From the SmA to the hexatic, including the SmC*, SmC*(A) and SmC*(re) phases: a 2H NMR relaxation study.

The molecular dynamics of a ferroelectric liquid crystal, denoted ZLL 7/*, is investigated by means of (2)H NMR relaxation. The spin-lattice (T(1Q) and T(1Z)) and spin-spin (T(2)) relaxation times of two isotopomers of ZLL 7/*, labeled on the phenyl and biphenyl fragments, are measured and their behavior upon passing from the SmA to the hexatic phase, through the ferroelectric SmC*, antiferroelectric SmC*(A), and re-entrant ferroelectric SmC*(re) phases, is discussed. A comparison between the measured T(2) and T(2)*, directly related to the experimental linewidth, provides information on the heterogeneity of the system, thus allowing confirmation of previous hypotheses concerning the structural and ordering properties of the SmC*(A) and SmC*(re) phases. The possibility to look at different sites of the core of the ZLL 7/* smectogen reveals a peculiar sensitivity of the phenyl moiety with respect to the biphenyl fragment, which may be justified by its vicinity to the chiral centers. Interestingly, the trend of the longitudinal relaxation times is characterized by a minimum that corresponds to the SmC*(A) and SmC*(re) phases, which is reproducible for the two isotopomers and at several Larmor frequencies. A quantitative analysis of T(1Q) and T(1Z) is performed in the SmA and SmC* phases, for which the narrowing regime approximation is valid. A multifrequency approach is applied to self-consistently determine the diffusion coefficients for the overall molecular motions, namely spinning and tumbling, and the internal rotations around the para axes of the phenyl and biphenyl fragments. The effect of the magnetic field in unwinding the helical structure of the SmC* phase (for H>9 T) allows observation of a sensitive change in the rotational diffusion coefficients in the frustrated unwound SmC* phase with respect to the SmC* phase.

Interactions at the surface of organophilic-modified laponites: a multinuclear solid-state NMR study.

Organically modified clays are largely employed in the preparation of nanostructured materials. The structural and dynamic characterization of the clay surface appears very important in the perspective of understanding the molecular mechanisms determining the improvement of the material properties. To this aim, in this work, a synthetic clay, Laponite, was studied in its untreated hydrophilic Na+-form, after ion exchange with alkylammonium cations and after subsequent grafting reaction with an alkoxysilane. These three samples were characterized by IR, SEM, TGA, and X-ray techniques and were deeply investigated by means of a wide combination of 29Si, 13C, and 1H high- and low-resolution solid-state NMR experiments. The grafting reaction with alkoxysilanes, occurring at the clay platelet edges, resulted in a reduction of the clay inter-platelet distances, and in an increased disorder in both the arrangement of the platelets and the conformational structure of the intercalated organic cation chains, probably due to the relative twisting of adjacent platelets.

Molecular properties of flurbiprofen and its solid dispersions with Eudragit RL100 studied by high- and low-resolution solid-state nuclear magnetic resonance.

PURPOSE: Investigation of the conformational and molecular dynamic properties of the acidic and sodium salt forms of Flurbiprofen and their solid dispersions with Eudragit RL100, obtained by two different preparation methods (physical mixtures and coevaporates), and of the mixing degree between the two components in the dispersions. MATERIALS AND METHODS: 1H and 13C high-resolution solid state NMR techniques, including Single Pulse Excitation-MAS, CP-MAS, FSLG-HETCOR; low-resolution 1H FID analysis; 1H spin-lattice relaxation time measurements. RESULTS: Conformational, molecular packing and dynamic differences were observed between the two pure forms of flurbiprofen, as well as between the pure drugs and the corresponding coevaporates. In the coevaporates of the two flurbiprofen forms, drug and polymer appear intimately mixed; their chemical interactions were detected and characterized. CONCLUSIONS: A combined analysis of several 13C and 1H high- and low-resolution solid state NMR experiments allowed the investigation of the conformational and dynamic properties of the pure drugs and of the solid dispersions with the polymer, as well as of the degree of mixing between drug and polymer and of the chemical nature of their interaction. Such information could be compared to the in vitro drug release profiles given by these solid dispersions.

Molecular properties of ibuprofen and its solid dispersions with Eudragit RL100 studied by solid-state nuclear magnetic resonance.

PURPOSE: The aim of this study was to investigate, at a molecular level, the structural and dynamic properties of the acidic and sodium salt forms of ibuprofen and their solid dispersions with Eudragit RL100, obtained by two different preparation methods (physical mixtures and co-evaporates), which may affect the release properties of these drugs in their dispersed forms. METHODS: (1)H and (13)C high-resolution solid-state nuclear magnetic resonance techniques, including single-pulse excitation magic-angle spinning, cross-polarization magic-angle spinning, and other selective 1D spectra, as well as more advanced 2D techniques Frequency Switched Lee-Goldburg HETeronuclear CORrelation (FSLG-HETCOR) and Magic Angle Spinning -J- Heteronuclear Multiple-Quantum Coherence (MAS-J-HMQC) and relaxation time measurements were used. RESULTS: A full assignment of (13)C resonances and precise (1)H chemical shift values were achieved for the first time for the two forms of ibuprofen that showed very different inter-conformational dynamic behavior; drug-polymer interactions were observed and characterized in the co-evaporates of the two forms but were much stronger for the acidic form. CONCLUSIONS: A combined analysis of several high-resolution solid-state nuclear magnetic resonance experiments allowed the investigation of the structural and dynamic properties of the pure drugs and of the solid dispersions with the polymer, as well as of the degree of mixing between drug and polymer and of the chemical nature of their interaction. Such information could be related to the in vitro drug release profiles observed for the tested co-evaporates.