The crystal structure of d-ribose derived from powder diffraction data

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Polyelectrolytes in Hot Melt Extrusion: A Combined Solvent-Based and Interacting Additive Technique for Solid Dispersions

Solid dispersions are important supersaturating formulations to orally deliver poorly water-soluble drugs. A most important process technique is hot melt extrusion but process requirements limit the choice of suitable polymers. One way around this limitation is to synthesize new polymers. However, their disadvantage is that they require toxicological qualification and present regulatory hurdles for their market authorization. Therefore, this study follows an alternative approach, where new polymeric matrices are created by combining a known polymer, small molecular additives, and an initial solvent-based process step. The polyelectrolyte, carboxymethylcellulose sodium (NaCMC), was tested in combination with different additives such as amino acids, meglumine, trometamol, and urea. It was possible to obtain a new polyelectrolyte matrix that was viable for manufacturing by hot melt extrusion. The amount of additives had to be carefully tuned to obtain an amorphous polymer matrix. This was achieved by probing the matrix using several analytical techniques, such as Fourier transform infrared spectroscopy, differential scanning calorimetry, hot stage microscopy, and X-ray powder diffraction. Next, the obtained matrices had to be examined to ensure the homogeneous distribution of the components and the possible residual crystallinity. As this analysis requires probing a sample on several points and relies on high quality data, X-ray diffraction and starring techniques at a synchrotron source had to be used. Particularly promising with NaCMC was the addition of lysine as well as meglumine. Further research is needed to harness the novel matrix with drugs in amorphous formulations

Synthesis of the aluminophosphate ICP-1 by self-assembly of 1,3-diphenylguanidine: Insights into supramolecular aggregation

© 2014 American Chemical Society1,3-Diphenylguanidine (DPG) has distinguishable polar and apolar groups, aromatic rings that can self-assemble through π-π type interactions, and high conformational flexibility. These features make it a potential self-assembling structure-directing agent in the synthesis of hybrid host-guest aluminophosphates. Computational simulations show that the molecule has a strong tendency to self-assemble in aqueous solution. Large supramolecular organic aggregates are produced, with the hydrophobic aromatic rings located in the center of the aggregates, stabilized by π-π type interactions, and the hydrophilic guanidine groups on the external surface in close contact with water molecules. With this organic molecule, a new 1-D AlPO framework material (ICP-1) was formed. Its structure, characterized by a combination of single-crystal and powder diffraction techniques, consists of AlP 2O8H chains connected to the polar groups of the organic DPG molecules through a complex H-bonding network. This material has an extremely high organic content, close to that of typical mesoporous materials. However, DPG molecules are part of the ICP-1 network, rather than guest molecules in the pores, so removal of DPG results in a collapse of the structure, limiting its potential applications. Nevertheless, this work demonstrates the potential of using self-assembling organic molecules for producing very open-framework materials.The research leading to these results has received funding from the Spanish Ministry of Science and Innovation MICINN (Projects MAT2009-13569 and MAT2012-31127) and the European Research Council, under the Marie Curie Career Integration Grant program (FP7-PEOPLE-2011-CIG), Grant Agreement PCIG09-GA-2011-291877. L.G.-H. acknowledges Ministerio de Economıa y Competitividad for a Ramón y Cajal ́ contract (RYC-2012-11794) A.B.P. acknowledges the support of the European Community under a Marie Curie IntraEuropean Fellowship for Career DevelopmentPeer Reviewe

Solid-state chemistry and polymorphism of the nucleobase adenine

The nucleobase adenine plays a pivotal role in the chemistry of life, but is also becoming increasingly interesting as a building block in the synthesis of functional solid materials. Although commercially available as a solid, adenine’s solid-state chemistry has so far been neglected. In this comprehensive study it is shown that adenine is most often marketed as a mixture of two polymorphs, one previously known, and a new polymorph. Both polymorphs exhibit layered structures with different hydrogen-bonding patterns within layers. The crystal structure of the new polymorph was elucidated using synchrotron powder X-ray diffraction. Polymorph occurrence conditions, interconversion and the difference in their thermodynamic stability were established theoretically and experimentally revealing the polymorph with Z' = 2 (known) as stable relative to the polymorph with Z' = 1 (new). The adenine layers in both polymorphs are connected by weak interaction likely resulting in stacking faults which are manifested in anisotropic line broadening of their powder diffraction patterns. Analysis of a few commercial samples of adenine revealed them all to be a polymorph mixture, which could be inconvenient in experiments where properties of the solid material could be relevant