Microscopic structure of phospholipid bilayers: comparison between molecular dynamics simulations and wide-angle X-ray spectra

We present results of molecular dynamics simulations of fully hydrated dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine bilayers in the disordered liquid crystalline phase (Lalpha) and compare them to wide-angle X-ray scattering experiments. Though we find a generally good agreement between the simulated and experimental spectra, there are some deviations whose origin has been investigated by a reparametrization of the aliphatic chains' force field. A detailed analysis of the various contribution to the X-ray spectra shows that a non-negligible contribution to the total scattered intensity comes from the headgroups and the head-tail cross correlation.     

Excitation energy dependence of the optical properties of InGaAs/GaAs quantum well heterostructures

Il Nuovo Cimento D - We report an experimental study on a large set of InGaAs/GaAs quantum well structures by means of continuous-wave photoluminescence and photoluminescence excitation. The...     

The Reduction of Benzofuroxans by Ferrous Salts and by Thiophenol

Treatment of benzofuroxan derivatives with ferrous sulphate in DMSO/water solution affords in high yield o-nitroanilines. o-Nitroaniline was also obtained by reduction of benzofuroxan with thiophenol in presence of catalytic amount of Fe²⁺ or Fe³⁺ salts.     

Free volume properties of a linear soft polymer: a computer simulation study

Molecular dynamics simulation of a linear soft polymer has been performed and the free volume properties of the system have been analyzed in detail in terms of the Voronoi polyhedra of the monomers. It is found that there are only small density fluctuations present in the system. The local environment of the monomers is found to be rather spherical, even in comparison with liquids of atoms or small molecules. The monomers are found to be, on average, eight coordinated by their nearest geometric neighbors, including intra-chain and inter-chain ones. The packing of the monomers is found to be rather compact, in a configuration of 1900 monomers there are, on average, only three voids large enough to incorporate a spherical particle as large as a monomer, indicating that the density of the large vacancies in the system is considerably, i.e., by a few orders of magnitude lower than in molecular liquids corresponding to roughly the same reduced densities.     

One-pot synthesis of aziridines from vinyl selenones and variously functionalized primary amines

Variously substituted aziridines were conveniently prepared by an aza-Michael Initiated Ring Closure (aza-MIRC) reaction starting from vinyl selenones and primary amines, aminoalcohols or diamines. The reactions proceed in very high yields at room temperature in toluene or water. A significant rate acceleration was observed under aqueous conditions.     

The development of a gas chromatographic–mass spectrometric analytical procedure for the determination of lipids,proteins and resins in the same paint micro-sample avoiding interferences from inorganic media

This paper presents a GC–MS analytical procedure for determining proteinaceous materials, glycerolipids, natural waxes and terpenoid resins in the same paint micro-sample. The procedure is also reliable when high amounts of interfering inorganic pigments, dryers and charges are present. The characterisation of proteinaceous binders in a paint sample can be subject to analytical interferences by inorganic materials. Such materials may form complexes with functional groups of proteins, thus preventing their efficient derivatisation, which is necessary prior to GC analysis. For this reason an analytical procedure has been developed based on two extractions and a clean-up step, in order to obtain two fractions: a lipid-resinous fraction and a proteinaceous fraction. The lipid-resinous fraction is subjected to salification/saponification assisted by microwaves, followed by acidification, extraction, derivatisation and GC–MS analysis. The proteinaceous fraction is analysed by GC–MS after hydrolysis and derivatisation of the freed amino acids. The desalting step is applied before the hydrolysis, and is based on the use of the monolithic sorbent tip technology with a C4 stationary phase. Reference paint replicas of egg, casein and animal glue were prepared with and without several metals containing pigments, and used to develop and validate the analytical procedure. The procedure proved to be efficient in desalting the proteinaceous materials both from cations and anions. Although non quantitative, it is reliable in the analysis of samples whose content of extractable proteins is <1 μg, thus showing it to be suitable for the characterisation of paint samples. An example of how the analytical procedure was used to characterise a sample from a 15th century panel painting is also discussed.     

Heart-cutting two-dimensional (size exclusion × reversed phase) liquid chromatography–mass spectrometry analysis of flavonol glycosides from leaves of Maytenus ilicifolia

Two-dimensional liquid chromatography–electrospray ionization mass spectrometry was employed to analyze flavonol glycosides present in leaves of Maytenus ilicifolia, frequently used in traditional Brazilian medicine. Since they contain many flavonol glycosides, including isomers, one-dimensional liquid chromatography did not give complete separation and identification, yielding overlapping of compounds with different molecular weights. Thus, employing size exclusion chromatography in the first and reversed phase in the second dimension, a great number of flavonol glycosides could be identified and its relative abundances determined. The majority of glycosides contained kaempferol or quercetin as aglycones, and glycosides with previously unreported structures were also present and characterized.     

Polymorphism and Phonon Dynamics of α‐Quaterthiophene

Two 4T: Low‐frequency micro‐Raman spectroscopy coupled with lattice dynamics calculations is an invaluable tool for investigating polymorphism in organic semiconductors. The Raman spectra of the low‐temperature (LT) and high‐temperature (HT) polymorphs of α‐quaterthiophene (4T) are presented and interpreted (see picture). Raman mapping is applied to investigate the phase purity.

     

Metal-organic chains constructed from pre-organized N2S2 donor ligands

Three new N₂S₂ donor ligands 1,1′-((2-(2-(phenylthio)phenylthio)phenyl)methylene)bis(3,5-R-1H-pyrazole), R = H (L^H), R = Me (L^Me), R = i-Pr (L^i-Pr) have been prepared and characterized. These bifunctional ligands incorporate two distinct chelate donor systems, by virtue of the presence of bispyrazole and bisthioether functions. The preferred conformation of these ligands is such that the N₂ and S₂ donor moieties may be oriented in opposite directions, thus favoring the formation of molecular chains when treated with AgBF₄. The X-ray structures of Ag(I) complexes show that, depending on the steric hindrance present on the pyrazole rings, these ligands behave as κ⁴-SSNN-μ bridging tetradentate (when R = H), or κ³-SNN-μ bridging tridentate (when R = Me, i-Pr). Interestingly, [Ag(L^H)]BF₄ crystallizes in the chiral space group P4₁, with the molecular chain that is folded around the 4₁ screw axis.     

An artificial ionophore based on a polyhydroxylated steroid dimer

The Na+ transporting properties of the first member of a new class of artificial ionophores, based on a C2-symmetric polyhydroxylated steroid dimer, are described.