Dinuclear Lanthanide(III)-m-ODO2A-dimer Macrocyclic Complexes: Solution Speciation, DFT Calculations, Luminescence Properties, and Promoted Nitrophenyl-Phosphate Hydrolysis Rates

Abstract

Potentiometric speciation studies, mass spectrometry, and DFT calculations helped to predict the various structural possibilities of the dinuclear trivalent lanthanide ion (Ln(III), Ln=La, Eu, Tb, Yb, Y) complexes of a novel macrocyclic ligand, m-ODO2A-dimer (H4L), to correlate with their luminescence properties and the promoted BNPP and HPNP phosphodiester bond hydrolysis reaction rates. The stability constants of the dinuclear Ln(2)(m-ODO2A- dimer) complexes and various hydrolytic species confirmed by mass spectrometry were determined. DFT calculations revealed that the Y2LH-1 and the Y2LH-2 species tended to form structures with the respective closed- and open-form conformations. Luminescence lifetime data for the heterodimetallic TbEuL system confirmed the fluorescence resonance energy transfer from the TbIII to Eu-III ion. The internuclear distance RTbEu values were estimated to be in the range of 9.4-11.3 a ( pH 6.7-10.6), which were comparable to those of the DFT calculated open-form conformations. Multiple linear regression analysis of the kobs data was performed using the equation: k(obs),(corr.)=k(obs) k(obs),(OH)=k(Ln2)LH(M)-(>1) [Ln(2)LH(-1)]broken vertical bar k(Ln2LH-2) [Ln(2)LH(-2)] for the observed Ln(2)L-promoted BNPP/HPNP hydrolysis reactions in solution pH from 7 to 10.5 (Ln=Eu, Yb). The results showed that the second-order rate constants for the Eu2LH-2 and Yb2LH-2 species were about 50-400 times more reactive than the structural analogous Zn-2(m-12N(3)O-dimer) system.