Complex solid state physical investigations of metal layers on plastics

Several plastics were coated with different metal layers. Different plasma etching methods of plastics were used before deposition of metal layers. The adhesion strength depends on etching methods. With XPS it was shown that different bonds between C-C, C-H, C-Cl and C-O are existing. With X-ray diffraction methods it was found that decreasing peak intensities depend on increasing adhesion strengths.     

Percolative Phenomena in Microemulsions of the ‘One-Component Macrofluid’ Type

The temperature dependence of the water self-diffusion coefficients (D), as well as those of low- and high-field (stationary and time-dependent) specific conductivities (K), have been determined in the percolation regime of ternary mixtures of water, AOT, and oil. For the first time a pronounced similarity in the behavior of D and κ was detected giving instructive hints about the large variations in the specific conductivities of these systems. Results from kinetic and stationary experiments are consistent with a network-structure model of micro phases in the percolation regime in which the micro phases retain their discrete character.     

Kinetic energy release during CO loss by rearrangement of α-benzoylcarbenium ions

Primary α-benzoylcarbenium ions (a) and tertiary α-benzoyldimethylcarbenium ions (b) are obtained by chemical ionization of ω-hydroxyacetophenone and its dimethyl derivative, respectively. Both α-acylcarbenium ions decompose by a rearrangement reaction and subsequent loss of a CO molecule. The kinetic energy released during this process by metastable ions a and b has been determined under different experimental conditions. The kinetic energy released during the CO elimination from the tertiary α-benzoyldimethylcarbenium ions b is independent of the experimental conditions and gives rise to dish-topped peaks with T₅₀=440±20 meV in the MIKE spectra of b. In contrast to this the kinetic energy releases and the peak-shapes in the MIKE spectra of the primary α-benzoylcarbenium ion a varies with the experimental conditions. The mechanism of this rearrangement reaction is discussed, and it is shown by a MNDO calculation of the heats of formation of the relevant ions that the different characteristics of the kinetic energy release during the fragmentation of primary and tertiary carbenium ions can be attributed to different types of reaction energy profiles.     

Structural and Functional Models for the Dinuclear Copper Active Site in Catechol Oxidases: Syntheses, X-ray Crystal Structures, Magnetic and Spectral Properties, and X-ray Absorption Spectroscopic Studies in Solid State and in Solution

Two novel tridentate dinucleating ligands containing benzimidazole were prepared, 1,3-bis(2-benzimidazolyl)-2-propanol (Hbbp, 1) and 1,5-bis(2-benzimidazolyl)-3-pentanol (Hbbpen, 2). Their complexing properties toward copper were studied in order to obtain structural and functional models for catechol oxidases. Syntheses and crystal structures of dinuclear Cu(II) complexes derived from these ligands are reported. [Cu(2)bbp(2)](ClO(4))(2).2MeOH, 3, crystallizes in the triclinic space group P&onemacr; with the following unit cell parameters: a = 7.702(3) ?, b = 10.973(6) ?, c = 12.396(6) ?, alpha = 100.59(4) degrees, beta = 99.02(4) degrees, gamma = 98.90(4) degrees, V = 998.7(8) ?(3), and Z = 1. [Cu(2)bbpen(2)](ClO(4))(2).3MeOH, 4, crystallizes in the orthorhombic space group Pccn, with the following unit cell parameters: a = 17.478(9) ?, b = 18.795(8) ?, c = 13.888(6) ?, V = 4562.2(4) ?(3), and Z = 4. Magnetic susceptibility measurements in the temperature ranges 4.6-459 K (3) and 4.6-425 K (4) indicate an antiferromagnetic coupling between the Cu(II) centers of both complexes. In order to determine the structures of the complexes in solution, XAS spectra (EXAFS and XANES) were recorded in the solid state and in solution. The interpretation of these data, including multiple scattering calculations, together with UV-vis titrations, shows that the complexes have the same structure in the crystalline state as well as in methanolic solution. Complex 4 is able to oxidize 3,5-di-tert-butylcatechol (3,5-DTBC) to the quinone (catecholase activity). This reaction was also studied by XAS and UV-vis spectroscopy. These measurements reveal the reduction of Cu(II) to Cu(I) accompanied by a decrease of the coordination number.     

