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

Potentiometric speciation studies, mass spectrometry, and DFT calculations helped to predict the various structural possibilities of the dinuclear trivalent lanthanide ion (LnIII , Ln=La, Eu, Tb, Yb, Y) complexes of a novel macrocyclic ligand, m-ODO2A-dimer (H4 L), to correlate with their luminescence properties and the promoted BNPP and HPNP phosphodiester bond hydrolysis reaction rates. The stability constants of the dinuclear Ln2 (m-ODO2A-dimer) complexes and various hydrolytic species confirmed by mass spectrometry were determined. DFT calculations revealed that the Y2 LH-1 and the Y2 LH-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 EuIII ion. The internuclear distance RTbEu values were estimated to be in the range of 9.4-11.3 Š(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: kobs,corr. =kobs -kobs,OH =kLn2LHM->1 [Ln2 LH-1 ]+kLn2LH-2 [Ln2 LH-2 ] for the observed Ln2 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 Eu2 LH-2 and Yb2 LH-2 species were about 50-400 times more reactive than the structural analogous Zn2 (m-12 N3 O-dimer) system.

Simulated annealing and density functional theoretical prediction of macrocyclic ligand conformations, protonation sites and complex metal-ligand exchange reaction directions.

The prediction of conformations and protonation sites for the macrocyclic ligands H2DO2A (1,4,7,10-tetraazacyclododecane-1,7-diacetic acid) and H2ODO2A (1-oxa-4,7,10-triazacyclododecane-4,10-diacetic acid) has been performed employing the simulated annealing (SA) method and density functional theory (DFT) calculations using the B3LYP/6-31G* method in a vacuum and aqueous solution. These SA method/DFT calculations reveal that, in contrast to the H2ODO2A ligand system, the H2DO2A ligand system is (i) pre-organized for trivalent lanthanide (Ln) and other metal ion complexation, (ii) structurally more symmetrical and slightly more compact in aqueous solution (i.e. more and/or shorter intra-molecular hydrogen bonds), and (iii) with a greater degree of partial positive charge accumulation on the hydrogen atoms bonded to macrocyclic ring nitrogen atoms when protonated. The H2ODO2A ligand system is not pre-organized. These observations are in accord with the experimental findings that the LnODO2A(+) complexes are less thermodynamically stable and kinetically more labile as compared to those of the corresponding LnDO2A(+) complexes. The results on the prediction of the ligand protonation sites are consistent with those experimentally obtained via NMR spectroscopy. The calculations of the first and second protonation constants are, however, not as accurate as compared to those experimentally determined using either the thermodynamic cycle (TC) or the isodesmic reaction (IRn) methodology, although the latter gave relatively better results. The lowest energy structures of the LnL(+) and ZnL (Ln = Eu, Y; L = DO2A, ODO2A) complexes are also calculated using the same method. The Gibb's free energies (ΔGaq) for a number of ligand and/or metal ion exchange reactions such as LnDO2A(+) + HnODO2A((2-n)-) -->/<-- LnODO2A(+) + HnDO2A((2-n)-) (Ln = Eu, Y; n = 0, 1, 2), LnDO2A(+) + Ln'ODO2A(+) -->/<-- LnODO2A(+) + Ln'DO2A(+) (Ln = Eu, Ln' = Y), LnDO2A(+) + Ln'(3+) -->/<-- Ln'ODO2A(+) + Ln(3+) (Ln = Eu, Ln' = Y) and LnDO2A(+) + ZnODO2A -->/<-- LnODO2A(+) + ZnDO2A (Ln = Eu, Y) have been calculated in aqueous phase and the reaction directions in some cases could be predicted to be consistent with experimental or expected results. The errors between the calculated and experimental Gibb's free energy data are in the range ΔG(aq,calc) - ΔG(aq,exp) = -1.89 to +7.00 kcal mol(-1) in seven selected cases involving LnDO2A(+), LnODO2A(+) (Ln = Eu, Y), ZnDO2A and ZnODO2A complexes. The predicted reaction directions with the small core effective core potential (ECP) data are not necessarily better than those using large core ECP. However, the former takes much longer computer time to obtain the energy data.

The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H2ODO2A.

