Range Molecular Interactions Research Articles

Comments on excess molar volumes reported in “Study of short range and long range molecular interactions in binary liquid mixtures of N,N-dimethylformamide (DMF) and 1-propanol”

• V m E values of Prajapati and coworkers compared to published literature data of ten other researchers. • Published V m E values are much smaller in absolute magnitude than values of Prajapati and coworkers. • Published V m E versus mole fraction curves show simple parabolic behavior. • V m E versus mole fraction curves of Prajapati and coworkers show several local minima and maxima. A polemic is given concerning the volumetric properties reported for binary N,N-dimethylformamide + 1-propanol mixtures in the published paper by Prajapati and coworkers. The reported excess molar volumes differ significantly from the published literature values of ten independent research groups, all of which are much smaller in absolute magnitude than the values reported by Prajapati and coworkers.

Study of short range and long range molecular interactions in binary liquid mixtures of N,N-dimethylformamide (DMF) and 1-propanol

In the present study precisely measured properties; static dielectric constant (ε0), refractive index (n) and density (ρ) of binary liquid mixtures of N,N-dimethylformamide (DMF) and 1-propanol (1-PN) have been used to determine linear correlation parameter (grr), mutual linear correlation parameter (gAB), excess Helmholtz free energy functions (ΔF) and excess molar polarization (ΔP). The dipolar contributions to these functions arising from long range electrostatic interaction, short range interaction between identical molecules and short range interaction between dissimilar molecules have been assessed separately. The excess thermodynamic functions calculated from the experimental data supports the formation of clusters with antiparallel or destructive angular correlation (β-clusters). The variation of excess static dielectric constant, excess refractive index and excess molar volume have been used to discuss the type, the strength and the nature of intermolecular interactions betweenconstituent species. Comparison of the predicted values of static dielectric constant and refractive index of the liquid mixtures using various mixing rules with the experimentally determined values have been assessed in terms of Average Percentage Deviation (APD).

Temperature-transferable coarse-graining of ionic liquids with dual graph convolutional neural networks.

Computer simulations can provide mechanistic insight into ionic liquids (ILs) and predict the properties of experimentally unrealized ion combinations. However, ILs suffer from a particularly large disparity in the time scales of atomistic and ensemble motion. Coarse-grained models are therefore used in place of costly all-atom simulations, accessing longer time scales and larger systems. Nevertheless, constructing the many-body potential of mean force that defines the structure and dynamics of a coarse-grained system can be complicated and computationally intensive. Machine learning shows great promise for the linked challenges of dimensionality reduction and learning the potential of mean force. To improve the coarse-graining of ILs, we present a neural network model trained on all-atom classical molecular dynamics simulations. The potential of mean force is expressed as two jointly trained neural network interatomic potentials that learn the coupled short-range and many-body long range molecular interactions. These interatomic potentials treat temperature as an explicit input variable to capture its influence on the potential of mean force. The model reproduces structural quantities with high fidelity, outperforms the temperature-independent baseline at capturing dynamics, generalizes to unseen temperatures, and incurs low simulation cost.

Polarity formation in crystals with long range molecular interactions: A Monte Carlo study

Stochastic formation of a bi-polar state in three dimensional arrays of polar molecules with full Coulomb interactions is reproduced by Monte Carlo simulation. The size of the system is comparable to that of a real crystal seed. The spatial decay of the average order parameter is significantly slowed down by the long range interactions and the exact representation of correlation effects in terms of a single characteristic length becomes impossible. Finite size effects and possible scale invariance symmetry of the order parameter are extensively discussed.

Electronic structure, dielectric response, and surface charge distribution of RGD (1FUV) peptide.

Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor.

Calculated line broadening parameters for methane perturbed by diatomic molecules

We report semiclassical line broadening calculations for methane perturbed by diatomic molecules: nitrogen, N2, oxygen, O2 and hydrogen, H2, at room temperature. For this, we have developed a symmetrized version of the Robert and Bonamy theory. The interaction potential was built from electrostatic (octopole and hexadecapole for methane, quadrupole for the diatomic molecules) and atom–atom contributions. The relative (classical) trajectories of the molecules were computed in the frame of the usual parabolic model, through analytical formula. High orders of developments had to be used for the short range molecular interactions in the case of N2 and O2. For H2, a lower order of development was found to be convenient. We have compared our calculations to some of the available experimental data for hydrogen and oxygen. For nitrogen, we have already reported some comparisons to measurements [T. Gabard, V. Boudon, J. Quant. Spectrosc. Radiat. Transfer 111 (2010) 1328–1343]. Thus, we report here new extensive calculations for the dyad (near 1300cm−1) and the pentad (near 3000cm−1) spectral regions.

