Amino acids characterization by reversed-phase liquid chromatography. Partial least-squares modeling of their transport properties

In the present work, the 20 coded free amino acids (AAs) were characterized with respect to their lipophilic behavior by means of reversed-phase liqui d chromatography (RPLC) and using two octadecyl silica (ODS) stationary pha ses and phosphate-buffered mobile phases at three pH values. To complement the results obtained with the ODS phases, one phenyl stationary phase was a lso used. The retention behavior of the AAs under study was investigated by means of the multiple linear regression (MLR) technique and several molecu lar descriptors were used as predictor variables. The results show that the obtained chromatographic parameters provide a different type of informatio n from both, the currently used lipophilic scales and several chromatograph ic hydrophobicity scales based upon derivatives of the AAs. The relationships between the obtained retention data and both the brain up take data, reported data on kinetic parameters, and lipid bilayer affinitie s for several AAs, multivariate projection techniques such as partial least -squares (PLS) regression were used. The results indicate that the combinat ion of RPLC techniques and chemometrics is a promising approach in assessin g the hydrophobic amino acid-membrane interactions.