Aggregate formation in oil and adsorption at oil/water interface: thermodynamics and its application to the oleyl alcohol system

The thermodynamic equations for examining aggregate formation in an oil phase and adsorption at the oil/water interface of a nonionic solute were derived. The total differentials of chemical potentials of species and the oil/water interfacial tension were expressed as functions of temperature, pressure, and the total concentration of solute in the oil phase after explicit consideration of aggregate formation. The partial derivatives of the chemical potentials and the interfacial tension with respect to the independent variables were found to provide the thermodynamic quantities of aggregate formation and adsorption from oil phase to the interface by introducing the concept of an ideally dilute associated solution. These equations were applied to the cyclohexane solution of oleyl alcohol/water system, and the adsorption and aggregate formation was examined.     

Photoinduced electron transfer at the polymer-solution interface. I. Surface property-reactivity relation

Photooxidation of leuco crystal violet(LCV) to the dye(CV⁺) by interfacial sensitization with polymer-bonded pyrenyl groups was studied. Poly(ethylene-g-acrylic acid) was esterified by 1-hydroxymethylpyrene in tetrahydrofuran (THF) (Film 1) or in acetonitrile (Film 2). Film 2 had a more condensed but thinner pyrene-containing surface layer than Film 1. Differences in surface structure were investigated by fluorescence and absorption spectra, as well as by measuring contant angle to water as a function of the total amount of bonded pyrene. Films 1 and 2 behaved differently in the photoreaction, which was interpreted as due to the difference in the affinity of LCV solution to the film surface, hence the diffusion of LCV into the film. The quantum efficiency of CV⁺ formation (?cv⁺) is therefore the function of the thickness of the photoabsorbing layer and the effective reaction volume determined by the depth of LCV diffusion. The role of excimer formation and energy migration among pyrenyl groups was concluded to be of minor importance.     

Surface wetting in liquid-liquid-solid triphase systems: solid-phase-independent transition at the liquid-liquid interface by lewis Acid-base interactions

Interfacial phenomena: A solid-phase-independent strategy for tuning the surface wettability is presented. Lewis acid-base interactions at the oil-water interface can greatly decrease the liquid-liquid interfacial tension and induce oleophilic to superoleophobic wetting transition on a nonresponsive microstructured surface.     

Surface thermodynamics of osteoblasts: relation between hydrophobicity and bone active biomaterials

Surface tensions of rat calvaria osteoblasts were determined by measuring the cell–liquid–vapor contact angle with sessile drops of water on the cell monolayer. The results indicated the hydrophobic character of osteoblastic cells with a contact angle of 26.89° (0.29°). This value could explain the ability of osteoblasts to specifically attach onto hydrophobic surfaces like titanium or hydroxyapatite. The first cellular step of bone healing requires the presence of osteoblasts and their adhesion to biomaterial surfaces is the crucial phase of the osteointegration process. The presence of a monolayer of a newly discovered hydrophobic bacterial exopolysaccharide on coverglass slides appeared to strongly encourage adhesion of osteoblastic cells. In that, providing surfaces with this hydrophobic material induced a selective adsorption of osteoblast cells and might enhance osteointegration.     

Specific intermolecular interactions in a heterogeneous system benzophenone-titanium dioxide

IR spectroscopy methods (experiment, theoretical simulation) have been applied to study the structural features and intermolecular interactions in a two-component heterogeneous nano-size system benzophenone-titanium dioxide (BPh-TiO₂). IR spectra of the sample were recorded at room temperature within the range 400–4000 cm^?1. The spectra display hydrogen bonding determining the intermolecular interactions between titanium dioxide, BPh molecules, and water in the near-surface layers of nanocrystalline TiO₂ particles. IR spectra of free BPh molecules, water, model H-complexes of BPh with water, and the fragment of hydrated titania surface (BPh…HOH and BPh…Ti≡) have been simulated. Experimental and theoretical spectra were analyzed in the region of stretching vibrations of carbonyl, hydroxyl, and other groups sensitive to a variation of intermolecular interactions. It is found that hydrogen bonding in the near-surface layers of nanocrystalline TiO₂ particles in the two-component heterogeneous nanosystem BPh-TiO₂ gives rise to the formation of complexes BPh-O-Ti(OH)-O-, BPh…HOH, along with complexes of-O-Ti(OH)-O-with water and pure water complexes.     

