New rearrangement of 4-isoxazoline system: conversion of ketones into alpha,beta-unsaturated amides

A new rearrangement pattern of the 4-isoxazoline system is reported. The reaction, starting from 3,3-disubstituted derivatives and leading to alpha,beta-unsaturated amides, proceeds through the quaternarization of the nitrogen atom and involves the heterolytic cleavage of C(3)-N bond, assisted by the formation of a relatively stable intermediate. The overall process represents a useful conversion of ketones into alpha,beta-unsaturated amides.     

A decade of vibrational micro-spectroscopy of human cells and tissue (1994-2004)

Instrumentation used in infrared microspectroscopy (IR-MSP) permits the acquisition of spectra from samples as small as 100 pg (10(-10) g), and as small as 1 pg for Raman microspectroscopy (RA-MSP). This, in turn, allows the acquisition of spectral data from objects as small as fractions of human cells, and of small regions of microtome tissue sections. Since vibrational spectroscopy is exquisitely sensitive to the biochemical composition of the sample, and variations therein, it is possible to monitor metabolic processes in tissue and cells, and to construct spectral maps based on thousands of IR spectra collected from pixels of tissue. These images, in turn, reveal information on tissue structure, distribution of cellular components, metabolic activity and state of health of cells and tissue.     

An elastic neutron scattering on dynamical transition in hydrogen-bonded systems

Elastic incoherent neutron scattering measurements have been performed on trehalose and sucrose/D₂O mixtures as a function of temperature. The study provides an effective way for characterizing the dynamical behaviour, furnishing a set of parameters characterizing the ‘flexibility’ and the ‘rigidity’ that justifies the better cryptobiotic effect of trehalose with respect to sucrose. Elastic scans make evident a non-Gaussian behaviour of the intensity profiles, which is more marked for sucrose, with a dynamical transition at T253 and 250 K for trehalose/D₂O and sucrose/D₂O mixtures, respectively.     

Electron-impact-induced rearrangements of organic ions: IV—Hydrogen and carbon scrambling in [t-C3H8N]+ metastable ions

Independent loss of positional identity of the hydrogen and carbon atoms in [t-C₃H₈N]⁺ metastable cations prior to fragmentation in the gas phase with loss of ethylene, has been demonstrated by ²H and ¹³C labelling experiments. The scrambling reaction is interpreted as a rearrangement in competition with the high activation energy unimolecular decompositions. The study of this fragmentation process indicates the occurrence of a primary isotope effect discriminating in favour of ²H and ¹³C retention in the original methylene group.     

Conus ventricosus venom peptides profiling by HPLC-MS: a new insight in the intraspecific variation

Conus is a genus of predatory marine gastropods that poison the prey with a complex mixture of compounds active on muscle and nerve cells. An individual cone snail's venom contains a mixture of pharmacological agents, mostly short, structurally constrained peptides. This study is focused on the composition of the venom employed by Conus ventricosus Gmelin, 1791, a worm-hunting cone snail living in the Mediterranean Sea. For this purpose, LC coupled to MS techniques has been successfully used to establish qualitative and quantitative differences in conopeptides from minute amounts of venom ducts. We were able to prove variability in the venom conopeptide complement, possibly related to different trophic habits of the species in the Mediterranean Sea. Moreover, the information-rich MS techniques enabled us to identify two novel C. ventricosus peptides, here named Conotoxin-Vn and -Conotoxin-Vn. On the basis of the structural data collected so far, we suggest that Conotoxin-Vn is a conopeptide belonging to the -family that recognizes calcium channels through a specific pharmacophore. Similarly, molecular modeling data suggest that -Conotoxin-Vn should represent a competitive antagonist of neuronal nicotinic acetylcholine receptors (nAChRs).     

Zinc(II) triflate-controlled 1,3-dipolar cycloadditions of C-(2-thiazolyl)nitrones: application to the synthesis of a novel isoxazolidinyl analogue of tiazofurin

[reaction: see text] The cycloaddition reaction between C-(2-thiazolyl) nitrones and allylic alcohol takes place with complete exo selectivity when the reactions are carried out in the presence of 1 equiv of zinc triflate. The rate of the reaction is increased enormously under microwave irradiation. The use of a chiral dipolarophile allowed application of the methodology to the synthesis of a hitherto unknown enantiomerically pure isoxazolidinyl analogue of the C-nucleoside tiazofurin.     

