Proton NMR Studies of the Conformation of an Octapeptide. An NMR Exercise for Biophysical Chemistry

We describe an exercise intended to introduce students to the proton NMR experiments used to define the molecular conformation of biological molecules in solution. Proton NMR spectra of the octapeptide [sar 1 ] angiotensin II are assigned and nuclear Overhauser effects are then used to develop constraints that define the three-dimensional shape of the peptide. The exercise demonstrates the utility of COSY, TOCSY, and NOESY types of experiments, while underscoring the limitations of these experiments in the determination of structure. The spectroscopic data used for the exercise are made available in several formats so that an instructor can design variations of the exercise to emphasize particular aspects related to data handling or the generation or comparison of derived structures. At least one quarter of biochemistry and a year of organic chemistry are reasonable prerequisites for the exercise, presuming that these courses provide the needed level of familiarity with the basic concepts of proton NMR spectroscopy. Junior- or senior-level chemistry and biochemistry students are probably most benefited from this exercise.