Photolithographic Patterning and Doping of Silica Xerogel Films

This study shows that conventional photolithography can be applied for patterning native or organic dye-doped silica films (0.5 m thick) obtained via a base-catalyzed sol-gel process. Photoresist was spin-coated onto high optical quality xerogel films, soft-baked, exposed to UV irradiation through a photomask, and developed with a commercial photoresist developing solution. Etching away of the photoresist-unprotected areas of the silica films was carried out with a dilute HF solution, while the remaining unexposed photoresist was removed with acetone. Interdigitated array patterns with features as small as 0.5 mm show a smooth surface and extremely sharp interfaces. Densification of the films at 550°C for 2 h decreases the film thickness by 11%, increases the refractive index from 1.420 to 1.456, and allows for well-defined patterning down to length scales of 10 m. Since the densification conditions are incompatible with organic dopants, it is demonstrated that sol-gel films can be doped after pattering (post-doping) by adsorption of cationic dyes from solution. Scanning electron microscopy reveals that the microstructure of patterned sol-gel films is similar to that of bulk monoliths, indicating that the photolithographic procedure is not harmful to the film quality. All patterned films demonstrate highly regular light diffraction patterns.     

Contribution to the quantitative x-ray analysis of individual submicrometre particles: Asbestos fibres

Summary A procedure for the analysis of individual asbestos fibres in the submicrometre diameter range, based on the ratio method of thin film analysis, is presented. The reliability of this method has been tested in a study of identification of asbestos fibres. The systematic and statistical errors were investigated.

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Beitrag zur quantitativen Röntgenmikroanalyse einzelner Submikrometerteilchen: Asbestfasern

Zusammenfassung Es wurde versucht, eine Quantifizierungsmethode analog der Verhältnismethode zur Analyse dünner Schichten für die Analyse von Asbestfasern mit Durchmessern im Submikrometerbereich zu entwickeln. Die Zuverlässigkeit der Methode wurde mit einem Anwendungsbeispiel überprüft, und alle systematischen und statistischen Fehler wurden dargelegt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Novel tocopheryl compounds. Part 16: Nitration of α-tocopheryl acetate—a mechanistic study

The reaction of α-tocopheryl acetate (vitamin E acetate, 3) with concentrated nitric acid proceeds according to a non-radical, two-step mechanism, producing 5-nitromethyl-γ-tocopheryl acetate (4) in good yields. In the first step, oxidation of 3 affords a benzylic cation intermediate (8), which in the second step adds nitrite to give 4. The acetyl group, which stabilizes intermediate 8 intramolecularly, remains bound to the tocopheryl moiety throughout the reaction.     

Photorefractive tuning of whispering gallery modes of a spherical resonator integrated inside a microstructured optical fibre

We demonstrate the photorefractive tuning of the whispering gallery modes of a single BaTiO₃ microsphere resonator integrated inside a grapefruit-shaped microstructured optical fibre, upon CW laser irradiation at 532 nm while using irradiation intensities up to 5.5 W/cm². Temporal evolution results of the WGM spectra are provided with respect to the illumination and relaxation conditions applied.     

Immobilization of Pd Catalysts on Mesoporous Silica for Amine- and Copper-Free Sonogashira Coupling Reactions

Immobilization of catalysts on solid supports is a promising approach to combine the advantages of heterogeneous and homogeneous catalysts. Pd(PPh₃)₂Cl₂, known as an extremely active homogeneous catalyst for the Sonogashira coupling reaction, has been immobilized on high-surface-area MCF (mesocellular foams)–type mesoporous silica powder modified with 3-aminopropyltriethoxysilane and subsequently with diphenylphosphine. The functionalized MCF-type silica and supported catalysts have been characterized by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), elemental analysis, nitrogen sorption porosimetry, and scanning electron microscopy (SEM). Such supported Pd catalysts have proven to be useful recyclable reagents for copper- and amine-free Sonogashira coupling reactions of haloaromatic compounds with terminal alkynes.     

Stabilization and first direct spectroscopic evidence of the o-quinone methide derived from vitamin E

[reaction: see text] The o-quinone methide (2) derived from vitamin E (1) can be stabilized at low temperatures in a complex with the highly polar N-methylmorpholine-N-oxide (5). The lifetime of 2 can thus be prolonged from less than 10 s to several minutes. In the complex formed, 2 adopts a zwitterionic, aromatic structure with the exocyclic methylene group in perpendicular arrangement to the ring plane, stabilized by the negatively charged oxygen in 5.     

Synthesis of C-8 Deuterated Glycosides of 3-Deoxy-D-manno-oct-2-ulosonic Acid (Kdo) Related to Chlamydial Lipopolysaccharides

Summary.  Methyl glycosides of Kdo and a (2→8)-linked Kdo disaccharide were prepared which contain a deuterium label at C-8 of the reducing unit. The label was introduced in fair diastereoselectivity upon reduction of an aldehyde group using a chiral borane complex derived from N-benzyloxycarbonyl-(S)-proline which produced the 8-(S)-deuterated derivative as the major isomer. Further coupling with a Kdo bromide gave the α-(2→8)-linked disaccharide in good yield. The deprotected disaccharide serves as a model for NMR spectroscopic studies on the side chain conformation of a carbohydrate epitope from the bacterial pathogen Chlamydia. Received September 17, 2001. Accepted October 17, 2001