Mott's law) between localized states. The electromagnetic (EM) response of composites was investigated in a broadband region (118–510 GHz). It was found that the dielectric properties of MWCNT/PE composites correlate with their electrophysical properties determined by the MWCNT distribution within the polymer matrix. Typical TEM image of MWCNT in polyethylene matrix. Distance between nanotubes filled with PE varies within a wide range

Detecting Relevant Interactions in High Dimensional Data Analysis

In high dimensional data, relevant interactions can be difficult to identify due to the extremely large number of possible interactions among variables. Conventional methods use a screening stage to vastly reduce the dimension of the variable space before examining the interaction effect. However, this type of screening relies on the assumption that the relevant variables of interactions also have significantly strong marginal effects, which may not be the case in many applications. Hence we propose a multi-stage screening method that considers interaction effects to ensure that variables with weak marginal effect can still be identified if their interactions are strong. The proposed screening method can achieve the same reduction of dimensionality in linear computational time using a random sampling scheme. Experimental studies on three simulated scenarios, a financial news dataset and a biostatistics dataset show that the proposed approach can effectively identify variables that are of weak marginal effect but relevant interaction effect.

Effect of weak attractive interactions on flow behavior of highly concentrated crystalline suspensions

Weak attractive interactions lead to a substantial broadening of the fluid-crystalline coexistence region of crystalline, colloidal hard-sphere dispersions. Here, we demonstrate that a weak depletion attraction introduced by nonadsorbing polymer added to the continuous phase results in a strong decrease of the low shear viscosity even at particle concentrations up to Φ = 0.65 analogous to the re-entry phenomenon in highly concentrated glassy systems. This promotes flow in macroscopic channels but the scenario changes in confined, microfluidic geometries. Pure crystalline suspensions exhibit flow induced melting in the region of highest shear rates close to the wall, and this promotes flow through microchannels (<100 μm). In contrast, weak attractive interactions fortify preferential crystallization at the channel walls finally resulting in channel clogging and cessation of flow. This wall crystallization phenomenon particularly impairs viscosity determination from classical parallel plate rotational rheometry if the gap width is set too low. These findings may find application in the important biotechnological field of protein preparation and crystallization.

Polyolefin ‐ Graphene Oxide Nanocomposites: Interfacial Interactions and Low Temperature Brittleness Reduction

SummaryThe interfacial interactions and low temperature brittleness of high density polyethylene (PE)‐chlorinated polyethylene (CPE) blends as well as their nanocomposites with graphene oxide (G) were characterized. The filler and the CPE phases were observed to have chemical interaction during solution mixing which enhanced during melt mixing of CPE‐graphene oxide masterbatch with PE matrix. Majority of the Cl atoms in the CPE chains were observed to be depleted during chemical reaction or thermal degradation at melt compounding temperature, thus, resulting in chlorine free materials. The samples with CPE35 could not be sufficiently hardened even at −180 °C and remained too soft for cryo‐sectioning. The composites had even higher degree of surface roughness due to additional effect of weak filler matrix interactions.

Variation of CO2 adsorption in isostructural Cd(ii)/Co(ii) based MOFs by anion modulation

A potential multidentate tris-pyridyl ligand has been synthesized, and later employed for the tailoring of four isostructural cadmium(II)/cobalt(II) two dimensional (2D) metal organic frameworks, [[M(dmpt)2(X)2]·xS]n, where S = solvent, M = Cd2+, (X = NO3− (1), Br− (2), I− (3)); M = Co2+ (X = Cl− (4)), dmpt = 4′-(3,4-dimethoxyphenyl)-4,2′:6′,4′′-terpyridine. These complexes have been characterized by infrared (IR) spectroscopy, elemental analysis, thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD) and single crystal X-ray diffraction analyses. Single crystal X-ray diffraction analysis reveals that the complexes (1–4) are isostructural and crystallize in the monoclinic C2/c space group. They possess similar structural features such as metal-coordination environment, network topology, π⋯π interactions and exhibit a 2D uninodal 44-sql topology with slightly tuned cavities. In complexes 1–4, the [[M(dmpt)2(X)2]·xS] coordination monomer acts as the building block, building 2D layers which are further stacked up via Van der Waals interactions into a three-dimensional (3D) framework. The effect of weak interactions on the structural dynamics of the systems has also been studied. Furthermore, a gas adsorption study of these complexes demonstrates that they are affected by the impact of directing anions inside the pores.

