Using guanidinium groups for the recognition of RNA and as catalysts for the hydrolysis of RNA.

The guanidinium functional group is commonly used in nature to recognize and bind anions through ion pairing and hydrogen bonding. Specific hydrogen-bonding patterns can be found in crystal structures of simple guanidinium salts. Analysis of these simple salts reveals a variety of features which are found in natural systems. These features have been applied to a series of artificial phosphodiesterases for RNA. These receptors incorporate guanidinium groups positioned to mimic the hydrogen-bonding patterns found in simple guanidinium salts and natural enzymes. This paper outlines general guanidinium hydrogen-bonding patterns. Next, the complexation of phosphodiesters with a series of artificial receptors are analyzed in terms of counterions, solvent mixtures, and cavity flexibility. In addition, strategies to enhance catalysis through a pKa analysis of phosphoranes are addressed. Next, we describe how our findings were incorporated into second generation receptors/catalysts. Finally, our future work is discussed.