A molecular insight on the supramolecular assembly of thiophene polymers

Herein, the relationship between supramolecularly self-assembled microstructures and the chemical structures of photoluminescent molecules is discussed. A series of non-amphiphilic molecules with different length alkyl chains (4–14), central mesogenic groups, and chemical linkers were designed and synthesized. Intricate analysis shows that the supramolecular assembly varies with change in torsion angle of the thiophene linking group on elongation of the alkyl chain. Small angle X-ray scattering measurement shows long range molecular interaction for lower alkyl chain length, AFM reveals circular domains for octyl and decyl alkyl group polymers. UV-Visible and photoluminescence studies in solution and thin-film show that the J-aggregate patterns for the circular domain of the polymer backbone has a major effect on the polymer absorbance, and produces a larger shift for the photoluminescence signals at higher wavelengths. Excitation polarisation studies show a change in molecular ordering in various colour regions with change in aggregation by means of maximum dichroic ratio for the circular domain assembly. Charge carrier mobility and cyclic voltammetry studies show higher mobility and reduced band gap for these circular domain polymers. Dynamic light scattering studies of octyl alkyl chain polymers show a bimodal distribution, which shows the apparent nature of anisotropy in solution.

Acoustical assessment of body water balance

A new medical application of acoustics has recently emerged: assessment of body hydration status by ultrasonic measurement of muscle water content. The need for an easy-to-perform method for the detection of water imbalance is of the utmost clinical importance. Body hypohydration may cause severe health and performance problems, decreasing cognitive and physical work capabilities, while excessive hydration is a common symptom of many other diseases. The speed of longitudinal acoustic waves in muscle, as well as in other soft tissues, is defined by tissue molecular composition because both the density and bulk compressibility of tissue depend mainly on short range molecular interactions. Skeletal muscle is the largest water compartment in the body; it comprises 40% of body mass and 75% of muscle is water. The ultrasound velocity in muscle is a linear function of water content with the slope of about 3.0 m/s per 1% change in water content. We will describe the design, measurement principles, and testing results for new acoustic devices for assessment of hydration status of elderly and infants, two most vulnerable groups of population. Advantages and disadvantages of acoustical method of hydration over currently available methods are discussed.

Line broadening coefficient calculations for methane perturbed by nitrogen

We report semiclassical line broadening calculations for methane perturbed by nitrogen at room temperature. For this, we have developed a symmetrized version of the Robert and Bonamy theory. The interaction potential was built from electrostatic (octopole and hexadecapole for methane, quadrupole for nitrogen) and atom–atom contributions. The relative (classical) trajectories of the molecules were computed in the frame of the usual parabolic model, through analytical formula. High orders of developments had to be used for the short range molecular interactions. As a consequence, a combination of symbolic computation and source code generation was employed to implement practical calculations. We have compared our calculations to the most recent experimental data available in the ν 4 band, the ν 3 band and the octad spectral region of methane.

Unusual halogen-bonded complex FBrδ+⋯Brδ+F and hydrogen-bonded complex FBrδ+⋯Hδ+F formed by interactions between two positively charged atoms of different polar molecules

Using ab initio calculations, the authors' predicted for the first time that the halogen-bonded complex FBrdelta+...delta+BrF and hydrogen-bonded complex FBrdelta+...delta+HF formed by the interactions between two positively charged atoms of different polar molecules can be stable in gas phase. It shows that halogen bond or hydrogen bond not only exists between oppositely charged atoms but also between like-charged atoms. That the attraction arising from the special halogen bond or hydrogen bond can exceed the electrostatic repulsion between two contact positively charged atoms stabilizes the complex. Of course, from the point of view of physics they can consider the interactions in FBrdelta+...delta+BrF and FBrdelta+...delta+HF as mainly the sum of the long range molecular interactions, namely, electrostatic, induction, and dispersion with some short-range repulsion. They found that the intermolecular electron correlation contribution representing dispersion interaction plays a crucial role in the stabilities of seemingly repulsive complexes FBrdelta+...delta+BrF and FBrdelta+...delta+HF.

Hydrodynamic theories for mixtures of polymers and rodlike liquid crystalline polymers

We develop a hydrodynamic theory for flows of incompressible blends of flexible polymers and rodlike nematic polymers (RNPs) or rodlike nematic liquid crystal polymers (RNLCPs) extending the thermodynamical theory of Muratov and E [J. Chem. Phys. 116, 4723 (2002)] for phase separation kinetics of the blend. We model the flexible polymer molecules in the polymer matrix as Rouse chains and assume the translational diffusion of the molecules is predominantly through the volume fraction of the flexible polymer and the molecules of rodlike nematic liquid crystal polymers. We then (i) derive the translational flux for the rodlike nematic liquid crystal polymers to ensure the incompressibility constraint; (ii) derive the elastic stress tensor, accounting for the contribution from both the rodlike nematic polymer and the flexible polymer matrix, as well as the extra elastic body force due to the nonlocal intermolecular potential for long range molecular interaction; (iii) show that the theory obeys positive entropy production and thereby satisfies the second law of thermodynamics. By applying the gradient expansion technique on the number density function of RNLCPs, we present an approximate, weakly nonlocal theory in differential form in which the intermolecular potential is given by gradients of the number density function of the RNLCP and the volume fraction of the flexible polymer. In the approximate theory, the elastic stress is augmented by an extra stress tensor due to the spatial convection of the macroscopic material point and long range interaction, whose divergence yields the analogous extra elastic body force with respect to the nonlocal intermolecular potential. Finally, we compare the model in steady simple shear with the Doi theory for bulk monodomains of rodlike nematic polymers.

