Attractive Dispersion Research Articles

Dispersion interactions between neighboring Bi atoms in (BiH3 )2 and Te(BiR2 )2.

Triggered by the observation of a short Bi⋯Bi distance and a BiTeBi bond angle of only 86.6° in the crystal structure of bis(diethylbismuthanyl)tellurane quantum chemical computations on interactions between neighboring Bi atoms in Te(BiR2 )2 molecules (R = H, Me, Et) and in (BiH3 )2 were undertaken. Bi⋯Bi distances atoms were found to significantly shorten upon inclusion of the d shells of the heavy metal atoms into the electron correlation treatment, and it was confirmed that interaction energies from spin component-scaled second-order Møller-Plesset theory (SCS-MP2) agree well with coupled-cluster singles and doubles theory including perturbative triples (CCSD(T)). Density functional theory-based symmetry-adapted perturbation theory (DFT-SAPT) was used to study the anisotropy of the interplay of dispersion attraction and steric repulsion between the Bi atoms. Finally, geometries and relative stabilities of syn-syn and syn-anti conformers of Te(BiR2 )2 (R = H, Me, Et) and interconversion barriers between them were computed. © 2018 Wiley Periodicals, Inc.

Interactions of Bovine Serum Albumin Molecules in an Aqueous Sodium Sulfate Solution Determined by an Osmotic Pressure Method

In this work, the interactions of aqueous bovine serum albumin (BSA) solutions at four pH values (4.5, 4.8, 5.4, and 7.4), and at three sodium sulfate (Na2SO4) concentrations (0.15, 0.50, and 1.00 mol·L−1), was investigated through the use of osmotic pressure measurements. The osmotic second virial coefficients of BSA were determined from the osmotic pressure data. According to the molecular thermodynamic model, as described in the literature (Moon et al. in Fluid Phase Equilib 168:229–239, 2000), the electrostatic repulsion potential, attractive dispersion potential and the ion-excluded-volume potential were calculated. The dependencies of the three potentials on the solution pH and on the ionic strength are discussed. We compared the potentials of BSA molecules in an aqueous sodium sulfate solution with the potentials in aqueous ammonium sulfate [(NH4)2SO4] and sodium chloride (NaCl) solutions. The order of the potential values in the aqueous solutions with the different salts was also discussed.

Anisotropic forces and molecular dynamics

The focus of the present work is on the detailed characterization of the most relevant components of the intermolecular interaction, which determine anisotropic force fields driving the molecular dynamics under a variety of conditions. This target is here achieved by combining in a unifying picture the results of different type of experiments, probing complementary aspects of the intermolecular interactions involved. In particular, the analysis of high-resolution scattering data led to an accurate evaluation of the strength and anisotropy of non-covalent interaction components, due to the balance of size (or Pauli) repulsion with dispersion and induction attraction, to which electrostatic contributions must be added. Moreover, for the complete representation of the intermolecular interaction other components of covalent (chemical) nature, mostly affected by charge (electron) transfer effects, must be properly taken into account. Particular attention has been recently devoted to some experimental findings probing in detail the strength, range, anisotropy and role of the charge transfer effects. Obtained results have been important to develop suitable analytical representations for the potential energy surfaces (PESs), tested and improved by exploiting also the comparison with results of ab initio calculations, useful to provide an internally consistent description of the intermolecular interaction both in the most and less stable configurations of the interacting system. The complete and appropriate formulation of the PESs must be then considered crucial not only to describe the dynamics of elementary processes occurring in interstellar medium and in planetary atmospheres, but also to control equilibrium and non-equilibrium phenomena of applied interest, as those occurring in combustion, flames and plasmas.

Studies on the effects of cenosphere on polypropylene matrix using silane coupling agent

Present research concentrates on the effects of a silane coupling agent on the properties and dispersibility of the polypropylene (PP)-cenosphere composite system. Improving the interfacial interaction between the hydrophobic PP matrix and cenosphere particles is important to get a good combination of properties. 3-Aminopropyltriethoxysilane and glycidyl methacrylate–grafted polypropylene (PP-g-GMA) were used as a coupling agent and compatibilizer, respectively. The surface characteristics of untreated and treated cenosphere and PP-g-GMA were characterized by Fourier transform infrared spectroscopy. The silane treated and untreated cenosphere particles were incorporated as fillers into PP and PP-g-GMA matrix composites by mixing at different weight ratios. Such cenosphere-filled polymer composites possess attractive mechanical, thermal, morphological, flow, dispersion and chemical resistance properties.

