Wolf-Dieter Stohrer

Basis set superposition error in MP2 and density-functional theory: A case of methane-nitric oxide association

A systematic study of basis set superposition error (BSSE) behavior in H(3)C-H[ellipsis (horizontal)][NO] complexes for both -H...N- and -H...O- orientations were carried out using MP2 and density-functional theory with Poples [6-31G(d,p),6-311++G(nd,nd), where n=1,2,3, and 6-311++G(3df,3pd)] and Dunnings augmented correlation consistent basis sets [aug-cc-pVXZ (X=D and T)]. Corrected and uncorrected counterpoise potential-energy surfaces (PESs) were explored and differences obtained between them indicate that reliable optimizations of these molecular interactions must be carried out in a PES free of BSSE, even in the case of large basis sets and popularly used functionals such as B3LYP. Although all basis used could be always considered within a margin of approximation for representing molecular orbitals and show important values of BSSE, 6-311++G(2d,2p) basis set shows the best results in uncorrected PES with respect to the corrected ones. B3LYP functional produces erratic results: complexes appear repulsive and the intermolecular distances are always large, evidencing the lack of a correct dispersive forces treatment in the original parameterization. According to the MP2 results, the -H...N- interactions appear as slightly more stable than those of the -H...O- orientation.

The effect of fluorination on the surface characteristics and adhesive properties of polyethylene and polypropylene

Abstract Polyethylene and polypropylene have been treated with fluorine/nitrogen or fluorine/oxygen/nitrogen mixtures at atmospheric pressure. Changes in surface chemistry and topography as well as depth of fluorination have been examined using Fourier transform infra-red analysis, X-ray photoelectron spectroscopy (X.p.s.), atomic force microscopy (AFM) and ellipsometry. Even very short exposure times caused a large substitution of the hydrogen atoms by fluorine. No change in surface topography was noticed at magnifications of up to 5000 times with the scanning electron microscope (SEM), but AFM showed that fluorination led to an increase of microroughness. The influence of fluorine or fluorine/oxygen concentration, as well as time of treatment and time of storage before adhesive bonding, on adhesion of polypropylene to steel was investigated with a bending peel test. Significant improvement in peel strength was already achieved with minor fluorination intensity. Increase of fluorination intensity did not lead to further improvement in peel strength. Analysis of the fracture surfaces was carried out with the SEM and by energy dispersive X-ray spectroscopy and X.p.s. The findings showed that the samples failed cohesively in the polymer or directly beneath the fluorinated layer. A model to describe the formation of specific interactions between substrate and adhesive is suggested.

Theoretical study of flavonoids and proline interactions. Aqueous and gas phases

Abstract Flavonoids are polyphenolic compounds found in all land plants and in plant-related foods. These compounds have many positive effects, and the interaction with proline aminoacid is one of the most important characteristics. The present work shows the results of the application of the multiple minima hypersurfaces procedures, in the study of the interactions of flavonoid monomers (catechin and robinetinidin) with proline. These results are compared with experimental and classical theoretical results reported in the available literature. The most important results of this work are related with the conformations of monomers in these interactions, the preferential position of interactions and the thermodynamic stability of these complexes. All the results are successfully compared in both, gas and aqueous phases.

Arylthiazylamides: syntheses, structures, and bonding properties.

Air-sensitive, thermally unstable tris(dimethylamino)sulfonium (TAS) salts (3) of the title anions [ArNSN]- have been prepared from corresponding sulfurdiimides Ar-N=S=N-SiMe3 (2) by Si-N bond cleavage with [(Me2N)3S]-[Me3SiF2]- (TASF). They are characterized by low-temperature X-ray crystallography as Z isomers. Because of the very short terminal S-N distance (144.2 (3h)-147.9 (3i)pm) and the relatively long internal S-N distance (158.3 (3i)-160.3 (3c) pm) the [ArNSN]- ions should be regarded as thiazylamides 1b, rare species containing a S triple bond N triple bond. A bonding model is developed and the experimental results are compared with those of restricted Hartree-Fock (RHF), density functional theory (DFT), and Møller-Plesset second-order (MP2) calculations.

Adhesion promotors for gold: Bis-(ω-aminoalkyl)-disulfides

Abstract Bis-(ω-aminoalkyl)-disulfides are prepared in a three-step procedure. Treatment of gold surfaces with ethanolic solutions of these disulfides results in the formation of self-assembled monolayers. Adhesive bonding by an epoxy resin of the pretreated gold samples leads to a bond strength which is at least two times higher than that of unmodified gold samples. The characterization of these modified surfaces by XPS is described.

F3CCN5S3, A BICYCLIC MULTIFUNCTIONAL SULFUR-NITROGEN LIGAND

The bicyclic sulfur-nitrogen heterocycle F3CCN5S3 (1) was investigated as a donor and acceptor toward H+, metal cations, and F−. Whereas the protonated species F3CCN5S3H+ AsF6 − (2) can be isolated, the product of the reaction with F− is unstable and decomposes among other products to TAS+ F3CCN5S3NC(NH2)CF3 − (3), which is isolated from this reaction in small amounts.

Synthesis and structures of fluorinated thiatriazines

Abstract Compared to trifluorotrithiatriazine A exchange of SF- by CF-groups greatly enhances the thermal stability of these ringsystems. The synthesis of B was achieved by fluorine addition to the dithiatriazine 1 via XeF 2 , C was obtained from the appropriate trichloro-derivative by metathesis with SbF 3 : Substitution of the sulfur bonded halogen by nucleophiles (e.g. silylamines) is possible without destruction of the ring system. Halide abstraction by fluoro-Lewis-acids will give stable salts, e.g. CF 3 CN 3 S 3 F + A 8 F 6 − and C 2 F 2 N 3 S + A 3 F 6 − , respectively. The structures of A - D were determined in the gas phase by electron diffraction, the bonding situation in these heterocycles is discussed with respect to increasing carbon content. The experimental results are compared with MNDO-calculations.

Structures and Bonding Properties of Halotriazines

Abstract Syntheses and structures of halotriazines (XCN)n(XSN)3-n, (XCN)n(X2PN)3 and (XSN)n(XS(O)N)3-n (X = Cl, F; n = 0-3) are systematically investigated. From the structural data simple bonding models are derived.

Härtung von Epoxidharzen mit Nanopartikeln

Nanopartikel werden vielfach wegen ihres Verbesserungspotenzials der mechanischen Eigenschaften von Klebstoffen untersucht. In einem neuen Ansatz lasst sich nachweisen, dass bei gezielter Einstellung der Oberflachenchemie und der Verarbeitung der Nanopartikel im Harz weit mehr moglich ist: Nanopartikel sind auch in der Lage, Epoxidharze zu harten.

Preparation and properties of chlorosulfenyl - aziridines

Abstract From (CISN)3 and highly fluorinated alkenes chlorosulfenylaziridines are isolated in good yield: Heating to 40–50°C is necessary to generate monomeric CISN as reactive intermediate in sufficient concentration. CISN adds as chlorosulfenylnitrene to the CC-double bond. The reaction temperature can be substantially lowered, if monomeric CISN is generated under mild conditions. e.g. The reaction mechanism of this cyclo-addition will be discussed. The properties and some reactions of the sulfenyl-aziridines 1 − 3 will be reported.