Quantum-chemical approach to the elementary steps of plasma etching

We derive for the first time a mechanism of reactive plasma etching in the system Si/F by the quantum-chemical approach. SiF₂-like species at the surface play an important role. SiF₃ surface complexes also occur. The final etching product SiF₄ is formed with high probability in the gas phase.     

Saturated heterocycles. 57. Synthesis of 4-substituted-9,10-dialkoxy-1,6,7,11b-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-2-ones

A large number of 4-substituted-9,10-dialkoxy-1,6,7,11b-tetrahydropyrimido[6,1-a]isoquinolin-2-ones were prepared by the reaction of 1-(ethoxycarbonylmethyl)-6,7-dialkoxy-1,2,3,4-tetrahydroisoquinolines with iminoethers. Reaction of the corresponding isoquinoline-1-acetic acid derivatives with iminoethers led to the formation of N-acyl-1,2,3,4-tetrahydroisoquinolin-1-acetamides. In the hydrolysis of the prepared 4-substituted-pyrimido[6,1-a]isoquinolin-2-ones, the corresponding N-acyl-1,2,3,4-tetrahydroisoquinolin-1-acetamides were obtained. While reduction of the 4-phenyl derivative resulted in the corresponding 1,3,4,6,7,11b-hexahydropyrimidinone. The steric structures of the tetrahydro- and hexahydropyrimido[6,1-a]isoquinolines were determined by nmr spectroscopy.     

Der Abbau des Insektizides GS 13005 in der Ratte. Strukturaufklärung der wichtigsten Metabolite [1]

The structures of the essential metabolites which are excreted by the rat after oral application of GS 13005 (O,O-dimethyl-S-[(2-methoxy-1,3,4-thiadiazole-5(4H)-one-4-yl)-methyl] dithiophosphate) have been elucidated. The product of final oxidation, CO₂, was found to be the main metabolite (up to 36% of the dose applied). Among the degradation products excreted in the urine (up to 45% of the dose applied) the two most important were isolated. They are 4-methylsulfinylmethyl and 4-methylsulfonylmethyl derivatives respectively of the intact 2-methoxy-1,3,4-thiadiazole-5-one heterocycle (metabolites III and II, in amounts of 20–25% and 5–7% of the dose applied, respectively). These metabolites originate by methylation and subsequent oxidation from the mercaptomethyl derivative liberated after hydrolysis of the P S bond of the dithiophosphoric acid ester.     

Reference electrodes based on conducting polymers

Several attempts to produce conducting polymer based all-solid-state reference electrodes are presented. Open circuit potential of conducting polymers is redox sensitive and Donan equilibrium dependent. Therefore, more sophisticated constructions are necessary. Most promising were bilayers composed of conducting polymers with different ion-exchanger properties.     

A new concept for isotope ratio monitoring liquid chromatography/mass spectrometry

A new interface for the on-line coupling of a liquid chromatograph to a stable isotope ratio mass spectrometer has been developed and tested. The interface is usable for (13)C/(12)C determination of organic compounds, allowing measurement of small changes in (13)C abundance in individual analyte species. All of the carbon in each analyte is quantitatively converted into CO(2) while the analyte is still dissolved in the aqueous liquid phase. This is accomplished by an oxidizing agent such as ammonium peroxodisulfate. The CO(2) is separated from the liquid phase and transferred to the mass spectrometer. It is shown that the whole integrated process does not introduce isotope fractionation. The measured carbon isotope ratios are accurate and reproducible. The sensitivity of the complete system allows isotope ratio determination down to 400 ng of compound on-column. By-passing the high-performance liquid chromatography (HPLC) separation allows bulk isotopic analysis with substantially lower sample amounts than those required by conventional elemental analyzers. The results of the first applications to amino acids, carbohydrates, and drugs, eluted from various types of HPLC columns, are presented. The wide range of chromatographic methods enables the analysis of compounds never before amenable to isotope ratio mass spectrometry techniques and may lead to the development of many new assays.     

