Sol-gel derived organic-inorganic composites recognizing molecular asymmetry

A new type of optically active organic-inorganic composite was prepared by a sol-gel method in which tetraethoxysilane (TEOS) is hydrolyzed in the pre sence of an optically active organic compound (D-lactose, D-glucose, D-sorb itol, D-fructose, L-tartaric acid, L-malic acid, or L-mandelic acid). Optic al resolution of tris(pentane-2,4-dionato)metal complexes was performed by using the new sol-gel derived composites, composites prepared by convention al techniques (kneading with L-lactose, L-fructose or L-tartaric acid, and impregnation with an L-lactose, L-fructose or L-tartaric acid solution) and the optically active organic compounds themselves. The sol-gel derived com posites showed much higher optical resolution abilities than the composites prepared by conventional techniques. In addition, the optically active org anic compounds could not resolve the racemate into the enantiomers under si milar conditions. X-ray diffraction and NMR results disclosed that an optic ally active organic compound in the sol-gel derived composite is highly dis persed, most likely, because it bonds to silicon atoms. Thus, it was deduce d that optically active molecules dispersed at a molecular level recognize the chirality of the metal chelate compound. The high-resolution ability of the sol-gel derived composites arises from the combined effect of the sili ca support (adsorbing power) and the highly dispersed molecules (chiral rec ognition power). (C) 1998 Elsevier Science Limited. All rights reserved.