Nature Of Intermolecular Forces Research Articles

Cineole – Decanoic acid hydrophobic natural Deep eutectic solvent for toluene absorption

The hydrophobic deep eutectic solvent formed by the equimolar combination of natural compounds cineole and decanoic acid is studied as an archetypical compound for aromatics (toluene) solubilization/extraction purposes. The physicochemical properties of toluene solutions in the solvents are studied as a function of composition and temperature. The nature of intermolecular forces between toluene and solvent molecules is analyzed using a minimal clusters approach through quantum chemistry methods. Classical molecular dynamics simulation on toluene solution allowed us to infer nanoscopic behavior and structuring of the toluene mixtures using static and dynamic approaches. Likewise, the possible biological effects of the considered solvent are studied considering its effect on lipid bilayers as a model of plasma membranes using coarse-grained molecular dynamics methods. The reported results provide a multiscale combined experimental and computational characterization of hydrophobic Deep Eutectics as suitable solvents for aromatic hydrocarbons.

Density functional theory computation of the intermolecular interactions of Al2@C24 and Al2@Mg12O12 semiconducting quantum dots conjugated with the glycine tripeptide.

The nature of intermolecular forces within semiconductor quantum dot systems can determine various physicochemical properties, as well as their functions, in nanomedical applications. The purpose of this study has been to investigate the nature of the intermolecular forces operating between Al2@C24 and Al2@Mg12O12 semiconducting quantum dots and the glycine tripeptide (GlyGlyGly), and also consider whether permanent electric dipole-dipole interactions play a significant role vis-à-vis these molecular systems. The energy computations, including the Keesom and the total electronic interactions and the energy decomposition, together with the quantum topology analyses were performed. Our results demonstrate that no significant correlation is found between the magnitude and orientation of the electrical dipole moments, and the interaction energy of the Al2@C24 and Al2@Mg12O12 with GlyGlyGly tripeptide. The Pearson correlation coefficient test revealed a very weak correlation between the quantum and the Keesom interaction energies. Apart from the quantum topology analyses, the energy decomposition consideration confirmed that the dominant share of the interaction energies was associated with the electrostatic interactions, yet both the steric and the quantum effects also made appreciable contributions. We conclude that, beside the electrical dipole-dipole interactions, other prominent intermolecular forces, such as the polarization attraction, the hydrogen bond, and the van der Waals interactions can also influence the interaction energy of the system. The findings of this study can be utilized in several areas in the field of nanobiomedicine, including the rational design of cell-penetrating and intracellular drug delivery systems using semiconducting quantum dots functionalized with a peptide.

Experimental and molecular dynamics study of graphene oxide quantum dots interaction with solvents and its aggregation mechanism

This work describes the aggregation process and explains the optical behavior of graphene oxide quantum dots (GOQDs) in different solvents using molecular dynamics, DFT, and experimental observations. The optical behavior of electrochemically synthesized GOQDs in different solvents was analyzed by UV–Vis spectroscopy, and dependence between the spectra and the solvents (water, ethanol, acetone, chloroform, toluene, and n-hexane) was found. Molecular dynamics methods were used to determine that the local structure of the solvent molecules and the nature of intermolecular forces between GOQDs dominate their aggregation state and their optical properties in each solvent. These computational studies based on liquid-liquid systems provide a fast and straightforward approach to develop synthesis and purification methods that allow tailored advanced optical properties of GOQDs.

