Potentiometric and UV titrations of pharmaceutical drugs: Hands-on measuring ionization constants, partition coefficients and other key parameters for understanding drug absorption

CHED 396

Arno Kraft, a.kraft@hw.ac.uk, Chemistry, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, United Kingdom and Nicola M. Howarth, n.m.howarth@hw.ac.uk, Chemistry, School of Engineering & Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, United Kingdom.
Over the last 3 years, we have used pharmaceutical drugs to illustrate important concepts in Physical Organic Chemistry to 12 project students of varying background. These included: BSc Honours students who carried out their final-year project (over 15 weeks, 3 hours each afternoon); exchange students for whom English was a foreign language (2 months); and four 16-year old students from local schools who took part in a science bursary scheme that allowed them to experience research for 4 weeks during the Summer holidays of their penultimate year at school. The students were asked to develop in-house methods for measuring the ionization constants (pKa), partition coefficients (log P), distribution coefficients (log D), and permeability for a selection of ionizable pharmaceutical drugs (e.g., acetylsalicylic acid, propranolol, sulfathiazole). These are important physicochemical properties that determine absorption and up-take of a drug in the body, and are routinely screened in modern drug development. The experiments were straightforward and made use of an automated titrator, a UV spectrometer and Excel spreadsheets (for data analysis). All students have expressed that they enjoyed this type of work and that they learned a lot about how a drug "works".