Role of counteranions in acid-induced aggregation of isomeric tetrapyridylporphyrins in organic solvents

The effect of adding various kinds of acids HX (X = Cl, Br, I, CF(3)COO, CF(3)SO(3), TFPB ((3,5-(CF(3))(2)C(6)H(3))(4)B) to isomeric tetra(2-pyridyl)porphyrin, tetra(3-pyridyl)porphyrin, and tetra(4-pyridyl)porphyrin (TpyP(2), TpyP(3), and TpyP(4)) in dichloromethane solution has been investigated through the combined use of UV/vis absorption, fluorescence emission, and resonance light scattering (RLS) techniques. The experimental evidence points to a marked dependence of the protonation and aggregation behavior on the nature of both acids and porphyrins. In general, three different trends can be recognized: (i) formation of a fully protonated species, followed by aggregation; (ii) formation of a tetraprotonated species, which aggregates and, on further addition of acid, disaggregates; and (iii) protonation of the four pyridyl moieties, leading to a tetraprotonated ion pair, in the unique case of the bulky TFPB(-) anion. In all cases, the protonated species and the resulting aggregates exhibit spectroscopic features that are markedly influenced by the nature of the counteranions. A model for J-aggregation has been proposed on the basis of an interplay of hydrogen bonding, electrostatic interactions, and dispersive interactions. Kinetic control of the aggregation process allows for a fine-tuning of the spectroscopic properties of the final aggregated species.     

On the law of mass action in fluid mixtures with several temperatures

Summary A mixture is considered in which each constituent is an electrically charged fluid and has its own temperature field. On starting from the usual balance equations and by adopting suitable constitutive equations, a reduced dissipation inequality is derived; this inequality is investigated in the case of constituents with the same velocity. Thus the law of mass action is obtained in a form which generalizes that for constituents at a common temperature. As an application, a plasma is considered, the chemical reaction being an ionization reaction. As a consequence of the law of mass action a relation between the number densities (Saha’s equation) is determined for mixtures with several temperatures.

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Riassunto Si considera una miscela di costituenti fluidi, elettricamente carichi, a ciascuno dei quali è associata una specifica temperatura. Partendo dalle usuali equazioni di bilancio e assumendo opportune equazioni costitutive si perviene ad una disuguaglianza di dissipazione ridotta la quale è esaminata nell’ipotesi che i diversi costituenti abbiano la stessa velocità. In tal modo si ottiene la legge di azione di massa in una forma che generalizza quella valida per temperature uguali. Come applicazione si considera un plasma nel caso di una reazione di ionizzazione; si perviene ad una generalizzazione dell’equazione di Saha valida anche per temperature diverse dei costituenti.

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Резюме Рассматривается смесь, в которой каждый компонент представляет электрически заряженную жидкость и имеет свое собственное температурное поле. Исхода из обычных уравнений баланса и применяя соответствующие конститутивные уравнения, выводится приведенное диссипативное неравенство. Полученное неравенство исследуется в случае компонентов с одинаковой скоростью. Таким образом, закон действия масс получается в форме, которая обобщает закон для компонентов при общей темпетаруре. В качестве иллюстрации, рассматривается плазма, причем химическая реакция представляет реакцию ионизации. Как следствие закона действия масс, получается соотношение между плотностями (уравнения Саха) для смесей с различными температурами.

     

Nuclear magnetic resonance of psychotherapeutic agents. IV—conformational analysis of 2,3-dihydro-1H-1,4-benzodiazepines

The lanthanide shift reagent (LSR)/¹H NMR study of some 7-chloro-5-phenyl-2,3-dihydro-1 H-1, 4-benzodiazepines shows that these compounds exist in CDCI₃ solution as two pseudo-boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1-substituent: this effect may be the result of the greater basicity of 4-N when the 1-N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1- to 4-N through the fused benzene ring. The detection of H-9/1-Me through space spin-spin coupling in medazepam (7-chloro-1-methyl-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of ³J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug-receptor interaction.