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The synthesis and the thermal behaviour of the (methylphenylsilyl)methyl carbonates \(CH_3(C_6H_5)Si(H)CH_2OC(O)X (6: X = OCH_3; 7: X = Cl; 8: X = N(CH_3)_2)\) is described. 8 rearranges in toluene solution at 100 °C quantitatively to give the carbam oyloxysilane \(C_6H_5(CH_3)_2SiOC(O)N(CH_3)_2\) (11), whereas neat 6 and 7 at 135 °C undergo quantitative formation of \(C_6H_5(CH_3)_2SiOCH_3\) (12) and \(C_6H_5(CH_3)_2SiCl\) (13), respectively. The formation of 12 and 13 is explained by a rearrangement reaction (by analogy to the rearrangement of 8), follow ed by a decarboxylation. The thermally induced transformations 6 →12, 7 →13, and 8 →11 were found to be first-order reactions with half-lifes of ~2.6 h (135 °C, neat), ~4.5 h (135 °C, neat), and ~3.7 h (100 °C, in toluene), respectively.
Hurritische Lexikographie
(1985)
No abstract available.
No abstract available.
Aus der Durchsicht neuerer Forschungsliteratur zum Thema Schulprognose läßt sich ableiten, daß im Gegensatz zur unbestrittenen Bedeutung von kognitiven Tätigkeitsmerkmalen die Relevanz von nicht-kognitiven (z. B. Angst- und Leistungs-)Merkmalen für die Schulleistung nicht klar abzuschätzen ist. In der vorliegenden Untersuchung wurde nun der Vetsuch unternommen, anhand von explorativen Kausalmodellen mit latenten Variablen (LVPLS) die relative Bedeutsarnkeit nichtkognitiver Variablen für den Schulerfolg zu bestimmen. Die anhand einer Stichprobe von 87 Viertkläßlern gewonnenen Befunde unterstreichen die herausragende Relevanz kognitiver Merkmale, deuten jedoch auch darauf hin, daß die Rolle von Angsrkomponenten und Leistungsmotivkennwetten aufgrund ihrer vorwiegend indirekten Einflußnahme nicht unterschätzt werden darf. Angesichts der immer noch defizitären Theorieentwicklung im Bereich der Schulerfolgsprognose wird dafür plädiert, hier weiterhin gezielt mit explorativen Modellen zu arbeiten.
Es wurde die Hypothese überprüft , daß ein enger Zusammenhang zwischen Metagedächtnis, Gedächtnisverhalten und -leistung bei Grundschulkindern dann hergestellt werden kann, wenn mittlere Aufgabenschwierigkeit und reliable Erfassungsinstrumente vorliegen sowie weiterhin Transferleistungen im Anschluß an eine Trainingsphase gefordert sind. Am Beispiel von semantischen Kategorisietungsaufgaben ergab sich für eine Stichprobe von Drinkläßlern, (N = 106), daß die postulierten korrelativen Zusammenhänge besonders für den Prätest (also vor Trainingsbeginn) nachweisbar waren. Die erwarteten Effekte eines aufgabenspezifischen Trainingsprogramms auf den Zusammenhang zwischen Wissen und Verhalten ließen sich nicht sichern. Anhand eines Kausalmodells ließen sich erste empirische Anhaltspunkte für die Bestätigung der sog. "Rückkoppelungshypotbese" (Brown, 1978; Flavell, 1978) finden, derzufolge kausale Wirkungsketten zwischen Metagedächtnis und Gedächtnisverhalten anzunehmen sind.
Melanotic melanoma (MM) of Xiphophorus (Teleostei: Poeciliidae) was studied by conventional preparations and freeze-etch preparations for electron microscopy. MM of Xiphophorus exhibits tightly packed pigment cells with prominent dendritic processes and interdigitations of their plasma membranes. The most impressive feature of MM cells is the occurrence of Iarge lobulated nuclei with numerous nuclear pores and some nuclear pockets. Abundant spheroidal or ellipsoidal melanosomes (diameter 200-650 nm) and vesicular structures are distributed throughout the cellular dendrites, whereas the perinucJear cytoplasm is free of melanosomes.
A further characteristic feature of melanoma cells in fish is the occurrence of melanosome complexes (i.e., "compound melanosomes"). These melanosome complexes consist of a few to numerous melanosomes, which are enveloped by a separate rnembrane. Pinocytotic vesicles couJd be demonstrated with distinct differences in frequency and distribution patterns, indicating differences in the metabolic activities of the cells in the same melanoma. Intercellular junctions are lacking in the MM cells.
The conventional TEM technique showed clear advantages in the demonstration of intemal architecture of organelles, whereas FE bad considerable potential in respect to the visualization of membrane surface specializations.
Barbiturates inhibit binding of radioligands to A 1(Ri) adenosine receptors of rat brain membranes. This inhibition is dose-dependent and stereospecific and occurs in the range of pharmacologically active concentrations. The displacement of radiolabelled A1antagonists by barbiturates is not modified by GTP, indicating that barbiturates might act as antagonists at this receptor. This action of barbiturates does not seem to be related to the binding of barbiturates to plasma membranes, as the latter process has different characteristics. Barbiturates also inhibit the binding of radioligands to solubilized A1receptors, and saturation and kinetic experiments suggest that this is due to a competitive antagonism. These results indicate that barbiturates interact with the recognition site of the A1adenosine receptor.
