Die Kalibrierung von Wärmeleitungsvakuummetern. The Calibration of Thermal Conductivity Vacuum Gauges

In many applications in the rough and fine vacuum thermal conductivity gauges are utilized. In order to determine the accuracy of the measuring values modern quality assurance systems require a regular calibration. The calibration laboratory of the German Calibration Service (DKD) at VACUUBRAND GMBH + CO KG features calibration equipment and procedures to calibrate vacuum gauges in the pressure range from 10^‐3 to 1000 mbar. The measuring techniques and calibration procedures are explained for thermal conductivity gauges with digital readouts. Besides general information on the calibration, particularities on thermal conductivity gauges and their effects on the calibration procedure are pointed out. The meaning of measuring deviation and measuring uncertainty and the interpretation of the calibration certificate for the user are discussed.     

Time-resolved fluorescence studies of dityrosine in the outer layer of intact yeast ascospores

The (time-resolved) fluorescence properties of dityrosine in the outermost layer of the spore wall of Saccharomyces cerevisiae were investigated. Steady-state spectra revealed an emission maximum at 404 nm and a corresponding excitation maximum at 326 nm. The relative fluorescence quantum yield decreased with increasing proton concentration. The fluorescence decay of yeast spores was found to be nonexponential and differed pronouncedly from that of unbound dityrosine in water. Analysis of the spore decay recorded at lambda ex = 323 nm and lambda em = 404 nm by an exponential series (ESM) algorithm revealed a bimodal lifetime distribution with maxima centered at tau 1C = 0.5 ns and tau 2C = 2.6 ns. The relative amplitudes of the two distributions are shown to depend on the emission wavelength, indicating contributions from spectrally different dityrosine chromophores. On quenching the spore fluorescence with acrylamide, a downward curvature of the Stern-Volmer plot was obtained. A multitude of chromophores more or less shielded from solvent in the spore wall is proposed to account for the nonlinear quenching of the total spore fluorescence. Analysis of the fluorescence anisotropy decay revealed two rotational correlation times (phi 1 = 0.9 ns and phi 2 = 30.6 ns) or a bimodal distribution of rotational correlation times (centers at 0.7 ns and 40 ns) when the data were analyzed by the maximum entropy method (MEM). We present a model that accounts for the differences between unbound (aqueous) and bound (incorporated in the spore wall) dityrosine fluorescence. The main feature of the photophysical model for yeast spores is the presence of at least two species of dityrosine chromophores differing in their chemical environments. A hypothetical photobiological role of these fluorophores in the spore wall is discussed: the protection of the spore genome from mutagenic UV light.     

Zum Copolymerisationsverhalten von Perfluorcyclohexadien-1,3

Probably due to the bulky fluorine substituents perfluorocyclohexadiene-1,3 (PFC) is not able to form homopolymers; likewise the copolymerization behavior is essentially influenced by this fact. Experiments in CCl₃ solutions with azobisisobutyronitrile as the initiator have shown, that α-methylstyrene does not yield copolymers; in the relatively low molecular products (P_n≈10) resulting from PFC and N-vinylpyrrolidone (NVP) and PFC and indene, two successive PFC units are separated by at least two or three comonomer units, respectively. The insertion of this minimum number of seperating links is a slow process compared with the monomer addition to the sterically unhindered radicals. This is borne out by the decrease of the overall rate of polymerization V_br with increasing PFC concentration and by the increase of V_br with increasing concentration of the chain transfer agent. The reactivity ratios at 50°C are r_nvp = 0,54 and rindene = 3,O. This results in Q_pfc < 0,02 and e_pfc > 1. The “dead end” of the reaction and the variation of the mean polymer compo-sition with conversion are calculated on the basis of the experimentally obtained kinetic equations. A discussion of the copolymerization behavior of PFC and butadiene-l,3 is given.     

Phytopathogenic filamentous (Ashbya, Eremothecium) and dimorphic fungi (Holleya, Nematospora) with needle-shaped ascospores as new members within the Saccharomycetaceae

Phylogenetic relationships between species from the genera Kluyveromyces and Saccharomyces and representatives of the Metschnikowiaceae (Holleya, Metschnikowia, Nematospora) including the two filamentous phytopathogenic fungi Ashbya gossypii and Eremothecium ashbyii were studied by comparing the monosaccharide pattern of purified cell walls, the ubiquinone system, the presence of dityrosine in ascospore walls, and nucleotide sequences of ribosomal DNA (complete 18S rDNA, ITS1 and ITS2 region). Based on sequence information from both ITS regions, the genera Ashbya, Eremothecium, Holleya and Nematospora are closely related and may be placed in a single genus as suggested by Kurtzman (1995; J Industr. Microbiol. 14, 523-530). In a phylogenetic tree derived from the ITS1 and ITS2 region as well as in a tree derived from the complete 18S rDNA gene, the genus Metschnikowia remains distinct. The molecular evidence from ribosomal sequences suggests that morphology and ornamentation of ascospores as well as mycelium formation and fermentation should not be used as differentiating characters in family delimitation. Our data on cell wall sugars, ubiquinone side chains, dityrosine, and ribosomal DNA sequences support the inclusion of plant pathogenic, predominantly filamentous genera like Ashbya and Eremothecium or dimorphic genera like Holleya and Nematospora with needle-shaped ascospores within the family Saccharomycetaceae. After comparison of sequences from the complete genes of the 18S rDNA the genus Kluyveromyces appears heterogeneous. The type species of the genus, K. polysporus is congeneric with the genus Saccharomyces. The data of Cai et al. (1996; Int. J. Syst. Bacteriol. 46, 542-549) and our own data suggest to conserve the genus Kluyveromyces for a clade containing K. marxianius, K. dobzhanskii, K. wickerhamii and K. aestuarii, which again can be included in the family Saccharomycetaceae. The phylogenetic age of the Metschnikowiaceae and Saccharomycetaceae will be discussed in the light of coevolution.     

