Interaction of cholesterol which is an essential structural component of animal cell membranes that is required to establish proper membrane permeability and fluidity and the bile chenodeoxycholic acid which significantly increased serum total cholesterol, and high-density-lipoprotein (HDL) cholesterol, and dissolves gallstones appears to be one of pivotal problem of biomedical gastroenterology. The methods of spin labels and spin probes have been proved to be power tools for solving structural and dynamical problems of chemistry and biology on molecular level. In present work the method of spin probes was used for investigation of quantitative interaction of cholesterol and chenodeoxycholic acid in ethanol possessing dielectric properties similar to ones of biological membranes. Using Electron Spin Resonance of nitroxide spin probe, it was shown that in the ethanol solution cholesterol molecules form aggregates, modeling a gallstone, which effectively bound chenodeoxycholic acid. The developed method can be used for study relationships between cholesterol and chenodeoxycholic acid in the in human blood, high-density-lipoproteins and gallstones.
