Synthetic Approach to Kdo Glycosides Via Exo-Glycal Epoxides and Rationalization of the Stereo Chemical Outcome

Abstract

The use of epoxides obtained by dimethyldioxirane epoxidation of 2,3-anhydro-1,3-dideoxy-4,5:7,8-di-O-isopropylidene-D-manno-oct-1-enitol as glycosyl donors is described. This method offers a simple and stereoselective access to precursors of Kdo glycosides. The stereochemical outcome of the reaction is rationalized by means of semiempirical calculations of the transition states leading to glycosides formation.     

Determination of the Composition of Cyclopolymers in Terms of Structural Units

A method based on the analytical evaluation of residual unsaturations and on the knowledge of the cyclization ratios is presented for the determination of the cyclopolymer composition in terms of structural units. The application of this method to the products of the free radical polymerization of vinyl-transcrotonate and of divinyl ether is described.     

Geometric Structures over Four-Dimensional Generalized Symmetric Spaces

We classify Walker structures, self-dual and anti-self-dual metrics among the invariant metrics of four-dimensional generalized symmetric spaces.     

5‐Benzoyl­amino‐3‐bromo‐4‐(4‐methoxy­phenyl)‐4,5‐di­hydro­isoxazole‐5‐carboxyl­ic acid

The title compound, C₁₈H₁₅BrN₂O₅, a promising N‐protected α‐amino acid, was synthesized directly from an unusual bromo dipole and a 4‐(aryl­methyl­ene)­oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph‐set motifs driven by the most important hydrogen bonds are described.     

Mechanistic Aspects of the Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction

The story of C−C bond formation includes several reactions, and surely Suzuki-Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction. Computational chemistry is key in identifying the rds and thus leading to milder conditions on an experimental level by means of predictive catalysis.     

R410A condensation inside a commercial brazed plate heat exchanger

This paper presents the heat transfer coefficients and the pressure drop measured during HFC-410A condensation inside a commercial brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass flux (<20 kg/m² s) the saturated vapour condensation heat transfer coefficients are not dependent on mass flux and are well predicted by Nusselt [W. Nusselt, Die oberflachenkondensation des wasserdampfes, Energy 60 (1916) 541–546, 569–575] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (>20 kg/m²s) the saturated vapour condensation heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [W.W. Akers, H.A. Deans, O.K. Crosser, Condensing heat transfer within horizontal tubes, Chem. Eng. Prog. Symp. Series 55 (1959) 171–176] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by Webb [R.L. Webb, Convective condensation of superheated vapor, ASME J. Heat Transfer 120 (1998) 418–421] model. A simple linear equation based on the kinetic energy per unit volume of the refrigerant flow is proposed for the computation of the frictional pressure drop.     

Efficient hydroxycarbonylation of aryl iodides using recoverable and reusable carbon aerogels doped with palladium nanoparticles as catalyst

Electron-rich and electron-poor aryl iodides are converted, in high to excellent yields, into the corresponding carboxylic acids through a hydroxycarboxylation reaction catalyzed by a recoverable and reusable phosphine free palladium-carbon aerogel catalyst using lithium formate and acetic anhydride as an internal condensed source of carbon monoxide. The catalyst system can be reused several times without any appreciable loss of activity.     

High performance parallel numerical methods for Volterra equations with weakly singular kernels

Non-stationary discrete time waveform relaxation methods for Abel systems of Volterra integral equations using fractional linear multistep formulae are introduced. Fully parallel discrete waveform relaxation methods having an optimal convergence rate are constructed. A significant expression of the error is proved, which allows us to estimate the number of iterations needed to satisfy a prescribed tolerance and allows us to identify the problems where the optimal methods offer the best performance. The numerical experiments confirm the theoretical expectations.