Ribonuclease Activity of an Artificial Catalyst That Combines a Ligated Cu^II Ion and a Guanidinium Group at the Upper Rim of a <i>cone</i>-Calix[4]arene Platform

A <i>cone</i>-calix­[4]­arene derivative, featuring a guanidinium group and a Cu^II ion ligated to a 1,4,7-triazacyclononane (TACN) ligand at the 1,3-distal positions of the upper rim, effectively catalyzes the cleavage of 2-hydroxypropyl <i>p</i>-nitrophenyl phosphate (HPNP) and a number of diribonucleoside 3′,5′-monophosphates (<i>N</i>p<i>N</i>′). Kinetic and potentiometric measurements support the operation of a general-base/general-acid mechanism and demonstrate that the hydroxo form of the ligated Cu^II ion is the sole catalytically active species. Rate enhancements relative to the background hydrolysis reaction at 1 mM catalyst concentration are 6 × 10⁵-fold for HPNP and cluster around 10⁷-fold with the most favorable catalyst–<i>N</i>p<i>N</i>′ combinations