CrystEngComm Blog

Posted on behalf of Gwenda Kyd, web writer for CrystEngComm

Many important drug molecules are hydrophobic so methods to successfully introduce these into the body and make them bioavailable must be developed. Peptide-based molecules are an attractive delivery vehicle due to their biocompatibility, recognition properties, biodegradability and hydrophobic-hydrophilic balance.

A new paper shows how three gamma-peptides, with different degrees of flexibility, can self-assemble to form porous microspheres (see diagram below). The anticonvulsant drug carbamazepine has been encapsulated in these microspheres, which range in diameter from 300nm-1µm. The microspheres have limited water solubility, so there is a sustained release of the drug by dissolution of the microsphere. The authors suggest tailoring of the capsule properties could lead to controlled drug delivery and release.

Find out more in the paper:

Fabrication of microspheres from self-assembled γ-peptides
Suman Kumar Maity, Santu Bera, Arpita Paikar, Apurba Pramanik and Debasish Haldar

CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40689J, Paper

Posted on behalf of Gwenda Kyd, web writer for CrystEngComm 

The stability and other properties of compounds in the solid state are important considerations when considering their potential uses. Two strategies commonly followed to enhance desirable properties are to form co-crystals (crystals containing more than one type of neutral molecule) and to form salts (ionic crystals). In both cases, the new crystal forms generated have different properties than the parent compounds. For example, forming a salt of a drug molecule often improves its solubility, hence making it more bioavailable. Salts, however, often have problematic properties including deliquescence (i.e. absorbing water until they dissolve). 

A new paper shows how co-crystals can be formed between ionic and neutral forms of the same molecule (conjugate acid-bases, or CABs) which are more stable than the parent molecule. The molecules studied are benzoic acids, salts of which are used as preservatives in the food and pharmaceutical industry. However, they are hygroscopic and degrade in air. Formation of CAB co-crystals significantly improves their stability, particularly at high relative humidity (RH), as shown in the figure below. X-ray crystal structures of the CAB co-crystals show formation of strong short hydrogen bonds between the components. The authors postulate that this interaction is more favourable than the interaction with water, and is the root of the improved stability. 

Moisture sorption profiles of (a) sodium benzoate (mono salt), 3, sodium dihydrogen tris(benzoate) (CAB cocrystal), 4, and (b) potassium benzoate (mono salt), 5, and potassium hydrogen bis(benzoate) (CAB cocrystal), 6.

Find out more from the paper: 

Improved solid-state stability of salts by cocrystallization between conjugate acid–base pairs
Sathyanarayana Reddy Perumalla and Changquan Calvin Sun
CrystEngComm, 2013, DOI: 10.1039/C3CE40593A 

Posted on behalf of Gwenda Kyd, web writer for CrystEngComm

PbS nanocrystals have potential use in the construction of nanodevices such as optical switches, solar cells and infra-red light-emitting devices. As their physical and chemical properties depend on their size and shape, preparing monodisperse crystals (i.e. crystals with the same size and shape) in a reliable and tunable way is important. Usually synthesis is carried out at high temperatures but a new paper challenges this traditional thinking, showing how successful synthesis can be carried out at much lower temperatures.

Nanocrystals were successfully prepared with mixing temperatures as low as -20°C, from solid precursors. Below 40°C the nature of the alkylamine(s) used in the synthesis is a highly influential factor in determining the shape (kinetic effect). Above this temperature, it is the subsequent ripening temperature which has a greater influence (thermodynamic effect). The ripening temperature determines the ultimate shape of the crystals, but the size is also influenced by the mixing temperature and alkylamine(s) used. Utilising the competing factors involved is shown to provide a facile route to size-tunable but shape-permanent PbS nanocrystals.

The results are summarised in the figure below:

Find out more from the paper:

Shape-controlled synthesis of PbS nanostructures from −20 to 240 °C: the competitive process between growth kinetics and thermodynamics
Yingnan Wang, Xinyi Yang, Guanjun Xiao, Bo Zhou, Bingbing Liu, Guangtian Zou and Bo Zou
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40337H, Paper

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. Currently she works as a scientific database editor.