A Kinetic Theory for Solutions of Nonhomogeneous Nematic Liquid Crystalline Polymers With Density Variations

The kinetic theory developed in [1] for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of spheroidal molecular configurations is extended to account for the translational diffusion and the related spatial density variation. The new theory augments the effect of the density variation to the intermolecular potential, Smoluchowski equation and the elastic stress. It accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from rodlike liquid crystals at large aspect ratios to discotic ones at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations. In the limit of weak distortional elasticity, weak translational diffusion, and weak flows, the theory yields the torque balance equation of the well-known Ericksen-Leslie theory.

A hydrodynamic theory for solutions of nonhomogeneous nematic liquid crystalline polymers of different configurations

A hydrodynamic theory is developed for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of a variety of molecular configurations in proximity of spheroids, extending the Doi kinetic theory for rodlike molecules. The new theory accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from the rodlike liquid crystal at large aspect ratios to the discotic one at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. When restricted to uniaxial symmetry in the weak flow limit, the theory recovers the director equation of the Leslie–Eriksen (LE) theory, but the stress tensor contains excessive gradient terms in addition to the LE stress tensor. The theory predicts that the elastic moduli K1, K2, and K3 obey the ordering K3<K1<K2 for stable, discotic (oblate spheroidal) LCPs in the weak flow limit. The ordering is reversed for rodlike (prolate spheroidal) LCPs. It yields a positive Leslie viscosity α2 (α3) in the flow-aligning (tumbling) regime for oblate (prolate) spheroidal LCPs. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations.

Correlation Length in PBnA Liquid Crystal Family

We present a study of the range molecular interactions inside layers in smectic phases Α and I of PBnA (phenyl-4 benzylidene 4'-alkylaniline) liquid crystals family. The purpose of this work is to determine the correlation length of the molecules, gravity centers in existing domain of smectic phases and at the transition between them. We used X-rays in-plane peaks of the pattern diffraction of aligned sample by a magnetic field. PACS numbers: 61.30.-v, 61.10.—i, 64.70.Md, 61.30.Gd

Disjoining pressure in soap film thermodynamics

A rigorous and essentially complete thermodynamic treatment is presented of a thin soap film formed from an adjacent meniscus solution. The entire soap film system includes the components: water (1), a surfactant (2), a salt (3) and an inert gas (4). Mechanically, the thin soap film is modeled as two weakly interacting surfaces of tension positioned a distance h t (= film thickness) apart. h t is an auxiliary independent variable that can be changed by varying the external excess pressure acting in the normal direction on the surfaces of tension and counteracting the effective disjoining pressure, π f, within the film. The resultant excess in lateral tension within the film is assumed to be acting in the planes of the surfaces of tension. The thermodynamics of the film are based on this mechanical model and are formulated both in terms of the overall film tension γ f and the film surface tension γ fs. Taking due account of the variance of the soap film system, a number of thermodynamic fundamental equations are derived which correspond to different experimental situations. Full congruence with the thermodynamics of curved, fluid interfaces is established. It is noted that γ f and π f as well as γ fs and π D (the Derjaguin disjoining pressure) are conjugate thermodynamic quantities. π D accounts for the long range molecular interactions between the film faces in a clearcut fashion insofar as the surfactant monolayer structures remain essentially unaffected by h t changes. Contact angle measurements are particularly useful when the chief object is to explore the thermodynamic properties of thin soap films. For such measurements h t variations are in general thermodynamically insignificant for NB films but not for CB films.

Kinetic Depolarization in Aqueous Solutions of Alkylammonium Bromides

AbstractThe extrapolated static permittivity of aqueous solutions of tetraalkylammonium bromides and azoniaspiroalkane bromides is discussed with respect to the recently predicted kinetic polarization deficiency. The experimental data are found to be not inconsistent with the theory. The large ions manifest universal hydration characteristics of organic particles, if the effect of kinetic depolarization is taken into consideration. Charged as well as neutral hydrophobic solutes seem to promote the short range molecular interactions of the water around them.

Note on the dynamics of binary collision among four particles

A respulsive short range molecular interaction is assumed. The dynamical events of five successive binary collisions among 4-particles are discussed by means of the method of binary collision expansion. Phase space diagrams of different events are sketched and events studied. The divergence of these diagrams in two dimensions is computed by doing phase space integration.

A comparison of the thermodynamic properties and spectra of the F.C.C. and H.C.P. lattices

By suitable use of electronic computers it has recently become possible to calculate large numbers of spectral moments on lattices with short range molecular interactions. In this paper the method is applied to the f.c.c. and h.c.p. lattice models with nearest neighbour central force interactions. Nineteen even moments have been obtained on both lattices. Using one term in the low temperature expansions, and the Pade approximant method of analytic continuation for the high temperature series, the specific heats and thermodynamic properties of both lattices can be accurately compared at all temperatures. The results therefore represent a considerable advance on the earlier calculations by Barron and Domb, and their relevance to the observed polymorphic transition in solid helium is noted.