Surface segregating kinetics in a ternary system

The physical metallurgy of iron and steel is exceedingly complicated and many of the complications arise from the behavior of solutes, which segregate to surfaces and interfaces, which alter the mechanical behavior. The modified Darken model was used to describe the complex segregation behavior of the species involved. Trends in the surface concentration changes as describe by the Darken model for a ternary alloy are shown. Simulations were done for different interaction parameters, different bulk concentrations of the species, different segregation energies of the species and different mobilities (diffusion coefficient and activation energy). Copyright © 2004 John Wiley & Sons, Ltd.     

Surface potential at the hematite-water interface

Construction of a metal oxide electrode enabling measurement of surface potential is described. The electrode was made using a hematite monocrystal, which avoids the problems arising from the possible porosity of the oxide layer. The potential of this electrode was measured as a function of pH. The hematite electrode provides reproducible results, especially in the acidic region. Surface potentials were calculated from electrode potentials using the electrokinetic isoelectric point. The slope of surface potential with respect to pH was found to be lower than the Nernstian, especially in the basic region. The effect was more pronounced at higher ionic strengths. It was shown how the measurement of surface potential can help to interpret the equilibrium data and evaluate the choice of a theoretical model describing the interfacial equilibrium at the metal oxide-water interface.     

The intermolecular interactions in the aminonitromethylbenzenes

The intermolecular non-covalent interactions in aminonitromethylbenzenes namely 2-methyl-4-nitroaniline, 4-methyl-3-nitroaniline, 2-methyl-6-nitroaniline, 4-amino-2,6-dinitrotoluene, 2-methyl-5-nitroaniline, 4-methyl-2-nitroaniline, 2,3-dimethyl-6-nitroaniline, 4,5-dimethyl-2-nitroaniline and 2-methyl-3,5-dinitroaniline were studied by quantum mechanical calculations at RHF/311++G(3df,2p) and B3LYP/311++G(3df,2p) level of theory. The calculations prove that solely geometrical study of hydrogen bonding can be very misleading because not all short distances (classified as hydrogen bonds on the basis of interaction geometry) are bonding in character. For studied compounds interaction energy ranges from 0.23 kcal mol⁻¹ to 5.59 kcal mol⁻¹. The creation of intermolecular hydrogen bonds leads to charge redistribution in donors and acceptors. The Natural Bonding Orbitals analysis shows that hydrogen bonds are created by transfer of electron density from the lone pair orbitals of the H-bond acceptor to the antibonding molecular orbitals of the H-bond donor and Rydberg orbitals of the hydrogen atom. The stacking interactions are the interactions of delocalized molecular π-orbitals of the one molecule with delocalized antibonding molecular π-orbitals and the antibonding molecular σ-orbital created between the carbon atoms of the second aromatic ring and vice versa.      

Energy screening for the incremental scheme: application to intermolecular interactions

A systematic screening procedure for small contributions in the incremental expansion of the correlation energy is presented. The performance of the proposed scheme is checked for the calculation of intermolecular interactions in realistic test systems as large as a guanine-cytosine base pair. It is found that the computational cost for the incremental expansion can be reduced considerably without significant loss of accuracy. Typically, the errors of the systems investigated here amount to <3.4, 0.22, and 0.06% for second-, third-, and fourth-order expansions, respectively. For almost all cases, the error in the total correlation energy can be kept below 1 kcal/mol with respect to the canonical CCSD result if the incremental series is truncated in a proper way.     

