Organic molecular beam deposition of oligophenyls on Au111: A study by X-ray absorption spectroscopy.

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been applied to reveal the molecular arrangement of ultrathin oligophenyl films [p-quaterphenyl (4P) and p-hexaphenyl (6P)] on Au(111). In the half-monolayer films the molecules lie flat on the surface but still have a considerable inter-ring twist of 30 degrees -40 degrees , similar to the gas-phase conformation. In the saturated monolayer film the second half of the molecules is side-tilted by an angle of less than 66 degrees with respect to the surface. This arrangement is already similar to that in bulk net planes of thicker films parallel to the surface, that is, the 4P(211) and 6P(21-3) planes, respectively.     

Mitteilungen aus dem Institut für Radiumforschung

Zusammenfassung Es wurde mit Hilfe des schon früher beschriebenen Quarzapparates Thoriumbromid aus reinem Thoroxyd dargestellt, das nach zwei verschiedenen Methoden gereinigt war und auf Grund spektroskopischer Untersuchung als absolut rein und frei von seltenen Erden angesehen werden mu\te.Das geschmolzene Thorbromid wurde nach zwei Methoden analysiert und dabei die beiden VerhÄltnisse ThBr₄4 Ag und ThBr₄4 AgBr bestimmt.Zwei unabhÄngige Serien von 12, respektive 15 Analysen gaben die folgenden Resultate:Serie I. 54·45867g Thorbromid verbrauchten 42·58666g Silber und gaben 74·13448g Silberbromid, entsprechend einem Atomgewicht des Thoriums Th=232·15±0·016.Serie II. 74·30630g Thorbromid verbrauchten 58·11096g Silber und gaben 101·15848g Silberbromid, woraus sich das Atomgewicht Th=232·12±0·014 berechnet.Als Mittel dieser beiden Werte ergibt sich Th=232·135.Da aber die Analysenserie aus den oben besprochenen, uns triftig erscheinenden Gründen als die zuverlÄssigere angesehen werden mu\, glauben wir, da\ der aus ihr resultierende WertTh=232·12 als das derzeit wahrscheinlichste Atomgewicht des Thoriums anzusehen ist, wenn Ag=107·880 angenommen wird. Aus dem in 27 Bestimmungen gefundenen VerhÄltnis von angewandtem Silber zu gefundenem Silberbromid, AgAgBr= 0·574453, ergibt sich dann das Atomgewicht des Broms zu Br=79·916 in vollster übereinstimmung mit der von Baxter seinerzeit gefundenen Zahl.     

Synthesis of Aristotelia-Type Alkaloids.. Part IV. Synthesis of (±)-aristoserratine

A convergent diastereoselective synthesis of racemic aristoserratine ((±)- 24 ) via an intramolecular iminium-ion cyclization is described. The pivotal imine (±)- 19 was prepared by condensation of the two building blocks (± )-trans-8-amino-3-(2,6-difluorobenzyloxy)-1-p-menthene ((±)- 11 ) and N-(p-methoxybenzenesulfonyl)-3-indo-leacetaldehyde ( 18 ) which were synthesized from (±)-trans-1-p-menthene-3,8-diol ((±)- 7 ) and 3-indoleacetic acid, respectively. On the route to the target (±)- 24 , two previously unknown indole alkaloids have been characterized, namely (±)-‘anti’-hobartin-15-ol ((±)- 22 ) and (±)-‘anti’-aristotelin-15-ol ((±)- 23 ).     

Molecular chaperones--cellular machines for protein folding

Proteins are linear polymers synthesized by ribosomes from activated amino acids. The product of this biosynthetic process is a polypeptide chain, which has to adopt the unique three-dimensional structure required for its function in the cell. In 1972, Christian Anfinsen was awarded the Nobel Prize for Chemistry for showing that this folding process is autonomous in that it does not require any additional factors or input of energy. Based on in vitro experiments with purified proteins, it was suggested that the correct three-dimensional structure can form spontaneously in vivo once the newly synthesized protein leaves the ribosome. Furthermore, proteins were assumed to maintain their native conformation until they were degraded by specific enzymes. In the last decade this view of cellular protein folding has changed considerably. It has become clear that a complicated and sophisticated machinery of proteins exists which assists protein folding and allows the functional state of proteins to be maintained under conditions in which they would normally unfold and aggregate. These proteins are collectively called molecular chaperones, because, like their human counterparts, they prevent unwanted interactions between their immature clients. In this review, we discuss the principal features of this peculiar class of proteins, their structure-function relationships, and the underlying molecular mechanisms.     

Rotational fluctuations of water inside the nanopores of SBA-type molecular sieves

The rotational molecular dynamics of water confined to nanoporous molecular sieves of a regular hexagonal (SBA-15) and of a foamlike pore structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(9) Hz and in a broad temperature interval. Two relaxation processes were observed: the process at lower frequencies is related to water molecules forming a layer, which is strongly adsorbed at the pore surface, whereas the relaxation process at higher frequencies is assigned to fluctuations of water molecules situated close to the center of the pore. The relaxation times of the low-frequency process for both materials and of the high-frequency process for the SBA-15 material have an unusual saddlelike temperature dependence, reported here for the first time. To describe this temperature dependence, a model developed for water confined to nanoporous glasses by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] was applied, which considers two competing effects. The characteristic features of these two competing processes were compared with those reported for other porous systems.     

Chiral Compounds Synthesized by Biocatalytic Reductions [New Synthetic Methods (51)]

It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H₂ and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques.     

7-Substituted prostaglandin analogues. A new synthetic approach

Starting from methyl 7-oxo-7-(1-cyclopentene)-heptanoate, a simple synthesis of the methyl esters of 7-oxo- and 7-hydroxy-9,11-dideoxy-PGF ₁ as a model for 7-substituted prostaglandin analogues is described.

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7-Substituierte Prostaglandin-Analoge — ein neuer Syntheseweg

Zusammenfassung Ausgehend von Methyl-7-oxo-7-(1-cyclopenten)-heptanoat wird eine einfache Synthese der Methylester von 7-Oxo- und 7-Hydroxy-9,11-dideoxy-PGF ₁ als Modellverbindungen für 7-substituierte Prostaglandinanaloge beschrieben.