Molecular insights into ionic liquid/aqueous interface of phosphonium based phase-separable ionic liquids

Phosphonium based phase-separable ionic liquids (PSILs) are promising green solvents for dissolution of cellulose and lignin, a necessary step for conversion of biomass to fuels and chemicals. The knowledge of interfacial behavior of ionic liquid/solvent systems is critical for designing efficient separation processes. Here, molecular dynamics simulations are carried out for aqueous interface of tetraalkylphosphonium ionic liquids with chloride and acetate as anions to investigate IL miscibility with water. The transition zone from miscible to immiscible behavior was observed for alkyl chain lengths of 6 to 8. Emulsion phase was observed for [P8888]+ ion and multiple IL/water interface was observed for [P12121212]+ phosphonium cation. IL/water interface is observed to be enriched with solvated anions with phosphorous atom oriented towards the aqueous phase. The potential of mean force calculations suggest that as the alkyl chain of the phosphonium cations increase, so does the driving force for aggregation of cations in the aqueous phase. Due to the difference in the molecular shape and size, anions are better solvated by the water molecules, and these ions diffuse into the aqueous phase. Furthermore, the analysis of selected pair interactions provides insights into the nature of intermolecular forces and the role of the alkyl side chains on the interfacial properties.

An In-Depth Look at DNA Crystals through the Prism of Molecular Dynamics Simulations

Summary X-ray crystallography is the primary tool for biomolecular structural determination. However, contacts formed through the crystal lattice are known to affect structures, especially for small and flexible molecules such as DNA oligomers, by introducing significant structural changes in comparison to solution. Furthermore, why molecules crystallize in certain symmetry groups, which role crystallization additives play, and whether they are just innocuous and unspecific crystallization catalysts remain unclear. By using one of the currently best-performing DNA force fields and applying significant computational effort, we described the nature of intermolecular forces that stabilize B-DNA crystals in various symmetry groups and solvent environments with an unprecedented level of detail. We showed a tight coupling between the lattice stability and the type of crystallization additives and that certain symmetry groups are stable only in the presence of a specific additive. Additives and crystal contacts induce small but non-negligible changes in the physical properties of DNA.

NO2···NO2 Contacts under Compression: Testing the Forces in Soft Donor–Acceptor Interactions

Intermolecular forces and energies are not directly observable and cannot be retrieved from a crystal structure determination, which simply pictures the resulting equilibrium between forces. In this work, using compression to sample the repulsive part of potentials, we show that high pressure studies may give insight in the nature of intermolecular forces. We focus our attention on controversial π* ← n interactions between NO2 groups, which exhibit several conformations. Using X-ray diffraction and ab initio calculations, we describe the high pressure behavior and phase transition of 4-amino-4′-nitrobiphenyl. To deepen our understanding of the nature of NO2···NO2 interactions, we used several theoretical tools, including pairwise atomic potential energies and forces. The results show that this interaction is associated with a mild stabilization. Since the repulsive forces are experimentally found to be weaker than those of other contacts, we conclude that also the attractive forces are weak, although in e...

Experiments in Dyes and Dyeing Means to better understand the nature of intermolecular forces

<span>The nature of intermolecular forces is responsible for a vast number of phenomena in our everyday life. It can explain for example, trends in solubility, differences in boiling points, adsorption effects (chromatography) and many other observations. Our teaching experience shows that it is not easy to explain this issue to students of all levels, but better understanding can be achieved through experimentation. One of the most effective practical experiences we offer our students at BIU or in high schools deals with dyeing fibers with synthetic or natural dyes.</span>

Classification of global fluid-phase equilibrium behaviors in binary systems

The study of phase equilibria is one of the most important sources of information about the nature of intermolecular forces in liquids and their mixtures and is of the highest importance for designing and optimizing processes. Many of the main features of vapor–liquid and liquid–liquid phase behavior were well characterized experimentally during the early part of the 20th century, and many equations of state were developed to reproduce the many types of phase diagrams observed for binary systems. In spite of the quasi-infinite number of possible configurations and rearrangements of fluid–fluid equilibrium phase diagrams, this paper presents a near-exhaustive classification scheme of fluid phase equilibria in binary systems. It starts from the one proposed by Van Konynenburg and Scott and brings it up-to-date by detailing the progress carried out on this topic since their classification scheme was first proposed. The second part of this paper is devoted to describing the transitions between the various types of systems.

