Formation and stability of mononuclear and dinuclear Eu(III) complexes and their catalytic reactivity toward cleavage of an RNA analog.
The complex between Eu(III) and 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N'-diacetic acid (L4) was characterized by pH potentiometric titration and 1H NMR spectroscopy. The conversion of the monomer to a dimeric complex is observed as the pH is increased from 7 to 10 in a reaction that releases one mol/HO- per dimer formed. The dimeric complex undergoes a further ionization with a pKa of 10.7. Kinetic parameters are reported for the cleavage of the simple phosphodiester 2-hydroxypropyl-4-nitrophenyl phosphate catalyzed by both the monomeric and the dimeric Eu(III) complexes. These data show that the monomer and dimer stabilize their bound reaction transition states with similar free energies of 7.1 and 7.6 kcal/mol, respectively. Clearly, a bridging hydroxide is not an optimal linker to promote cooperative catalysis between Eu(III) centers in macrocycles with multiple polyaminocarboxylate pendent groups.
Farquhar
Erik R
ER
Department of Chemistry, University at Buffalo, State University of New York, Amherst, NY 14260-3000, USA.
Richard
John P
JP
Morrow
Janet R
JR
D000085:Acetates / Q000737:chemistry*; D002384:Catalysis; D005063:Europium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011199:Potentiometry; D012313:RNA / Q000737:chemistry*
D000085:Acetates; D009942:Organometallic Compounds; D005063:Europium; D012313:RNA