The way that molecules arrange themselves as solids can be changed with just a drop of solvent

William Jones at Cambridge University, UK, and colleagues in Singapore have developed a method for obtaining unstable polymorphs of anthranilic acid and succinic acid.

Molecules and materials often assume more than one polymorph - a different way of packing crystals in the solid state - each with unique physical and chemical properties. Pharmaceutical and pigment researchers often investigate each polymorph of a new compound in order to control its physical properties. Changing the crystallising solution leads to different polymorphs.

Jones and his colleagues have used their ’solvent-drop grinding’ approach to make anthranilic and succinic acid polymorphs. One crystal form transforms into another after grinding it with a trace of solvent at room temperature.

The researchers hope that their solvent-economical approach could become routine for screening polymorphs, and are now investigating known polymorphic systems to see how this phenomenon can be broadly applied.

Sula Armstrong