Theoretical Study on the Low-Energy and High-Energy Conformers of the Three Isomers of 1,4-Difluorobutadiene

Partially fluorinated butatrienes: a coupled cluster study

The geometries of 19 different partially fluorinated butatrienes and their related butenyne isomers have been calculated at the Møller-Plesset second order perturbation theory level with Dunning's valence triple-zeta basis set. Final energies were determined at the CCSD(T)/cc-pVQZ level of theory. Increasing fluorine substitution has only a limited effect on the bond lengths but a substantial effect on the angles. The CCC bond angles of 4 of the 5 partially fluorinated butatrienes show a deviation of more than 2 degrees from collinearity, therefore representing angle-strained butatrienes. Increasing degree of fluorination has a substantial effect on the isomerization energies. The energy difference between the least stable enyne nonfluorinated at the acetylenic center and the most stable enyne fluorinated at the acetylenic center decreases from 66.8 kJ/mol, in case of the monofluorinated system, to 29.7 kJ/mol in the triple fluorinated system. The acetylenic F substitution is crucial in raising the energies of fluorinated but-1-en-3-yne relative to their butatriene isomers. Within the triple fluorinated system and unprecedented for all discussed molecules, 1,1,4-trifluoro-but-1-en-3-yne represents the only molecule fluorinated at the acetylenic center that is more stable than its triene isomer.

Chemical interpretation of molecular electron density distributions

In this study, the two small molecules HS(CH)(CH(2)), 1, and F(CH)(4)F, 2, are presented, which yield different chemical interpretations when one and the same density is interpreted either by means of Natural Bond Orbital and subsequent Natural Resonance Theory application or by the Quantum Theory of Atoms In Molecules. The first exhibits a S-C bond in the orbital based approach, whereas the density based Quantum Theory of Atoms In Molecules detects no corresponding bond. In F(CH)(4)F a F...F bond is detected in the density based approach, whereas in the orbital based approach no corresponding bond is found. Geometrical reasons for the presence of unexpected and the absence of expected bond critical points are discussed.

Adsorption thermodynamics of short-chain peptides on charged and uncharged nanothin polymer films

The present work describes experimental measurements of submolecular-level interaction energies involved in the process of peptide adsorption on polymer films using surface plasmon resonance spectroscopy. Gibbs energy change on adsorption (DeltaG(ad)) for tyrosine, phenylalanine, and glycine homopeptides were measured at 25 degrees C and pH 7 on highly uniform, nanothin polymer films, and the results were used to predict DeltaG(ad) for homologous homopeptides with a larger number of residue units. Nanothin poly(2-vinylpyridine), poly(styrene), and poly(1-benzyl-2-vinylpyridinium bromide) films were used for the adsorption studies; they were prepared using a graft polymerization methodology. In-situ swelling experiments were done with ellipsometry to examine the uniformity of the surfaces and to ensure that the graft densities of the different polymer films were similar to facilitate the comparison of adsorption results on these surfaces. The swelling experiments showed that the films were uniform, and the grafting densities were found to be 0.14-0.17 chains/nm(2). For uncharged surfaces, predicted and measured DeltaG(ads) values for homopeptides deviated by < or =4.9%. To extend this approach to a mixed-residue peptide, measurements were made for glycine, phenylalanine, and tyrosine-leucine subunits found in leucine enkephalin. The predicted DeltaG(ads) values for leucine enkephalin deviated by 3.0% and -9.1% for poly(2-vinylpyridine) and poly(styrene) films, respectively. Deviations between measured and predicted adsorption energies were larger for the charged poly(1-benzyl-2-vinylpyridinium bromide) surface relative to uncharged surfaces. While the adsorption energies were found to be additive within experimental uncertainties for the charged surface, generally speaking, measured uncertainty values were also larger for the charged surface.

Computational Study of the Structure and Behavior of Aqueous Mixed System Sodium Unsaturated Carboxylate-dodecyltrimethylammonium Bromide

The mixed surfactant system sodium 10-undecenoate (SUD)-dodecyltrimethylammonium bromide (DTAB) was studied by computational simulation to determine the composition and structure of the mixed microstructures. Results were contrasted with experimental data obtained from literature and our own laboratory. The modelization predicts spherical or cylindrical micelles with a preferential composition of SUD-DTAB of about 1:2, while the system predicts a lamellar structure with a proportion of 1:1 when SUD is replaced by the saturated soap sodium undecanoate. The model also predicts the deep inclusion of bromide ions in the micelle Stern layer. All predictions were in agreement with previous experimental results.

Selective solubilization of polycyclic aromatic hydrocarbons from multicomponent nonaqueous-phase liquids into nonionic surfactant micelles

This research investigates the equilibrium solubilization behavior of naphthalene and phenanthrene from multicomponent nonaqueous-phase liquids (NAPLs) by five different polyoxyethylene nonionic surfactants. The overall goal of the study was to achieve an improved understanding of surfactant-aided dissolution of polycyclic aromatic hydrocarbons (PAHs) from multicomponent NAPLs in the context of surfactant-enhanced remediation of contaminated sites. The extent of solubilization of the PAHs in the surfactant micelles increased linearly with the PAH mole fraction in the NAPL. The solubilization extent and micelle-water equilibrium partition coefficient of the PAHs increased with the size of the polar shell region of the micelles rather than the size of the hydrophobic core of the micelle. The presence of both PAHs in the shell region of the micelles was confirmed by 1H NMR analysis. This is an important observation because it is commonly assumed that in multi-solute systems the solutes with relatively greater hydrophobicity are solubilized only in the micellar core. A comparison of the 1H NMR spectra of pure surfactant solutions and solutions contacted with various NAPLs demonstrated that the distribution of PAHs between the shell and the core changed with the concentration of PAHs in the micelles and in the NAPL. Competitive solubilization of the PAHs was observed when both PAHs were present in the NAPL. For example, in surfactant solutions of Brij 35 and Tween 80, the solubilization of phenanthrene was decreased in the presence of naphthalene as compared to systems that contained phenanthrene as the only solute. In contrast, with micellar solutions of Tergitol NP-10 and Triton X-100, phenanthrene solubilization was enhanced in the presence of naphthalene. The activity coefficients of the PAHs in the micellar phase were generally found to increase with PAH concentrations in the micelle.