Strength Of Intermolecular Interactions Research Articles

Densities and derived thermodynamic properties of binary mixtures of diethylcarbonate, acetophenone, and 1-hexanol at T = (293.15 to 323.15) K for the liquid region and at ambient pressure

Densities of the binary mixtures of (diethylcarbonate + acetophenone), (diethylcarbonate + 1-hexanol), and (acetophenone + 1-hexanol) were measured at T = (293.15, 303.15, 313.15, and 323.15) K for the liquid region and at ambient pressure over the whole composition range using a vibrating U-tube densimeter. The excess molar volumes V m E , partial molar volumes V ¯ m, i , limiting partial molar volumes V ¯ m, i ∞ , thermal expansion coefficients α, and their excess values α E, and isothermal excess molar enthalpy–pressure derivative ( ∂ H m E / ∂ P ) T , x , were calculated from experimental densities. The binary data of V m E and α E were correlated as a function of the mole fraction by using the Redlich–Kister type function to determine the fitting parameters and the standard deviations. The experimental data of the constituent binaries are analysed to discuss the nature and strength of intermolecular interactions in these mixtures.

Voltammetric Characterization on the Hydrophobic Interaction in Polysaccharide Hydrogels

Cyclic voltammetric (CV) investigations on the properties of microdomains in polysaccharide hydrogels, methyl cellulose (MC) and kappa-carrageenan (CAR), coated on glassy carbon electrodes were reported in which methylene blue (MB), tris(1,10-phenanthroline)cobalt(III) (Co(phen)3(3+/2+)) cations, and ferricyanide/ferrocyanide (Fe(CN)6(3-/4-)) anions were used as electroactive probes. Information on the patterns and strength of intermolecular interactions in these polysaccharide hydrogels can be inferred from the net shift of normal potentials (E degrees'), the change of peak currents (ip), the ratio of binding constants (K(red)/K(ox)) for reduced and oxidized forms of bound species, and the apparent diffusion coefficients (D(app)) of probe in hydrogels. The transition of hydrophobic interaction in MC hydrogel with temperature was manifested by the CV method, which is in agreement with the evolution of the storage modulus (G') during gelation. It was also found that, in addition to inducing the change of E degrees' and ip of these probes used, the hydrophobic-hydrophilic nature of the microenvironment in hydrogels coated on the substrate electrodes greatly influenced the peak-peak separation (DeltaEp) of MB and the redox reversibility of Fe(CN)6(3-/4-) via modulation of both the heterogeneous electron-transfer process at the gel-substrate interface and the charge-transfer process in hydrogels. The results imply that the CV method is of significant benefit to the understanding of the gelation driving forces in the polysaccharide hydrogels at a molecular level.

Nonparallel solutions of extended nematic polymers under an external field

We continue the study on equilibria of the Smoluchowski equation for dilute solutions of rigid extended (dipolar) nematics and dispersions under an imposed electric or magnetic field [25]. We first provide an alternative proof for the theorem that all equilibria are dipolar with the polarity vector parallel to the external field direction if the strength of the permanent dipole ($\mu$) is larger than or equal to the product of the external field ($E$) and the anisotropy parameter ($\alpha_0$) (i.e. $\mu \ge |\alpha_0| E$). Then, we show that when $\mu < |\alpha_0| E$, there is a critical value $\alpha^$*$\geq 1$ for the intermolecular dipole-dipole interaction strength ($\alpha$) such that all equilibria are either isotropic or parallel to the external field if $\alpha \le \alpha^$*; but nonparallel dipolar equilibria emerge when $\alpha > \alpha^$*. The nonparallel equilibria are analyzed and the asymptotic behavior of $\alpha^$* is studied. Finally, the asymptotic results are validated by direct numerical simulations.

Non-adiabatic E → D, D′, β, γ, δ transitions in the first ion-pair tier of molecular iodine induced by collisions with I 2, He, Ar, Kr, Xe

Optical–optical double resonance spectroscopy and quantum scattering calculations are used to obtain total rate constants, electronic branching ratios, and vibrational product state distributions for non-adiabatic transitions among the first-tier ion-pair states of the I 2 molecule excited to the E 0 g + , v E = 8 , 19 , J E ≈ 55 rovibronic levels in collisions with I 2, He, Ar, Kr and Xe. Theoretical predictions agree well with the experiment and reveal that the near-resonant E 0 g + → D0 u + transition dominates for collisions with He, while somewhat more statistical distributions are typical of collisions with heavier rare gas atoms. This trend is correlated to the dipole polarizability of the collision partner that determines the strength of intermolecular interactions.

