Determination of Log K[subscript ow] Values for Four Drugs

Though many undergraduates are interested in medicine, relatively few experiments related to drug design and development are included in introductory chemistry laboratory courses. In this experiment, aqueous solutions of four different drugs (acetaminophen, caffeine, phenacetin, and sulfanilamide) are extracted using 1-octanol, a mimic of the amphiphilic lipids that constitute cell membranes. UV analysis of the aqueous solutions before and after extraction allows determination of each compound's log K[subscript ow] value (partition coefficient), a property that influences a drug's bioavailability. The concepts of equilibrium and hydrophobicity-hydrophilicity are emphasized, and students gain experience with micropipets in making dilutions. The lab has been implemented in a second-year undergraduate analytical chemistry course but may be suitable for organic, general, or medicinal chemistry depending on an institution's particular curriculum.