Synthesis and absolute configuration of novel N,O-psiconucleosides using (R)-N-phenylpantolactam as a resolution agent

A series of novel N,O-psiconucleosides has been prepared in both enantiomeric forms by resolution of an advanced racemic synthetic intermediate using (R)-N-phenylpantolactam as a chiral resolution agent. The absolute configuration of all of these compounds has been unequivocally established by chemical correlation with the novel (R)- or (S)-1-methyl-5-phenylpyrrolidine-2,3-dione, prepared from the known (R)- and (S)-1-methyl-5-phenylpyrrolidin-2-one, respectively.     

Configurational and conformational aspects of some 5-methylenedisubstituted-3-pyrrolin-2-ones

The influence of the disubstitution at the exocyclic carbon atom of 5-methylene-3-pyrrolin-2-ones upon the configurational and conformational equilibria is studied. The results obtained confirm and extend the observations reported in the literature about the factors determining the configurational and conformational equilibria in monosubstituted systems, i.e.: 5-arylmethylene-3—pyrrolin-2-ones and 5(1H)-pyrromethenones.

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Zur Konfiguration und Konformation von einigen 5-Methylen-disubstituierten-3-pyrrolin-2-onen

Zusammenfassung Es wird der Einfluß der Disubstitution des exocyclischen C-Atoms von 5-Methylen-3-pyrrolin-2-onen auf das Konfigurations- und Konformationsgleich-gewicht untersucht. Die erhaltenen Resultate stehen im Einklang mit der Literatur, die sich auf monosubstituierte Verbindungen [5-Arylmethylen-3-pyrrolin-2-one, 5 (1H)-Pyrromethenone und strukturverwandte Gallenpigmente] beziehen, und vertiefen das Verständnis der Faktoren, die für diese Gleichgewichte maßgebend sind.

     

High-efficiency,high-energy performance of a pulsed HF laser pumped by phototriggered discharge

A comparison of the performance of pulsed infrared HF lasers pumped by phototriggered discharges using either Ne/SF₆/H₂ or Ne/SF₆/C₂H₆ mixtures are presented. For an active volume of 50 cm³, a specific output energy as high as 11 J/ has been achieved with an efficiency higher than 3% when C₂H₆ is used as H atom fuel. The replacement of ethane by molecular hydrogen reduces the laser performance by 40%. The investigation of the temporal evolution of the laser intensity shows that this dramatic decrease results from a shortening of the laser pulse duration rather than from a decrease of the peak power. Indications are given that this behavior is correlated to a very different temporal evolution of the discharge parameters, especially at low reduced electric field E/N.     

An improved model for band tail states inn-type degenerate semiconductors

Summary Using two screened donor potential energy models and a wave vectork-positionr uncertainty relation, the results of the exponential band tail states, inn-type degenerate semiconductors, obtained in our previous paper, are improved. The second-order cumulant or the correlation functionW (ϱ,E) is expressed as a function of the total donor concentration ϱ and total carrier energyE. Near band edges, the conduction and valence band tails are, respectively, proportional to exp [E/E ₀(ϱ)] and exp [−E/E ₀(ϱ)], whereE ₀(ϱ) is the energy characteristic of the appropriate band tail, in good accordance with those experimentally obtained by Pankove. Far below the conduction band edge, our result of the conduction band tail is proportional to exp [−BE ² exp [A ]], whereA andB are the functions of ϱ, which is reduced to zero more rapidly in comparison with the corresponding result obtained by Halperin and Lax (i.e. exp [−|E| ⁿ , wheren varies between 1/2 and 2). To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Liquid Droplet excitation of freestanding poly(methyl methacrylate)/graphene oxide films for mechanical energy harvesting

A simple and solvent‐free practical way to obtain freestanding poly(methyl methacrylate)/graphene oxide films is reported. Falling liquid droplets are used to produce an impulse necessary for the mechanical excitation of such composite films. A pressure wave is generated on the surface of the films by the impact. It is reported how such films are able to convert mechanical energy of the impact to electrical power. The reported example is of interest to enhance the mechanical energy harvesting and to add new functionalities to traditional polymer nanocomposites. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1028–1032     

Ruin probability and time of ruin with a proportional reinsurance threshold strategy

In this paper, we present a threshold proportional reinsurance strategy and we analyze the effect on some solvency measures: ruin probability and time of ruin. This dynamic reinsurance strategy assumes a retention level that is not constant and depends on the level of the surplus. In a model with inter-occurrence times being generalized Erlang(n)-distributed, we obtain the integro-differential equation for the Gerber?CShiu function. Then, we present the solution for inter-occurrence times exponentially distributed and claim amount phase-type(N). Some examples for exponential and phase-type(2) claim amount are presented. Finally, we show some comparisons between threshold reinsurance and proportional reinsurance.     

A Barrel-Shaped Metal–Organic Blue-Box Analogue with Photo-/Redox-Switchable Behavior

Donor–acceptor interactions are ubiquitous in the design and understanding of host–guest complexes. Despite their non-covalent nature, they can readily dictate the self-assembly of complex architectures. Here, a photo-/redox-switchable metal–organic nanocapsule is presented, which was assembled by using lanthanide ions and viologen building blocks, by relying on such donor–acceptor interactions. The potential of this unique barrel-shaped structure is highlighted for the encapsulation of suitable electron donors, akin to the well-investigated “blue-box” macrocycles. The light-triggered reduction of the viologen units has been investigated by single-crystal-to-single-crystal X-ray diffraction experiments, complemented by magnetic, optical, and solid-state electrochemical characterizations. Density functional theory (DFT) calculations were employed to suggest the most likely electron donor in the light-triggered reduction of the viologen-based ligand.     

Star-drops formed by periodic excitation and on an air cushion – A short review

When simply put on a solid, a liquid drop usually adopts the shape of a spherical cap or a puddle depending on its volume and on the wetting conditions. However, when the drop is subjected to a periodic field, a parametric excitation can induce a transition of shape and can break the drop’s initial axial symmetry, provided that the pinning forces at the contact-line are weak enough. Therefore, a standing wave appears at the drop interface and induces a periodic motion, with a frequency that equals half the excitation frequency. In the first part, we review the different situations where star drops can be generated from various types of periodic excitations. In the second part, we show that similar star drops can occur in a much less intuitive fashion when the drop is put on an air cushion, where no periodic motion is imposed a priori. Preliminary experiments as well as theoretical clues for a hydrodynamic interpretation, suggest that the periodic vibration is due to an inertial instability in the air layer below the drop.     

A kinetic study on the thermal behaviour of chitosan

The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min⁻¹. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.     

High nuclearity in azido/oximate chemistry: Ni14 and Ni13 clusters with S = 6 and 9 ground states

In the present work, we report a family of Ni(14) and unprecedented Ni(13) clusters linked by end-on azido and oximato bridges. Ferrimagnetic response gives S = 6 and 9 ground states, resulting in the largest nuclearities and spins in nickel oximato chemistry.