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The diverse crystal forms of rifaximin

07 Sep 2012

Drugs, as with many molecular compounds, often exist in different crystal forms, and in these different forms they will exhibit different chemical and physical properties. Different solubilities and dissolution rates result in different absorption rates so the ability to control what form crystals take on, is of key importance throughout many stages of the pharmaceutical industry.

This HOT paper from Braga, Grepioni et al. looks at the crystal structures of four crystal forms of the synthetic antibiotic rifaximin. The study increases our understanding of how water molecules interact with rifaximin and/or amongst themselves in the crystal packing as well as providing information on the phase relationship of the hydration-dehydration process.

Supramolecular engineering via halogen bonding

06 Sep 2012

Applications of halogen bonding

In this HOT Highlight, Franck Meyer and Philippe Dubois discuss the emergence of halogen bonding over the last decade for crystal engineering of supramolecular complexes. Whilst hydrogen bonding has received a great deal of interest in this respect, very little work has focused on halogen bonding until now. The first applications to highly functional materials are presented. Other recent applications have also included solution phase recognition (catalysis, anion sensing and resolution) and macromolecular organizations (porous, polymeric and hybrid systems). Thus, the potential cooperation between weak
non-covalent bonds opens the door for new applications in materials science and synthetic chemistry.

Screw growth of crystals can copy nature’s spirals

20 Aug 2012

Screw growth of crystals can copy nature's spirals Nacre, a material found on the outer-coating of pearls, has incredible mechanical strength thanks to its arrangement of parallel laminars of inorganic layers separated by organic layers of macromolecules.

Scientists at Zhejiang University, China, have combined calcium phosphate and sodium bis(2-ethylhexyl)sulfosuccinate in the presence of bovine serum albumin to create hybrid crystals with a nacre-like structure.

The hybrid crystals grew by a classical screw growth mechanism which is similar to the actual biological pathway for nacre formation. Further development of such biomimetic pathways will progress research into new, and perhaps stronger, organic-inorganic composites.

Download the manuscript which will be free to access for 4 weeks.

Lamellar organic–inorganic architecture via classical screw growth
Yan Quan, Halei Zhai, Zhisen Zhang, Xurong Xu and Ruikang Tang
CrystEngComm, 2012
DOI: 10.1039/C2CE25805F, Paper

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Polymorphism in ionic liquids

17 Aug 2012

Ethambutol dibenzoate trimorphs

Cherukuvada and Nangia report the first example of polymorphism in ionic liquids. Three polymorphs of ethambutol dibenzoate were crystallized as ionic liquids and characterized. 15N NMR spectroscopy was used to identify the three polymorphs and their stability was investigated with the use of DSC and other experiments. The polymorphic transformations from forms 1 to 3 were also investigated by PXRD. Further work on crystallization and characterization will prove useful for new pharmaceutical formulations.

Chemical Vapour Deposition for engineering oxide nanosystems

07 Aug 2012

Chemical Vapour Deposition-based growth can help tailor the properties of oxide-based nanomaterials.

Davide Barreca and colleagues survey the current literature on multi-component oxide nanosystems obtained by Chemical Vapour Deposition (CVD) in their HOT Highlight article. Three bi-component categories of nanomaterials are discussed in detail; these are metal/oxide, oxide/oxide and carbon/oxide systems.

The metal/oxide materials include zinc oxide-based systems which are some of the most investigated composites obtained by CVD-based methods. Tin dioxide nanowires covered by iron oxide nanocrystals are an example of the oxide/oxide nanomaterials examined, with CVD techniques being critical for obtaining interconnected magnetite superstructures. A combined plasma enhanced-CVD and electrodeposition approach to create nanofibers coated with manganese oxide is an example of a carbon/oxides systems.

Future challenges include controlling phenomena occurring at interfaces between the materials but the flexibility of CVD techniques can help with overcoming these to further exploit and develop novel oxide nanosystems. Download the Highlight today to find out more; it’s free for 4 weeks.

Multi-component oxide nanosystems by Chemical Vapor Deposition and related routes: challenges and perspectives
Daniela Bekermann, Davide Barreca, Alberto Gasparotto and Chiara Maccato
CrystEngComm, 2012
DOI: 10.1039/C2CE25624J, Highlight

Here are some other articles from the team that you might find interesting…

Controlled synthesis and properties of beta-Fe₂O₃ nanosystems functionalized with Ag or Pt nanoparticles
Giorgio Carraro, Davide Barreca, Elisabetta Comini, Alberto Gasparotto, Chiara Maccato, Cinzia Sada and Giorgio Sberveglieri
CrystEngComm, 2012
DOI: 10.1039/C2CE25956G, Paper

Strongly oriented Co₃O₄ thin films on MgO(100) and MgAl₂O₄(100) substrates by PE-CVD
Davide Barreca, Anjana Devi, Roland A. Fischer, Daniela Bekermann, Alberto Gasparotto, Marco Gavagnin, Chiara Maccato, Eugenio Tondello, Elza Bontempi, Laura E. Depero and Cinzia Sada
CrystEngComm, 2011, 13, 3670-3673
DOI: 10.1039/C1CE05280B, Communication

