Blog Science Stories

After more than 40 years, the long C-C bond in 5-cyano-1,3-didehydroadamantane (CTCDEC) has been re-determined.  The long bond between the bridgehead carbon atoms in the cyclopropane ring was originally reported in the paper by C.S.Gibbons and J.Trotter.[1] At 1.643(4) Å in length, it has been used as an example of a long C-C bond and is highlighted here by the yellow spheres. 

​I recently came across a report about the largest known aromatic molecule, to date,¹ and it got me thinking about similar entries in the CSD. I know from editing structures into the database that a significant proportion of new entries contain an aromatic system. The structures also seem to be getting bigger and bigger but I had never really connected these two features in any detail. First of all, I was delighted to learn that the supersized structures from the report were already in the CSD.  Our new automated systems could deal with them without a problem and one of my colleagues had already cast their expert eye over them. In the report Dongho Kim and co-workers synthesised a [50]dodecaphyrin (KUHHIG, see below), the full name of which is in our curated entry but would have taken up half this blog so I decided not to include it! If you are wondering how to make your own supersized aromatic then the structure was synthesised to contain Hückel aromaticity by oxidising a non-aromatic [52]dodecaphyrin with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Dongho Kim and co-workers appear to be record breakers in the world of these structures; the largest known aromatic prior to this was a [46]decaphyrin palladium(II) complex (DONZEN), also synthesised by the same research groups.²

​I recently found a blog post from regular Chemistry World contributor Derek Lowe, highlighting an Early View Angewandte Chemie communication (doi: 10.1002/anie.201406886) in which the authors determined the crystal structures of two new polymorphs of the amino acid L-Phenylalanine. The paper also helps to clarify the relationship between several other Phenylalanine structures published over the last 20 years. Although Derek was surprised that determining the structure of a seemingly simple molecule had proved such a challenge for small-molecule crystallography, this type of challenge is not unusual. A notable example is the case of the two polymorphs of D-Ribose which evaded full determination for over 50 years (see ZZZFEE in the CSD from 1956!) until Jack Dunitz and co-workers published an article triumphantly exclaiming “The Crystal Structure of D-Ribose—At Last!” in 2010 (doi: 10.1002/anie.201001266).

The challenges involved in obtaining good quality single crystals to determine a structure should not be underestimated. Prior to the findings of this latest paper, the Cambridge Structural Database (CSD) contained five determinations of the structure of L-Phenylalanine (QQQAUJ-QQQAUJ04), from four different groups of researchers, all proposing different polymorphic forms based on the crystal structure data that they obtained.

​The European Crystallographic Meeting (ECM-28) at Warwick University in August this year marked my personal return to the world of crystallographic conferences after a gap of some eleven years. I recently returned to work at the CCDC, having left in 2002, and spent the intervening 11 years working in the drug discovery software industry which, although related and relevant, is quite a different community.

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We are pleased to announce that a recently published scientific communication involving researchers at the Pfizer Institute of Pharmaceutical Materials Science and CCDC has appeared as a CrystEngComm hot-article. The article summarises exciting results assessing the potential of the Mercury Solid Form Suite’s hydrogen bond propensity tool in screening potential co-crystal formers, and is available to view free of charge for 4 weeks from 20^th March.

We at CCDC are keen advocates of the use of 3D structure to aid with the teaching of key chemical concepts.  Following a demo of WebCSD and existing teaching material intended for undergraduate teaching, Dr Peter Hoare at the University of Newcastle has been developing (with the help of A level and masters students) bite-size worksheets intended for A Level standard chemistry, making use of our free teaching subset and WebCSD.  Here, Peter's current MChem student Steve Carman explains a bit more about the exercises they have developed and how you can get your hands on them!

How important is solubility? Well, if like me you enjoy a sugar in your coffee, the answer is “pretty important”. In order for the sugar to be able to reach my taste-buds in adequate concentration to achieve that welcome sensation of sweetness, the sugar needs to be soluble enough in hot milky water.  So too, for a successful drug, which, like the sugar, must dissolve and then reach a site of action in sufficient quantity to elicit a pharmacological response. Solubility is taken very seriously by pharmaceutical scientists.