MECHANISM OF PHOSPHATE ADSORPTION TO A 3-DIMENSIONAL STRUCTURE OF BOEHMITE IN THE PRESENCE OF BOVINE SERUM-ALBUMIN

A new microcrystalline boehmite (tentatively named PT-A) was synthesiz ed as an efficient phosphate adsorbent to replace aluminum hydroxide g el. The characteristic structure of PT-A was examined by nitrogen adso rption/desorption, X-ray diffraction, deviation microscopy, and scanni ng electron microscopy to establish a pore structural model of PT-A. W ith this model structure, the details of the mechanism of interaction between PT-A and phosphate in the presence of bovine serum albumin (BS A) are discussed. PT-A is a spherical particle with a diameter of appr oximately 100 mum and a porous surface structure, and its inside is pa cked with boehmite microcrystals (crystallite size, 2 nm). PT-A has th ree types of pores in its structure: a micropore with a narrow size-di stribution, a mesopore with a broad size-distribution, and a macropore (radii of pores are 0.7, 1-20, and approximately 300 nm, respectively ). When phosphate was incubated with PT-A in human gastric and intesti nal juices or in an aqueous solution containing BSA, the amounts of ph osphate adsorbed by PT-A were not affected by the presence of proteins . The nitrogen adsorption/desorption isotherms and energy dispersive X -ray analyses demonstrated that phosphate could diffuse to the smaller tunnels freely even if the external surface of PT-A was covered with BSA. It was also demonstrated that the main site of adsorption for pho sphate was in micropores of PT-A, whereas BSA was adsorbed only to the external surface and none entered inside smaller tunnels consisting o f micro- and mesopores.