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William H. Casey Laboratory




Edina Balogh

   


    ebalogh@ucdavis.edu
    (530) 752 2107
    1475 Chemistry Annex

    Post-doc. Touro College, 2008-present
    Post-doc. UC Davis, 2006-2008
    PhD Swiss Federal Institute of Technology, Lausanne 2002-2006
    MSc University of Debrecen 1997-2002

   

As an undergraduate Edina studied the thermodynamic stability and binding modes of Pd(II) complexes with nitrogen donor bioligands (amino acids, peptides, nucleobases, nucleotides and derivatives), in the group of Prof. Imre Sóvágó at the University of Debrecen, Hungary. Her PhD thesis in the group of Prof. André Merbach at EPFL, supervised by Dr. Éva Jakab Tóth, was concerned the study of thermodynamic and kinetic stability as well as relaxation properties of new potential MRI contrast agents. Beside her research activities, she supervised practical courses in general and analytical chemistry. In her present position as a postdoctoral fellow in the group of Prof. William H. Casey at UC Davis she studies ligand exchange rate and its mechanism on polyoxometalates and Fe(III) complexes of geochemical interest.

Research

The Lindquist ion: The early transition metals in their high oxidation states form multimeric metal-oxide clusters, called polyoxometalates, in aqueous solutions.  Although there is much interest in these molecules, relatively little is known about the pathways by which they react and transform in an aqueous solution. We performed 17O NMR study on the [HxTa6O19](8-x)-(aq) to extend the work that was previously carried out in our group on the [HxNb6O19](8-x)-(aq). Figure 1. shows the structure and the bond lengths of both molecules as well as the 17O NMR spectrum of the Ta(V) version.

Figure 1. In the ball-and-stick representation, the oxygens are red and the metals (either Ta(V) or Nb(V)) are green. The bond lengths were determined from X-ray structures of the alkali-metal salts of the Nb(V) and Ta(V) Lindqvist ions in various stoichiometries. 17O NMR peaks of the Ta(V) version assigned to the bridging oxygen (top, ~320 ppm) and terminal oxygen (~470 ppm), the bulk-water peak (0 ppm) and the central oxygen  (~-40 ppm).

Although one would think that these isostructural molecules would react identically, we showed that they are profoundly different, indicating that predictions about site reactivities in complicated structures, such as the interface of aqueous solutions and oxide solids, should be approached with great caution.

The main differences in reactivities of these two molecules can be summarized as the following:

1.The terminal oxygens in the Ta(V) molecule reacts ~10 times faster than the bridging ones, which is opposite to what is observed in the Nb(V) version molecule where the bridging O reacts faster than the terminal oxygens in the pH range ~12<pH<14.5.

2. Unlike in the HxNb6O19(8-x)- molecule, the bridging and terminal oxygens in the HxTa6O19(8-x)- molecule never react at the same rates.

3. The activation parameters for the HxNb6O19(8-x)- and HxTa6O19(8-x)- suggest that the oxygen sites react via different pathways, in spite of the similarities of these molecules in electronic and physical structure.

Figure 2. Rates as a function of pH and temperature for the [HxNb6O19](8-x)- and [HxTa6O19](8-x)- Lindqvist ions. The data for the bridging oxygens are in blue circles and the data for the terminal ones are in red squares. The lines correspond to fits.

Mo72Fe30: a nanometer-size aqueous cluster
Research of reactivity on individual functional groups at oxide mineral surfaces, relies heavily on computer simulation because so few minerals exist that have well-constrained surface structures in water. In a new approach, we used a nanometer-size aqueous clusters ([Mo72Fe30O252(CH3COO)12[Mo2O7(H2O)]2[H2Mo2O8(H2O)](H2O)91]. ca150 H2O. [Mo72Fe30, Figure 3.], also called Keplerates) to provide experimental models that isolate the key functional groups for spectroscopic characterization.

Figure 3. A near-spherical aqueous cluster, containing 72 Mo(VI)-oxide polyhedra (purple) and 30 Fe(III) as Fe(O)6 octahedra (brown).

17O NMR measurements and calculation of kex298
The water-exchange rates were obtained by measuring the longitudinal- and transverse-relaxation times (T1 and T2) as well as the chemical shift as a function of temperature for the Mo72Fe30 molecule in water. (Figure 4.) The values were simultaneously fitted to the Swift and Connick equations:

 

Figure 4. (left) Reduced values of T1 (red squares) and T2 (green circles) 17O relaxation rates. (right) Reduced chemical shift at 11.7 T. The solid lines correspond to the simultaneous fit of all measured data to the Swift-Connick equations for relaxation.

