Browsing by Author "Meng, Ching-Ning"

Now showing 1 - 2 of 2

Dinuclear Lanthanide(III)-m-ODO2A-dimer Macrocyclic Complexes: Solution Speciation, DFT Calculations, Luminescence Properties, and Promoted Nitrophenyl-Phosphate Hydrolysis Rates
(2018-04-25)
Chang, C. Allen
;
Lee, Hwa-Yu
;
Lin, Syue-Liang
;
Meng, Ching-Ning
;
Wu, Tsung-Ta
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.
The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H(2)ODO2A
(2012)
Chang, C. Allen
;
Wang, I-Fan
;
Lee, Hwa-Yu
;
Meng, Ching-Ning
;
Liu, Kuan-Yu
The trivalent lanthanide complex formation constants (log K-f) of the macrocyclic ligand H(2)ODO2A (4,10-dicarboxymethyl-1-oxa-4,7,10-triazacyclododecane) have been determined by pH titration techniques to be in the range 10.84-12.62 which increase with increasing lanthanide atomic number, and are smaller than those of the corresponding H(2)DO2A (1,7-dicarboxylmethyl-1,4,7,10-tetraazacyclododecane) complexes. The equilibrium formation of the dinuclear hydrolysis species, e.g. Ln(2)(ODO2A)(2)(mu-OH)(+) and Ln(2)(ODO2A)(2)(mu-OH)(2), dominates over the mononuclear species, e.g. LnODO2A(OH) and LnODO2A(OH)(2)(-). Mass spectrometry confirmed the presence of [Eu(ODO2A)](+), [Eu(ODO2A)(OH)+H](+), [Eu-2(ODO2A)(2)(OH2)(2)+H](+), [Eu(ODO2A)(OH)(2)](-) and [Eu-2(ODO2A)(2)(OH2)(3)](-) species at pH > 7. Density function theory (DFT) calculated structures of the EuODO2A(H2O)(3)(+) and EuDO2A(H2O)(3)(+) complexes indicate that three inner-sphere coordinated water molecules are arranged in a meridional configuration, i.e. the 3 water molecules are on the same plane perpendicular to that of the basal N3O or N-4 atoms. However, luminescence lifetime studies reveal that the EuODO2A(+) and TbODO2A(+) complexes have 4.1 and 2.9 inner-sphere coordinated water molecules, respectively, indicating that other equilibrium species are also present for the EuODO2A(+) complex. The respective emission spectral intensities and lifetimes at 615 nm (lambda(ex) = 395 nm) and 544 nm (lambda(ex) = 369 nm) of the EuODO2A(+) and TbODO2A(+) complexes increase with increasing pH, consistent with the formation of mu-OH-bridged dinuclear species at higher pH. Additional DFT calculations show that each Y(III) ion is 8-coordinated in the three possible cis-[Y-2(ODO2A)(2)(mu-OH)(H2O)(2)](+), trans-[Y-2(ODO2A)(2)(mu-OH)(H2O)(2)](+) and [Y-2(ODO2A)(2)(mu-OH)(2)] dinuclear complex structures. The first and the second include 6-coordination by the ligand ODO2A(2-), one by the bridged mu-OH ion and one by a water molecule. The third includes 6-coordination by the ligand ODO2A(2-) and two by the bridged mu-OH ions. The two inner-sphere coordinated water molecules in the cis- and trans-[Y-2(ODO2A)(2)(mu-OH)(H2O)(2)](+) dinuclear complexes are in a staggered conformation with torsional angles of 82.21 degrees and 148.54 degrees, respectively.