The study of molecular motions of small organic molecules in the solid state has a considerable interest, not only for the intrinsic value of such a deep knowledge of a chemical system, but also because molecular motions can be intimately connected with physical properties, such as stability, intermolecular interactions and chemical reactivity.
In this PhD thesis, the various tools offered by SSNMR have been intensively exploited in order to characterize in detail some peculiar aspects of the dynamic properties of small organic molecules in crystalline phases. The nuclei observed, 1H and 13C, present different characteristics of the two nuclear species often al- lowed us to get complementary dynamic information. A wide variety of nuclear observables has been investigated, ranging from isotropic and anisotropic chemical shifts, scalar and dipolar couplings, to different kinds of relaxation properties, by using many advanced SSNMR pulse sequences. The work is also characterized by the extension of the measurements over an unconventional range of temperatures, in particular some 13C CP-MAS spectra have been acquired at temperatures down to 20 K. Moreover the combination of measurements at different experimental frequencies was exploited in many cases. A last important feature of the thesis work is the use of many mathematical models for the data analysis. In particular the use of motional models for relaxation time analyses, like BBP and Cole-Cole models for spectral densities, the Mc Connell equations for modeling exchange motions, in some cases integrated with other models for the description of interference phenomena; finally the extension of a model firstly proposed by Wittebort et al. for the quantitative analysis of the effect of small-amplitude motions, such as vibrations and librations, on chemical shielding tensors. In all the cases studied the aid of DFT calculations resulted to be very important and in some cases crucial.
The developed approaches were applied to four small organic molecules in crystalline phases, chosen for some similar chemical characteristics and for their pharmacological interest, since they are widely used non-steroidal anti-inflammatory drugs. The systems chosen are Ibuprofen, Sodium Ibuprofen, Naproxen and Sodium Naproxen, all of them in their stable crystalline phases
