Image of the week - Anti-cancer agent in watery bind

Water molecules bind to anti-cancer agent 5-fluorouracil to prevent formation of a newly discovered form II polymorph. All molecules are immersed in liquid nitromethane, which is not shown for reasons of clarity. Image courtesy of Said Hamad

These images show the interactions of water molecules with each other and with molecules of anti-cancer agent 5-fluorouracil in nitromethane solution.

These interactions are strong enough to prevent the formation of 5-fluorouracil clusters, which in turn prevents the formation of a more stable 5-fluorouracil polymorph: the elusive “form II”.

Only when water molecules are completely absent from the system will “form II” crystals appear.

This molecular dynamics investigation was carried out by investigators now at the University College London, as part of the Control and Prediction of the Organic Solid State project.

CPOSS is dedicated to predicting the crystalline structures of organic molecules and uses the e-science grid computing Condor pool at UCL to hunt for thermodynamically stable crystalline structures.

This search often reveals the existence of many equally stable crystal structures, which raises the possibilities of polymorphism and can lead to problems in producing the original solid form in a controlled manner.

The existence of crystal polymorphs poses a major problem for pharmaceutical companies, who are only licensed to sell their products in a specified solid form. Image courtesy of Said Hamad

The existence of crystal polymorphs poses a major problem for pharmaceutical companies, who are only licensed to sell their products in a specified solid form, since although polymorphs are chemically identical, their physical properties, such as dissolution rates, differ.

CPOSS is funded by Research Councils UK.

CPOSS is having a free Open Day on 6 September 2007. Visitors are requested to pre-register for catering purposes.