Personally, I never need an excuse to eat chocolate, but many associate it with holidays, particularly Valentine’s Day. Let’s look at chocolate from a molecular perspective. Cocoa butter (or more precisely the triglyceride fats within it) has six polymorphic forms [1-3]. The formation of chocolate bloom, the white spots on chocolate, is in part due to a polymorphic transformation from Form V to Form VI – the thermodynamically more stable polymorph. Chocolate tempering is the process of heating and cooling the chocolate to crystallize the Form V polymorph, giving chocolate its pleasant mouth sensation. Yum! Two examples from the CSD are refcodes JEMRUP and JEMSAW, which are triglyceride polymorphs found in cocoa butter.
What does this have to do with love? The reason we associate chocolate with love is that many believe it to have aphrodisiac properties. While that link hasn’t been proved, there are quite a few alkaloids in chocolate that may have a positive physiological effect; Theobromine ( SEDNAQ ) being the most studied. Interestingly, it forms quite a few metal complexes, salts and co-crystals (e.g. MUPPET) which makes it a good drug delivery platform; better still is a Quercetin based co-crystal (MUPPOD). Quercetin is a flavonoid found in red wine, so a co-crystal with theobromine would make the perfect gift!!
Of course, the day would not be complete without some overpriced flowers, especially roses. The aroma of many flowers comes from the essential oils they contain. Rose oils are rich in several compounds including geraniol, citronellol, eugenol and other terpenes. Unusually, very few of these compounds have had their crystal structure determined by X-ray, especially for their pure phases, but derivatives including a eugenol inclusion complex ( TEZZUV ) and a co-crystal of the ketone derivative of citronellol (DABFIV) are in the CSD.
In closing, we all know that love and romance require human chemistry, but real chemistry is all about molecular structure! For the last fifty years the CSD, which now contains over 750,000-curated structures has offered the most comprehensive source of structural chemistry information in the world.
For those who might benefit, here is a shopping list, but you had better be quick!
1. Chocolate – The Noblest Polymorphism II, Klaus Roth, ChemViews Magazine, September 2010 · DOI: 10.1002/chemv.201000030
2. S. T. Beckett, The Science of Chocolate, Royal Society of Chemistry, London 2000.
3. Polymorphism of cocoa butter, R. L. Wille, E. S. Lutton Journal of the American Oil Chemists Society, August 1966, Volume 43, Issue 8, pp 491-496 DOI: 10.1007/BF02641273