Molecule matters van der Waals molecules

van der Waals introduced his equation of state in 1867 modifying the ideal gas equation. His equation had two constants a and b, which accounted for the fact that molecules have attractive forces and finite size. The constant a accounted for the attractive forces, the nature of which was not outlined by van der Waals. This series of articles will discuss about the nature of intermolecular forces.

Viscous synergy and isentropic compressibility of some monoalkanols and cyclic ethers in water at 298.15 K

Pure or aqueous alcohols are most widely used in industry, including in the manufacture of pharmaceuticals and cosmetic products. However, in the case of insolubility of some solutes in water, non-water solvents may be used possessing the common characteristic of being soluble in water; as a result, such solvents may be used with different purposes, such as increasing water solubility, or modifying the viscosity or absorption of the dissolved substance. Also, the nature of intermolecular forces between the solvents brings a marked effect on the thermodynamic properties such as density, viscosity and surface tension etc. The present study investigates viscous synergy and isentropic compressibility in the systems comprising some monoalkanols (C 1–C 4) and cyclic ethers (1,4-dioxane and tetrahydrofuran) in the proportion w/ w = 1:1, in water at different concentrations ( w/ w) at 298.15 K to determine the proportion of monoalkanol + cyclic ether + water, at which maximum synergy occurs. The density and viscosity data have been analyzed using the equation developed by Kaletunc–Gencer and Peleg. Also a correlation between the density and viscosity increment for all the systems has been attempted. The ratio between maximum viscosity reached by the mixtures and pure state viscosity is expressed by the enhancement index defined as E n = η max/ η 0.

Estimation of Water−Organic Interfacial Tensions. A Linear Free Energy Relationship Analysis of Interfacial Adhesion

The work of adhesion between water and a series of immiscible organic liquids has been found to obey a linear solvation free energy relationship (LSER) on the basis of solute parameters for the organic compound. This relationship, together with the surface tensions of water and of the pure organic liquids, allows reasonably accurate estimation of the corresponding interfacial tensions and provides insight into the nature of intermolecular forces at the water−organic interface. Furthermore, the similarity of this multiparametric LSER to that for partitioning of organic solutes between water and the gas phase (log LW) leads to a much simpler two-parameter relationship. Estimation of the interfacial tension with this latter relationship requires a knowledge of only two parameters, log LW and the surface tension of the pure organic liquid. Since reasonably accurate group contribution methods are available for estimating both log LW and surface tensions from molecular structure, this result provides a novel ap...

Critical Lines and Phase Equilibria in Polymer Mixture Solutions

The study of phase equilibria is historically one the most important sources of information about the nature of intermolecular forces in non-electrolyte liquids and their mixtures. Phase equilibria have also played an important role for the process development in the chemical industry in the last decades. In this paper, critical lines and the phase equilibria of polymer mixture solutions are investigated for various combinations of the chain length parameters. The model used, which was introduced by Gençaslan et al., combines the lattice gas model of Schouten, ten Seldam and Trappeniers with the Flory- Huggins theory. Critical lines are displayed in the density-density, P,T-and T,x-planes for the "right corner" and "left corner" cases. The crossing point, a point at which two critical lines meet and exchange branches, is also calculated analytically. The P,T-diagrams are discussed according to Scott and van Konynenburg phase diagram classifications.

The perturbed-hard-chain theory. Extensions and applications

The Perturbed-Hard-Chain theory (PHCT) was developed by Prausnitz and coworkers in the late 1970s. It can be used to calculate the properties of fluids and fluid mixtures containing both small and large molecules, including polymers, and at all fluid densities. Since that time, the theory has been extended to treat a wider variety of systems. This was done by taking into account several intermolecular interactions which were not considered in the original PHCT. The PHCT and the equations based on it now provide valuable tools for calculating thermodynamic properties of numerous systems since they can treat mixtures of fluids with large differences in molecular size and shape, and differences in both the strength and the nature of intermolecular forces.