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)(µ-OH)(+) and Ln(2)(ODO2A)(2)(µ-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)(OH(2))(2)+H](+), [Eu(ODO2A)(OH)(2)](-) and [Eu(2)(ODO2A)(2)(OH(2))(3)](-) species at pH > 7. Density function theory (DFT) calculated structures of the EuODO2A(H(2)O)(3)(+) and EuDO2A(H(2)O)(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 N(3)O 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 (λ(ex) = 395 nm) and 544 nm (λ(ex) = 369 nm) of the EuODO2A(+) and TbODO2A(+) complexes increase with increasing pH, consistent with the formation of µ-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)(µ-OH)(H(2)O)(2)](+), trans-[Y(2)(ODO2A)(2)(µ-OH)(H(2)O)(2)](+) and [Y(2)(ODO2A)(2)(µ-OH)(2)] dinuclear complex structures. The first and the second include 6-coordination by the ligand ODO2A(2-), one by the bridged µ-OH ion and one by a water molecule. The third includes 6-coordination by the ligand ODO2A(2-) and two by the bridged µ-OH ions. The two inner-sphere coordinated water molecules in the cis- and trans-[Y(2)(ODO2A)(2)(µ-OH)(H(2)O)(2)](+) dinuclear complexes are in a staggered conformation with torsional angles of 82.21° and 148.54°, respectively.

An ab initio/RRKM study of product branching ratios in the photodissociation of buta-1,2- and -1,3-dienes and but-2-yne at 193 nm.

Ab initio G2M(MP2)//B3LYP/6-311G** calculations have been performed to investigate the reaction mechanism of photodissociation of buta-1,2- and -1,3-dienes and but-2-yne after their internal conversion into the vibrationally hot ground electronic state. The detailed study of the potential-energy surface was followed by microcanonical RRKM calculations of energy-dependent rate constants for individual reaction steps (at 193 nm photoexcitation and under collision-free conditions) and by solution of kinetic equations aimed at predicting the product branching ratios. For buta-1,2-diene, the major dissociation channels are found to be the single Cbond;C bond cleavage to form the methyl and propargyl radicals and loss of hydrogen atoms from various positions to produce the but-2-yn-1-yl (p1), buta-1,2-dien-4-yl (p2), and but-1-yn-3-yl (p3) isomers of C(4)H(5). The calculated branching ratio of the CH(3) + C(3)H(3)/C(4)H(5) + H products, 87.9:5.9, is in a good agreement with the recent experimental value of 96:4 (ref. 21) taking into account that a significant amount of the C(4)H(5) product undergoes secondary dissociation to C(4)H(4) + H. The isomerization of buta-1,2-diene to buta-1,3-diene or but-2-yne appears to be slower than its one-step decomposition and plays only a minor role. On the other hand, the buta-1,3-diene-->buta-1,2-diene, buta-1,3-diene-->but-2-yne, and buta-1,3-diene-->cyclobutene rearrangements are significant in the dissociation of buta-1,3-diene, which is shown to be a more complex process. The major reaction products are still CH(3) + C(3)H(3), formed after the isomerization of buta-1,3-diene to buta-1,2-diene, but the contribution of the other radical channels, C(4)H(5) + H and C(2)H(3) + C(2)H(3), as well as two molecular channels, C(2)H(2) + C(2)H(4) and C(4)H(4) + H(2), significantly increases. The overall calculated C(4)H(5) + H/CH(3) + C(3)H(3)/C(2)H(3) + C(2)H(3)/C(4)H(4) + H(2)/C(2)H(2) + C(2)H(4) branching ratio is 24.0:49.6:4.6:6.1:15.2, which agrees with the experimental value of 20:50:8:2:2022 within 5 % margins. For but-2-yne, the one-step decomposition pathways, which include mostly H atom loss to produce p1 and, to a minor extent, molecular hydrogen elimination to yield methylethynylcarbene, play an approximately even role with that of the channels that involve the isomerization of but-2-yne to buta-1,2- or -1,3-dienes. p1 + H are the most important reaction products, with a branching ratio of 56.6 %, followed by CH(3) + C(3)H(3) (23.8 %). The overall C(4)H(5) + H/CH(3) + C(3)H(3)/C(2)H(3) + C(2)H(3)/C(4)H(4) + H(2)/C(2)H(2) + C(2)H(4) branching ratio is predicted as 62.0:23.8:2.5:5.7:5.6. Contrary to buta-1,2- and -1,3-dienes, photodissociation of but-2-yne is expected to produce more hydrogen atoms than methyl radicals. The isomerization mechanisms between various isomers of the C(4)H(6) molecule including buta-1,2- and -1,3-dienes, but-2-yne, 1-methylcyclopropene, dimethylvinylidene, and cyclobutene have been also characterized in detail.