Innocenti F.,Dip. di Chimica |
Milani A.,Dip. di Chimica |
Castiglioni C.,Dip. di Chimica
Journal of Raman Spectroscopy | Year: 2010
The molecular and vibrational structures of cumulenic carbon chains are investigated by density functional theory calculations and compared with that of hydrogen-capped polyynes. The small value of bond length alternation (BLA) along the CC bonds sequence obtained by geometry optimization of uncapped Cn chains and vinyl-capped carbon chains confirms their cumulenic structure. It is demonstrated that for finite length chains the structural parameters are determined by end effects as far as the Peierls distortion, expected for very long molecules, does not occur. The Raman spectra of such molecules are calculated to verify the possibility of identifying markers of cumulenic chains by means of vibrational spectroscopy. As expected, the longitudinal mode consisting of the BLA oscillation, which is responsible for the strongest Raman transition of polyynes, becomes very weak for cumulenes; this behaviour is rationalized in terms of local polarizability derivatives. However, other longitudinal modes can be observed in the Raman spectra of Cn chains. The wavenumber behaviour and the optical activity of these modes are interpreted on the basis of the phonon dispersion branch of an ideally infinite cumulenic polymer. Raman intensities computed for chains of different lengths allow to conclude that cumulenic molecules could be detected and identified by means of Raman spectroscopy. © 2009 John Wiley & Sons, Ltd.
Gaglioti K.,Dip. di Chimica |
Chierotti M.R.,Dip. di Chimica |
Grifasi F.,Dip. di Chimica |
Gobetto R.,Dip. di Chimica |
And 3 more authors.
CrystEngComm | Year: 2014
Tolfenamic acid (HTA) is a drug characterized by very poor water solubility (13.6 nM under acidic conditions) and moderate solubility in ethanol (0.17 M). A series of new multicomponent crystals have been obtained by applying mechanochemical methods (i.e. kneading) to mixtures of HTA with sodium acetate, sodium carbonate, sodium hydroxide and imidazole. These reactions resulted in two salts (NaTA·0.5H2O and NaTA HT Form), a co-crystal of salts (NaTA·HTA·0.5NaAc·2H2O) and two salt co-crystals (NaTA·HTA·H2O/NaHCO3 and IMH-TA·HTA). Due to the lack of suitable crystals for single-crystal X-ray diffraction analysis, the structural features of the samples have been characterized by solid-state NMR (1H MAS, 13C CPMAS, 1H-13C FSLG LG-CP HETCOR and 15N CPMAS), IR(ATR) and Raman spectroscopy, VT-XRPD and elemental analysis. The evaluation of thermal stability and dissolution behavior was performed using thermogravimetry, differential scanning calorimetry and dissolution kinetic tests. The new solid-state forms show better thermal stability than pure HTA and an improved dissolution rate, which is most pronounced in NaTA· HTA·H2O/NaHCO3, NaTA HT Form and NaTA·0.5H2O. This journal is © the Partner Organisations 2014.