Chemometric and conformational approach to the analysis of the aggregation capabilities in a set of bile salts of the allo and normal series

• Allo derivates of bile salts have aggregation numbers (n) in the range from 6.3 to 8.2.
• Allo derivatives in a plane lnk-n enter to linear hydrophobic congeneric group.
• There is a possibility that allo derivatives’ A ring is in conformation of twisted-boat.
• Bile salts of normal series with GE (H-bonds) must have C3-α-(e)OH and C12-α-(a)OH groups.

Bile salts are steroid biosurfactants that have a significant role in fat digestion, cholesterol micellar solubilization, and regulation of metabolism. They are important in pharmaceutical studies as modulators of the transport-permeability of drugs or as ligands for certain receptors. For the rational application of bile salts in medicine, it is necessary to have detailed knowledge of their aggregation capabilities (which determine their membranotoxicity and solubilization capacity). From the examination of bile salt derivatives, the in plane of lnk (RPHPLC) and micelle aggregation number n, as well as the anion of 7-oxodeoxycholic acid (7-OxD) and anion of cholic acid (C), are considered to be outliers, related to linear hydrophobic congeneric groups, which means that their micelles, in addition to being determined by hydrophobic interactions, are determined by hydrogen bonds, i.e., they form micelles with higher aggregation numbers than would be expected from the hydrophobicity of their steroid skeleton. For bile salts of the normal series in the formation of hydrogen bonds in secondary micelles, the crucial structural elements of the steroid skeleton are: α-equatorial-C3OH group and α-axial-C12OH group. Bile salts of the allo series, including allocholic (aC), allodeoxycholic (aDC) and allochenodeoxycholic acid (aCD), belong to the linear hydrophobic congeneric group. Their micelles are determined by hydrophobic interactions. It is assumed that for the analyzed allo derivatives, the A ring of the steroid skeleton is in the twisted boat conformation, which explains the spatial sheltering of their C3OH group in micelles.

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