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We recently noted [R. K. Harris, P. Hodgkinson, V. Zorin, J.-N. Dumez, B. Elena, L. Emsley, E. Salager, and R. Stein, Magn. Reson. Chem. 48, S103 (2010)] anomalous shifts in apparent 1H chemical shifts in experiments using 1H homonuclear decoupling sequences to acquire high-resolution 1H NMR spectra for organic solids under magic-angle spinning (MAS). Analogous effects were also observed in numerical simulations of model 13C,1H spin systems under homonuclear decoupling and involving large 13C,1H dipolar couplings. While the heteronuclear coupling is generally assumed to be efficiently suppressed by sample spinning at the magic angle, we show that under conditions typically used in solid-state NMR, there is a significant third-order cross-term from this coupling under the conditions of simultaneous MAS and homonuclear decoupling for spins directly bonded to 1H. This term, which is of the order of 100 Hz under typical conditions, explains the anomalous behaviour observed on both 1H and 13C spins, including the fast dephasing observed in 13C{1H} heteronuclear spin-echo experiments under 1H homonuclear decoupling. Strategies for minimising the impact of this effect are also discussed. [ABSTRACT FROM AUTHOR]

NMR crystallographic techniques are used to validate a structure of β-piroxicam determined from powder X-ray diffraction (PXRD) with a relatively poor R-factor. Geometry optimization of PXRD- and single-crystal XRD- derived structures results in convergence to the same energy of the structures, with minimal atomic displacements, and good agreement of gauge-included projector augmented wave (GIPAW) calculated and experimentally determined NMR 1H, 13C, and 15N chemical shifts, and 14N quadrupolar parameters. Calculations on isolated molecules combined with 2D magic-angle spinning (MAS) 1H double-quantum (DQ) and 14N–1H NMR experiments confirm the 3D packing arrangement of β-piroxicam. NMR crystallography is shown to be an effective means of validating crystal structures that might otherwise be considered sceptically on the basis of diffraction data alone. [ABSTRACT FROM AUTHOR]

The aqueous sol-gel synthesis of γ-Al2O3 modified with different silicon precursors {trimethoxysilane, triethoxysilane and N-[3-(trimethoxysilyl)propyl]ethylene diamine} has been investigated. Two parameters have been studied: the silicon addition step and the type of silicon alkoxide. A first observation was that adding a silicon alkoxide either before or just after the precipitation step influences both the crystallinity and structure, whereas adding the alkoxide after a long agitation time only slightly modifies the support properties. It was also highlighted that due to their higher reactivity, silicon precursors with methoxy groups interact more strongly with the bulk alumina than the silicon precursors with ethoxy groups. This difference of Si location in the alumina structure permitted not only their resistance toward phase transition to be increased at high temperature, but also to stabilize them more efficiently against sintering under normal and steam conditions. Among the different silicon alkoxides tested, samples prepared with N-[3-(trimethoxysilyl)propyl]ethylene diamine showed very unusual properties. The alumina supports modified with this precursor showed grain-shaped nanocrystallites, whereas all other samples were platelet-like. As a result, this sample presented a very narrow pore diameter distribution of around 5 nm and a remarkably high specific surface area (530 m2/g). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Porphyrin based hybrid SiO 2 -TiO 2 materials synthesized by sol-gel method. • Anatase-brookite TiO 2 nanoparticles. • Strong Si O Ti covalent linkages between porphyrin and titania. • Highly visible light active catalysts for p- nitrophenol degradation. Abstract A silylated porphyrin derivative is co-hydrolyzed with Ti(OiPr) 4 to produce a hybrid TiO 2 photocatalyst, and three different ratios between porphyrin and TiO 2 are made. In this way, the porphyrin fragments are held in the resulting matrix through strong Si-O-Ti covalent bonds to limit porphyrin leaching. Thanks to its photoactive character the porphyrin fragment can act as an actuator for the TiO 2 to degrade organic pollutants using light from ultra-violet to the visible range. The photocatalysts are synthesized using an easy aqueous route allowing "green conditions" for synthesis. For comparative purposes, the corresponding pure TiO 2 and a grafted catalyst are also synthesized and studied. For all samples, a mixture of anatase/brookite TiO 2 is obtained, resulting in crystalline materials with low temperature synthesis. The three porphyrin-doped samples prepared in water prove to be efficient photocatalysts for the degradation of p -nitrophenol (PNP) under visible light, and an improvement in photoactivity is observed when the amount of porphyrin increases. The photocatalyst activity is very stable over time as the PNP degradation remains nearly constant after 264 h of testing, showing no leaching of porphyrin. In recycling tests, the grafted sample presents bond breaking between POR-Si and TiO 2 and a decrease in photoactivity towards pure TiO 2 sample activity. A comparison with the commercial Evonik P25 catalyst shows that the porphyrin-doped TiO 2 is nearly 6 times more photoactive under visible light for PNP degradation. [ABSTRACT FROM AUTHOR]

