Why is NMR spectroscopy on large proteins so difficult?
1 Answer
Because of its diverse and complicated molecular structure.
Explanation:
Before going through the details of the answer, let us ask the following question: Polymers are like proteins , they are also macromolecules; however, their H NMR spectra are often easy to interpret! Why?
A polymer is usually made of the same repetitive unit that is called monomer, and the H NMR spectrum of a polymer, is at a certain extent similar to the H NMR of its monomer. For example:
in contrast, co-polymers (contain more than one type of repetitive units) have more complicated H NMR spectra.
Proteins have even more complicated (or diverse) molecular structures than co-polymers; they are made from several repetitive units called amino acids (AA) [up to 9 AA/protein] -every amino acid possesses a different H NMR spectrum- and the H NMR spectrum of a protein will be the overall sum of all H NMR spectra of amino acids present in the protein which will appear as unresolved (or wide) peaks through a large area of chemical shifts (aliphatic and aromatic).
