An efficient high-yield synthesis of D-ribo-phytosphingosine

[Structure: see text] [4R-[4alpha(S),5alpha]]-2,2-Dimethyl-4-(2-oxo-5-vinyl[1,3]dioxolan-4-yl)oxazolidine-3-carboxylic acid tert-butyl ester 5a, obtained in excellent yield and diastereoselectivity by the alpha-hydroxyallylation of the Garner aldehyde (4), is exploited in a novel high-yield synthesis of D-ribo-phytosphingosine (8), using microwave-enhanced cross metathesis as the key step in the chain elongation.     

A theoretical basis for parameter selection and instrument design in comprehensive size-exclusion chromatography x liquid chromatography

A novel approach for the selection of the operational parameters (linear velocity, column length) for a comprehensive 2D-LC system is discussed. Starting point for the calculations is a given second dimension ((2)D) separation and a desired peak capacity for the 2D system. Using the theory developed here the optimum settings for the first dimension ((1)D) column can be derived. Theory clearly indicates that the choice of the (1)D conditions is basically limited to just one set of column lengths and linear velocities. The new method is tested on a comprehensive two-dimensional liquid chromatography system which uses size-exclusion chromatography (SEC) followed by reversed phase liquid chromatography (RPLC). A novel LC/LC interface, using a six-port valve rather than storage loops, joins the two chromatographic dimensions. From a theoretical comparison of continuous low flow and stop-flow operation the latter method was found to be an attractive mode of interfacing. The common idea that stop-flow operation results in additional band broadening is shown to be incorrect. The new interface design operated in the stop-flow mode permits the use of conventional analytical diameter HPLC columns, 7.8mm for SEC and 4.6mm for RPLC. The reversed phase chromatography utilizes a monolithic C-18 modified silica column, which produces fast and efficient analyses. As test samples complex mixtures of peptides were analyzed.     

Analytic Features of Reproducing Groups for the Metaplectic Representation

We introduce the notion of admissible subgroup of relative to the (extended) metaplectic representation via the Wigner distribution. Under mild additional assumptions, it is shown to be equivalent to the fact that the identity holds (weakly) for all We use this equivalence to exhibit classes of admissible subgroups of We also establish some connections with wavelet theory, i.e., with curvelet and contourlet frames.     

Noise-enhanced classical and quantum capacities in communication networks

The unavoidable presence of noise is thought to be one of the major problems to solve in order to pave the way for implementing quantum information technologies in realistic physical platforms. However, here we show a clear example in which noise, in terms of dephasing, may enhance the capability of transmitting not only classical but also quantum information, encoded in quantum systems, through communication networks. In particular, we find analytically and numerically the quantum and classical capacities for a large family of quantum channels and show that these information transmission rates can be strongly enhanced by introducing dephasing noise in the complex network dynamics.     

Vinylidene-quinone methides, photochemical generation and β-silicon effect on reactivity

Irradiation of 2-alkynylphenols resulted in the generation of vinylidene-quinone methides (QMs), which were detected by laser flash photolysis in organic solvents and aqueous acetonitrile. QMs' spectroscopic properties and electrophilicity were both significantly affected by β-silicon effect. The hydration of the alkynyl moiety (22 and 900 M(-1) s(-1)for QM-1 and QM-2, in aqueous acetonitrile) was an acid- and base-catalyzed process. The addition of amines was fast (9.2 × 10(3) M(-1) s(-1) < k(2) < 1.3 × 10(8) M(-1) s(-1)), yielding ketimines, with primary amines.     

Strongly damped wave equations with critical nonlinearities

This note deals with the strongly damped nonlinear wave equation

_utt−Δ_ut−Δu+f(_ut)+g(u)=h$u_{tt}-\Delta u_t-\Delta u+f\left(u_t\right)+g\left(u\right)=h$

with Dirichlet boundary conditions, where both the nonlinearities f$f$ and g$g$ exhibit a critical growth, while h$h$ is a time-independent forcing term. The existence of an exponential attractor of optimal regularity is proven. As a corollary, a regular global attractor of finite fractal dimension is obtained.     

Chemical Identification of Specialized Metabolites from Sulla (Hedysarum coronarium L.) Collected in Southern Italy

Sulla (Hedysarum coronarium L.) is a biennal forage legume originated from the Mediterranean basin and used for animal feeding due to its high forage quality and palatability. Several species of Hedysarum have been considered for their nutritional, pharmaceutical, and biological properties, and different applications have been reported, both for human consumption and animal nutrition. Although a systematic investigation of the chemical constituents of Hedysarum spp. has been performed in order to provide chemotaxonomic evidences for the genus and to support the pharmacological application of several species within the genus, few data are available on the chemical constituents of H. coronarium, and only the content of condensed tannins and flavonoids in leaves has been previously reported. In the present paper, results from a detailed chemical analysis of the extracts from the leaves and flowers of H. coronarium grown wild in southern Italy are presented. Identification of the main specialized metabolites within the chemical classes of flavonoids, proanthocyanidins and saponins, is described, including considerations on their content in the two plant organs. Information acquired from this study expands the knowledge on H. coronarium as a source of valuable phytochemicals for different applications in human and animal health and nutrition.     

Regularity via duality in calculus of variations and degenerate elliptic PDEs

A technique based on duality to obtain $H^1$ or other Sobolev regularity results for solutions of convex variational problems is presented. This technique, first developed in order to study the regularity of the pressure in the variational formulation of the Incompressible Euler equation, has been recently re-employed in Mean Field Games. Here, it is shown how to apply it to classical problems in relation with degenerate elliptic PDEs of p-Laplace type. This allows to recover many classical results via a different point of view, and to have inspiration for new ones. The applications include, among others, variational models for traffic congestion and more general minimization problems under divergence constraints, but the most interesting results are obtained in dynamical problems such as Mean Field Games with density constraints or density penalizations.     

Probing phase transitions under extreme conditions by ultrafast techniques: Advances at the Fermi@Elettra free-electron-laser facility

Novel possibilities for studying matter under extreme conditions are opened by the forthcoming availability of free electron laser (FEL) facilities generating subpicosecond photon pulses of high intensity in the VUV and X-ray range, which are able to heat thin samples up to the warm dense matter (WDM) regime. Pump-and-probe ultrafast techniques can be used to study the dynamics of phase transitions and characterize the states under extreme and metastable conditions. Ultrafast (10-100 fs) bulk heating is seen as a novel route for accessing extremely high temperature regimes as well as the transition region between low-density and high density fluids, that is presently considered a no man's land in simple liquids and glasses. Here we briefly describe the present status of the TIMEX end-station devoted to those experimental activities at the Fermi@Elettra FEL facility, and some preliminary results obtained in a pilot ultrafast experiment using a laser source as a pump and a supercontinuum probe aimed to characterize the melting process of Silicon.     

Potential of alkyl orthoformates as alkylating agents of non-electron rich nitrogen heterocycles

Findings and suggestions about the potential of the alkyl orthoformates as alkylating agents of non electron rich nitrogen heterocycles and unambiguous instrumental and chemical characterization of the alkylated compounds are reported.