Theoretical Mechanism Studies on the Enantioselectivity of aza-MBH-type Reaction of Nitroalkene to N-tosylimine Catalyzed by Thiourea-tertiary Amine

The enantioselective aza-Morita Baylis Hillman reaction of nitroalkene and N-tosylimine catalyzed by thiourea-tertiary amine has been investigated using density functional theory. Enantioselectivity is dominated by the cooperative effect of non-covalent and weak covalent interactions imposed by different units of catalyst. As Lewis base, the tertiary amine unit activates nitroalkene via weak covalent bond. The weak covalent interaction orients the reaction in a major path with smaller variations of this bond. The aromatic ring unit activates N-tosylimine via <TEX>${\pi}-{\pi}$</TEX> stacking. The non-covalent interaction selects the major path with smaller changes of the efficient packing areas. Thiourea unit donates more compact H-bonded network for species of the major path. The calculated ee value in xylene solution phase (97.6%) is much higher than that in N,N-Dimethylformamide (27.2%). Our conclusion is also supported by NBO analysis.

The Synergetic Interplay of Weak Interactions in the Ion‐Pair Recognition of Quaternary and Diquaternary Ammonium Salts by Halogenated Resorcinarenes

AbstractThe influence of halogens on the noncovalent interactions of different upper‐rim‐substituted hexylresorcinarenes with quaternary and diquaternary ammonium iodide salts was investigated in the gas phase by electrospray ionization Fourier‐transform ion‐cyclotron‐resonance (ESI‐FTICR) mass spectrometry and in solution by 1H NMR titration studies. The electronic nature of the substituents on the upper rim of the resorcinarene was directly reflected in the order of binding strengths of the hosts towards quaternary and diquaternary ammonium cations in the gas phase. In solution, the opposite trend was observed, with generally higher binding constants for the diquaternary over the quaternary salts. This phenomenon is explained by the synergetic effect originating from the interaction of the halogenated resorcinarenes with the counteranions through enhanced hydrogen bonding, leading to ion‐pair binding in solution. The electronegativity of the halogens renders the hydrogen of the hydroxy group more acidic, and hence enforces hydrogen bonding in solution. The collective effect of several weak interactions is manifested in solution, thereby emphasizing the benefits of comparing solution and gas‐phase studies in recognition processes.

19F NMR Spectroscopy as a Probe of Cytoplasmic Viscosity and Weak Protein Interactions in Living Cells

Protein mobility in living cells is vital for cell function. Both cytosolic viscosity and weak protein-protein interactions affect mobility, but examining viscosity and weak interaction effects is challenging. Herein, we demonstrate the use of (19) F NMR spectroscopy to measure cytoplasmic viscosity and to characterize nonspecific protein-protein interactions in living Escherichia coli cells. The origins of resonance broadening in Escherichia coli cells were also investigated. We found that sample inhomogeneity has a negligible effect on resonance broadening, the cytoplasmic viscosity is only about 2-3 times that of water, and ubiquitous transient weak protein-protein interactions in the cytosol play a significant role in governing the detection of proteins by using in-cell NMR spectroscopy.

