In this chapter, we investigate the Raman spectra of proteinogenic amino acid crystals. Amino acids are fundamental organic molecules that compose polypeptides (a linear chain of amino acids) and proteins (folded polypeptides with specific functions) found in all living beings. Surprisingly, the number of these basic molecules is not more than 22 (20 of them commonly known as the standard amino acids, plus pyrrolysine and selenocysteine). They are defined as a molecule formed by an NH2 group, a COOH group, a lateral chain (the R group), and a hydrogen atom, all of them connected to a single carbon, the α-carbon. Interestingly, α-amino acids show chirality, i.e., they present different distributions of group of atoms around the α-carbon, being defined as l- and d-form. For amino acids and proteins found in the living beings, the l-form is the dominant form, although some exceptions have been discovered in the last decades. In this chapter, we present the Raman spectra of all standard amino acids and discuss the different kinds of vibrations found, comparing them. As complementary part of the work, we present results on vibrational properties of some amino acids using Raman spectroscopy when subjected to specific conditions, with variation in temperature or pressure. Finally, we present some perspectives as the investigation of purines, a group of molecules associated with the DNA molecule.
Part of the book: Raman Spectroscopy and Applications