158,670 research outputs found
The occurrence of electron transfer in aromatic nitration: dynamical aspects
No full textElectron transfer (ET) from toluene to the nitronium ion in the region of van der Waals intermolecular distances has been investigated by a quantum dynamical analysis performed on potential-energy surfaces computed at the ab initio multireference configuration interaction level. The results show that ET is very fast, occurring on a timescale of a few picoseconds. This has important implications for the mechanism of aromatic nitration: the ET path can compete efficiently with the direct attack of the nitronium ion to the aromatic substrate to yield the Wheland intermediate and that could explain some unsettled points in the mechanism of aromatic nitration
Detection of diagenetic alterations by spectroscopic analysis on archaeological bones from necropolis of Poseidonia (Paestum: a case of study)
No full textUnderstanding the chemical and physical alteration in archaeological bones, occurred after burial, is very interesting for researchers. In this paper,
we present a study on the diagenetic alteration of human archaeological bony tissues from Paestum (South Italy), by combining complementary
spectroscopic techniques, such as solid-state nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and X-ray diffraction. In particular,
13C nuclear magnetic resonance–cross polarization-magic angle spinning (13C NMR CP-MAS) spectroscopy allows to identify and discriminate
the adsorbed calcite, that is a diagenetic contaminant, from the structural one of apatite and 1H NMR-MAS spectroscopy shows how the degradation
of organic phase of collagen is related to the time. The NMR data are combined with crystalline index, measured by X-ray diffraction, and with the
splitting factor obtained by infrared spectroscopy. Moreover, the evaluation of the relative content of biogenic structural carbonate and of diagenetic
fluorine is reported
Evaluation and improvement of the official methods for the detection of quarantine bacteria in potato seeds tubers.
No full textInfrared linear dichroism as a tool to evaluate volatile guest partition between amorphous and nanoporous-crystalline polymer phases
No full textDesorption kinetics of ethene, propene, and butadiene from films exhibiting axially oriented nanoporous-cryst. δ phases of syndiotactic polystyrene (s-PS) have been followed by gravimetric and IR linear dichroism measurements. The reported data can be rationalized by assuming that, after the initial desorption mainly involving mols. absorbed in the amorphous phase, most gaseous mols. are included as guest in the nanoporous-cryst. phase. This allows establishing a simple method to evaluate guest partition between nanoporous-cryst. and amorphous polymeric phases, which possibly can be applied for most volatile guest mols. The described method also allows establishing the presence of one guest mol. (ethene, propene, or butadiene) per cavity of the nanoporous δ form
Polymer/Gas Clathrates for Gas Storage and Controlled Release
No full textThe nanoporous cryst. phase of a cheap com. polymer shows, already at room temp., large uptake of gas mols. (e.g., butadiene and carbon dioxide) leading to polymer/gas clathrate phases. These clathrate phases have been characterized by X-ray diffraction and IR linear dichroism measurements. Gas release kinetics are strongly reduced as a consequence of clathrate formation and can be further reduced by (010) orientation of the host phase, i.e., by placing the ac layers of close-packed enantiomorphous polymer helixes nearly parallel to the film plane. The reported results indicate that this robust and easy-to-process polymeric cryst. framework is suitable for gas storage and controlled release
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