1,720,984 research outputs found
An improved iterative solution to solve the electrostatic problem in the polarizable continuum model
No full textCombined Use of Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy and Fourier Transform Infrared Imaging Coupled with Principal Component Analysis in the Study of Ancient Egyptian Papyri
No full textThis paper reports the results of a spectroscopic study on the chemistry of some small papyrus fragments arising from three Egyptian excavation sites. The aim of this investigation was to verify the possibility to identify significant differences in ancient Egyptian papyri using noninvasive analytical methods, that is, ATR (attenuated total reflection)-FTIR (Fourier transform infrared) spectroscopic imaging and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Differences in both lignin and cellulose compositions, which are difficult to detect with traditional FTIR and FTIR imaging spectral analysis, were revealed by the multivariate approach, and the second derivative spectroscopy was applied to enhance the spectrum resolution. Thus, it has been possible to recognize a fragment characterized by the presence of lead and of long chain aliphatic organic compound, which are not present in the other fragments, in the ink region. These data show not only that the combination of these techniques can provide important chemical information, such as to evidence the different compositions and manufacture of each papyrus, but also that metal inks were probably used also in ancient Egyptian papyri
An improved iterative solution to solve the electrostatic problem in the polarizable continuum model
No full textEffective generation of molecular cavities in the polarizable continuum model by the DefPol procedure
No full textEffective generation of molecular cavities in the polarizable continuum model by the DefPol procedure
No full textToward an effective and reliable representation of solvent effects in the study of biochemical systems
No full textNovel access to ionic liquids based on trivalent metal–EDTA complexes and their thermal and electrochemical characterization
No full textTwo series of ionic liquids (ILs) consisting in metal-EDTA complex anions ([MEDTA], with V, Cr, Mn, Fe and Co as metal center) and 1-butyl-3-methylimidazolium ([BMIM]) or trioctylmethylphosphonium ([TOMP]) cations have been prepared via a new synthetic approach based on the related acidic EDTA complexes (HMEDTA). A strong influence of both the coordinated metal and the cation type on the thermal behavior of the obtained ILs was assessed through DSC and TGA, while the solubility features were found to be primarily affected by the cation nature. The observed solubility results for [TOMP] series ILs in organic solvents showed the preparation of ILs as an effective way to solubilize metal-EDTA complexes into non-aqueous solutions, opening new investigation potential and applicative perspectives. The electrochemical properties of the synthesized ILs have been studied both in aqueous and non-aqueous environments, providing insights on the strong solvent effect on metal-EDTA complexes electrochemistry and, for many of the ILs, showing promising characteristics for electrochemical applications both in water and in organic solvents
Synthesis, thermal behavior and kinetic study of N-morpholinium dicationic ionic liquids by thermogravimetry
No full textSix N-morpholinium dicationic ionic liquids (DILs) with the following general formula [C4H8NO]2(CH2)n[X]2, being n = 4, 6 and 8 and X = Br, NTf2 (where NTf2 = bis(trifluoromethane)sulfonimide) have been synthesized. Their thermal behavior was studied by thermogravimetry (TG) using five different heating rates (2, 4, 8, 10 and 12 K min−1) aiming at assessing their relative thermal stability. All the DILs investigated undergo a single step of mass loss in the temperature range between 200 and 520 °C, except in the case of both the C4 DILs (with bromide and NTf2 imide anion), where two partially overlapping steps occur. NTf2 DILs are more stable than bromide ones according to the thermal stability scale based on the onset decomposition temperature. Taking into account the kinetic analysis of the thermal decomposition, the estimated decomposition time at given degree of conversion for the same temperature (250 °C) was evaluated as an alternative stability parameter. A substantial agreement between the stability trends assessed with the two different approaches was found, and the effect of the length of the linker between the two morpholinium rings of the dicationic structures was also considered. The reaction mechanism beneath the decomposition of the shortest member (C4) of the bromide series was investigated by DFT. A double retro-SN2 pathway was found to be the reasonable two-step mechanism for the first thermal degradation event. This hypothesis was further corroborated by analyzing the samples obtained from TG after heating the bromide and NTf2 C4 DILs up to the first degradation temperatures as well as the thermal behavior of the assumed spiro intermediate ILs
Temperature and angle resolved XPS study of BMIm Cl and BMIm FeCl4
No full textIonic liquids (ILs) have progressively acquired a central position in chemical and material sciences landscapes due to their peculiar physical and solvation properties. Thanks to their metal-complexing ability as well as wide thermal stability and the capability to be easily reused, ILs constitute ideal candidates for applications in metal-catalyzed reactions. However, to exploit their full potential as solvents in heterogeneous catalysis, it is essential to achieve a deeper knowledge on the phenomena that govern both ILs's surface physical chemistry and chemical composition. With the aim of shedding some light on these aspects, we used X-ray photoelectron spectroscopy in angle-resolved mode, to analyze the surface of BMIm Cl and BMIm FeCl4 at different probing depths. Our results show that iron species are located nearly the liquid/vacuum interface, immediately under the hydrophobic layer constituted by the aliphatic chains of the imidazolium rings. The presence of iron ions also affects the composition of the outermost part of the liquid/vacuum interface which clearly differs from the one constituted by the parent BMIm Cl
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