Didesoxy-Ribonucleoside durch Schmelzkondensation

Dideoxy Ribonucleosides by Fusion Method The dideoxy nucleosides 2 , 4 and 6 are synthesized from the 1-O-acetyl-2,3-dideoxyribose derivatives 1 , 3 and 5 by fusion with chlorinated purines and other nitrogen heterocycles at 110–120°C without added catalyst. The ¹H-NMR and ¹³C-NMR spectra of the compounds are given.     

Electrical Conduction Behavior of La1+xSr1−xGa3O7–δ Melilite-Type Ceramics

Ceramics of the melilite-type compound La_{1+ x} Sr_{1− x} Ga₃O_7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x =−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four-point direct-current conductivity measurements and electromotive force measurements. La_{1+ x} Sr_{1− x} Ga₃O_7−δ samples exhibited a p -type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10⁻¹ S·cm⁻¹ at 950°C.     

Azacrown Ethers with Naphthyl Branches. Fluorescence Properties,Protonation and Metal Coordination

Starting from 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, we have prepared two compounds by replacing the amine hydrogens with naphthyl or 3,5-bis(2′-oxymethylnaphthyl)benzyl units. The absorption and emission spectra of compounds 2 (N,N′-bis(2-naphthylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) and 3 (N,N′-bis[3,5-bis(2′-oxymethylnaphthyl)benzyl]-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) have been studied in CH₃CN:CH₂Cl₂ 1:1 (v/v) solution. For comparison purposes, the spectroscopic properties of N-methyl(2-methylnaphthalene)ethylamine (1) have also been investigated. For each compound, the absorption spectra are qualitatively very similar to that of naphthalene, with molar absorption coefficients as expected for the presence of one (1), two (2), and four (3) naphthyl chromophoric groups. The fluorescence spectra, however, are quite different from that of naphthalene. The naphthalene-type fluorescence (λ_max = 337 nm) is strongly quenched, particularly for compounds 1 and 2 which also exhibit a broad emission band in the visible region (λ_max ≈ 480 nm) assigned to a low lying charge-transfer excited state. In the case of compound 3, a quenched naphthalene-type band is accompanied by weak exciplex and excimer emissions. Upon titration with CF₃SO₃H, the charge transfer bands of 1 and 2 and the exciplex emission of 3 disappear and the naphthalene-type bands regain intensity. Titration plots show that in compounds 2 and 3 the protonation of the two nitrogens occurs stoichiometrically in two distinct steps. Titration with Zn²⁺ gives rise to 2.Zn²⁺ and 3.Zn²⁺ complexes. This article is dedicated to Professor Dedier Astruc.     

Redox processes in pressurised smoked salmon studied by resonance Raman spectroscopy

Non-thermal food preservation technology is based on the application of high pressures up to 600 MPa. Here we report a resonance Raman (RR) spectroscopic analysis of smoked salmon meat after high pressure processing. High quality spectra, which can be obtained even from packed salmon without spectral interference of the packing foil, allow determining pressure-dependent irreversible changes of the main RR-active components of salmon meat, astaxanthin and myoglobin/haemoglobin. High pressure-treatment causes a decrease of the relative RR intensities of astaxanthin as probed with 514 nm excitation which is in line with a slight attenuation of the originally intense red colour of the salmon meat. 413-nm excited RR spectra indicate a heterogeneous broadening of astaxanthin bands accompanied by the formation of deoxy-myoglobin or deoxy-haemoglobin. The results suggest that pressure-treatment facilitates the oxidative degradation of astaxanthin coupled to the reduction of metmyoglobin (methaemoglobin).     

Pulsed electric fields and their impact on the diffusion characteristics of potato slices

Mass transfer in potato slices and strips after Pulsed Electric Fields (PEF) treatment was examined to evaluate potential application of PEF in potato processing. PEF treatment on cell material leads to pore formation in cell membrane and thus modifies diffusion of intra- and extracellular media. Results showed enhanced release of intracellular molecules from permeabilized tissue as well as improved uptake of low molecular substances into the sample. Sugar, one substrate for the Maillard reaction, was decreased in PEF treated potatoes, while conductivity increased after electroporation and soaking in sodium chloride solution, indicating the improved diffusion of salt caused by PEF. Higher release of cell liquid during drying of PEF treated potatoes was noticed in comparison to untreated potato slices. This effect increased with the treatment intensity. Furthermore, it was revealed that PEF application leads to a distinct reduction of fat content after deep fat frying and thus provides a potential for the production of low-fat French fries. It can be presumed that PEF is a capable assistance to thermal treatments in the processing of potato chips or French fries for the achievement of structural modifications and improved process conditions.     

Enzymes in organic synthesis. 2. Synthesis of enantiomerically pure prostaglandin intermediates by Enzymatic Hydrolysis of (1SR, 5RS, 6RS, 7RS)-7-acetoxy-6-acetoxymethyl-2-oxabicyclo[3.3.0]octan-3-one

Subtilisin DY as well as alkaline protease from Bacillus licheniformis 41 p catalyze the hydrolysis of (1SR, 5RS, 6RS, 7RS)-7-acetoxy-6-acetoxymethyl-2-oxabicyclo[3.3.0]octan-3-one ( rac-1 ) with practically useful enantio- and regioselectivity. Under the hitherto found optimal conditions (1S, 5R, 6R, 7R)-7-hydroxy-6-hydroxymethyl-2-oxabicyclo[3.3.0]octan-3-one ( 4 ), an important intermediate in prostaglandin syntheses, could be prepared in a yield of 16% with an enantiomeric excess of 99%. The enantiomer ( ent-4 ) was obtained with the same enantiomeric excess in 20% yield. The chemical yields are related to the racemic starting material rac-1 .     

Reaktionen mit Cyclobutendionen. LII. Reaktionen von 4-Hydroxy-3-phenyl-cyclobut-(3)-en-onen-(1) mit Arylhydrazinen

Reactions of Cyclobutendiones. LII. Reaction of 4-Hydroxy-3-phenyl-3-cyclobuten-1-ones with Arylhydrazines In the reaction of hydroxycyclobutenones of the typ 1 – 4 with arylhydrazines 5 an unexpected reaction behaviour is found. The major products are hydrazones of different structure, the well known hydroxy-cyclopropane-carboxylicacid hydrazines 6 [1] are byproducts. The direction of the reaction depends on the substituents X, on the different substituted arylhydrazines and the solvents.     

Injection molding of products with functional surfaces by micro-structured, PVD coated injection molds

Molding of micro structures by injection molding leads to special requirements for the molds e.g. regarding wear resistance and low release forces of the molded components. At the same time it is not allowed to affect the replication precision. Physical vapor deposition (PVD) is one of the promising technologies for applying coatings with adapted properties like high hardness, low roughness, low Young’s modulus and less adhesion to the melt of polymers. Physical vapor deposition technology allows the deposition of thin films on micro structures. Therefore, the influence of these PVD layers on the contour accuracy of the replicated micro structures has to be investigated. For this purpose injection mold inserts were laser structured with micro structures of different sizes and afterwards coated with two different coatings, which were deposited by a magnetron sputter ion plating PVD technology. After deposition, the coatings were analyzed by techniques regarding hardness, Young’s modulus and morphology. The geometries of the micro structures were analyzed by scanning electron microscopy before and after coating. Afterwards, the coated mold inserts were used for injection molding experiments. During the injection molding process, a conventional and a variothermal temperature control of the molds were used. The molded parts were analyzed regarding roughness, structure height and structure width by means of laser microscopy.