Synthesis of dihydropyridine and piperidine derivatives via an unexpected reaction of pyridine with acetyl chloride

Acetyl chloride reacts with pyridine to give a mixture of N-acetyl-1,4- and 1,2-dihydropyridyl acetic acid (1a,b) after water quenching. The reactioninvolves the formation of a zwitterionic ketene enolate intermediate which results from deprotonation of the acetyl moiety of the in situ formed N-acetyl pyridinium ion. The effect on the reaction outcome of different parameters as temperature, pyridine/acetyl chloride molar ratio, and as Lewis acids and triflate counterion presence has been studied in detail, and a reaction mechanism has been proposed

The nature and strength of inter-layer binding in graphite

We computed the inter-layer bonding properties of graphite using an ab-initio many body theory. We carried out variational and diffusion quantum Monte Carlo calculations and found an equilibrium inter-layer binding energy in good agreement with most recent experiments. We also analyzed the behavior of the total energy as a function of interlayer separation at large distances comparing the results with the predictions of the random phase approximation.Comment: 5 pages; to appear in Phys. Rev. Let

Theoretical constraints for the magnetic-dimer transition in two-dimensional spin models

From general arguments, that are valid for spin models with sufficiently short-range interactions, we derive strong constraints on the excitation spectrum across a continuous phase transition at zero temperature between a magnetic and a dimerized phase, that breaks the translational symmetry. From the different symmetries of the two phases, it is possible to predict, at the quantum critical point, a branch of gapless excitations, not described by standard semi-classical approaches. By using these arguments, supported by intensive numerical calculations, we obtain a rather convincing evidence in favor of a first-order transition from the ferromagnetic to the dimerized phase in the two-dimensional spin-half model with four-spin ring-exchange interaction, recently introduced by A.W. Sandvik et al. [Phys. Rev. Lett. 89, 247201 (2002)].Comment: 7 pages and 5 figure

Ab initio investigation of the melting line of nitrogen at high pressure

Understanding the behavior of molecular systems under pressure is a fundamental problem in condensed matter physics. In the case of nitrogen, the determination of the phase diagram and in particular of the melting line, are largely open problems. Two independent experiments have reported the presence of a maximum in the nitrogen melting curve, below 90 GPa, however the position and the interpretation of the origin of such maximum differ. By means of ab initio molecular dynamics simulations based on density functional theory and thermodynamic integration techniques, we have determined the phase diagram of nitrogen in the range between 20 and 100 GPa. We find a maximum in the melting line, related to a transformation in the liquid, from molecular N_2 to polymeric nitrogen accompanied by an insulator-to-metal transition

La scrittura politico-culturale: Callisto Cosulich tra televisione, critica e lotta alla censura

1L'opera di Callisto Cosulich, come risultato di una pratica costante: la scrittura come strumento privilegiato di divulgazione professionale e cinefiliaca dei contenuti, come luogo prediletto d’appassionata enunciazione politico-culturale, mezzo e fine di lotta intellettuale atti alla trasformazione, verso un miglioramento complessivo e istituzionale, attraverso la difesa e la divulgazione del bello e dell’etico nel proprio specifico estetico, quello critico e cinematografico. La sua scrittura come impegno radical, anche quando mestierante: mai organica, sempre militante, pur libera da specifiche militanze.nonemixedSpanu M.Spanu, Massimilian

II Ruolo dei cereali autunno-vernini nell'approvvigionamento foraggero delle aziende meridionali

During 1974/75 season has been tested the productive performance of 5 autumn sown cereals utilized as pasture or fodder at different growing stages: grass, dough stage and fully ripe. Once winter utilization as grass pasture does not prejudice the future yield as far F.U. produced, so that Rogar 8 variety exceeds at dough stage the 10,000 F.U. per hectare whereas barley and triticale reach out value of about 9,500 F.U. per hectare. When utilized twice in winter as grass pasture a sensible yield loss is recorded either at dough stage or at fully ripe. For all the cereals tested it has been observed a decreasing of nutritional value when utilized at fully ripe in comparison to dough stage

Lattice effects on the spin dynamics in antiferromagnetic molecular rings

We investigate spin dynamics in antiferromagnetic (AF) molecular rings at finite temperature in the presence of spin-phonon (s-p) interaction. We derive a general expression for the spin susceptibility in the weak s-p coupling limit and then we focus on the low-frequency behavior, in order to discuss a possible microscopic mechanism for nuclear relaxation in this class of magnetic materials. To lowest order in a perturbative expansion, we find that the susceptibility takes a Lorentzian profile and all spin operators ($S^x$, $S^y, S^z$) contribute to spin dynamics at wave vectors $q\ne 0$. Spin anisotropies and local s-p coupling play a key role in the proposed mechanism. Our results prove that small changes in the spatial symmetry of the ring induce qualitative changes in the spin dynamics at the nuclear frequency, providing a novel mechanism for nuclear relaxation. Possible experiments are proposed.Comment: 4 pages, 2 figures. to appear in PR

Sintesi stereoselettiva di ureido-zuccheri via 5-(alditol-1-C-il) idantoina building blocks: effetto del gruppo protettivo dell'idantoina sulla diastereoselettività

In questo lavoro verrà presentata la sintesi stereoselettiva di interessanti ureido-zuccheri che sfrutta 5-poliidrossialchil-idantoine come building blocks. Presenteremo inoltre uno studio sull’effetto del gruppo protettivo dell’idantoina sulla disatereoselettività della reazione con aldeidi omochirali

Microbiological challenge testing for Listeria monocytogenes in ready-to-eat food: a practical approach

Food business operators (FBOs) are the primary responsible for the safety of food they place on the market. The definition and validation of the product’s shelf-life is an essential part for ensuring microbiological safety of food and health of consumers. In the frame of the Regulation (EC) No 2073/2005 on microbiological criteria for foodstuffs, FBOs shall conduct shelf-life studies in order to assure that their food does not exceed the food safety criteria throughout the defined shelf-life. In particular this is required for ready-to-eat (RTE) food that supports the growth of Listeria monocytogenes. Among other studies, FBOs can rely on the conclusion drawn by microbiological challenge tests. A microbiological challenge test consists in the artificial contamination of a food with a pathogen microorganism and aims at simulating its behaviour during processing and distribution under the foreseen storage and handling conditions. A number of documents published by international health authorities and research institutions describes how to conduct challenge studies. The authors reviewed the existing literature and described the methodology for implementing such laboratory studies. All the main aspects for the conduction of L. monocytogenes microbiological challenge tests were considered, from the selection of the strains, preparation and choice of the inoculum level and method of contamination, to the experimental design and data interpretation. The objective of the present document is to provide an exhaustive and practical guideline for laboratories that want to implement L. monocytogenes challenge testing on RTE food