The non-additive dispersion energies for N molecules: a quantum electrodynamical theory

With the aid of the Heisenberg operators for the electromagnetic field in the neighbourhood of several molecules, the many-body interaction potentials are calculated by finding the energy of a test molecule in this field. In the first instance the calculation is made for the case where the intermolecular separations are very large. In this far-zone range, the energies depend on the molecules through their static polarizabilities. The three-body non-additive dispersion energy is calculated for an arbitrary configuration and the dependence on the geometry is investigated. The four-body non-additive potential is found for the regular tetrahedral configuration. The theory is extended to cover all separations outside regions of overlap. It is shown that the interaction energy in this case depends on the dynamic polarizabilities. The full Casimir-Polder potential follows directly from the general expression. The near-zone limit of the complete formula tends to the form obtained by using electrostatic couplings only: as with, for example, the Axilrod-Teller potential for N = 3. The work described here presents an alternative viewpoint to the conventional perturbation theory and lends further insight into the nature of intermolecular forces.

Critical lines and phase equilibria in binary van der Waals mixtures

The study of phase equilibria is historically one of the most important sources of information about the nature of intermolecular forces in non-electrolyte liquids and their mixtures. Many of the main features of vapour-liquid and liquid-liquid phase behaviour were already well characterized experimentally during the early part of this century, but the theoretical explanation of phase equilibria for a wide variety of substances and over a large range of pressures and temperatures has lagged far behind. This paper presents theoretical studies of phase equilibria in binary mixtures obeying the van der Waals equation, especially liquid-liquid equilibria that can occur at high pressures. The variety of fluid phase behaviour that occurs in binary mixtures can be qualitatively discussed in terms of the changes in thermodynamic properties near critical points. Upper critical solution temperatures (UCSTs) occur when a heterogeneous (two-phase) system becomes a homogeneous (one-phase) system when the temperature is raised. The maximum temperature along the temperature-mole fraction (T, x) coexistence curve for constant pressure is the UCST at this pressure. Lower critical solution temperatures (LCSTs) occur when a homogeneous system becomes a two-phase system when the temperature is increased. The LCST is at the minimum of theT, xcoexistence curve. Thermodynamic considerations of critical points yield requirements for the curvature of the mixing functions plotted againstx.

Theoretical Basis for Coomber's Relationship

THE almost linear relation found empirically by Coomber1,2 between the dielectric constant e and internal pressure pi for several non-polar liquids appears so far to have received no theoretical justification. By making some assumptions it is possible to show that a simple explanation follows from the nature of intermolecular forces. The internal pressure of a liquid is defined as where E is the potential energy of N molecules occupying a liquid volume V at absolute temperature T. Hildebrand and Scott3,4 have shown that E may be written in the form −a(T).V−n where n is approximately unity for many organic dielectric liquids5, a(T) being slightly dependent on temperature, but not volume, so that pi = n.a(T).V−n−1. If molecular repulsion is assumed5 to contribute negligibly to E, then for non-polar liquids E is due only to the attractive dispersion forces of London5. According to London, the dispersion energy of a molecular pair having random mutual orientation and separation r may be written −3/4.I.α2.f(r), where f(r) = r−6 for monatomic atoms and is a more complicated function for polyatomic molecules; α and I are the atomic or molecular polarizability and ionization potential respectively. Noting that N molecules consist of 1/2N2 molecular pairs and making the usual assumption that E may be calculated from a pair interaction summation, then a(T) may be factorized into a temperature independent part equal to IN2α2 and a temperature dependent part denoted by b(T) which includes numerical constants of the pair summation arising from the interparticle geometry. Thus Assuming the Clausius–Mossoti equation to be valid for non-polar dielectrics, then Thus For the range 2 < e < 3, in which most non-polar dielectric liquids lie, the function (e−1/e+2)2 can be represented by 0.0975e − 0.1325 with a maximum error of ±0.2 per cent. Because n differs from unity by typically 0.1 and b varies slowly4 with T, pi is seen to be a linear function of e, as found by Coomber. Values of I differ from molecule to molecule and so the linear relation found by Coomber between pi and e for different liquids cannot be explained by the theory above. The theory does, however, predict that dielectric constants when extrapolated to zero pi have a value 1.36 for all liquids for which n = 1. Values of n have been given as 1.09, 1.09, 1.05 and 0.89 for hexane4, carbon tetrachloride4, benzene5 and carbon disulphide5 respectively. Coomber1 (his Fig. 2) has plotted e against pi for the liquids hexane, carbon tetrachloride, cyclohexane, benzene and carbon disulphide, and finds each graph to be linear as demanded by the above theory. Moreover, these lines intersect the pi = 0 axis at values of 1.35, 1.37, 1.35, 1.40 and 1.54 respectively, compared with the theoretical intercept of 1.36. The large discrepancy in the case of carbon disulphide may be due to neglect of molecular repulsion forces in the theory. Hildebrand4 has shown that its potential energy does not follow the V−1 law in the density range considered by Coomber.