The difficulty to find a relevant in vitro dissolution test to evaluate poorly soluble drugs is a well-known issue. One way to enhance their aqueous solubility is to formulate them as amorphous solid dispersions. In this study, three formulations containing itraconazole (ITZ), a model drug, were tested in seven different conditions (different USP apparatuses and different media). Two of the formulations were amorphous solid dispersions namely Sporanox®, the marketed product, and extrudates composed of Soluplus® and ITZ produced by hot melt extrusion; and the last one was pure crystalline ITZ capsules. After each test, a ranking of the formulations was established. Surprisingly, the two amorphous solid dispersions exhibited very different behavior depending primarily on the dissolution media. Indeed, the extrudates showed a better release profile than Sporanox® in non-sink and in biphasic conditions, whilst Sporanox® showed a higher release profile than the extrudates in sink and fasted simulated gastric conditions. The disintegration, dynamic light scattering and nuclear magnetic resonance results highlighted the presence of interaction between the surfactants and Soluplus®, which slowed down the erosion of the polymer matrix. Indeed, the negative charge of sodium dodecyl sulfate (SDS) and bile salts interacted with the surface of the extrudates that formed a barrier through which the water hardly diffused. Moreover, Soluplus® and SDS formed mixed micelles in solution in which ITZ interacts with SDS, but no longer with Soluplus®. Regarding the biphasic dissolution test, the interactions between the octanol dissolved in the aqueous media disrupted the polymer — ITZ system leading to a reduced release of ITZ from Sporanox®, whilst it had no influence on the extrudates. All together these results pointed out the difficulty of finding a suitable in vitro dissolution test due to interactions between the excipients that complicates the prediction of the behavior of these solid dispersions in vivo. [ABSTRACT FROM AUTHOR]

By means of the 1H chemical shifts and the proton-proton proximities as identified in 1H double-quantum (DQ) combined rotation and multiple-pulse spectroscopy (CRAMPS) solid-state NMR correlation spectra, ribbon-like and quartet-like self-assembly can be identified for guanosine derivatives without isotopic labeling for which it was not possible to obtain single crystals suitable for diffraction. Specifically, characteristic spectral fingerprints are observed for dG(C10)2 and dG(C3)2 derivatives, for which quartet-like and ribbon-like self-assembly has been unambiguously identified by 15N refocused INADEQUATE spectra in a previous study of 15N-labeled derivatives (Pham, T. N.; et al. J. Am. Chem. Soc.2005, 127, 16018). The NH 1H chemical shift is observed to be higher (13-15 ppm) for ribbon-like self-assembly as compared to 10-11 ppm for a quartet-like arrangement, corresponding to a change from NH…N to NH…O intermolecular hydrogen bonding. The order of the two NH21H chemical shifts is also inverted, with the NH2 proton closest in space to the NH proton having a higher or lower 1H chemical shift than that of the other NH2 proton for ribbon-like as opposed to quartet-like self-assembly. For the dG(C3)2 derivative for which a single-crystal diffraction structure is available, the distinct resonances and DQ peaks are assigned by means of gauge-including projector-augmented wave (GIPAW) chemical shift calculations. In addition, 14N-1H correlation spectra obtained at 850 MHz under fast (60 kHz) magic-angle spinning (MAS) confirm the assignment of the NH and NH2 chemical shifts for the dG(C3)2 derivative and allow longer range through-space N…H proximities to be identified, notably to the N7 nitrogens on the opposite hydrogen-bonding face. [ABSTRACT FROM AUTHOR]