Patterns of the Adsorption of Proteins of Different Molecular Weights on Natural Aluminosilicate Nanotubes

A study is performed of the adsorption of proteins with different molecular weights (lysozyme (M_R = 14 300), hemoglobin (M_R = 65 000), bovine serum albumin (M_R = 66 000), and alkaline phosphatase (M_R = 138 000)) on halloysites. The average values of the internal diameters of nanotubes are 12.5, 30, and 50 nm. Adsorption isotherms are obtained, the limit values of adsorption are determined, from which the areas per one protein molecule on the halloysite surface are calculated. It is concluded that the magnitude of protein adsorption depends on both its molecular weight (size) and the internal diameter of the nanotubes. The inner surface of halloysite samples has different accessibility for protein molecules: with a nanotube diameter of 12.5 nm, it is not accessible for the adsorption of all the studied proteins. The greatest accessibility of the internal surface for protein molecules is displayed by halloysite with a 50 nm internal diameter of nanotubes.