Fast chromatographic determination of the bile salt critical micellar concentration

In a line of research focused on the design, synthesis and development of new bile acid-based compounds, the physico-chemical profile of the molecules must be thoroughly explored and analyzed. In this scenario, a fast and reliable information on the critical micellar concentration (CMC) of specific compounds through a profitable chromatographic parameter can be of aid to rationally direct the synthesis of new molecular entities, mainly during the early stages of the drug-discovery process. The derived ‘chromatographic hydrophobicity index’ (CHI), usually employed for a fast access to the log P/log D value of physico-chemically diverse compounds and obtained via RP-gradient elution, was for the first time engaged in the bile acid field. Accordingly, 14 unconjugated bile acids harboured with a different number, position and orientation of hydroxy groups, as well as other substituents onto the steroidal backbone and side chain, were selected to build up a calibration curve. Such a collection of compounds was rationally assembled in order to manage an almost continuous range of CMC values (spanning the spectrophotometrically obtained CMCs between 5 and 25 mM). A high degree of correlation between CMC and CHI values was obtained (R ² and cross-validated R _xv² of the pCMC vs CHI plot equal to 0.975 and 0.966, respectively). A selected new subset of five confidential research bile acids with experimental CMCs in the range 6–19 mM was finally recruited to validate the proposed method. The high statistical quality of the established mathematical model turned out into a very appreciable predictive power.