An MEDT study of the mechanism and selectivities of the [3+2] cycloaddition reaction of tomentosin with benzonitrile oxide

The [3+2] cycloaddition (32CA) reaction of tomentosin with benzonitrile oxide yielding a spiro-isoxazoline has been studied within the Molecular Electron Density Theory at the B3LYP/6-31(d,p) computational level. Given the multifunctionality of tomentosin, this 32CA reaction can take place along 16 competitive reaction paths. The chemo-, regio-, and stereoisomeric reaction paths involving the two C C double bonds of tomentosin have been studied. Density functional theory (DFT) calculations account for the total chemo- and regioselectivity, in complete agreement with the experimental outcomes, being suggestive of low diastereofacial selectivity. Analysis of the conceptual DFT indices accounts for the nonpolar character of this 32CA reaction. On the other hand, the topological analysis of the electron localization function of the selected points of the intrinsic reaction coordinate associated with the formation of the C C and C O single bonds emphasizes the zw-type reactivity of the phenyl nitrile oxide; the reaction taking place through a non-concerted two-stage one-step mechanism initialized with the formation of the C C single bond involving the β-conjugated carbon of tomentosin.     

Mod-retractable strongly π-regular rings and group algebras

Abstract

In this work, we show that a two-sided mod-retractable and strongly π-regular ring is two-sided semiartinian. On the other hand, a strongly π-regular von Neumann regular ring is left mod-retractable if and only if it is a left semiartinian V-ring. We apply these results to group algebras and thereby we give the complete structure of groups whose group algebras are mod-retractable.

Communicated by Toma Albu     

Convex composite functions in Banach spaces and the primal lower-nice property

Primal lower-nice functions defined on Hilbert spaces provide examples of functions that are ``integrable' (i.e. of functions that are determined up to an additive constant by their subgradients). The class of primal lower-nice functions contains all convex and lower- functions. In finite dimensions the class of primal lower-nice functions also contains the composition of a convex function with a mapping under a constraint qualification. In Banach spaces certain convex composite functions were known to be primal lower-nice (e.g. a convex function had to be continuous relative to its domain). In this paper we weaken the assumptions and provide new examples of convex composite functions defined on a Banach space with the primal lower-nice property. One consequence of our results is the identification of new examples of integrable functions on Hilbert spaces.

     

A new polymorph of (O‐ethyl dithio­carbonato‐κ2S,S′)­bis­(tri­phenylphosphine‐κP)silver(I)

A new triclinic polymorphic modification of the title compound, [Ag(C₃H₅OS₂)(C₁₈H₁₅P)₂], has been found and compared with the previously known orthorhombic modification [Tiekink (1988). Coord. Chem. 17 , 239–243]. The two polymorphs have the same molecular shape, viz. a distorted tetrahedral geometry, with a chelating di­thio­carbonate (xanthate) and two PPh₃ ligands bonded to the Ag atom. However, in this new polymorph, the xanthate ligand is bonded asymmetrically to the Ag atom, with Ag—S distances of 2.5489 (6) and 2.8055 (7) Å, while for the orthorhombic polymorph these distances are 2.686 (4) and 2.601 (4) Å. The Ag—P distances are similar in both structures.     

Stabilization of linear control systems in Hilbert space with nonlinear feedback

This paper considers the problem of stabilization of linear control systems in Hilbert space with nonlinear feedback. Extensions of known results in the linear feedback case to the nonlinear one are given.     

Nonlinear homogeneous retarded differential equations and population dynamics via translation semigroups

In this paper nonlinear homogeneous retarded differential equations and models from population dynamics and epidemiology are considered and studied by the use of translation semigroup theory. We show that the corresponding solution semigroups are equivalent to appropriate translation semigroups. Existence results for the retarded equations are established by taking the space of initial functions of the form W ^1,p ((-r,0),F) where F is a Banach space, 1≤ p<∈fty and 0<r\le∈fty . June 28, 1999     

Plasmonic properties of silver nanostructures coated with an amorphous silicon-carbon alloy and their applications for sensitive sensing of DNA hybridization

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.     

Plasma Chemical and Electrical Modeling of a Dielectric Barrier Discharge in Kr–Cl2 Gas Mixtures

This paper reports the study of the Kr–Cl₂ plasma chemistry in terms of the homogenous model of a dielectric barrier discharge and for two kinds of the applied voltage excitation shape. The effect of Cl₂ concentration in the gas mixture, as well as gas pressure and power frequency on the discharge efficiency and the 222 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to ultraviolet emission in the lamp is in the range of 4.4–12 %, and it will be very affected at high chlorine percentage (>1 %) and high gas pressure (>200 Torr). A comparison between the sinusoidal and the burst excitation waveforms reveals that the burst excitation method provides an enhanced light source performance compared to the sinusoidal wave.