Retention of Halogenated Solutes on Stationary Phases Containing Heavy Atoms

To examine the effects of weak intermolecular interactions on solid-phase extraction (SPE) and chromatographic separation, we synthesized some novel stationary phases with a heavy atom effect layer by immobilizing halogenated aromatic rings and hydroxyl groups onto the surface of a hydrophilic base polymer. Using SPE cartridges packed with the functionalized materials, we found that the heavy atom stationary phases could selectively retain halophenols in organic solvents, such as 1-propanol which blocks the hydrogen bonding, or acetonitrile which blocks the π-π interaction. The extraction efficiency of the materials toward the halophenols depended on the dipole moments of phenoxy groups present as functional groups. On the other hand, the extraction efficiency of solutes toward the functional group depended on their molar refractions, i.e., induced dipole moments. The retention of the solutes to the stationary phase ultimately depended on not only strong intermolecular interactions, but also the effects of weak interactions such as the dispersion force.

Scaling of entanglement entropy across Lifshitz transitions

We investigate the scaling of the bipartite entanglement entropy across Lifshitz quantum phase transitions, where the topology of the Fermi surface changes without any changes in symmetry. We present both numerical and analytical results which show that Lifshitz transitions are characterized by a well-defined set of critical exponents for the entanglement entropy near the phase transition. In one dimension, we show that the entanglement entropy exhibits a length scale that diverges as the system approaches a Lifshitz critical point. In two dimensions, the leading and subleading coefficients of the scaling of entanglement entropy show distinct power-law singularities at critical points. The effect of weak interactions is investigated using the density matrix renormalization group algorithm.

PE-CPE blends and their graphene oxide nanocomposites with reduced low temperature brittleness

The low-temperature flexibility of polyethylene (PE)–chlorinated polyethylene (CPE) blends and their composites with a small amount of graphene oxide filler was studied. Quantitative height variation in the AFM images, rheological as well as fracture analyses were employed to gain insights into the generation of flexibility in the matrix phase. The semi-crystalline CPE (CPE25) polymer did not induce viscoelastic behavior at temperatures lower than the glass transition temperature of PE, whereas the amorphous CPE (CPE35) had completely different behavior. The samples with CPE35 could not be sufficiently hardened even at −180 °C and remained too soft for cryosectioning. Therefore, compression, which results in a 30–60 % reduction in length along the cutting direction with no change in the dimension perpendicular to it, was very prominent for both thin section and block face of the sample. The composites had even higher degree of compression due to additional effect of weak filler matrix interactions and as a consequence, the topographical variations led to filler pull out during sectioning. It was also confirmed using the rheological analysis that composites (and blends with 10 % CPE35 content) had phase immiscibility as CPE phase was suspected to concentrate near the graphene oxide phase leading to generation of chlorine-rich phases. The addition of graphene oxide did not lead to reduced flexibility and the composites also retained the modulus similar to pure polymer. The mechanical fracture of the samples also confirmed the flexibility of the CPE containing blends and composites as these samples were still flexible at −195 °C.

Solid-State Coordinative Behavior of a New Asymmetrical Bis-hydrazone Ligand Containing Two Different Binding Pockets

The potentially multidentate (O2N–NO) trianionic bis(bencylhydrazone) derived from 4-hydroxyisophthaldehyde (H3L) ligand has been synthesized and characterized. The coordinative behavior of the ligand has been explored toward different MII salts (M = Co, Ni, Zn, and Cu), and four complexes, of general formula [M(HL)]·solv (2·solv = molecules of water, dmf, or dmso), have been isolated and characterized. Furthermore, the species [M(H2L)2]·solv (M = Co, 1a·solv; M = Ni, 1b·solv; solv = molecules of water and/or dmf), where the ligand is monodeprotonated and tridentate, has also been detected. The structures of H3L, four solvates of {[Cu(HL)]·solv}n (2c·solv), 1a·5H2O, and 1b·H2O·3dmf were determined by single-crystal X-ray diffraction. The effect of weak interactions on the crystal packing has also been analyzed. The thermal stability and the structural dynamics of the 2c·solv systems have also been investigated.