Thermodynamics of sorption and retention patterns of halogen adamantanes on cyclodextrin-containing cyclobond sorbent under HPLC conditions

Experimentally, under HPLC conditions, the thermodynamic characteristics of sorption (retention factors, heats and entropy factors of sorption) of various chlorine, bromine and iodine derivatives of adamantanes from water-methanol eluent on sorbents octyl silica gel (SiO2-C8) and b-CD-octyl silica gel (CYCLOBOND) are determined for the first time. It is found that sorption of halogen adamantanes on these sorbents has a different mechanism, viz. distributive on SiO2-C8 and macrocyclic on CYCLOBOND. The isomers of halogen adamantanes on the studied sorbents differ in the retention order under the same elution conditions. High structural selectivity of the CYCLOBOND sorbent for separation of position isomers and stereoisomers of halogen adamantanes is shown. The values of separation factors of position isomers increase with the growth of van der Waals radii of halogen atoms. It is hypothesized that halogen adamantanes, for which it is difficult to form inner-sphere complexes with b-CD fragments, can form outer-sphere complexes with exocyclic OH-groups of b-CD, realizing the sorption mechanism similar to the hydrophilic chromatography variant.