Exploring Drug Diffusion through a Membrane: A Physical Chemistry Experiment for Health and Life Sciences Undergraduate Students

Abstract

The transport of molecules across biological membranes are critical for most cellular processes. Membrane permeability is also a key determinant for drug absorption, distribution, and elimination. Diffusion, that is, the migration of matter down a concentration gradient, is a simple mechanism by which both endogenous and drug molecules can enter (or exit) cells. This paper describes a simple and engaging physical chemistry undergraduate laboratory experiment for health and life sciences students studying diffusion of drug and dye molecules in solution. In this experiment, the diffusion of amitriptyline hydrochloride, ranitidine hydrochloride, and tartrazine across a cellulose dialysis membrane is evaluated using an innovative macro and microscale approach. Compound concentration in solution as a function of time is obtained both from conductivity measurements of 25 mL solutions and from absorbance measurements of 100 μL samples taken in a 96-well microplate. By using solutions of different concentrations, the permeability coefficient of the membrane and the diffusion coefficient of the tested compounds are determined. Comparison of both methods, which yield similar values, is performed, which shows that either one of the approaches is suitable to independently conduct the experiment. On the basis of diffusion phenomena, the important pharmaceutical issue of absorption and transport of drugs through passive diffusion across biological or artificial membranes is presented.