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31.
Benati L Calestani G Leardini R Minozzi M Nanni D Spagnolo P Strazzari S Zanardi G 《The Journal of organic chemistry》2003,68(9):3454-3464
Aryl radicals react with 2-(2-phenylethynyl)phenyl isothiocyanate through a novel radical cascade reaction entailing formation of alpha-(arylsulfanyl)imidoyl radicals and affording a new class of compounds, i.e. thiochromeno[2,3-b]indoles. These derivatives are formed as mixtures of substituted analogues arising from competitive [4 + 2] and [4 + 1] radical annulations. The isomer ratio is strongly dependent on the aryl substituent and is correlated to its capability to delocalize spin density. The presence of a methylsulfanyl group in the ortho-position of the initial aryl radical results in complete regioselectivity and better yields, as the consequence of both strong spin-delocalization effect, which promotes exclusive [4 + 1] annulation, and good radical leaving-group ability, which facilitates aromatization of the final cyclohexadienyl radical. Theoretical calculations support the hypothesis of competitive, independent [4 + 2] and [4 + 1] annulation pathways. They also suggest that rearrangement onto the sulfur atom of the [4 + 1] intermediate does not occur via a sulfuranyl radical but rather through either a transition state or a sulfur-centered (thioamidyl) radical; the latter is possibly the preferred route in the presence of an o-methylsulfanyl moiety that can act as a leaving group in the final ipso-cyclization process. 相似文献
32.
Marco Bettinelli Adolfo Speghini Daniele Falcomer Enrico Cavalli Gianluca Calestani Marta Quintanilla Eugenio Cantelar Fernando Cussó 《Journal of luminescence》2008,128(5-6):738-740
LiLa9(SiO4)6O2 (LLS) crystals activated with Er3+ have been grown by the flux growth method. Their apatite structure has been characterized by single-crystal X-ray diffraction. The absorption and emission spectra have been measured in the visible and NIR regions. They are affected by a significant inhomogeneous broadening making these crystals interesting active media for tunable solid-state laser operation. 相似文献
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34.
Beltrami D Calestani D Maffini M Suman M Melegari B Zappettini A Zanotti L Casellato U Careri M Mangia A 《Analytical and bioanalytical chemistry》2011,401(4):1401-1409
An integrated approach based on the use of inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy
(SEM) for the qualitative and quantitative analyses of metal particles in foods was devised and validated. Different raw materials
and food products, like wheat, durum wheat, wheat flour, semolina, cookies, and pasta were considered. Attention was paid
to the development of sample treatment protocols for each type of sample to avoid potential artifacts such as aggregation
or agglomeration. The analytical protocols developed followed by ICP-MS and SEM investigations allowed us the quantitative
determination and the morphological and dimensional characterization of metal nano- and microparticles isolated from the raw
materials and finished food products considered. The ICP-MS method was validated in terms of linearity (0.8–80 μg/g and 0.09–9 μg/g
for Fe and Ti, respectively), quantification limits (0.73 μg/g for Fe and 0.09 μg/g for Ti), repeatability (relative standard
deviation (RSD) % equal to 10% for Fe and 20% in a wheat matrix as an example), and extraction recoveries (93 ± 2–101 ± 2%).
Validation of the scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS) measurements was performed working
in a dimensional range from 1 to 100 μm with an estimated error in the size determination equal to 0.5 μm. ICP-MS data as
well as SEM measurements showed a decrease in the concentration of metal particles from wheat to flour and from durum wheat
to semolina samples, thus indicating an external contamination of grains by metal particles. These findings were confirmed
by environmental SEM analysis, which allowed investigation of particles of lower dimensions. Generally, the largest number
of particles was found in the case of iron and titanium, whereas particles of copper and zinc were only occasionally found
without any possibility of quantifying their number. 相似文献
35.
Mosca R. Ferro P. Besagni T. Calestani D. Chiarella F. Licci F. 《Applied Physics A: Materials Science & Processing》2011,104(4):1181-1187
Impedance spectroscopy measurements show that complex conductivity of thermally ablated CH3NH3SnCl3 films is strongly enhanced when humidity increases. Coplanar two-electrode test devices are modeled through an equivalent
circuit comprising one resistance and two constant phase elements. It is shown that the influence of ambient humidity is mainly
resistive. The dynamic responses of the devices to humidification/dehumidification cycles point out that the a.c. current
varies by more than three orders of magnitude when humidity is varied between dry air and 80% relative humidity. The rise
times are few hundred seconds while fall times are as short as few tens of seconds. This observation suggests that impedance
variations are determined by mechanisms involving loosely bound water molecules physisorbed at the surface of the hybrid film.
The results obtained are discussed in terms of protonic conduction. 相似文献