A new insight in the dynamo-mechanical behavior of poly(ethylene terephthalate)

Dynamic mechanical experiments performed on a semicrystalline sample of poly(ethylene terephthalate) evidenced the relaxation processes (α and β) that occur in the polymer. Multifrequency experiments were used both in order to calculate the apparent activation energy of relaxation and to point out how the dynamic conditions alter not only the main relaxations, but the overlapping melting/recrystallization events that succeed after the glass transition. Heating rate seems to affect these phenomena in a way similar to frequency. Also, a consecutive heating step was carried out to support the statements.     

Locally supported rational spline wavelets on a sphere

In this paper we construct certain continuous piecewise rational wavelets on arbitrary spherical triangulations, giving explicit expressions of these wavelets. Our wavelets have small support, a fact which is very important in working with large amounts of data, since the algorithms for decomposition, compression and reconstruction deal with sparse matrices. We also give a quasi-interpolant associated to a given triangulation and study the approximation error. Some numerical examples are given to illustrate the efficiency of our wavelets.

     

Widely tunable optical parametric oscillator driven by a pulsed diode-pumped nonlinear-mirror mode-locked Nd:YAG laser

We report on the development of a pulsed diode end-pumped Nd:YAG laser mode-locked by a nonlinear mirror and stabilized by an acousto-optical modulator. With the introduction of appropriate intracavity loss, the laser is able to generate 22.8 ps pulses with the energy of 4.5 μJ. After amplification and frequency doubling stages, the second harmonic radiation is used to non-collinearly synchronously pump a β-barium borate optical parametric oscillator in a walk-off compensated scheme. The system demonstrates a wide-tuning range from 635 nm to 2.55 μm for the signal output, with maximum average conversion efficiency as high as 42%.     

Mild and reliable cleavage sequence for phenoxy acetates

A novel combination of reliable transformations like ester saponification and subsequent Curtius-rearrangement employing mild reaction conditions, offers the first synthetically interesting strategy for the removal of methoxycarbonylmethyl groups from phenolic oxygens. This methodology gives also access to labile iodosubstituted phenols.     

A convenient synthesis of iminosugar-C-glycosides via organometallic addition to N-benzyl-N-glycosylhydroxylamines

N-Benzyl-N-glycosylhydroxylamines were prepared in very good yield via condensation of furanoses and pyranoses with N-benzylhydroxylamine at 110°C for 30 min under solvent-free conditions. These anomeric sugar-hydroxylamines exist in equilibrium with the open-chain nitrone form. In fact upon treatment with various organometallic reagents, the corresponding adducts were obtained with good to high diastereoselectivity. These adducts were converted into iminosugar-C-glycosides by reductive dehydroxylation and intramolecular cyclization.     

Photochemistry and Photobiology of Furocoumarin Hydroperoxides Derived from Imperatorin: Novel Intercalating Photo-Fenton Reagents for Oxidative DNA Modification by Hydroxyl Radicals*

Photochemical and photobiological properties of the im-peratorin-derived furocoumarin hydroperoxides la, la', 2a and 2a’have been investigated. Irradiation (350 nm) of the hydroperoxide 2a’afforded the alcohol 2b (2%), a diastereomeric mixture of the hydroxy epoxide 2c (40%; diastereomeric ratio = 80:20) and the epoxide 2d (8%). The formation of these products was rationalized in terms of homolysis of the hydroperoxide bond initiated by intramolecular energy transfer from the photoexcited furocoumarin chromophore. The quantum yields for the photolytic decomposition of hydroperoxides were estimated to be in the range of 0.03–0.85 and decreased in the order 2a ? 2a′? 1a′≥ 1a. The involvement of hydroxyl radicals in these reactions was established by trapping experiments with benzene and spectroscopic evidence was obtained by EPR spin trapping with 5,5-di-methylpyrroline-N-oxide. Fluorescence titration, DNA melting and linear dichroism studies of furocoumarins indicated that these compounds undergo efficient com-plexation and also intercalation into the DNA. The binding parameters K (intrinsic binding constant) and l/n (frequency of binding sites) of complexes between furocoumarin derivatives and DNA were determined to be in the range of 3900–23 900 M-^l and 0.017–0.045. The pho-toreaction of la’and lb’with 2′-deoxyguanosine (dGuo) afforded exclusively 7,8-dihydro-8-oxo-2′-deoxy-guanosine (8-oxodGuo), presumably through singlet oxygen, which was formed in a type II photooxidation process. In contrast, the hydroperoxide 2a oxidized dGuo to oxazo-lone as major and 8-oxodGuo as minor products through hydroxyl radicals, which were generated from 2a under photolytic conditions. Interestingly, the photoreactions of furocoumarins with salmon testes DNA showed that the highly reactive (φ= 0.85) hydroperoxide 2a is also most efficient in inducing the mutagenic DNA oxidation product 8-oxodGuo. Hence, the novel furocoumarin hydroperoxide 2a constitutes the first intercalating photo-Fen-ton reagent and serves as convenient hydroxyl radical source for genotoxicity studies.     

Second Generation Nitrogen Doped Titania Nanoparticles: A Comprehensive Electronic and Microstructural Picture

A state‐of‐the‐art overview of N‐dopant characterizations in nano‐TiO₂ second‐generation photocatalysts is provided. The related literature is very rich and sometimes offers contrasting interpretations. Here we critically discuss up‐to‐date literature results and our own findings, as retrieved by several experimental (BET, HR‐TEM, XPS, DRS, HR‐XRPD, EXAFS, electrochemical tools) and theoretical (periodic DFT) techniques. Our intent is to pull together outcomes from very different and complementary sources to make an as much as possible coherent picture of the morphological, electrochemical and electronic properties of N‐TiO₂ materials. It is commonly accepted that critical issues to be considered in the design of high‐performing N‐TiO₂ photocatalysts are synthetic strategy, defect concentration and chemical nature of the lattice point defects. We focus on the latter two issues, with emphasis on sol‐gel prepared materials, according to the specific area of expertise of our group. The problem of the chemical nature of guest N species into the lattice is crucial, as substitutional (N_s) or interstitial (N_i) nitrogen place their valence states just above the valence band or deeper into the band gap. Overall, we show how synergism among experimental and theoretical techniques is decisive to disentangle structural, electronic and morphological effects in complex N‐doped TiO₂ matrices.