Metal Oxoclusters as Molecular Building Blocks for the Development of Nanostructured Inorganic–Organic Hybrid Thin Films

Silica-based inorganic–organic hybrid thin films embedding the organically modified oxohafnium clusters (Hf₄O₂(OMc)₁₂, OMc=OC(O)–C(CH₃)=CH₂) were obtained by photo-activated free radical copolymerisation of the methacrylate groups of the cluster with those of the pre-hydrolysed (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH₂=C(CH₃)C(O)O)(CH₂)₃Si(OCH₃)₃). By this route, a covalent anchoring of the cluster to the forming silica network was achieved. Samples characterized by two different Si/Hf compositions (18:1, 5:1) were prepared. The surface and in-depth composition of the thin films were investigated through Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). XPS depth profiles performed on the thin layers evidenced a homogenous in depth distribution of the hafnium guest species within the whole silica films and sharp film-substrate interfaces. Broad band dielectric spectroscopy (BDS) measurements permitted to investigate the electric response of the obtained films in the frequency and temperature range of 40 Hz – 1 MHz and 0–160°C.     

Photocatalytic TiO2 Coatings: Effect of Substrate and Template

Summary. Transparent TiO₂ films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles, higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template (i.e. Pluronic F127) to the sol.     

Desorption ionization combined with tandem mass spectrometry: Advantages for investigating complex lipids,disaccharides and organometallic complexes

Combining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure-proof of a minor component of an ornithine-containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision-activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision-activated dissociations of the [M + Na]⁺ of sucrose, desorbed by field desorption, and [M + H]⁺, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated.     

Mesomorphism,isomerization, and dynamics in a new series of pyramidic liquid crystals

Nona-alkanoyloxy tribenzocyclononene (CTV-n, where n is the number of carbons in the side chains) were prepared for n = 2 to 14. The homologues of this series appear in two stable isomeric forms, rigid crown and flexible saddle. We report on their isomerization equilibria and dynamics in solution and on their mesomorphic properties in the neat state. The crown-saddle equilibrium and interconversion kinetics of the CTV-8 isomers were studied in dimethyl formamide solutions using high-resolution (1)H NMR in the temperature range from 50 to 130 degrees C. At lower temperatures, the isomerization is too slow to measure. In this range the equilibrium saddle fraction increases from approximately 0.40 to approximately 0.65, whereas the isomerization rate increases from approximately 10(-)(4) to approximately 1 s(-)(1). The saddle isomer undergoes fast pseudorotation at room temperature, but below about -50 degrees C, it becomes slow enough to affect the NMR line width. The rate parameters for this process were estimated from the carbon-13 spectra in methylene chloride solutions to be, k(p)(-100 degrees C) approximately 1.7 x 10(3) s(-)(1) and E(a) approximately 9.6 kJ/mol. The slow crown-saddle isomerization at room temperature (half-life of about one year) allows quantitative separation (by chromatography) of the two isomers and their separate investigation. When the alkanoyloxy side chains are sufficiently long both isomers are mesogenic (n >or= 4 for the saddle and n >or= 5 for the crown), exhibiting hexagonal columnar mesophases. The structure, dynamics, and mesomorphic properties of these mesophase were investigated by X-ray diffraction, optical polarizing microscopy, differential scanning calorimetry, and NMR. The lattice parameters of the crown and saddle mesophases of corresponding homologues are almost identical and increase monotonically with increasing length of the side chains. The clearing temperatures of the saddle isomers are consistently lower than those of the corresponding crowns. Within each series, the clearing temperatures are almost independent of the length of the side chains (156 to 170 degrees C for the crown and 115 to 148 degrees C for the saddle). The thermal and kinetic properties of the neat compounds lead to peculiar phase sequences, as observed in the polarizing microscope and in the DSC thermogram, involving repeated, back and forth, interconversion between the two isomers. Carbon-13 MAS NMR measurements of the crown and saddle mesophases of several homologues were carried out. The spectra of the crown mesophase exhibit dynamic features consistent with planar 3-fold molecular jumps about the column axes. A quantitative analysis for the CTV-8 crown homologue yielded the following Arrhenius parameters, A = 3.1 x 10(22)s(-)(1) and E(a) = 130.1kJ/mol. These unusually high values suggest that the barrier to the jump process is temperature dependent, decreasing with increasing temperature. The rate of this 3-fold jump process is slower for the lower homologues and faster for the higher ones. In contrast, the saddle isomers in the mesophase do not show dynamic effects in their carbon-13 MAS spectra. They do not undergo pseudorotation, and it appears that the molecules remain locked within the columns in a saddle conformation, up to the clearing temperature. However, on (super-)cooling to room temperature and below, selective line broadening is observed in their carbon-13 MAS spectra. This suggests that the saddle conformation is twisted in the mesophase and undergoes fast high-amplitude jumps between the twisted forms. On cooling, these high-amplitude librations freeze out to give an orientationally disordered state. On a very long time scale (of the order of days at 100 degrees C), the saddle mesophase transforms into that of the crown, apparently by sublimation.     

