How to uncover the arrangement of molecules when they are not long-range ordered

What is it about?

When small molecules form into solids the do so by packing together in a well defined way. Typically the order extends over long range and the material forms a crystal. The packing arrangement can be solved using the venerable approach of x-ray crystallography. But what if the packing is not perfect--the molecules have a well defined local structure but a few molecules over the packing gets muddled and the order is lost--then crystallography fails. This paper describes a new method for uncovering the molecular packing even in this important case where the molecules are just short-range ordered.

Featured Image

Why is it important?

Most drugs, many foods and plastics we use in everyday life are made of molecules, small, well-ordered, tightly bound clusters of carbon and other atoms. But when we take a drug, it is a solid lump of material made of billions of molecules. How the molecules pack together in space is known as the crystal structure of the solid form, and has a huge effect on various properties of the material, not least how well it is absorbed into the body. It is exceptionally important to elucidate the nature of the crystal packing for drug safety, quality control, stability control, as well as gaining basic understanding of molecular packing and interactions themselves.