Dipeptide Structural Analysis Using Two-Dimensional NMR for the Undergraduate Advanced Laboratory

A laboratory experiment was developed to introduce students in either an organic chemistry or biochemistry lab course to two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy using simple biomolecules. The goal of this experiment is for students to understand and interpret the information provided by a 2D NMR spectrum. Students are provided three unknown samples: a dipeptide and each of the two amino acids that make up the dipeptide. A Fourier transform-NMR (60 MHz) instrument is used to record standard proton (1H) NMR spectra for each of the unknown samples. By interpreting the 1H NMR spectra for the two single amino acid unknown samples, students identify the amino acids in the dipeptide. For the dipeptide molecule, students record the 1H and correlation spectroscopy (COSY or 1H–1H) NMR spectra. The students use the COSY spectrum information to assign all of the proton peaks in the more complicated 1D 1H spectrum of the dipeptide. A comparative analysis of the NMR spectra for dipeptides with ...