Momentum exchange theory of photon diffraction

Momentum exchange theory (MET) provides an alternative picture for optical diffraction based on a distribution of photon paths through momentum transfer probabilities determined at the scattering aperture. This is contrasted with classical optical wave theory that uses the Huygens–Fresnel principle and sums the phased contributions of wavelets at the point of detection. Single-slit, multiple-slit (Talbot effect), and straight-edge diffraction provide significant clues to the geometric parameters controlling momentum transfer probabilities and the relation to Fresnel zone numbers. Momentum transfer is primarily dependent on preferred momentum states at the aperture and the specific location and distance for momentum exchange. Diffraction by an opaque disc provides insight to negative (attractive) dispersions. MET should simplify the analysis of a broadened set of aperture configurations and experimental conditions.

Enantiocontrol by assembled attractive interactions in copper-catalyzed asymmetric direct alkynylation of α-ketoesters with terminal alkynes: OH···O/sp3-CH···O two-point hydrogen bonding combined with dispersive attractions.

Copper-catalyzed asymmetric direct alkynylation of α-ketoesters with terminal alkynes with chiral prolinol-phosphine ligands, most preferably (αR,2S)-1-(2-dicyclohexylphosphinobenzyl)-α-neopentyl-2-pyrrolidinemethanol, afforded various enantioenriched chiral propargylic tertiary alcohols. Quantum-chemical calculations using the BP86 density functional including Grimme's empirical dispersion correction [DF-BP86-D3(BJ)-PCM(tBuOH)/TZVPP//DF-BP86-D3(BJ)/SVP] show the occurrence of OH···O/sp3-CH···O two-point hydrogen bonding between the chiral ligand and the carbonyl group of the ketoester in the stereo-determining transition states. Combined with the hydrogen-bonding interactions orienting the ketoester substrate, dispersive attractions between the chiral ligand (P-cyclohexyl groups) and the ketoester in the favored transition states, rather than steric repulsions in the disfavored transition state explain the enantioselectivity of the asymmetric copper catalysis.

Attraction or repulsion? Theoretical assessment of bulky alkyl groups by employing dispersion-corrected DFT.

London dispersion, which is the most widespread attractive part of van der Waals force, can be enhanced by introducing a bulky alkyl group to the interacting molecules. However, this strategy will also result in increased steric repulsion. Our theoretical investigation of the attraction–repulsion balance of alkyl groups is implemented, based on an intramolecular configuration torsion system, by varying the sizes and positions of alkyl groups and employing density functional theory (DFT) with or without dispersion correction. The more stabilized folded configurations, higher conversion energy barriers, and stronger alkyl–π interactions are all obtained within the dispersion-corrected DFT calculations. The position of the alkyl is the obvious controlling factor in the configuration conversion. The attractive dispersion effect of the bulky alkyl is better reflected than the steric repulsion. Furthermore, the present findings separate two different reaction pathways depending on two different stereoisomers of the unfolded reactants and the DFT+D3 simulated pathways were proved to be more reasonable.

Dispersion and distortion in heavy group 2 and lanthanide decamethylmetallocenes: The (C5Me5)2(Sr,Sm) connection

Identification of the source(s) of the counterintuitive bending (non-linearity) in heavy group 2 (Ca–Ba) dihalides and metallocenes has long been in dispute, a difficulty compounded by the low values of energy involved (ca. ≲ 2 kcal mol−1). Analogous issues exist with compounds of the divalent lanthanides Sm(II), Eu(II), and Yb(II), despite the substantially different electronic structures of the metals involved. The assertion that the bent structure of (C5Me5)2Sr, for example, can be attributed exclusively to the operation of attractive dispersion forces between the ring methyl groups has been argued on the basis of molecular mechanics calculations, and more recently with the aid of DFT studies that employed dispersion-corrected density functionals (Organometallics, 32(5) (2012), 1265). In contrast, covalent interactions have been identified as the primary source of bending in the similarly distorted (C5Me5)2Sm. The case of bent (C5Me5)2Sr has been reinvestigated with the use of larger basis sets for strontium, and with the employment of the “dispersion-free” APF density functional. We find that given flexible enough basis sets, bending can be modeled even in the absence of explicitly included dispersion effects, and that both inherent electronic effects and dispersion interactions contribute to the bending of (C5Me5)2Sr.