Isolation of a functional human interleukin 2 gene from a cosmid library by recombination in vivo
(1985)
A method has been developed that allows the isolation of genomic clones from a cosmid library by homologaus recombination in vivo. This method was used to isolate a human genomic interleukin 2 (IL2) gene. The genomic cosmid library was packaged in vivo into A. phage particles. A recombination-proficient host strain carrying IL2 cDNA sequences in a non-homologaus plasmid vector was infected by the packaged cosmid library. After in vivo packaging and reinfection, recombinants carrying the antibiotic resistance genes of both vectors were selected. From a recombinant cosmid clone the chromosomal IL2 genewas restored. After DNA mediated gene transfer into mouse Ltk- cells human IL2 was expressed constitutively.
The c, b and ö subunit genes of the Escherichia coli atp operon were cloned individually in an expression vector between the tac fusion promoter and the galK gene. The relative rates of subunit synthesis directed by the cloned genes were similar in vitro andin vivo and compared favourably with the subunit stoichiometry of the assembled proton-translocating A TP synthase of E. coli in vivo. The rate of synthesis of subunit c was at least six times that of subunit b and 18 times that of subunit ö. Progressive shortening of the long intercistronic sequence lying upstream of the subunit c gene showed that maximal expression of this gene is dependent upon the presence of a sequence stretching > 20 bp upstream of the Shine-Dalgarno site. This sequence thus acts to enhance the rate of translational initiation. The possibility that similar sequences might perform the same function in other operons of E. coli and bacteriophage A is also discussed. Translation of the subunit b cistron is partially coupled to translation of the preceding subunit c cistron. In conclusion, the expression of all the atp operon genes could be adjusted to accommodate the subunit requirements of A TP synthase assembly primarily by means of mechanisms which control the efficiency of translational initiation and re-initiation at the respective cistron start codons.
The gene for the FeS protein of the Rhodopseudomonas sphaeroides b/c1 complex was identified by means of crosshybridization with a segment of the gene encoding the corresponding FeS protein of Neurospora crassa. Plasmids (pRSF1-14) containing the cross-hybridizing region, covering in total 13.5 kb of chromosomal DNA, were expressed in vitro in a homologous system. One RSF plasmid directed the synthesis of all three main polypeptides of the R. sphaeroides blc1 complex: the FeS protein, cytochrome b and cytochrome c1• The FeS protein and cytochrome c1 were apparently synthesized as precursor fonns. None of the pRSF plasmids directed the synthesis of the 10-kd polypeptide found in b/c1 complex preparations. Partial sequencing of the cloned region was performed. Several sites of strong homology between R. sphaeroides and eukaryotic polypeptides of the b/c1 complex were identified. The genes encode the three b/c1 polypeptides in the order: (5') FeS protein, cytochrome b, cytochrome c1• The three genes are transcribed to give a polycistronic mRNA of 2.9 kb. This transcriptional unit has been designated the jbc operon; its coding capacity corresponds to the size of the polycistronic mRNA assuming that only the genes for the FeS protein (jbcF), cytochrome b (jbcß) and cytochrome c1 (jbcC) are present. This could indicate that these three subunits constitute the minimal catalytic unit of the b/c1 complex from photosynthetic membranes.
Nine hierarchical and four nonhierarchical clustering algorithms were compared on their ability to resolve 200 multivariate normal mixtures. The effects of coverage, similarity measures, and cluster overlap were studied by including different levels of coverage for the hierarchical algorithms, Euclidean distances and Pearson correlation coefficients, and truncated multivariate normal mixtures in the analysis. The results confirmed the findings of previous Monte Carlo studies on clustering procedures in that accuracy was inversely related to coverage, and that algorithms using correlation as the similarity measure were significantly more accurate than those using Euclidean distances. No evidence was found for the assumption that the positive effects of the use of correlation coefficients are confined to unconstrained mixture models.
Die Synthese des selektiven Antimuskarinikums Cyclohexylpheny\{3-piperidinopropyl)sila· nol (1 b) wird beschrieben. 1 b wurde - ausgehend von (3·Chlorpropyl)trimethoxysilan - durch eine vierstufige Reaktionsfolge erhalten und als Hydrochlorid 2b mit einer Gesamtausbeute von etwa 45°/o isoliert. - 1 b ist aufgrund seiner großen pharmakologischen Se· lektivität zu einer Standardsubstanz in der experimentellen Pharmakologie bei der Differenzierung von Muskarinrezeptoren geworden.
A new in situ preparation of trimethylsilyl trifluoromethanesulfonate (3) is described: 3 is generated by a thermally induced rearrangement of (dimethylsilyl)methyl trifluoromethanesulfonate (2), which can be prepared by reaction of (CH\(_3\))\(_2\)Si(H)CH\(_2\)OH (1) with (CF\(_3\)SO\(_2\))\(_2\)O. Starting with C\(_6\)H\(_5\)(CH\(_3\))Si(H)CH\(_2\)OH (5), the derivative (methylphenylsilyl)methyl trifluoromethanesulfonate (6) can be obtained by a similar method. Its thermally induced rearrangement Ieads to dimethylphenylsilyl trifluoromethanesulfonate (7). The rearrangements 2---> 3 and 6---> 7 were found to be first-order reactions with half-lifes at 80 oc of 0.75 and 1.7 h, respectively.