In their complexes, natural amino acids are typically coordinated through the α-amino and carboxyl (ate) groups as bidentate ligands forming stable five-membered rings. The stability, structure, reactivity, and solubility of these complexes are influenced in a broad range by the structure of the α-substituent. Several classifications based on the structure of these side chains have been done, which are widely used in biochemistry to interpret (or predict) the behavior of amino acids, as well as their oligo- and polycondensates. One of the most important features is the polarity of the side chain. The following natural amino acids can be regarded typically apolar: Ala, Val, Leu, He, Pro, Phe, Tyr, Trp, Cys, and Met. These representatives are characterized by low solubility and micelle formation in water. The members of other group (Lys, Arg, His, Asp, Glu, Asn, and Gin) bear polar, mostly dissociable groups in their side chain, which assures a good solvation in water and higher solubility. Although the majority of the natural amino acids possess groups with typical ligand properties in the side chain, in aqueous solution these are only weakly or not coordinated. Only three natural amino acids can be regarded as tridentate (His, Asp, and Cys). All natural amino acids, with the exception of Gly, contain at least one stereogenic center (the α-carbon atom) and belong to the L-series in majority of cases.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)