Distorted Molecules: Perturbation Design,Preparation and Structures

The structure of a molecule can change considerably as its energy and thus its electron distribution within the time-domain of dynamic relaxation varies. Based on comparison of approriate measured data of related compounds and supported by quantum chemical calculations, therefore, charge-perturbed and/or sterically overcrowded molecules can be designed. Their preparation, handling, and structural characterization, frequently under extreme and especially largely aprotic conditions, provides some surprises. New structural principles become evident and old-fashioned ones are confirmed. Thus the contact-ion aggregates that form on ultrasonically supported reduction of unsaturated hydrocarbons with sodium metal partly contain dibenzene sodium sandwiches. Vicinal dimethylamino substituents or isoelectronic isopropyl groups cause steric overcrowding and facilitate oxidation to molecular cations by energetically favorable delocalization of the generated positive charge. Molecules and molecular ions in which an even number of π electrons are distributed over a σ skeleton containing an odd number of centers preferentially form cyanine subunits. This is demonstrated by the novel ethene dication and dianion salts with central C? C single bonds and molecular halves twisted relative to each other. Altogether in two years well over 50 structures have been determined. Much has been learned from them, especially about electron transfer and contact ion-pair formation in aprotic solvents. Nevertheless, we had to realize that answers to many questions, above all “what crystallizes, how, and why”, are still out of reach.     

Zum mechanismus Massenspektrometrischer Fragmentierungsreaktionen–III: Stereospezifische Reaktionen in den Massenspektren der Methyläther cyclischer Polyalkohole

The mass spectra of stereoisomers of polymethoxy cycloalkanes depend on the geometry of the molecular ions. The magnitude of the stereochemical effect is influenced by the stability of the cyclic molecular ions. Due to energetically favourable ring-fragmentations the effect is cancelled by vicinal methoxy substituents and diminished by a methyl group next to a methoxy substituent. Stereochemically controlled fragmentations are the eliminations of a methoxy group in the form of a methanol or formaldehyde molecule from the molecular ions. By an investigation of di- and trimethoxy cyclohexanes, specifically labelled with deuterium, it is shown that both reactions are initiated by a transfer of an H-atom from a carbinol-C-atom to an O-atom of a methoxy group. Whether or not these energetically favourable reactions will occur depends on how close the H- and O-atoms involved can approach each other in the possible conformations of the molecular ion. The stereochemical control of the fragmentation of 1,3-dimethoxy cyclopentane, containing a more or less fixed five membered ring is small, that of dimethoxy cycloheptanes with a flexible seven membered ring is of comparable magnitude as the steric effect in the mass spectra of cyclohexane derivatives.     

Secondary ion mass spectrometry of nucleic acid components: Pyrimidines,purines, nucleosides and nucleotides

Biologically important involatile organic compounds including nucleotides, nucleosides, purines and pyrimidines have been analysed by secondary ion mass spectrometry. For the emission of molecule-like secondary ions small amounts of the substances were deposited as thin layers on silver foils and bombarded with 3 keV [AR]⁺ ions. All the compounds investigated yielded intense molecular ions of the general composition [M±H]^± and [M + Ag]⁺, but only a few characteristic fragment ions due to simple bond cleavages. Similarities and differences as compared with spectra obtained by other mass spectrometric ionization techniques are illustrated and discussed.     

Lokalisierte intermolekulare Induktionswechselwirkung endlicher Dipole mit apolaren Lösungsmittelmolekeln: Die Deutung temperaturabhängiger Dipolmomente von Carbonyl- und Thionderivaten der 1,2-Dithiacyclopentene

Solute-solvent interactions of the 1,2-dithiacyclopentenones and the analogue dithiathiones with non-polar solvent molecules as well as the formation of hetero-association complexes of these compounds is attributed to localized electrostatic induction. The distribution of the electric field around the oxo and thiono groups, respectively, is of special importance in determining the strength of the association. The temperature dependent solute-solvent interactions are correlated with changes in the observed dipole-moments. A plausible quantitative model based on finite dipole-moments is proposed in order to interpret the fundamental process of association.     

Spontaneous fragmentations of protonated benzaldimines mediated by intermediate ion-neutral complexes

4-Methoxymethylbenzaldimmonium ions (a) and the corresponding N-methylated ions (b) and N,N-dimethylated ions (c) were easily generated in the ion source by electron impact-induced dissociation from 1-(4-methoxymethylphenyl)ethylamine and its N-methylated derivatives. The spontaneous fragmentations of metastable ions a-c and of specifically deuterated derivatives in the second field-free region of a VG ZAB-2F mass spectrometer were studied by mass-analysed ion kinetic energy Spectrometry. The formation of an amino-p-quinodimethane radical cation by loss of the methoxy group is observed for all ions. In the case of a and b carrying at least one proton at the immonium group, competing fragmentations are the loss of CH₂O and CH₃OH, respectively, and the formation of ions CH₃OCH₂ ⁺, m/z 45, and C₇H₇ ⁺, m/z 91. Deuterium-labelling experiments indicated the migration of a proton from the protonated imino group of a and b to the aromatic ring followed by the loss of methanol from the methoxymethyl side-chain or protolysis of the bond to either side-chain to form ion-neutral complexes, in close analogy with the reactions of the corresponding protonated benzaldehydes. The intermediate ion-neutral complexes dissociate eventually by internal ion-neutral reactions resulting in the loss of CH₂ O and the formation of C₇H₇ ⁺, respectively.