Nanostructured surfaces

Sorptive removal of bile salts from aqueous solutions by MCM‑41 silica with chemically immobilized steroid groups
Roik N.V., Belyakova L.A., Dziazko M.O.
Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., Kyiv, 03164, Ukraine
E-mail: roik_nadya@ukr.net

Bile acids (BAs) play the important role as biological surfactants for dietary fats and oils solubilization as well as signaling molecules that influence metaboliс processes. Enterohepatic circulation of BAs affects cholesterol metabolism and plays crucial role in pathogenesis of atherosclerosis. Therefore, development of strategies for cholesterol excretion in the form of neutral sterols or BAs has noticeable importance in treatment of hypercholesterolemia.
Regulation of the cholesterol level in human organism can be achieved by removal of BAs excess from the gastrointestinal tract with enterosorbents. Taking into account low binding capacity of oral nonabsorbable anion‑exchange resins, which are used in clinical practice, the attempts to design highly efficient adsorbents for regulation of cholesterol level via removal of overproduced BAs from human blood or gastrointestinal tract were made. Silica materials attract interest of scientists as promising candidates for design of medical adsorbents due to good biocompatibility, low toxicity, and high synthetic availability.
In the present work, mesoporous silica of MCM‑41 type with chemically immobilized BA-containing functional groups was prepared by hydrothermal‑assisted base‑catalyzed sol‑gel condensation of structure forming silanes in the presence of micelles of long‑chain quaternary ammonium salt. Sorption properties of synthesized material towards sodium cholate (NaCh) and taurocholate (NaTCh) were studied in dependence of solution pH, duration of contact, and adsorbate equilibrium concentration. It was found that introduction of steroid groups in surface layer of silica sorbent leads to the substantial enhancement of sorption efficiency towards bile salts. Maximal values of bile salts sorption are predetermined by the protolytic properties of corresponding BAs and achieved in the pH range from 4 to 5 for NaCh and at pH 2 for NaTCh. Analysis of experimental isotherms using Langmuir, Freundlich, Redlich‑Peterson, and BET models proves the crucial role of cooperative interactions in sorptive removal of NaCh and NaTCh by mesoporous silica with chemically immobilized BA‑containing functional groups. Prepared material may be useful as sorbent for hypercholesterolemia treatment and atherosclerosis prevention.