Ligand-Substrate Dispersion Facilitates the Copper-Catalyzed Hydroamination of Unactivated Olefins.

The current understanding of ligand effects in transition metal catalysis is mostly based on the analysis of catalyst-substrate through-bond and through-space interactions, with the latter commonly considered to be repulsive in nature. The dispersion interaction between the ligand and the substrate, a ubiquitous type of attractive noncovalent interaction, is seldom accounted for in the context of transition-metal-catalyzed transformations. Herein we report a computational model to quantitatively analyze the effects of different types of catalyst-substrate interactions on reactivity. Using this model, we show that in the copper(I) hydride (CuH)-catalyzed hydroamination of unactivated olefins, the substantially enhanced reactivity of copper catalysts based on bulky bidentate phosphine ligands originates from the attractive ligand-substrate dispersion interaction. These computational findings are validated by kinetic studies across a range of hydroamination reactions using structurally diverse phosphine ligands, revealing the critical role of bulky P-aryl groups in facilitating this process.

Intramolecular London Dispersion Interaction Effects on Gas-Phase and Solid-State Structures of Diamondoid Dimers.

The covalent diamantyl (C28H38) and oxadiamantyl (C26H34O2) dimers are stabilized by London dispersion attractions between the dimer moieties. Their solid-state and gas-phase structures were studied using a multitechnique approach, including single-crystal X-ray diffraction (XRD), gas-phase electron diffraction (GED), a combined GED/microwave (MW) spectroscopy study, and quantum chemical calculations. The inclusion of medium-range electron correlation as well as the London dispersion energy in density functional theory is essential to reproduce the experimental geometries. The conformational dynamics computed for C26H34O2 agree well with solution NMR data and help in the assignment of the gas-phase MW data to individual diastereomers. Both in the solid state and the gas phase the central C-C bond is of similar length for the diamantyl [XRD, 1.642(2) Å; GED, 1.630(5) Å] and the oxadiamantyl dimers [XRD, 1.643(1) Å; GED, 1.632(9) Å; GED+MW, 1.632(5) Å], despite the presence of two oxygen atoms. Out of a larger series of quantum chemical computations, the best match with the experimental reference data is achieved with the PBEh-3c, PBE0-D3, PBE0, B3PW91-D3, and M06-2X approaches. This is the first gas-phase confirmation that the markedly elongated C-C bond is an intrinsic feature of the molecule and that crystal packing effects have only a minor influence.

Molecular dynamics simulation of ZnO wurtzite phase under high and low pressures and temperatures

Isothermal and isobaric ensembles behaviours of ZnO wurtzite phase have been investigated, by parallel molecular dynamics method and using Buckingham potential, which contains long-range Coulomb, repulsive exponential, and attractive dispersion terms. To conduct our calculations, we have used dl_poly 4 software, under which the method is implemented. We have examined the influence of the temperature and pressure on molar volume in the ranges of 300–3000 K and 0–200 GPa. Isothermal-isobaric relationships, fluctuations, standard error, equilibrium time, molar volume and its variation versus time are predicted and analyzed. Our results are close to available experimental data and theoretical results.

Nonlinear size-dependent pull-in instability and stress analysis of thin plate actuator based on enhanced continuum theories including nonlinear effects and surface energy

In recent years, size dependent continuum theories have been commonly used to simulate material discontinuities in micro/nano-scales. In the present article, modified strain gradient theory (MSGT) and Gurtin–Murdoch surface elasticity, are used to investigate the size-dependent nonlinear pull-in instability and conduct a stress analysis of thin microplates. This paper modifies the classical equations and surface elasticity theory as a non-classical method which is able to account for the surface effect of nanomaterials with sufficient precision and lower calculation cost in comparison to atomic methods. The effects of van der Waals and Casimir forces are incorporated into the nonlinear governing equation of the system. A finite difference method (FDM) is employed to solve the nonlinear differential equation, and the pull-in parameters of the microplate are extracted. The effect of dispersion attractions and size-dependency on instability as well as the importance of the coupling between them is discussed. The most common types of thin-plates, including fully-clamped, simply-supported, and plates with mixed boundary conditions, are investigated. It is found that the significant difference between the pull-in instability parameters in the MSGT and the classical theory for thin microplates is merely due to the consideration of the size effect parameter in the modified strain gradient theory. The effect of surface/interface is also accounted for in the numerical FDM approach. Then, the stress analysis of the microplate is studied numerically by examining the surface/interface effect on the microplate with a square/rectangular section. The results obtained through this numerical method are plotted graphically.