Preparation, characterization, and condensation of copper tellurolate clusters in the pores of periodic mesoporous silica MCM-41

The copper-tellurolate cluster [(Cu(6)(TePh)(6)(PPh(2)Et)(5)] has been loaded into the pores of MCM-41 by solid-state impregnation techniques. It was found that the best loading conditions are 110 degrees C and 10(-)(3) Torr static vacuum. The resulting material was analyzed by powder X-ray diffraction (PXRD), nitrogen adsorption isotherms, thermogravimetric analysis (TGA), (31)P CP MAS NMR spectroscopy, and TEM. It was observed that loading is accompanied by loss of the phosphine shell, with retention of the copper-tellurium core. Condensation of the impregnated material may proceed thermally or photochemically. Thermal condensation results in the formation of Cu(2)Te nanoparticles as demonstrated by PXRD, and TEM data suggests that the process has taken place inside the pores of MCM-41. Photochemical condensation yields larger metal-chalcogen clusters in the pores as suggested by the result of UV-vis diffuse reflectance spectroscopy and TEM measurements.     

Determination of Arsenic Species in Fish Oil After Acid Digestion

Arsenic speciation is of increasing interest to the food industry, as concerns about high total arsenic concentrations in food can often be alleviated to a great extent if the ratio of toxic, less toxic and non-toxic arsenic compounds in the sample is known. The lipid matrix of fish oil is a challenge in the determination of arsenic species, as current methods for this type of analysis require the analyte to be water-soluble. In this study, two sample preparation techniques were applied. One the one hand water-soluble species were extracted with methanol/water, on the other, acid digestion was applied to release lipid-soluble arsenic compounds into the aqueous phase. Ion chromatography – inductively coupled plasma mass spectrometry (IC-ICP-MS) was used for separation and sensitive element-specific detection of arsenic compounds. Additional experiments, including alkaline hydrolysis, were carried out to find out more about the type of lipids arsenic is bound to in fish oil. Up to eight different arsenic species were detected and quantified in fish oil with dimethylarsinate being the major compound both in the aqueous extract and in the acid digest. No inorganic arsenic was detected in the aqueous extract, and the maximum concentration of arsenate determined in the acid digest was 0.05 μg g⁻¹. The total arsenic concentration determined by ICP-MS ranged from <0.1 to 5 μg g⁻¹. With regard to the mass balance, approximately 1% of the total arsenic content was extractable with methanol/water, whereas the sum of arsenic species quantified after acid digestion yielded 85–100% of the total arsenic content. It was confirmed that the large fraction of arsenic in fish oil not extractable on an aqueous basis consists of organoarsenic compounds. This new approach in sample preparation makes the complete characterization of the arsenic content in the sample possible with regard to the respective species, providing necessary information required for risk assessment.     

Spectrophotometric and direct-reading methods for the analysis of gas phase peroxyacetic acid

A new method for the determination of peroxyacetic acid (PAA) in gas phase samples is described. It is based on the oxidation of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate) by PAA with formation of a radical cation which is characterized by four strong absorption maxima between 405 nm and 810 nm. These allow for sensitive spectrophotometric determination of the peracid. The selectivity of the method towards hydrogen peroxide is strongly dependent on the sampling method used. Impinger sampling and sampling based on the use of coated solid sorbents (test tubes) was performed. Limits of detection are 10(-8) mol, limits of quantification are 5 x 10(-8) mol, the linear range consists of 1.5 concentration decades in both cases. Using ABTS-coated test tubes above 1 x 10(-7) mol, direct reading of the results is possible and may be used as rapid screening method for the PAA concentration.     

Intra- vs intermolecular photoinduced electron transfer reactions of a macrocyclic donor-acceptor dyad

The synthesis, structural characterization, and photophysical behavior of a 14-membered tetraazamacrocycle with pendant 4-dimethylaminobenzyl (DMAB) and 9-anthracenylmethyl groups is reported (L3, 6-((9-anthracenylmethyl)amino)-trans-6,13-dimethyl-13-((4-dimethylaminobenzyl)amino)-1,4,8,11-tetraazacyclotetradecane). In its free base form, this compound displays rapid intramolecular photoinduced electron transfer (PET) quenching of the anthracene emission, with both the secondary amines and the DMAB group capable of acting as electron donors. When complexed with Zn(II), the characteristic fluorescence of the anthracene chromophore is restored as the former of these pathways is deactivated by coordination. Importantly, it is shown that the DMAB group, which remains uncoordinated and PET active, acts only very weakly to quench emission, by comparison to the behavior of a model Zn complex lacking the pendant DMAB group, [ZnL2]2+ (Chart 1). By contrast, Stern-Volmer analysis of intermolecular quenching of [ZnL2]2+ by N,N-dimethylaniline (DMA) has shown that this reaction is diffusion limited. Hence, the pivotal role of the bridge in influencing intramolecular PET is highlighted.