The yeast growth control gene GRC5 is highly homologous to the mammalian putative tumor suppressor gene QM

We isolated the Saccharomyces cerevisiae GRC5 (gr owth control) gene by functional complementation in vivo of a ts (t emperature s ensitive) mutation. Phenotypic analysis suggested involvement of GRC5 in cell growth and proliferation. Mutant cells arrest their cell cycles after one to three cell divisions predominantly as mother cells with a large bud. In the region of the septum, a massive accumulation of cell wall material is observed. The mother and daughter nuclei are well separated and spindles are no longer present, while the cytoskeleton is of aberrant appearance. Arrested cells do not perform protein synthesis and are unable to mate. Furthermore, grc5-1^ts cells rapidly lose viability at the restrictive temperature (37°C) only on full media, but not under nitrogen-starvation conditions, indicating that proper response to this nutrient limitation is still intact in mutant cells after cell cycle arrest. The sequence of GRC5 translates into a basic protein of 221 amino acids with a corresponding M_r of 25·4 kDa. GRC5 is a member of the highly conserved QM gene family, members of which have been reported from plants, invertebrates and vertebrates. The amino acid sequence of GRC5 over its entire length is more than 60% identical to the human QM protein, expression of which is associated with loss of the tumorigenic phenotype in a cell line derived from Wilms' tumor, a malignancy of the embyronic kidney. Here, we show that GRC5 is an essential yeast gene, the function of which as inferred from analysis of the grc5-1^ts mutant is crucial for establishment of proper cytoskeletal structure and regulation of growth in yeast cells.     

Behead and live long or the tale of cathepsin L

In recent decades Saccharomyces cerevisiae has proven to be one of the most valuable model organisms of aging research. Pathways such as autophagy or the effect of substances like resveratrol and spermidine that prolong the replicative as well as chronological lifespan of cells were described for the first time in S. cerevisiae. In this study we describe the establishment of an aging reporter that allows a reliable and relative quick screening of substances and genes that have an impact on the replicative lifespan. A cDNA library of the flatworm Dugesia tigrina that can be immortalized by beheading was screened using this aging reporter. Of all the flatworm genes, only one could be identified that significantly increased the replicative lifespan of S.cerevisiae. This gene is the cysteine protease cathepsin L that was sequenced for the first time in this study. We were able to show that this protease has the capability to degrade such proteins as the yeast Sup35 protein or the human α‐synuclein protein in yeast cells that are both capable of forming cytosolic toxic aggregates. The degradation of these proteins by cathepsin L prevents the formation of these unfolded protein aggregates and this seems to be responsible for the increase in replicative lifespan.     

(R)-(-)- and (S)-(+)-Synadenol: synthesis, absolute configuration, and enantioselectivity of antiviral effect

Synthesis of (R)-(-)- and (S)-(+)-synadenol (1a and 2a, 95-96% ee) is described. Racemic synadenol (1a + 2a) was deaminated with adenosine deaminase to give (R)-(-)-synadenol (1a) and (S)-(+)-hypoxanthine derivative 5. Acetylation of the latter compound gave acetate 6. Reaction with N, N-dimethylchloromethyleneammonium chloride led to 6-chloropurine derivative 7. Ammonolysis furnished (S)-(+)-synadenol (2a). Absolute configuration of 1a was established by two methods: (i) synthesis from (R)-methylenecyclopropanecarboxylic acid (8) and (ii) X-ray diffraction of a single crystal of (-)-synadenol hydrochloride. Racemic methylenecyclopropanecarboxylic acid (10) was resolved by a modification of the described procedure. The R-enantiomer 8 was converted to ethyl ester 13 which was brominated to give vicinal dibromides 14. Reduction with diisobutylaluminum hydride then furnished alcohol 15 which was acetylated to the corresponding acetate 16. Alkylation-elimination procedure of adenine with 16 yielded acetates 17 and 18. Deprotection with ammonia afforded a mixture of Z- and E-isomers 1a and 19 of the R-configuration. Comparison with products 1a and 2a by chiral HPLC established the R-configuration of (-)-synadenol (1a). These results were confirmed by X-ray diffraction of a single crystal of (-)-synadenol hydrochloride. The latter forms a pseudosymmetric dimer with adenine-adenine base pairing in the lattice with the nucleobase in an anti-like conformation. Enantiomers 1a and 2a exhibit varied enantioselectivity toward different viruses. Both enantiomers are equipotent against human cytomegalovirus (HCMV) and varicella zoster virus (VZV). The S-enantiomer 2a is somewhat more effective than R-enantiomer 1a in herpes simplex virus 1 and 2 (HSV-1 and HSV-2) assays. By contrast, enantioselectivity of antiviral effect is reversed in Epstein-Barr virus (EBV) and human immunodeficiency virus type 1 (HIV-1) assays where the R-enantiomer 1a is preferred. In these assays, the S-enantiomer 2a is less effective (EBV) or devoid of activity (HIV-1).     

Viscose‐based porous carbon fibers: improving yield and porosity through optimization of the carbonization process by design of experiment

Journal of Porous Materials - In this study, the production of porous carbon fibers from viscose fibers was investigated. The effects of final carbonization temperature...