Trenched raised cosine FMF for differential mode delay management in next generation optical networks

Dispersion management in few mode fiber (FMF) technology is crucial to support the upcoming standard that reaches 400 Gbps and Terabit/s per wavelength. Recently in Chebaane et al. (2016), we defined two potential differential mode delay (DMD) management strategies, namely sawtooth and triangular. Moreover we proposed a novel parametric refractive index profile for FMF, referred as raised cosine (RC) profile. In this article, we improve and optimize the RC profile design by including additional shaping parameters, in order to obtain much more attractive dispersion characteristics. Our improved design enabled to obtain a zero DMD (z-DMD), strong positive DMD (p-DMD) and near-zero DMD (nz-DMD) for six-mode fiber, all appropriate for dispersion management in FMF system. In addition, we propose a positive DMD (p-DMD) fiber designs for both, four-mode fiber (4-FMF) and six-mode fiber (6-FMF), respectively, having particularly attractive dispersion characteristics.

Energy-decomposition analysis of ion-neutral complexes along reaction coordinates of unimolecular proton-transfer reaction in gas phase: Comparison between 2-butanol radical ion and protonated 2-ethoxypropane ion

An energy-decomposition analysis clarified the physical origins that change in gas-phase unimolecular proton-transfer reactions via ion-neutral complexes of the 2-butanol radical ion and protonated 2-ethoxypropane ion. In the bond cleavage and new bond-formation parts of the reaction coordinates, exchange and polarization energies provide a major source of the attraction. In the ion-neutral complex-formation part of the reaction coordinate, different major attractive sources, dispersion, and electrostatic energies were observed. The physical origins of weak interaction in the ion-neutral complexes were affected by the local charges and distances between the ion moieties and the neutral moieties.

Characteristic Features of CO2 and CO Adsorptions to Paddle-Wheel-type Porous Coordination Polymer

Adsorptions of CO, N2, NO, and CO2 in a paddle-wheel-type porous coordination polymer (PCP) [Cu(aip)]n (aip = 5-azidoisophthalate) were investigated with ONIOM[MP4(SDQ):ωB97XD] method using a model system consisting of two [Cu2(O2CC6H4-R)4] units (R = H and Me) and one [Cu2(O2CC6H4–R)4] unit, namely, dimer and monomer models. The experimental CO adsorption position was reproduced well by the present calculation with the dimer model. For adsorptions of CO, N2, NO, and CO2 in the dimer model, the position of gas molecule deviates from the normal one that is found in the monomer model and becomes more distant from the surrounding phenyl group(s) of the neighbor [Cu(aip)] unit. For all of these gas molecules, the calculated binding energy (BE) at the deviating adsorption position is larger than that at the normal one against our expectation that the normal position is the best for the gas adsorption. The deviation of gas adsorption position arises from the interaction between the organic linker (O2CC6H4–R moiety) and gas molecule. For all cases, the exchange repulsion with the organic linker decreases to a larger extent than the attractive electrostatic and dispersion interactions decrease when going from the normal position to the deviating one. To enhance the binding energy of gas molecule, the introduction of electron-donating substituent on phenyl moiety is computationally recommended for this PCP.

Phase Behavior of Magnetic Nanocolloids of Different Sizes Suspended in an Apolar Solvent.

We employ classical density functional theory (DFT) to investigate the phase behavior and composition of binary mixtures; each compound consists of hard spheres of different sizes with superimposed dispersion attraction. In addition to the dispersion attraction, molecules of one component carry an additional three-dimensional magnetic "spin" where the orientation-dependent spin-spin interaction is accounted for by the Heisenberg model. We are treating the excess free energy using a modified mean-field approximation (second virial coefficient) for the orientation-dependent pair correlation function. Depending on the concentration of the magnetic particles, the strength of the spin-spin coupling, and the size ratio of the particles, the model predicts the formation of ordered (polar) phases in addition to the more conventional gas and isotropic liquid phases. Key features of our model are a particle-size dependent shift of the gas-liquid critical point (critical temperature and density) and a change in the width of the phase diagram. In the near-critical region, the latter can be analyzed quantitativly in terms of an effective critical exponent βeff that may differ from the classical critical exponent [Formula: see text]; the classical value is attained in the immediate vicinity of the critical point as it must. The deviation between βeff and β can be linked to nontrivial composition effects along the phase boundaries.

