Cryst.Growth Des. (2008), 8, 4343

​S. Roy, N. R. Goud, N. J. Babu, J. Iqbal, A. K. Kruthiventi, A. Nangia, Cryst. Growth Des., 8, 4343–4346, 2008.
​Norfloxacin is known to form hydrates of water stoichiometry 1.5 (sesquihydrate), 2 (dihydrate), 2.5 and 3.5. New hydrate forms of lower water content (1.25 and 1.125) have been obtained from attempts to cocrystallise norfloxacin with eugenol. Crystal structures have also been determined for all hydrate forms confirming the zwitterionic state of norfloxacin in each form, which potentially explains their greater solubility in relation to the known anhydrate form.

Cryst.Growth Des. (2008), 8, 3856

​M. K. Stanton, A. Bak, Cryst. Growth Des., 8, 3856-3862, 2008.
​The pharmaceutical co-crystal approach has been introduced recently to address poor physicochemical properties of new chemical entities. Ten 1:1 co-crystals of AMG 517 were investigated with commercially available acids, which are all commonly used in salt screening or on the GRAS list. The authors found a 78% correlation between melting point of the co-crystal former and the melting point of the co-crystal as well as a 55% correlation between the melting point and the Log solubility of the co-crystals. This shows that some design may be possible within a defined series of co-crystals, and consequently the approach can be useful for the pharmaceutical industry.

Cryst.Growth Des. (2008), 8, 4533

​ T. R. Shattock, K. K. Arora, P. Vishweshwar, M. J. Zaworotko, Cryst. Growth Des., 8, 4533–4545, 2008.
​A detailed analysis of supramolecular synthons formed by carboxylic acid, alcohol and aromatic nitrogen functional groups has been performed. CSD statistics indicate that hetero-synthons formed between either -COOH or -COH and N(aromatic) are strongly favoured in comparison to the homo-dimers formed by -COOH or -COH. 15 new forms containing combinations of coformers exhibiting -COOH, -COH and N(aromatic) functional groups have also been crystallised and analysed (13 co-crystals and 2 salts). These experiments suggest that the -COOH to N(aromatic) interaction is comparable, but preferred in respect to the -COH to N(aromatic) synthon.

Cryst.Growth Des. (2008), 8, 4546

​ B. Sarma, L. S. Reddy, A. Nangia, Cryst. Growth Des., 8, 4546–4552, 2008.
​Co-crystallisation studies of phloroglucinol (PHG) and phenazine (Phen) using grinding with various starting ratios have been performed which produced co-crystals of 1:1.5, 1:1.75 and 1:2 PHG:Phen stoichiometry. The stoichiometry is guided by π-stacking motifs in the crystal structures which make finite and infinite aromatic stacks. The π-stack dimer motif of phenazine that is templated by the PHG hydrogen-bonding is postulated to promote the crystallisation of the β-phenazine polymorph which has a sandwich herringbone motif. These results suggest a role for co-crystal formers as hydrogen bond additives that favour and stabilise specific motifs for the crystallization of new polymorphs.

Cryst.Growth Des. (2008), 8, 4031

​T. S. Thakur, G. R. Desiraju, Cryst. Growth Des., 8, 4031–4044, 2008.
​The 1:1 binary crystal of 2-methylbenzoic acid and 2-amino-4-methylpyrimidine was one of the test systems for the recently held fourth Crystal Structure Prediction (CSP) blind test (organized by the Cambridge Crystallographic Data Centre). A supramolecular synthon based approach was originally applied, but this failed to predict the experimental structure. Further work was done on this system after the blind test was concluded and a combination of quantum mechanical calculations and a Cambridge Structural Database (CSD) study did manage to predict the structure using a synthon-based strategy.

New J.Chem. (2008), 32, 1788

​D. Braga, F. Grepioni, L. Maini, K. Rubini, M. Polito, R. Brescello, L. Cotarca, M. T. Duarte, V. André, M. F. M. Piedade, New J. Chem., 32, 1788-1795, 2008.
​The various crystal forms of the neuroleptic drug gabapentin have been investigated, and in some cases re-investigated, by a combination of calorimetric and diffraction techniques. In slurry experiments in the absence of water, the most stable form, Form II, is invariably obtained, whereas in water, the slurry leads to the conversion of all crystal forms to the hemihydrated Form I. A co-crystal of gabapentin-lactam and benzoic acid was also obtained during experiments to co-crystallise gabapentin.

New J.Chem. (2008), 32, 1796

​A. Othman, R. K. Harris, P. Hodgkinson, E. A. Christopher, R. W. Lancaster, New J. Chem., 32, 1796-1806, 2008.
​Several crystal modifications of two steroids (androsterone and beclomethasone dipropionate) have been characterised by solid-state NMR methods, and the chemical shifts between the different forms compared. The gradual loss of water from androsterone hemihydrate has been monitored by XRPD and the crystal structures are discussed in relation to the NMR data.

New J.Chem. (2008), 32, 1776

​D. Cincic, T. Friscic, W. Jones, New J. Chem., 32, 1776-1781, 2008.
​The authors have demonstrated a cocrystallisation-based strategy for the systematic construction of sets of isostructural solids. This strategy utilises the geometric similarity of halogen-bond interactions formed from I...N and from Br...N to create pairs of isostructural co-crystals with different halogen bond donors. In the same way, an aromatic CH group could be used to replace an unused N group in the halogen bond acceptor to produce further pairs of isostructural co-crystals and four isostructural solids in total.

New J.Chem. (2008), 32, 1659

​N. Blagden, D. J. Berry, A. Parkin, H. Javed, A. Ibrahim, P. T. Gavan, L. L. De Matos, C. C. Seaton, New J. Chem., 32, 1659-1672, 2008.
​This review focusses on the area of crystal growth as applied to co-crystals, especially those containing drug-like molecules. Examples from the literature are discussed with regards to co-crystal crystallisation and the allied supramolecular concepts. Specific examples from the authors\' work are used to explore topics including; nucleation templates, in situ synchrotron XRD studies, solid-state synthesis through mixing and screening strategies.