A new approach to 6-deoxy-D-allofuranose- and 6-deoxy-L-talofuranose derivatives from 1,2:5,6-di-O-isopropylidene α-D-glucofuranose

3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet.     

New designs for inhibitors of the NF-κB: DNA binding

We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-^12,14 -prostaglandin J₂ (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs.     

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N₂ (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects.     

Fast graphs for the random walker

 Consider the time T _oz when the random walk on a weighted graph started at the vertex o first hits the vertex set z. We present lower bounds for T _oz in terms of the volume of z and the graph distance between o and z. The bounds are for expected value and large deviations, and are asymptotically sharp. We deduce rate of escape results for random walks on infinite graphs of exponential or polynomial growth, and resolve a conjecture of Benjamini and Peres. Received: 31 October 2000 / Revised version: 5 January 2002 / Published online: 22 August 2002     

Meshless method for nonlinear heat conduction analysis of nano-composites

Carbon nanotubes (CNTs) may become ideal reinforcing materials for high-performance nano-composites due their exceptional properties. Still, much work is needed to be done before the potentials of CNT based composites can be fully realized. The evaluation of effective material properties of nano-composites is one of many difficult tasks. Simulations using continuum mechanics approach can play a significant role in the analysis of these composites. In the present work, nonlinear heat conduction analysis of CNT based composites has been carried out using continuum mechanics approach. Element free Galerkin method has been applied as a numerical tool. Thermal conductivities of nanotube and polymer matrix are assumed to vary quadratically with temperature. Picard and quasi-linearization schemes have been utilized to obtain the solution of a system of nonlinear equations. Cylindrical representative volume element has been used to evaluate the thermal properties of nano-composites. Present simulations show that the temperature dependent matrix thermal conductivity has a significant effect on the equivalent thermal conductivity of the composite, whereas temperature dependent nanotube thermal conductivity has a small effect on the equivalent thermal conductivity of the composite. The results obtained by Picard method have been found almost similar with those obtained by quasi-linearization approach.     

Information theory for experiments with known conditional probabilities: Application to the prediction of branching ratios

Information theory is used, under conditions of incomplete data, to provide a maximally conservative prior expectation of a population distribution. This is done by systematically refining the estimates of the full distribution via the incorporation of fragmentary data in the form of conditional probabilities. The net effect is to reduce the available phase space volume of the distribution as more data are incorporated. The above refinements are then applied to calculate estimates of branching ratios for chemical reactions with more than one possible product. Two new branching ratio expressions are derived: one for the case where each product's internal state distribution is known for reactions originating from various specific reactant state?, and when the joint state-to-state reactive probability is known.     

Determination of naphthoquinones (K vitamins) and Methylene Blue with electrogenerated titanium(III)

Summary Trace quantities of naphthoquinones and Methylene Blue are titrated with titanium (III) electrogenerated at a platinum cathode from an electrolyte of 0.4M titanium tetrachloride and 8M sulphuric acid, with potentiometric detection of the end-point. For naphthoquinones, 15–50% of methanol is added to prevent adsorption of the naphthohydroquinone product onto the generating electrode. For Methylene Blue, 2×10^–6 M selenium(IV) is added as a catalyst and the titration is performed at 70° C to speed up the titration reaction.

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Zusammenfassung Spurenmengen von Naphthochinonen und von Methylenblau lassen sich mit Titan(III) titrieren. Dieses wird auf elektrochemischem Weg an einer Platinkathode aus 0,4-m Titantetrachlorid und 8-m Schwefelsäure gewonnen. Die Endpunktanzeige erfolgt potentiometrisch. Bei der Bestimmung von Naphthochinonen setzt man 15–50% Methanol zu, um die Adsorption von Naphthohydrochinon an der Generatorelektrode zu vermeiden. Für die Bestimmung von Methylenblau verwendet man 2 · 10^–6-m Selen(IV)lösung als Katalysator und titriert bei 70° C, um die Reaktion zu beschleunigen.

     

Mutual binary separations of cadmium(II), indium(III) and thallium(III) as chlorides by their extraction in high molecular weight amines

The extraction of cadmium(II), indium(III) and thallium(III) with high molecular weight amines have been studied from aqueous hydrochloric acid solutions. Using the data mutual binary separations of these three elements with high separation coefficients are proposed. Various variables like type of amine, amine concentration and organic diluent were explored to propose the best conditions of separations.     

(E)-3-(2-Alkyl-10H-phenothiazin-3-yl)-1-arylprop-2-en-1-ones: Preparative, IR, NMR and DFT study on their substituent-dependent reactivity in hydrazinolysis and sonication-assisted oxidation with copper(II)nitrate

A series of novel 3(5)-aryl/ferrocenyl-5(3)-phenothiazinylpyrazoles and pyrazolines were obtained by substituent-dependent regioselective condensation of the corresponding (E)-3-(2-alkyl-10H-phenothiazin-3-yl)-1-aryl/ferrocenylprop-2-en-1-one with hydrazine or methylhydrazine in acetic acid. The different propensity of the primary formed beta-hydrazino adducts to undergo competitive retro-Mannich reaction was interpreted in terms of tautomerisation equilibrium constants calculated by DFT using a solvent model. The regioselectivity of the cyclisation reactions with methylhydrazine and the substituent-dependent redox properties of pyrazolines were also rationalized by comparative DFT calculations performed for simplified model molecules. On the effect of ultrasound-promoted oxidation with copper(II)nitrate phenothiazine-containing pyrazolines, enones and oxo-compounds were selectively transformed into sulfoxides. Only one sulfoxide enone was partially converted into an oxirane derivative. The structure of the novel products was determined by IR and NMR spectroscopy including COSY, HSQC, HMBC and DNOE measurements.     

The spectrum of the random environment and localization of noise

We consider random walk on a mildly random environment on finite transitive d-regular graphs of increasing girth. After scaling and centering, the analytic spectrum of the transition matrix converges in distribution to a Gaussian noise. An interesting phenomenon occurs at d = 2: as the limit graph changes from a regular tree to the integers, the noise becomes localized. The graphs of the noise covariance structure for d = 4, 3, 2.1 from above.