Intramolecular interactions in sterically crowded hydrocarbon molecules.

A molecular fragmentation method has been used to analyze the intramolecular interactions in the three molecules coupled diamantane, hexaphenylethane, and all-meta-tert-butyl substituted hexaphenylethane. The significance of these systems lies in the fact, that steric crowding effects enable a stabilization of the central carbon bond that possesses an extended length (1.6 to 1.7 Å) beyond conventional carbon-carbon bonds due to the steric repulsion of the attached hydrocarbon groups. The total stability of these molecules therefore depends on a delicate balance between attractive interaction forces on the one hand and on repulsive forces on the other hand. We have quantified the different interaction energy contributions using symmetry-adapted perturbation theory based on a density functional theory description of the monomers. It has been found that the attractive dispersion interactions increase more strongly with the level of crowding in the systems than the counteracting exchange interactions. This shows that steric crowding effects can have a significant impact on the structure and stability of large and branched molecules. © 2017 Wiley Periodicals, Inc.

Dispersion control of silicon nanophotonic waveguides using sub-wavelength grating metamaterials in near- and mid-IR wavelengths

Controlling the group velocity dispersion of silicon nanophotonic waveguides has been recognized as a key ingredient to enhance the development of various on-chip optical applications. However, the strong wavelength dependence of the dispersion in waveguides implemented on the high index contrast silicon-on-insulator (SOI) platform substantially hinders their wideband operation, which in turn, limits their deployment. In this work, we exploit the potential of non-resonant sub-wavelength grating (SWG) nanostructures to perform a flexible and wideband control of dispersion in SOI waveguides. In particular, we demonstrated that the overall dispersion of the SWG-engineered metamaterial waveguides can be tailored across the transparency window of the SOI platform, keeping easy-to-handle single-etch step manufacturing. The SWG silicon waveguides overcladded by silicon nitride exhibit significant reduction of wavelength dependence of dispersion, yet providing intriguing and customizable synthesis of various attractive dispersion profiles. These include large normal up to low anomalous operation regimes, both of which could make a great promise for plethora of emerging applications in silicon photonics.

The Interplay between Various σ- and π-Hole Interactions of Trigonal Boron and Trigonal Pyramidal Arsenic Triiodides

Boron and arsenic triiodides (BI3 and AsI3, respectively) are similar molecules that differ mainly in their geometries. BI3 is a planar trigonal molecule with D3h symmetry, while AsI3 exhibits a trigonal pyramidal shape with C3v symmetry. Consequently, the As atom of the AsI3 molecule has three σ-holes, whereas the B atom of the BI3 molecule has two symmetrical π-holes. Additionally, there are σ-holes on the iodine atoms in the molecules studied. In the first step, we have studied σ-hole and π-hole interactions in the known monocrystals of BI3 and AsI3. Quantum mechanical calculations have revealed that the crystal packing of BI3 is dominated by π-hole interactions. In the case of AsI3, the overall contribution of dihalogen bonding is comparable to that of pnictogen bonding. Additionally, we have prepared the [Na(THF)6]+[I(AsI3)6]−(AsI3)2 complex, which can be described as the inverse coordination compound where the iodine anion is the center of the aggregate surrounded by six AsI3 molecules in the close octahedral environment and adjacent two molecules in remote distances. This complex is, besides expected dihalogen and pnictogen bonds, also stabilized by systematically attractive dispersion interactions.

The Viologen Cation Radical Pimer: A Case of Dispersion-Driven Bonding.

The π bonds between organic radicals have generated excitement as an orthogonal interaction for designing self-assembling architectures in water. A systematic investigation of the effect of the viologen cation radical structure on the strength and nature of the pimer bond is provided. A striking and unexpected feature of this π bond is that the bond strength is unchanged by substitution with electron-donating groups or withdrawing groups or with increased conjugation. Furthermore, the interaction is undiminished by sterically bulky N-alkyl groups. Theoretical modeling indicates that strong dispersion forces dominate the interaction between the radicals, rationalizing the insensitivity of the bonding interaction to substituents: The stacking of polarizable π radicals leads to attractive dispersion forces in excess of typical dispersion interactions of small molecules and helps overcome the Coulombic repulsion of bringing two cationic species into contact.