Structure−Property Correlations in Bending and Brittle Organic Crystals

Bending of crystals of molecular solids occurs when the strength of intermolecular interactions in orthogonal directions is significantly different. We report here a survey of 60 molecular crystals and establish a causative correlation between bending and crystal packing. This group contains crystals with 4 and 8 Å crystal axes and includes 1D, 2D, 3D, isostructural, polymorphic, stacked, interlocked, single, and multicomponent crystals and solvates. We found that 17 of these 60 crystals may be bent, whereas the rest are brittle and cannot be bent plastically. The bending crystals could be deformed into many shapes; sometimes, they could even be flattened upon themselves without breakage. A model for bending is proposed using the information obtained from X-ray diffraction, face indexing, and mechanical property measurements on both bending and non-bending (brittle) crystals. The bending and brittleness of these molecular crystals are discussed in comparison with the deformation behavior of metals. Molecular crystals show practically no change in volume and the lengths of the inner and the outer arcs and the sample thickness are unchanged following plastic bending. This is in contrast with the bending of metallic materials, in which a decrease in thickness is evident. Isotropic crystals with comparable intermolecular interactions in the three orthogonal directions are “cross-linked” and do not bend; they are hard and brittle. Mechanical properties of molecular crystals are important because they vary with the crystal form and have major implications for large-scale processing and handling of materials in industry, especially the pharmaceutical industry.

Miscibility with Asymmetrical Interactions in Blends of Two Carbonyl‐Containing Polymers: Poly(vinyl acetate) with Aliphatic Polyesters

AbstractSummary: Phase behavior, miscibility, or immiscibility in blends of two polymers with carbonyl groups, PVAc and homologous polyesters of different CH2/CO ratios, were examined using DSC, OM and SEM. Polyesters used in this study included PES, PEA, PPA, and PBA. PVAc/polyester blends were found to be immiscible with distinctly a two‐phase morphology when the polyesters' structural CH2/CO ratios are lower than 3 or higher than 4; whereas miscibility is seen in three blend systems: PVAc/PEA (CH2/CO = 3.0), PVAc/PPA (CH2/CO = 3.5), and PVAc/PBA (CH2/CO = 4.0). Asymmetry in the Tg‐composition relationships is seen in all three miscible blend systems. Such non‐specific, weak and asymmetrical interactions, though sufficient to maintain borderline miscibility in the blends, may be partially responsible for leading to the noted asymmetry in the Tg‐composition relation of the blends. Mechanism and origin of this phenomenon of asymmetry in Tg‐composition relationships in some blends may be still puzzling. Strictly speaking, the non‐equilibrium phenomenon of glass transition may not be ideal for evaluating the strength of intermolecular interactions in blends. Future perfection on more suitable approaches may yet be needed.Tg vs. composition for the miscible PVAc/PPA blend.magnified imageTg vs. composition for the miscible PVAc/PPA blend.

Polaron dynamics in highly ordered molecular crystals

From a numerical solution of the time-dependent Schrödinger equation and the lattice equation of motion we obtain a microscopic picture of polaron transport in highly ordered molecular crystals in the presence of an external electric field. We have chosen the pentacene single crystal as a model system, but study the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaronic drift process over the regime 20 < J < 120 meV. For intermolecular interaction strengths above ∼120 meV the polaron is no longer stable and the transport becomes band like.

Directed Assembly and Separation of Self-Assembled Monolayers via Electrochemical Processing

Separated domains of 1-dodecanethiolate were fabricated via solution displacement of preformed 1-adamantanethiolate self-assembled monolayers on Au{111}. Subsequently, the 1-adamantanethiolate domains were desorbed selectively, and the substrate was exposed to a 1-octanethiol solution, creating artificially separated self-assembled monolayers of 1-dodecanethiolate and 1-octanethiolate. The molecular order of each lattice type and the apparent height differences imaged with scanning tunneling microscopy and the two distinct cathodic peaks observed with cyclic voltammetry indicated distinct separated domains of each lattice type in the separated self-assembled monolayers. By manipulating the intermolecular interaction strengths of the patterned molecules, we are able to control the structure and properties of the separated self-assembled monolayers via the exploitation of competitive adsorption and the utilization of electrochemical processing, which can be extended to other self-assembly patterning techniques such as microdisplacement printing.