Surface light-scattering at the air-liquid interface: from newtonian to viscoelastic polymer solutions

The dynamics of the liquid-air interface of aqueous solutions of a tensioactive triblock copolymer (Pluronic F-68) has been studied using surface quasielastic light scattering over a broad range of concentrations and temperatures. Ancillary surface tension and bulk rheometry data have been obtained for the same system. The results show that the classical theoretical spectrum for monolayers on a Newtonian fluid can be applied only for concentrations below 4.10(-2) mM. For concentrations above c = 14 mM a clear peak centered at zero frequency appears in the spectrum. This feature is incompatible with the classical theoretical spectrum. The SQELS spectra have been described in terms of the theory of Wang and Huang [Wang, C. H.; Huang, Q. R. J. Chem. Phys. 1997, 107, 5898] considering that the loss modulus of the concentrated solutions shows the existence of two relaxation modes even at low frequencies. The theory is able to explain the existence of a peak centered at zero frequency in the spectra, and the theoretical spectra point out the existence of an elastic peak together with the capillary one. There is a reasonable agreement between the relaxation times and the product Gtau obtained from the fits of the SQELS spectra to the theory of Wang and Huang and those obtained from bulk rheology.     

Surface tension and capillary waves at the nematic-isotropic interface in ternary mixtures of liquid crystal, colloids, and impurities

In mixtures of thermotropic liquid crystals with spherical poly(methyl methacrylate) particles, self-supporting networklike structures are formed during slow cooling past the isotropic-to-nematic phase transition. Experimental results support the hypothesis that a third component, alkane remnants slowly liberated from the particles, plays a crucial role. A theoretical model, based on the phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories, is developed to describe the continuous phase separation in a ternary nematic-impurity-colloid mixture. The interfacial tension and the dispersion relation of the surface modes of the nematic-isotropic interface are determined. The colloids decrease the interfacial tension and the damping rate of surface waves, whereas impurities act in an opposite way. This should strongly influence the formation of abovementioned networklike structures and could help explain some of their rheological properties.     

Surface activity and orientation of inosine at a mercury/solution interface

Summary A systematic investigation on the adsorption and association of inosine at a hanging mercury drop electrode by phase-sensitive ac voltammetry has been performed. The adsorption equilibrium bas been determined as a function of various parameters such aspH, adsorption potential, adsorption time, and bulk concentration of inosine. It was found that the association of the adsorbed species depends predominantly on the stacking interactions of neutral inosine molecules. Over a wide potential range, inosine exhibits a dilute adsorption characteristic where it is adsorbed with the base flat on the electrode surface. Above a certain threshold value, inosine appears to undergo a surface reorientation and adopts a perpendicular position. The nucleation and growth mechanism is analyzed applying theAvrami equation. Characteristic properties and adsorption parameters of dilute and compact layers of inosine were evaluated from the two-stepFrumkin isotherm and from the potential dependence of adsorption.

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Oberflächenaktivität und Orientierung von Inosin an einer Quecksilber/Lösungs-Grenzfläche

Zusammenfassung Die Adsorption und Assoziation von Inosin an einer Quecksilbertropfelektrode wurde mittels phasensensitiver AC-Voltammetrie systematisch untersucht. Die Abhängigkeit des Adsorptionsgleichgewichts von Parametern wiepH-Wert, Adsorptionspotential, Adsorptionszeit und Inosinkonzentration wurde gemessen. Dabei zeigte sich, daß die Assoziation der adsorbierten Spezies vorwiegend von der Anordnung und den Wechselwirkungen der neutralen Inosinmoleküle abhängt. Inosin bildet über einen weiten Potentialbereich eine dünne Adsorptionsschicht aus, wobei die Base flach auf der Elektrodenoberfläche aufliegt. Ab einem bestimmten Grenzwert der Konzentration tritt eine Reorientierung zu einer senkrechten Anordnung ein. Keimbildung und Wachstumsmechanismus wurden mittels derAvrami-Gleichung analysiert. Eigenschaften und Adsorptionsparameter der verdünnten und der kompakten Inosinschicht konnten aus der zweistufigenFrumkin-Isotherme und aus der Potentialabhängigkeit der Adsorption bestimmt werden.

     

Applications of the simulated annealing method to intermolecular interactions

The Simulated Annealing method using a quantum mechanical potential energy surface is used to study the interactions of molecules and the formation of clusters. The results obtained for a range of systems are in good agreement with other theoretical calculations and experimental data where available.     

