COMMUNICATIONSdeveloping negative charge is stabilized by the cationic metal center, while in the latter case the developing negative charge is not stabilized by the metal. The metal center in 4 is providing double Lewis acid activation, while the metal center in 5 is providing single Lewis acid activation. We recently showed that a dinuclear metal complex can rapidly cleave an RNA model compound by providing double Lewis acid activation.['] The two methyl groups in the neocuproine ligand should decrease the 0-Cu-0 bond angle in 3, which should facilitate the chelation of phosphate diesters. In octahedral Co"' complexes, the 0-Co-0 bond angles in chelated phosphates are significantly smaller than the 90" angle found in regular octahedral complexes.I91Among simple compounds, lanthanides and their complexes are the most reactive for hydrolyzing nucleic acids.["] However, enzymes use transition metals, Mgz+, or Ca2+ to cleave phosphate esters. Consequently, there is considerable interest in developing simple transition metal, Mg2+, or Ca2+ complexes that efficiently hydrolyze the phosphate diester bonds of RNA. Complex 3 represents by far the most reactive transition metal complex reported to date for hydrolyzing RNA.
Experiinen tal ProcedureThe copper chloride complexes [Cu(terpy)CI]CI, [Cu(bpy)CI,], and [Cu(neocuproine)CI,] were prepared by mixing the appropriate ligands with CuCI, in methanol. All of the ligands and CuCI, are soluble in methanol, whereas the complexes precipitate out of the solvent. Cleavage of ApA was monitored by HPLC (Hewlett-Packard 1090). In a typical kinetic experiment, a solution of ApA (0.5m~),3(10m~),andHEPES(10m~) wasallowed toreactatpH 7.0and25"C.Aliquots (50 pL) of the reaction mixture were quenched with 100 mM ethylenediaminetetraacetic acid (EDTA) (50 pL). The quenched solutions (10 pL) were injected onto a C-18 reversed-phase column (5 pm Hypersil maintained at 40'C) and eluted for 5 min with NH,H,PO, (0.2 M at pH 5.5) followed by a 0-50% linear gradient of NH,H2P0, (0.2 M at pH 5.5) and methanol/water (3:2) solutions over 10 min with a flow rate of 0.5 m l m i n -' .