Selective adsorption of phytochemicals with carboxyl or o-phenolic hydroxyls by Fe3O4 nanoparticles

Catechol (1,2-diphenols) derivatives are often used as dispersant anchors for Fe₃O₄ nanoparticles because of the high affinity of catechols for the nanoparticles (see Figure, J. Phys. Chem . 2011, 115, 682–691). This “grafting to” approach implies that Fe₃O₄ nanoparticles could be applied to selectively adsorb some phytochemicals with carboxyl or ortho-phenolic hydroxyls. This possibility was explored. Using ˜30nm Fe₃O₄ nanoparticles, ginkgolic acid, ascorbic acid, cichoric acid, citrinin (with carboxyl) and some flavones containing a catechol moiety in Scutellaria baicalensis Georgi roots could be successfully adsorbed from methanol, acetonitrile or water solutions. After separating the nanoparticles from the herbal extract solution with a magnet, the adsorbed phytochemicals could be simply desorbed at a low pH, e.g. with formic acid solution. The adsorptive capacity of nanoparticles was ˜1.0% (w/w). The whole purification process is solvent-efficient and also energy-efficient when using a permanent magnet. The method can be used as a first step in the large scale production of fine chemicals.