Structural characterization of crystalline ternary inclusion compounds at the air-water interface

Crystalline ternary inclusion monolayers consisting of a two-dimensional hydrogen-bonded host network of guanidinium (G) ions and organosulfonate (S) amphiphiles, and biphenylalkane guests, can be generated at the air-water interface through synergistic structural enforcement by hydrogen bonding and host-guest packing. Surface pressure-area isotherms of the 4'-hexadecylbiphenyl-4-sulfonate (C16BPS) amphiphile in the presence of G, with or without guest, are characterized by lift-off molecular areas expected for the GS sheet based on single-crystal X-ray structures of homologous bulk crystals. Intercalation of biphenylalkane guests (4-C(n)()H(2)(n)()(+1)-C(6)H(4)-C(6)H(5), n = 1, 4, 6, 10, 16; denoted CnBP) between organosulfonate hydrophobes, which define pocketlike cavities in the GS monolayer host, afford ternary inclusion monolayers with a 1:1 host-guest stoichiometry. These inclusion monolayers are less compressible than the guest-free host, consistent with dense packing of the biphenylalkane moieties of the host and the biphenylalkane guests. The inclusion monolayers are distinguished from the amorphous guest-free host and from selected guanidinium-free mixed monolayers by structural characterization with grazing-angle incidence X-ray diffraction (GIXD). The GIXD data for the ternary (G)C16BPS:C16BP and (G)C16BPS:C6BP inclusion monolayers obtained upon compression are consistent with a rectangular unit cell. The dimensions of these unit cells and refinement of the GIXD data suggest a "rotated shifted ribbon" GS hydrogen-bonding motif similar to that observed in some bulk GS crystals, including (G)(ethylbiphenylsulfonate). GIXD reveals that (G)C16BPS:C16BP and (G)C16BPS:C6BP are more crystalline than the corresponding guanidinium-free mixed monolayers. The (G)C16BPS:C6BP inclusion monolayer is stable upon compression, even though the alkyl-alkyl host-guest interactions are reduced due to the shorter hexyl substituents of the guest, demonstrating an important reinforcing role for the hydrogen-bonded GS sheet. The structure of a C16BPS:tetracosane (C24) mixed monolayer is independent of G; the unit cell symmetry and dimensions suggest a structure governed by alkyl-alkane interactions that prohibit formation of a GS network. These results illustrate that the existence of ternary inclusion monolayers with an intact GS network requires guest molecules that are structurally homologous with the hydrophobes of the host, in this case biphenylalkanes. The observation of these inclusion compounds suggests an approach for introducing functional nonamphiphilic molecules to an air-water interface through inclusion in a well-defined host.     

Tuning the photocatalytic activity of CdS nanocrystals through intermolecular interactions in ionic-liquid solvent systems

Synthetic solvent systems for the fine-tuned preparation of CdS nanocrystallites, active in visible-light photocatalytic hydrogen production, were studied. To control crystallite size and spectral properties, the CdS crystals were synthesised by using different solvent systems, containing a series of tetrabutylammonium amino carboxylate ionic liquids as the crystal-growth control agents. Six samples of CdS, all with similar physical and spectral properties, exhibited greatly varying photocatalytic activity, with the most active sample outperforming the least active one by almost 60%. To rationalise this effect, the intermolecular interactions of the synthesis solvent system with the growing CdS nanocrystallites were characterised by using the Reichart betaine dye and the E(T)(N) polarity scale. A correlation was observed between the E(T)(N) values of the solvent system and the photocatalytic activity of the CdS nanocrystallite, suggesting that the hydrogen-bond-donating ability and/or dipolarity/polarisability interactions of the solvent system led to the preferential formation of active surfaces/surface sites on the CdS crystals.     

13C NMR study of the intermolecular interactions in the polyethylene glycol-cellulose acetate-solvent system

As a result of measuring the spin-lattice relaxation rates of¹³C nuclei of polyethylene glycol in different solvents in the presence of cellulose acetates, it was found that polyethylene glycol forms H complexes with cellulose acetate in nonaqueous solvents, and the probability of binding increases with a decrease in the molecular weight of the polyethylene glycol. The formation of H complexes results in an effect of inversion of the mobility of the polyethylene glycol molecules of different weights in concentrated solutions of a mixture of polymers. The value of the effect is determined by the donor-acceptor properties of the solvent and the degree of substitution of hydroxyl groups by acetate groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1766–1768, August, 1989.     