Confinement Effect in Diffusion-Controlled Stepwise Polymerization by Monte Carlo Simulation

Diffusion-controlled stepwise polymerization of a linear polymer confined in nanoscopic slits is simulated through a Monte Carlo approach. A noticeable influence of the confinement on the kinetics is found. The confinement modifies both the spatial pair distribution function and the diffusive properties of the polymers. As a consequence, the confined system can show either faster or slower reaction kinetics with respect to the bulk system, depending on the strength of intermolecular interactions. The predicted polydispersity of the polymer is in agreement with recent theories of diffusion-controlled stepwise polymerization, and can be slightly affected by the confinement.

AN AB INITIO STUDY OF INTERMOLECULAR INTERACTION OF HYDROGEN FLUORIDE TETRAMER

Possible HF tetramer geometries have been optimized employing the density functional B3LYP method and the aug-cc-pVQZ basis set. Deformation energy has been calculated at the B3LYP/aug-cc-pVQZ level. After the BSSE correction with the CP method, two-body intermolecular interaction energy, three-body nonadditive intermolecular interaction energy, and four-body nonadditive intermolecular interaction energy (Δ E c[4]) have been obtained at the levels of B3LYP/aug-cc–pVQZ, B3LYP/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ, and MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ. Calculated results show that the three-body nonadditive intermolecular interaction energy is important for the optimized structures of HF tetramer. At the MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ level, the four-body nonadditive intermolecular interaction strength arrives at -4.5kJ/mol in the optimized eight-membered ring structure, but is extremely weak in other optimized structures. The comparison between MP2 and B3LYP calculated intermolecular interaction energies shows that the B3LYP method is applicable to the calculation of the intermolecular interaction energy of HF tetramer when the basis set reaches aug-cc-pVTZ. ΔEc[4] occupies 8–32% of the total intermolecular interaction energy when the intermolecular distances of the eight-membered ring structure are in the range of 1.06–1.37 Å.

Structure–property relationships for sulfonated poly(butylene terephthalate)

AbstractStructure–property relationships have been developed for sulfonated poly(butylene terephthalate) copolymers. The compositional variables investigated were sulfonate content, molecular weight, and polymer endgroup composition, and the fundamental polymer properties evaluated were melt viscosity, crystallization kinetics, and impact strength. It was found that all compositional variables significantly affect all of the polymer properties of interest. The most interesting effect is the influence of polymer endgroup composition on polymer properties. The trends indicate that the carboxylic acid endgroups form intermolecular interactions with sodium sulfonate groups, resulting in a decrease in the strength of intermolecular ionic interactions between sodium sulfonate groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4662–4771, 2006

Excess molar volumes and dynamic viscosities for binary mixtures of toluene + n-alkanes (C 5–C 10) at T = 298.15 K – Comparison with Prigogine–Flory–Patterson theory

Densities ρ, dynamic viscosities η, for binary mixtures of toluene with some n-alkanes, namely, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane have been measured over the complete composition range. Excess molar volumes V E, viscosity deviations Δ η, and excess Gibbs free energy of activation Δ G ∗E, were calculated there from and were correlated by Redlich–Kister type function in terms of mole fractions. For mixtures of toluene with n-pentane and n-hexane the V E is negative and for the remaining systems is positive. The Δ η values are negative for all the studied mixtures. The Δ G ∗E values shows the positive values for the binary mixtures with n-decane, whereas the negative values have been observed for all the remaining binary mixtures. From the results, the excess thermal expansivities at constant pressure α E, is also estimated. The Prigogine–Flory–Patterson (PFP) theory and its applicability in predicting V E is tested. The results obtained for viscosity of binary mixtures were used to test the semi-empirical relations of Grunberg and Nissan, Tamura and Kurata, Hind et al., Katti and Chaudhri, McAllister, Heric, Kendall, and Monroe. The experimental on the constituted binaries are analyzed to discus the nature and strength of intermolecular interactions in these mixtures.

Thermal Resistance of Nanoscopic Liquid−Liquid Interfaces: Dependence on Chemistry and Molecular Architecture

Systems with nanoscopic features contain a high density of interfaces. Thermal transport in such systems can be governed by the resistance to heat transfer, the Kapitza resistance (RK), at the interface. Although soft interfaces, such as those between immiscible liquids or between a biomolecule and solvent, are ubiquitous, few studies of thermal transport at such interfaces have been reported. Here we characterize the interfacial conductance, 1/RK, of soft interfaces as a function of molecular architecture, chemistry, and the strength of cross-interfacial intermolecular interactions through detailed molecular dynamics simulations. The conductance of various interfaces studied here, for example, water-organic liquid, water-surfactant, surfactant-organic liquid, is relatively high (in the range of 65-370 MW/m2 K) compared to that for solid-liquid interfaces ( approximately 10 MW/m2 K). Interestingly, the dependence of interfacial conductance on the chemistry and molecular architecture cannot be explained solely in terms of either bulk property mismatch or the strength of intermolecular attraction between the two phases. The observed trends can be attributed to a combination of strong cross-interface intermolecular interactions and good thermal coupling via soft vibration modes present at liquid-liquid interfaces.

