Monday 16 December 2019

What is crystallography?

Dr Sarah Hayes explains the facinating link between snowflakes, salt and chocolate

Sarah Hayes

Crystals are everywhere throughout nature and our lives – from gemstones, to snowflakes, shells, plastics, soil, salt and even chocolate. What are they? Crystals are solids that form by a regular repeated pattern of molecules connecting together.

In some solids (non-crystalline ones), the arrangements of the building blocks (atoms and molecules) can be random or very different throughout the material.

In crystals, however, a collection of atoms called the unit cell is repeated in exactly the same arrangement over and over throughout the material. Because of this repetitive nature, crystals can take on strange and interesting looking forms, naturally.

The branch of science related to crystals’ inner structure and properties is crystallography, which has allowed us to study the chemical bonds that draw one atom to another.

Crystal engineers can modify a crystal’s inner structure, which then changes its properties and behaviour. Crystallisation is the process of forming (through natural or artificial growth and design) solid crystals. A large amount of materials around us, and indeed consumed by us in everyday life is made up of crystals. 

Crystals are particularly important when making medicines. Most marketed pharmaceuticals consist of molecular crystals. The arrangement or packing of the molecules in a crystal determines its physical properties and, in certain cases, its chemical properties, and so greatly influences the processing and formulation of solid pharmaceuticals, as well as key drug properties such as how long it takes the medicine to dissolve in the body and its stability – or, indeed, if it has any therapeutic effect at all.

In medicine manufacture, the crystal is the main part of the Active Pharmaceutical Ingredient (API), which needs to be ‘formulated or packed’ into a tablet. Therefore, the shape and size of the crystals are very important, as the crystalline material still needs to undergo the rest of the manufacturing process. There is so much involved in the manufacturing process, you want to make sure that your crystalline material remains stable and does not change form (as can happen with chocolate), or far more worryingly with diamond and graphite (both carbon structures).


Dr Sarah Hayes is Education and Outreach Officer at the Synthesis and Solid State Pharmaceutical Centre (SSPC), where research is focussed on emerging science such as growing nanocrystals, which can alter the properties of a drug and improve its dissolution rate. Other work involves co-crystallisation; this involves growing one crystal, the API, on top of another ‘carrier’ crystal, which may improve its ability to be taken up into the bloodstream. The SSPC, a global hub of pharmaceutical process innovation and advanced manufacturing, funded by SFI and industry, is a unique collaboration between 22 industry partners, nine research performing organisations and 12 international academic collaborators.

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