One of the most highly applied areas of terahertz spectroscopy is in the pharmaceutical sciences. Many pharmaceutical materials are crystalline solids, and in many cases these materials can exist in a number of different crystalline forms, known as polymorphs. Each individual pharmaceutical polymorph has its own set of thermodynamic parameters, dictating things like solubility and bioavailability. Even though these different polymorphs contain the exact same chemical, they can have totally different efficacies when ingested.

Using terahertz spectroscopy and DFT simulations, we can completely and unambiguously understand these phenomena. We can easily discern the different crystalline forms with terahertz spectroscopy, and using that information we can interpret and predict the stability of the different forms, often as a function of temperature. We are able to observe when the materials undergo a phase transition, and thus we can confirm all of our predictions with a single set of measurements. Cool!

Terahertz spectra of the two polymorphs of glutamic acid, along with the crystal structures and individual molecular confirmations. Examination of L-Glutamic Acid Polymorphs by Solid-State Density Functional Theory and Terahertz Spectroscopy, Journal of Physical Chemistry A, 120 (38), 7490-7495, doi:10.1021/acs.jpca.6b05702 (2016).