Malonate complexes of dysprosium: synthesis, characterization and application for LI-MOCVD of dysprosium containing thin films
Andrian P. Milanov, Rüdiger W. Seidel, Davide Barreca, Alberto Gasparotto, Manuela Winter, Jürgen Feydt, Stephan Irsen, Hans-Werner Becker and Anjana Devi
Dalton Trans., 2011, 40, 62-78
DOI: 10.1039/C0DT00455C, Paper

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Understanding hydrogen bonding

30 Jul 2012

Co-crystallisation is an important tool for establishing the importance of intermolecular interactions in the solid state. One strategy adopted by Christer Aakeröy and his team at Kansas State University is to examine whether crystallisation of two molecules results in a homomeric interaction (essentially recrystallisation) or a heteromeric interaction (co-crystallisation). Combining 2-aminopyrazine derivatives with numerous carboxylic acids, the team discovered that they could attribute the success of co-crystallisation with electrostatic charges on the hydrogen bond acceptor sites – as they predicted, the lower the charge, the lower the supramolecular yield of the reaction.

Although hydrogen bonding is a fundamental concept taught to us in the classroom, we still have a lot to learn!

Read the article to find out more…

Exploring the structural landscape of 2-aminopyrazines via co-crystallizations
Christer B. Aakeröy, Prashant D. Chopade, Claudia Ganser, Arbin Rajbanshi and John Desper

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Porous aromatic frameworks

27 Jul 2012

Teng Ben and Shilun Qiu discuss porous aromatic framework network formation and the relationship between secondary building units and function in this hot Highlight article. The ability to control the pore size in porous aromatic frameworks lends itself to numerous applications, including in molecular separation, catalysis, photoelectric materials, clean energy and carbon dioxide capture and storage.

You can download the full article below, which is free to access for 4 weeks.

Porous aromatic frameworks: Synthesis, structure and functions
Teng Ben and Shilun Qiu
CrystEngComm, 2012
DOI: 10.1039/C2CE25409C, Highlight

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Hydrogels for studying biomineralisation

23 Jul 2012

Hydrogel-based double-diffusion systems for studying biomineralization

This Highlight presents an overview of hydrogel-based double-diffusion systems to study biomineralization. The authors describe two types of diffusion systems: static and dynamic. They evaluated four such systems to design an optimized system taking into account the type of hydrogel, the boundary conditions and design strategy.

Gels represent a good model to study and understand biomineralization because the mineral deposition that occurs in many mineralization processes in vivo takes place in gelling environments; however, they are not often used due to their complexity and poor knowledge of ionic diffusion.

Read more about biomineralisation for FREE at:

Rediscovering hydrogel-based double-diffusion systems for studying biomineralization
Jason R. Dorvee , Adele L. Boskey and Lara A. Estroff
CrystEngComm, 2012, Advance Article
DOI: 10.1039/C2CE25289A

Other articles by Lara A. Estroff and co-workers which may also be of interest are:

Gel incorporation inside of organic single crystals grown in agarose hydrogels
Hanying Li, Yuzo Fujiki, Kazuki Sada and Lara A. Estroff
CrystEngComm, 2011, 13, 1060-1062
DOI: 10.1039/C0CE00118J, Communication

Porous calcite single crystals grown from a hydrogel medium
Hanying Li and Lara A. Estroff
CrystEngComm, 2007, 9, 1153-1155
DOI: 10.1039/B709068D, Communication
From themed issue: CrystEngComm focuses on biomineralisation

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Competing cocrystals: Hydrogen-bonding vs. Halogen-bonding

05 Jul 2012

Tomislav Friscic and colleagues report a cocrystal system that bonds by either hydrogen or halogen bonding depending on the stoichiometric ratio of the two components of the crystal. Interactions within crystal structures such as hydrogen bonding, ionic bonds, van der Waals forces and pi-interactions determine a material’s structure and properties.

Understanding these interactions and engineering crystals with specific structures is important, the ability to switch the interaction between hydrogen and halogen bonds by altering the ratio of molecules is an interesting discovery and helps establish the role halogen bonds play in molecular self-assembly.

Switching between halogen- and hydrogen-bonding in stoichiometric variations of a cocrystal of a phosphine oxide
Se Ye Oh, Christopher W. Nickels, Felipe Garcia, William Jones and Tomislav Friščić

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Single-crystal study on brownmillerite type frameworks

22 Jun 2012

Werner Paulus and colleagues report on studies into low temperature oxygen mobility in terms of anisotropic oxygen in brownmillerite type frameworks. By using a floating zone method they were able to optimise the paramaters so as to obtain large and homogenous crystals of CaFeO_2.5 that were essential for detailed structural and lattic dynamic studies. Understanding oxygen mobility in non-stoichiometric perovskites will aid the development of electrolytes in solid-oxide fuel cells which currently work at high temperatures but low temperature conditions would be preferable.

Typical CaFeO2.5 crytals obtained in this study were 120 mm long and had a shiny, silver-blck surface with metallic luster.

Typical CaFeO2.5 crystals obtained in this study were 120 mm long and had a shiny, silver-black surface with metallic luster.

Download the paper to find out more…

Growth and characterization of large high quality brownmillerite CaFeO_2.5 single crystals
Monica Ceretti, Andrea Piovano, Alain Cousson, Tanguy Berthier, Martin Meven, Giovanni Agostini, Jurg Schefer, Olivier Hernandez, Carlo Lamberti and Werner Paulus
CrystEngComm, 2012
DOI: 10.1039/C2CE25413A

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