Fragmentation of electrospray-produced oligodeoxynucleotide ions adducted to metal ions

In this article, we describe the unique fragmentations of oligodeoxynucleotides (ODNs) whose phosphate groups are completely depleted of protons and replaced with metal ions. The production of the ubiquitous [a(n) - base] ions still occurs, but no longer by transfer of an acidic phosphate proton to an adjoining 3' base. Nor is the extent of the reaction determined by the proton affinity of that base. Rather, the reaction now occurs via a cleavage 3' to both pyrimidines and purines; cleavage 3' to pyrimidine is more favorable than that 3' to purine. We also demonstrate that an ODN is more stable in the gas phase when its phosphate groups are bound to metal ions than when its phosphate groups are attached to hydrogens. This study also provides further evidence for the ODN fragmentation mechanism that involves H transfer to a nucleobase. To establish the structural utility of this new fragmentation, we applied it to distinguishing small ODNs containing a photomodified cis,syn-cyclobutane pyrimidine dimer from the parent ODNs, a system that cannot be distinguished by collisional activation of precursor species that do not contain metal ions.     

Die chemie der schweren carben-analogen R2M,M = Si,Ge, Sn: IX. Eigenschaften und thermolyse von neuen 7-silabicyclo[2.2.1]heptadienen

Factors governing the ease and mechanism of 7-silabicyclo[2.2.1]heptadienes thermolysis in order to generate free silylenes and the corresponding benzene derivatives are investigated. For this purpose, 29 new compounds of the types VII–X have been prepared. No indications for a polar mechanism or an intermediate biradical could be found. The degradation is exactly of first order in all cases investigated sofar, and is enhanced by phenyl groups at the bridgehead C atoms, if a conformation coplanar with the basic ring is allowed by the neighbouring substituents, but is not enhanced by phenyl groups at the Si. The X-ray structure of two typical derivatives is discussed with this respect. A special mechanism is operating in the easy thermolysis of carbomethoxy-substituted compounds leading to cyclic sila enolether intermediates.     

Alkane loss from collisionally activated alkylmethyleneimmonium ions

The collision-induced dissociation (CID) spectra of five alkylmethyleneimmonium ions (H₂C-N⁺R¹R², (a) R¹ = R² = C₂H₅, (b) R¹ = n-C₃H₇, R² = H, (c) R¹ = n-C₃H₇, R² = CH₃, (d) R¹ = n-C₃H₇, R² = C₂H₅, (e) R¹ = R² = n-C₃H₇) are reported and discussed in terms of the mechanism of alkane loss. The most abundant alkane losses result from 2-azaallylic bond cleavages within R¹ and R² leading to daughter ions of m/z 84. Ion d (R¹ = n-C₃H₇, R² = C₂H₅) was chosen for a deuterium-labelling study because it exhibited methane loss nearly free from interferences with other fragmentations. The methane lost consists to a great extent (95%) of the methyl moiety of R². Whereas the methyl moiety obviously stays intact during the fragmentation process, the hydrogen additionally needed originates from all positions of R¹ and the double-bonded methylene in an approximately random distribution, suggesting extensive hydrogen migrations preceding the transfer step.     

Photocatalytic TiO2 Coatings: Effect of Substrate and Template

Transparent TiO₂ films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles, higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template (i.e. Pluronic F127) to the sol.     

High-dimensional quantum dynamical study of the dissociation of H2 on Pd110

We report the first six-dimensional quantum dynamical study of the dissociative adsorption of H(2) on a (110) surface. We have performed quantum coupled-channel calculations for the system H(2)/Pd(110) based on a potential energy surface (PES) that was derived from ab initio electronic structure calculations. In particular, we have focused on the effects of the corrugation and anisotropy of the PES on the H(2) dissociation probability. Our results agree well with the available experimental data for the sticking probability as a function of the initial kinetic energy and the angle of incidence. Because of the coupling between the anisotropy and corrugation of the potential energy surface our calculations predict an unusual rotational heating and a rather small rotational alignment in desorption.