Fluorescence approaches for monitoring interactions of Rho GTPases with nucleotides, regulators, and effectors

To understand the manner in which biological macromolecules interact with each other, we need not only structural information, but also details of kinetics and thermodynamics of the processes involved. This is particularly important for key proteins acting in signal transduction such as the small GTPases of the Ras superfamily. The complexity of their roles is constantly increasing since a large number of GTPases have been identified and each of these in turn interacts with a variety of regulatory and signaling proteins such as GAPs, GEFs, and downstream effectors. There are a number of methods that can be used to characterize the specificity, strength, and stoichiometry of such intermolecular interactions, to understand the effect of binding on the protein structure, and, ultimately, to obtain insights into their biological functions. This article discusses the use of fluorescence spectroscopic methods, which allows real-time monitoring of ligand- and protein–protein interactions at submicromolar concentrations, and quantification of the kinetic and equilibrium constants. Fluorescently labeled guanine nucleotides serve as fluorescence reporter groups to investigate the interactions of GTPases of the Rho family (e.g., RhoA, Rac1, and Cdc42). We present examples for quantitative characterization of (i) Rac1·GDP interaction, (ii) Cdc42-interaction with the GTPase binding domain of the Wiskott Aldrich syndrome protein (three alternative approaches), (iii) accelerated nucleotide exchange reaction of RhoA by the catalytic domains of p190RhoGEF, and (iv) intrinsic and stimulated GTP-hydrolysis reaction by the catalytic domain of p50RhoGAP.

Viscosities and Excess Molar Volumes of the Ternary System Toluene (1) + Cyclohexane (2) + Pentane (3) at 298.15 K

The viscosity and density of ternary mixtures of toluene (1) + cyclohexane (2) + pentane (3) have been measured at 298.15 K and atmospheric pressure over the entire range of compositions. Excess molar volumes (V E) and viscosity deviations (Δη) were obtained from the experimental results for the binary and ternary systems and fitted to Redlich−Kister's and Cibulka's equations in terms of mole fractions. The data was positive, and inversion of the sign was observed over some concentrations at x ≈ 0.2 for mixtures at three fixed compositions (fm = x1/x2). The Δη123 data were negative values at three fixed compositions. The results obtained for excess molar volume and viscosity of liquid mixtures were used to test the semiempirical relations of Tsao−Smith, Jacob−Fitzner, Kohler, Rastogi et al., Radojkovic et al., Colinet, Toop, and Scatchard et al. The experimental and the constituted ternaries are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures.

Volumetric and viscometric studies of molecular interaction of the ternary system toluene (1) + cyclohexane (2) + n-hexane (3) at 298.15 K

The densities ρ, and viscosities η, of pure toluene, cyclohexane, and n-hexane and those of their binary and ternary mixtures have been measured at 298.15 K and atmospheric pressure over the entire range of compositions. Excess molar volumes V 123 E , viscosity deviations Δ η 123, and excess Gibbs energy of activation G 123 * E , were obtained from the experimental results and those values for the binary and ternary systems were fitted to Redlich–Kister's and Cibulka's type function in terms of mole fractions. The V 123 E data were positive and Δ η 123 and G 123 * E , values were negative. Several semi-empirical relations are used to predict the ternary excess molar volumes and viscosity deviations from experimental results on the constituted ternary and analyzed to discuss the nature and strength of intermolecular interactions in these mixtures.

Thermodynamics of anionic dye–cationic surfactant interactions in cationic–nonionic surfactant mixtures in comparison with binary systems

The thermodynamics of the interactions between the anionic dye Acid Red 88 (AR88) and the cationic surfactant dodecyltrimethylammonium bromide (DTA) in the aqueous solution of the nonionic surfactant Triton X-100 (TX100) at different temperatures has been investigated by using potentiometry. The standard free energy change, Δ G o 1, the standard enthalpy change, Δ H o 1, and the standard entropy change, Δ S o 1, for the first association step of DTA–AR88 complex formation in the presence of TX100 micelles were determined and compared to the thermodynamic functions of DTA–AR88 and DTA–TX100 interactions in binary systems. From Δ G o 1 results, it has been observed that irrespective of the studied temperature the binding free energy of DTA cation to AR88 anion as well as the complex stability is lower in TX100 solution than in binary mixture. The increase in the TX100 concentration causes the decrease in the tendency of DTA–AR88 complex formation. From this it can be seen that the mode and the strength of intermolecular interactions strongly depend on the presence of TX100 micelles. The values of Δ H o 1 and Δ S o 1 for DTA–AR88 complex formation in TX100 solution which are directly affected by the ratio of AR88 and TX100 concentrations are much higher compared to those obtained in binary mixtures without TX100. These results also lead to a conclusion that the binding of DTA cation to AR88 anion in the presence of TX100 micelles, which is an entropy-driven process, is much more different from the enthalpy-controlled formation process of DTA–AR88 complex in binary mixtures.

