Electron paramagnetic resonance studies on copper(II)-cyclodextrin systems

Three copper(II) complexes containing beta-cyclodextrin (betaCD) derivatives as ligands [mono-6-methylamino-6-deoxy-betaCD dithiocarbamate (CDTC), mono-6-histamino-6-deoxy-betaCD (CDHM) and mono-6-Nalpha-arginyl-6-deoxy-betaCD (CDARG)] have been studied by electron paramagnetic resonance. The spectra have been recorded at X- and S-bands and different temperatures and simulated to obtain the best set of magnetic parameters. In particular, the 300 K spectra are typical of the slow motion regime, as expected considering the high molecular weight of the ligands. Some structural characteristics of the complexes are proposed on the basis of dynamic and covalency parameters obtained from simulation.     

Deciphering the Electronic Transitions of Thiophene-Based Donor-Acceptor-Donor Pentameric Ligands Utilized for Multimodal Fluorescence Microscopy of Protein Aggregates

Anionic pentameric thiophene acetates can be used for fluorescence detection and diagnosis of protein amyloid aggregates. Replacing the central thiophene unit by benzothiadiazole (BTD) or quinoxaline (QX) leads to large emission shifts and basic spectral features have been reported [Chem. Eur. J. 2015 , 21, 15133-13137]. Here we present new detailed experimental results of solvent effects, time-resolved fluorescence and examples employing multi-photon microscopy and lifetime imaging. Quantum chemical response calculations elucidate how the introduction of the BTD/QX groups changes the electronic states and emissions. The dramatic red-shift follows an increased conjugation and quinoid character of the π-electrons of the thiophene backbone. An efficient charge transfer in the excited states S₁ and S₂ compared to the all-thiophene analogue makes these more sensitive to the polarity and quenching by the solvent. Taken together, the results guide in the interpretation of images of stained Alzheimer disease brain sections employing advanced fluorescence microscopy and lifetime imaging, and can aid in optimizing future fluorescent ligand development.     

Trace metal concentration in wild avian species from Campania,Italy

This study was conducted to determine heavy metals concentrations in tissues of 94 birds belonging to different species from coastal areas of Naples and Salerno (Southern Italy) in order to provide baseline data concerning trace element levels in wild birds living in or close to an area characterized by high anthropogenic impact. Additional aim of this study was to verify if diet influenced metal accumulation, so birds were classified as birds of prey, fish eating birds and insectivorous birds.     

Analysis of Optical Erasure Efficiency in WDM-PONs Employing Carrier Remodulation

This paper proposes a method to monitor the operation performance of reflective semiconductor optical amplifier (RSOA)-based optical network units (ONUs) in wavelength-reuse wavelength-division-multiplexing passive optical network topologies. For this goal, the optical erasure efficiency of ONU RSOA is numerically evaluated through remote measurements at the optical line terminal site, using the VPI Transmission Maker software. The results show good correlation with the optical erasure behavior of RSOA in the injection power range of –20 to –5 dB, bias current of 50 and 150 mA, and confinement factor of 0.2 and 0.3. As a consequence, this method can be used to qualitatively estimate the optical and electrical features of ONU RSOA from the central office, instead of performing a local direct measurement.     

A simple multiaxial fatigue criterion for metals

A new simple multiaxial high-cycle fatigue endurance criterion, suitable for situations where the convex hull associated with the stress path approximates well an ellipsoid, is proposed. It considers, as measures of fatigue solicitation: (i) a new definition for the equivalent shear stress amplitude; and (ii) the maximum principal stress along the stress history. Assessment of the resulting criterion for a wide range of in-phase and out-phase cyclic loads shows that it compares very well with experimental data published in the literature. To cite this article: C.A. Gonçalves et al., C. R. Mecanique 332 (2004).

Résumé

On propose un critère simple d'endurance à la fatigue polycyclique, applicable à des situations pour lesquelles l'envelope convexe associé à l'histoire des contraintes s'approche bien d'une ellipse. Le critère considère, comme mesures de solicitation à la fatigue : (i) une nouvelle définition de l'amplitude de contrainte de cisaillement ; et (ii) la contrainte principale maximale au cours de l'histoire de chargement. Pour citer cet article : C.A. Gonçalves et al., C. R. Mecanique 332 (2004).     

Wittig Reaction: Role of Steric Effects in Explaining the Prevalent Formation of Z Olefin from Nonstabilized Ylides

Abstract

For understanding the mechanism involved in the Wittig reaction, it is important to know the factors which influence the stability of 1,2-oxaphosphetane intermediates with pentacoordinate phosphorus; in these intermediates, the steric factor plays a predominant role. Studying the Wittig reaction between nonstabilized ylides and different aldehydes, we noted that the stereochemical outcome driving toward Z-olefin formation was influenced only by different steric factors. The proposed mechanism differs from those previously reported because it underlines the fundamental role of the two cis/trans oxaphosphetane intermediates with the oxygen atom in equatorial position.     

Fluorine Substitution Effects on Flexibility and Tunneling Pathways: The Rotational Spectrum of 2‐Fluorobenzylamine

The effect of ring fluorination on the structural and dynamical properties of the flexible model molecule 2‐fluorobenzylamine has been studied by rotational spectroscopy in free‐jet expansion and quantum chemical methods. The complete potential energy surface originating from the flexibility of the aminic side chain has been calculated at the B3LYP/6‐311++G** level of theory and the stable geometries were also characterized with MP2/6‐311++G**. The rotational spectra show the presence of two of the predicted four stable conformers: the global minimum (I), in which the side chain’s dihedral angle with the phenyl plane is almost perpendicular, is stabilized by an intramolecular hydrogen bond between the fluorine atom and one hydrogen of the aminic group; and a second conformer II (E_II?E_I≈5 kJ mol^?1) in which the dihedral angle is smaller and the amino group points towards the aromatic ortho hydrogen atom. This conformation is characterized by a tunneling motion between two equivalent positions of the amino group with respect to the phenyl plane, which splits the rotational transition. The ortho fluorination increases, with respect to benzylamine, the tunneling splitting of this motion by four orders of magnitude. The motion is analyzed with a one‐dimensional flexible model, which allows estimation of the energy barrier for the transition state as approximately 8.0 kJ mol^?1.     

Pressurized-liquid extraction for determination of illicit drugs in hair by LC–MS–MS

An LC–MS–MS-based procedure for determination in hair of 14 different drugs of abuse belonging to the classes cocaine, amphetamine-like compounds, opiates, and hallucinogens has been developed. A pressurized-liquid extraction procedure was used and proved useful for quantitative recovery of all the analytes tested. This procedure, in conjunction with a simple decontamination step, performed to avoid false-positive samples, enabled the detection of all the analytes with LOQ ranging from 1.8 to 16 pg mg^?1 and accuracy varying from 85 to 111 %. The procedure was validated in accordance with the SOFT/AAFS guidelines and seems to be suitable for routine determination of the drugs tested in hair.