| Liquid chromatography is one of the most widely used analytical techniques for the separation of complex mixtures. In this study, the LC column is used as a measurement tool, specifically for the measurement of pairwise interactions of amino acids. There are only a select number of studies in the literature on studying these pairwise interactions which are important to better understand the folding process of proteins. Initial studies involved designing bonded stationary phases made up of particular amino acids. Various synthetic schemes were examined including direct bonding of the amino acid to the silica surface and the use of difunctional silanes. Later studies required the synthesis of amino acid surfactants. These surfactants were introduced at a submicellar concentration into the mobile phase and pumped across a reversed phase C18 column resulting in a pseudostationary. Upon preparation of the phase, L-amino acids were injected individually onto the column and their retention was measured over a wide temperature range. van't Hoff plots (natural log of the retention factor versus temperature) provided thermodynamic values corresponding to the interactions between the amino acids and the pseudostationary phase. Four different pseudostationary phases were examined namely N-Decanoyl-L-alanine, phenylalanine, leucine, and valine. The data obtained from these studies show a minimal contribution from enthalpy for the interactions of phenylalanine with N-Decanoyl-L-phenylalanine and a large contribution from entropy. Interactions between the isomer pair leucine and isoleucine with N-Decanoyl-L-alanine and phenylalanine illustrated the behavior of the hydrophobic effect. The large entropy contribution was also observed for several aromatic-aliphatic and aliphatic-aliphatic pairs indicating that these interactions are hydrophobic interactions. This would be expected should these be nonpolar interactions between amino acids. |