Molecular Structure Dependence of the Phase Transition Spike Response of Viologens at an HOPG Electrode Using Bisviologen and Carboxylated Viologen

Behavior of a bisviologen and a carboxylated viologen in their faradaic phase transition at a highly ordered pyrolytic graphite (HOPG) electrode between a gas-like adsorption layer and a two-dimensional condensed phase was studied. Bisviologen (bis-V) possesses two -bipyridinium moieties, and a carboxylated viologen (V-COOH) does carboxyl groups at both terminals of the alkyl chains. The results of the voltammetric measurements were compared with heptyl viologen (HV) with a focus on the intermolecular lateral interaction among radical cations of the viologens in the condensed phase. It was found that the intermolecular attractive interaction between neighboring reduced forms of bis-V is stronger than that of HV, indicating that intermolecular stacking of two radical cation moieties per molecule appears dominant over the negative effect of the possible chance of the presence of out-of-gear molecule pairs due to the mismatch in the neighboring molecule stacking upon the transition. The potential width of the bistable region of the phase transition for V-COOH exceeded in an acidic medium due to the effective positive contribution of hydrogen bonding to the intermolecular attraction in the condensed phase on the hydrophobic basal plane of the HOPG electrode, while the contribution vanished in a basic medium. These results revealed that the voltammetric spike response of the phase transition can be a direct measure of the strength of two-dimensional intermolecular interaction on the electrode surface. Characteristics of the phase transition behavior of V-COOH were also described in regard to temperature, concentration, and potential sweep rate dependencies. Implications of these characteristics were discussed in consideration of the dynamics of the assembling process of reduced forms of V-COOH into the condensed layer. In the tests of the additives, only trimesic acid among the carboxylic acids used exhibited the activity as a hydrogen bonding inhibitor.

Volumetric, ultrasonic and viscometric studies of molecular interactions in binary mixtures of aromatic+aliphatic alcohols at different temperatures

The densities, ρ, ultrasonic speeds, u and viscosities, η of pure benzyl alcohol, 1-propanol, 2-propanol and those of their binary mixtures, with benzyl alcohol as a common component, have been measured at 298.15, 303.15, 308.15 and 313.15 K over the entire composition range. The excess molar volume, V E, deviation in isentropic compressibility, Δk s , excess thermal expansivity, αE, deviations in ultrasonic speed, Δu and viscosity, Δη, partial molar volume and compressibility, and of 1-propanol/2-propanol in benzyl alcohol at infinite dilution have been evaluated from the experimental data. The results have been used to discuss the nature and strength of intermolecular interactions in these mixtures. The V E values have also been calculated theoretically by using the Flory's statistical theory and Prigogine–Flory–Patterson theory. The calculated V E values were found in good agreement with the experimental V E values. The thermal expansivity, α and isothermal compressibility, k T have been calculated theoretically by using Flory's theory and various hard sphere models, and were compared with experimental α and k T values.

Intra and intermolecular hydrogen bonding effects in the electrochemical reduction of α-phenolic-naphthoquinones

The electrochemical reduction of 1,4-naphthoquinone (NQ), 5-hydroxy-1,4-naphthoquinone (HNQ) and 5,8-dihydroxy-1,4-naphthoquinone (H 2NQ) has been studied in dimethylsulfoxide and acetonitrile, both in the absence and in the presence of proton donors such as methanol and acetic acid. It was established that the intervention of intramolecular hydrogen bonds in the α-phenolic-naphthoquinones (β-hydroxy-naphthoquinones) contributes significantly to the stabilization of the quinone reduced species. This effect is particularly important as a factor determining the strength of intermolecular interactions between the quinone dianion and proton donors. The intramolecular hydrogen bond diminishes the association capacity of the quinones and of their reduction products with molecules of methanol, and avoids the protonation of the semiquinone with acetic acid, favoring only association processes. The low reactivity of the reduced intermediates towards the protonation by acetic acid suggests that analogues structures of HNQ and H 2NQ will not be protonated.