High‐and low‐resolution solid‐state nuclear magnetic resonance (SSNMR) applications to the study of pharmaceuticals are reviewed. Examples are shown involving the use of mono‐and bidimensional SSNMR techniques based on different nuclear interactions and the measurement of several nuclear parameters, such as chemical shifts, line widths, and relaxation times (T1, T2, T1ρ). The systems investigated include pure active pharmaceutical ingredients (APIs), substances used as drug excipients, and solid dispersions formed by APIs and excipients, up to final drug formulations. The most important aspects treated concern structural, dynamic, and morphological properties, and, in particular, identification, characterization, and quantitation of polymorphs and related forms, conformational and crystalline packing behavior, amorphous phase properties and stability, effects of drug processing, molecular motions, API‐excipient and excipient‐excipient chemical and physical interactions, and phase mixing in heterophasic systems.
1 October 2012 in International Journal of Hydrogen Energy
Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M–S–H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M–S–H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative 29Si solid-state NMR data. M–S–H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M–S–H of “chrysotile-like” and “talc-like” sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M–S–H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.
The characterization of a variety of organic/inorganic multicomponent materials (OIMM) through solid-state NMR (SSNMR) spectroscopy will be reviewed. Many examples of applications to OIMM will be described, based on the observation of different nuclei and the use of various SSNMR methods, such as 1D and 2D techniques, measurements on relaxation and spin diffusion processes. OIMM are a very general category of systems differing, for example, by chemical nature and relative amount of organic and inorganic components, shape and size of the domains, and type of organic-inorganic interface. Some of the most investigated classes of OIMM are organically modified silicates, polymer/clay composites, polymer/inorganic filler systems, polymer electrolytes, stationary chromatographic phases, zeolites, and mesoporous silicas including small organic molecules. The aspects most efficiently investigated by SSNMR and discussed in this review include physical and/or chemical interactions occurring at the organic-inorganic interface, structural and dynamic behavior of the organic components, and dimensions and dispersion of organic and inorganic domains.
28 May 2004 in The Journal of Physical Chemistry B
Black phosphorus (bP) has been recently investigated for next generation nanoelectronic multifunctional devices. However, the intrinsic instability of exfoliated bP (the bP nanoflakes) towards both moisture and air has so far overshadowed its practical implementation. In order to contribute to fill this gap, we report here the preparation of new hybrid polymer-based materials where bP nanoflakes exhibit a significantly improved stability. The new materials have been prepared by different synthetic paths including: i) the mixing of conventionally liquid-phase exfoliated bP (in DMSO) with PMMA solution; ii) the direct exfoliation of bP in a polymeric solution; iii) the in situ radical polymerization after exfoliating bP in the liquid monomer (methyl methacrylate, MMA). This last methodology concerns the preparation of stable suspensions of bPn-MMA by sonication-assisted liquid phase exfoliation (LPE) of bP in the presence of MMA followed by radical polymerization. The hybrids characteristics have been compared in order to evaluate the bP dispersion and the effectiveness of the bPn interfacial interactions with polymer chains aimed at their long-term environmental stabilization. The passivation of bPn results particularly effective when the hybrid material is prepared by in situ polymerization. By using this synthetic methodology, the nanoflakes, even if with a gradient of dispersion (size of aggregates), preserve their chemical structure from oxidation (as proved by both Raman and 31P-Solid State NMR studies) and are particularly stable to air and UV light exposure. The feasibility of this approach, capable of efficiently exfoliating bP while protecting the bPn, has been then verified by using different vinyl monomers (styrene and N-vinylpyrrolidone), thus obtaining hybrids where the nanoflakes are embedded in polymer matrices with a variety of intriguing thermal, mechanical and solubility characteristics.