3.2 Hierarchical shifts

Proteins are molecules formed by 20 units called amino acids. Each amino acid can appear in a protein 0 or more times. Just as a melody is defined by a sequence of musical notes, a protein is defined by a sequence of amino acids. Some musical note variations can result in small variations of the melody and other variations in completely different melodies. Something similar happens with proteins. One way to study proteins is by using nuclear magnetic resonance (the same technique used for medical imaging). This technique allows us to measure various quantities, one of which is called a chemical shift. You may remember that we saw an example using chemical shifts in Chapter 2.

Suppose we want to compare a theoretical method of computing chemical shift against the experimental observations to evaluate the ability of the theoretical method to reproduce the experimental values. Luckily for us, someone has already run the experiments and carried out the theoretical...