Biomimetic Catalysts for Hydrolysis (AASERT Award).

Abstract : Synthetic molecular receptors are of interest as tools for the selective detection of ions and molecules and as mimics of biological systems. One part of this project focuses on the use of cholic acid, a readily available steroid natural product, as the basic design element of new molecular receptors for the complexation of neutral organic molecules. Cholic acid is ideally suited to this task since, (1) it possesses a rigid hydrocarbon framework upon which hydrogen-bonding groups (hydroxyls) are appended in an orientation suitable for bonding to substrates, and (2) considerably less synthetic effort is required to build a large receptor molecule than in the case of molecular receptors designed in an ab initio fashion. Molecular receptors are constructed from two cholic acid groups linked by a diamine group. The diamine linking groups under study include simple aromatic diamines providing a rigid spacer, diamines with additional ligating groups such as phenolate and carboxylate for ion-pairing with partially charged substrates, and diamines containing indicators or metal ions (p-nitrophenol, ferrocene, metal-salen complex). Substrates under study include simple diols and triols (ethylene glycol, glycetol), sugars (glucose, ribose), and amino-sugars (glucosamine). Results of these studies will lead to a better understanding of hydrogen bonding in non-polar solvents and to the development of chemical sensors for neutral polar molecules. A second area of the project involves design and synthesis of dinucleating ligands capable of binding two transition metal ions for catalysis of hydrolytic reactions. The complexes utilize a disfunctional mechanism to both coordinate and activate a carbonyl or phosphoryl oxygen in a lewis acid sense, as well as binding and activating a water molecule.