Abstract:

There is considerable interest in examining new ways to deliver the chemistry curriculum, and much of the activity in this area has been directed at significant improvements in classroom teaching methods and in laboratory experiments.[1][2] We present here a physicochemical laboratory experiment aimed to determine the partition constants of both ionizable and non-ionizable selected bioactive compounds between a model oil (olive) and water. The experiment is aimed to cover the lack of specifically designed pedagogical experiments dealing with hydrophobic interactions, though they play a central role in both the chemistry and biochemistry curricula.

The experiment fits into the physical-chemistry curricula, and it is designed to introduce students to concepts of thermodynamics, activity, chemical potentials and to show them how ionization affects the distribution of the compound into the phases of the system. Students will have the opportunity of exploring the role of the acidity, oil to water ratio and temperature on the distributions and local concentrations of the bioactive molecules. Prior to the laboratory period, the students are reminded of the hazards working with bioactive compounds and on the proper use of laboratory material. The experiment described here consists in three parts designed to increase their skills in separatory techniques, analytical methodologies and physical-chemistry calculations. In the first part, students extract aliquots of the bioactive from previously prepared oil-water mixtures. In a second part, students are required to choose an appropriate analytical technique to quantify the amount of bioactive in each phase, requiring the in-advance preparation of calibration plots. In the third part, students are required to perform appropriate quantitative calculations to determine the partition constants and to write a report where a brief introduction, data presentation, experimental conditions, calculations and conclusions will be required and evaluated.
This laboratory exercise has been well received and executed by more than 150 students. It can be carried out in groups of two students, and collaboration between groups for scientific discussion is allowed because of application of the obtained data and conclusions to daily life: students are aimed to discuss on the design new molecules for a better interpretation of diffusion across biological membranes and of screening results in complex biological systems such as liposomes, cells.

References:
[1] C. P. Schaller, K. J. Graham, B. J. Johnson, M. A. Fazal, T. N. Jones, E. J. McIntee, H.V. Jakubowski, J. Chem. Educ. 2014, 91, 321−328
[2] S. R. Miller, J. Chem. Educ. 2016, 93, 1536−1542

Keywords:

Partition coefficients, distribution, hydrophobic interactions.