A model study of the intermolecular interactions of amino acids in aqueous solution: The glycine-water system

We have performed calculations of the glycine zwitterion surrounded by water molecules with the help of the mutually consistent field (MCF) method and perturbation theoretical expressions. Two different models for the hydration shell have been chosen, the glycine·6H₂O and glycine·12H₂O complexes, representing the most probable first and second solvation shell, respectively. To calculate the exchange and charge transfer energy contributions we have applied approximative expressions derived from perturbation theory for weakly overlapping subunits. For the sake of comparison we also calculated the interaction energy in the supermolecule approach for the smaller of the two solvation complexes. Furthermore, we have investigated the part of the potential energy surface which is determined by varying the lengths of the hydrogen bonds between glycine and water in the complex glycine·12H₂O using the electrostatic approach. The exchange energy contribution to the interaction energy for different points on the surface was approximated with the help of an analytical expression fitted to three directly calculated points. For the charge transfer energy a polynomial expansion of second order was established on the basis of five values, computed with the aid of the perturbation theoretical expression. To get a more detailed insight in the relatively strong hydrogen bonds between the water molecules and the ionic hydrophilic parts of glycineab initio model studies on NH ₄ ⁺ ·3H₂O and HCOO⁻·3H₂O systems are reported.     

Bistability in Fc-PTM crystals: the role of intermolecular electrostatic interactions

Fc-PTM is a valence tautomeric radical, where the ferrocene (Fc) group, a good electron donor, is linked by an ethylenic spacer to a perchlorotriphenylmethyl radical (PTM(*)), a good electron acceptor. In solution this compound exists mainly in the neutral Fc-PTM(*) form which can be photoexcited through an intramolecular electron transfer to the zwitterionic Fc(+*)-PTM(-) form. By contrast, in crystals of Fc-PTM at room temperature both the neutral and the zwitterionic forms coexist, pointing to a true bistability phenomenon. We rationalize these findings accounting for the role of intermolecular electrostatic interactions in Fc-PTM crystals. In fact the energy of the zwitterionic Fc(+*)-PTM(-) form is lowered in the crystal by attractive electrostatic intermolecular interactions and the cooperative nature of these interactions explains the observed coexistence of neutral Fc-PTM(*) and zwitterionic Fc(+*)-PTM(-) species. The temperature evolution of Mossbauer spectra of Fc-PTM is quantitatively reproduced adopting a bottom-up modeling strategy that combines a molecular model, derived from optical spectra of Fc-PTM in solution, with a model for intermolecular electrostatic interactions, supported by quantum-chemical calculations. Fc-PTM then offers the first experimental demonstration of bistability induced by electrostatic interactions in crystals of valence tautomeric donor-acceptor molecules.     

A model for describing the thermodynamics of multivalent host-guest interactions at interfaces

A model has been described for interpreting the binding of multivalent molecules to interface-immobilized monovalent receptors through multiple, independent interactions. It is based on the concept of effective concentration, C(eff), which has been developed before for multivalent binding in solution and which incorporates effects of lengths and flexibilities of linkers between interacting sites. The model assumes: (i). the interactions are independent, (ii). the maximum number of interactions, p(max), is known, (iii). C(eff) is estimated from (simple) molecular models. Simulations of the thermodynamics and kinetics of multivalent host-guest binding to interfaces have been discussed, and competition with a monovalent competitor in solution has been incorporated as well. The model was successfully used to describe the binding of a divalent guest to self-assembled monolayers of a cyclodextrin host. The adsorption data of more complex guest-functionalized dendrimers, for which p(max) was not known beforehand, was interpreted as well. Finally, it has been shown that the model can aid to deconvolute contributions of multivalency and cooperativity to stability enhancements observed for the adsorption of multivalent molecules to interfaces.