Linear Relation of Temperature and Density at Unit Compressibility Factor

A linear relation is found for the experimental temperatures and densities at which the compressibility factor PV/RT equals unity. The two characteristic constants of the relation are evaluated for 12 gases for which appropriate data exist. The pertinent range of temperature and density for gases is from the critical temperature to the Boyle temperature, and from zero density to over twice the critical density. For one gas, Ar, the available data extend over this entire range and fit the linear law to within two parts per thousand. For CH4, Xe, and C2H4 over shorter ranges, the data are linear to within a few parts in ten thousand. Implications of the relation are discussed, including its usefulness as a necessary condition for equations of state, as a basis for a corresponding states treatment, as a means for detecting and correcting experimental errors in PVT measurements, and in providing a possible insight into the nature of intermolecular forces.

Viscosity of polar gases

Abstract Viscosity data for several polar gases have been interpreted in terms of a modified Stockmayer potential. Potential parameters have been evaluated by a graphical method. Computed values of viscosity have been compared with the experimental data as function of temperature. This procedure has thrown some light on the nature of intermolecular forces and has lead to the conclusion that the modified potential can be relied upon for moderately polar gases. For highly polar gases, this potential may at best serve the purpose of an empirical correlating function for the experimental data.

Introduction

It was difficult to find a suitable title for this discussion, and perhaps I had better explain at the start why this particular title was chosen and what we shall try to discuss. We now know a good deal about the magnitude and nature of interatomic forces, and much of this knowledge has been acquired from the study of molecular spectra. Less is understood about the nature of intermolecular forces, although a number of experimental methods are being used to examine them. Among these methods, molecular spectroscopy again looks promising, probably because it is now possible to obtain a greater precision of measurement as regards the position and intensity of absorption bands or lines, so that small spectral variations which arise in different physical conditions can be detected. In this way, the effect of neighbour molecules upon an absorbing chromophore can be examined, and attempts can be made to interpret the interactions in terms of the appropriate energy levels. This is the leitmotif of our discussion.

Pressure broadening studies on vibration-rotation bands II. The effective collision diameters

Using the methods described in part I, the line widths in the fundamental vibration rotation bands of deuterium chloride and carbon monoxide have been measured, under conditions of self-broadening and also in the presence of added gases. The optical collision diameters have been calculated an d com pared with the molecular diameters derived from viscosity data. An attempt has been made to interpret the high effective collision diameters found in term s of intermolecular interactions of different types, and it is concluded that London dispersion forces, resonant dipole effects and quadrupole interactions may be important. The variatin of line width in aband as a function of J quantum number has been measured and considered in terms of these interactions. The results suggest th t further studies of this kind may throw further light not only upon the nature of intermolecular forces but also upon the factors affecting energy transfer in collision.