**2. Materials and Methods**

### *2.1. Materials*

Alanine, C3H7NO2, and serine, C3H7NO3, (Figure 1) are aliphatic proteinogenic amino acids and are found in many naturally occurring proteins. Both amino acids have one chiral center and, therefore, can exist as L- and D-enantiomers. In the serine molecule (Figure 1b), the methyl (CH3) end group in alanine (Figure 1a) is replaced by a methylene (CH2) moiety with an OH group.

**Figure 1.** Structural formulae of alanine (**a**) and serine (**b**) molecules.

The known crystal structures of both amino acids are characterized by the same space group *P*212121. The first results of deciphering the crystal structures of alanine and serine were reported several decades earlier [24,25]. Later, these results were refined and high-pressure data were added [26,27]. Moreover, numerous investigations included studies of the mechanical, optic, magnetic, and electron properties of alanine and serine crystals [28–32].

L-alanine and L-serine (99% purity) were obtained from Merck, Zug, Switzerland, and were used as obtained. As a solvent, deionized water was applied.