The results establish a link between the nanoclusters and smaller aqueous molecules. The rates of solvent exchange from >FeIII-OH2 sites on the Mo72Fe30 complex are ~104 more rapid than for the simple aquo ion, Fe(H2O)63+, but slightly slower than the FeIII-EDTA and its derivatives, and indicates a correlation between the bond length and the water exchange rate (Figure 5). Recently, geochemists established  correlation between calculated <Al-OH2> bond lengths and rates of solvent exchange that extends across many orders of magnitude (Wang et al., 2007). The motivation for establishing this correlation was a desire to assign reactivities to the functional groups on colloidal mineral surfaces. A similar correlation will ultimately be possible for high-spin FeIII solid surfaces if more aqueous complexes can be added to the correlation.

Figure 5. Correlation between <FeIII-OH2> bond-lengths and values of log(kex298), the rates of water exchange, for a series of high-spin FeIII complexes. The uncertainties correspond to the range in values calculated for the bond length: 2.075 Ĺ < rFeO < 2.088 Ĺ.


Research prior to UC Davis

Novel chelators for MRI applications: Stability and relaxation properties
Since the first clinical application of MRI contrast agents in the eighties, many attempts have been made to ameliorate their efficiency. The aim of my PhD research at EPFL, Lausanne, was to enlarge our knowledge on the physical chemistry of MRI related paramagnetic metal chelates in the perspective of contributing to the development of more efficient, more tissue specific and safer contrast agents.

Thermodynamic stability and kinetic inertness of the metal complexes are crucial features for their safe biomedical application. We have carried out detailed kinetic studies on the dissociation of various Gd(III) chelates which have been recently proved to have optimal water exchange rate. The ligand involved both acyclic and macrocyclic molecules. In order to approach the biologically relevant conditions, we studied exchange reactions between these Gd(III) complexes and the endogeneously most abundant Zn2+ ion. For the macrocyclic compounds, formation kinetic studies have also been performed for various lanthanides.


Publications

 

  1.   Edina Balogh, Travis M. Anderson, James R. Rustad, May Nyman and William H. Casey, Rates of oxygen-isotope exchange between sites in the [HxTa6O19]8-x(aq) Lindqvist ion and aqueous solutions, Inorg. Chem. 2007, 46(17); 7087-7092.  
  2. Edina Balogh, Ana Maria Todea, Achim Müller, William H. Casey, Rates of ligand exchange between >FeIII-OH2 functional groups on a nanometer-size aqueous cluster and bulk solution, Inorg. Chem. 2007, 46(17); 7032-7039.
  3. Edina Balogh, Raphaël Tripier, Petra Fouskova, Felipe Reviriego, Henri Handel, Éva Tóth, Monopropionate analogues of DOTA4- and DTPA5-: kinetics of formation and dissociation of their lanthanide(III) complexes, Dalton Trans. 2007, 3572-3581.  
  1. Marta Mato-Iglesias, Edina Balogh, Carlos Platas-Iglesias, Eva Toth, Andres de Blas, Teresa Rodriguez Blas,   Pyridine and phosphonate containing ligands for stable lanthanide complexation. An experimental and theoretical study to assess the solution structure. Dalton Trans,  2006,  (45), 5404-5415. 
  1. Edina Balogh, Marta Mato-Iglesias, Carlos Platas -Iglesias, Éva Tóth, Kristina Djanashvili, Joop A. Peters, Andrés de Blas and Teresa Rodríguez-Blas; Pyridine- and phosphonate-containing ligands for stable Ln Complexation. Extremely fast water Exchange on the Gd(III) Chelates,  Inorg. Chem. 2006, 45(21), 8719-8728.  
  1. Edina Balogh, Hsieh He, Wenyuan Zhenjie, Shuang Liu, Eva Toth,   Dinuclear complexes formed with the triazacyclononane derivative ENOTA4-: High-pressure 17O NMR evidence of an associative water exchange on Mn2(ENOTA)(H2O)2. Inorg. Chem., 2007, 6(1), 238-250.  
  1. Jerome Costa, Edina Balogh, Veronique Turcryl, Raphael Tripier, Michel Le Baccon, Francoise Chuburu, Henri Handel, Lothar Helm, Eva Toth, Andre E. Merbach, Unexpected aggregation of neutral, xylene-cored dinuclear GdIII chelates in aqueous solution. Chem. Eur. J., 2006, 12(26), 6841-6851.  
  1. Marta Mato-Iglesias, Carlos Platas-Iglesias, Kristin Djanashvili, Joop A Peters, Eva Toth, Edina Balogh, Robert N Muller, Elst Luce Vander, Andres de Blas, Teresa Rodriguez-Blas, The highest water exchange rate ever measured for a Gd(III) chelate. Chem. Comm. 2005, (37), 4729-31.  
  2. Edina Balogh, Raphael Tripier, Robert Ruloff and Éva Tóth, Kinetics of formation and dissociation of lanthanide(III) complexes with the 13-membered macrocyclic ligand TRITA4- Dalton Trans. 2005, 1058-1065.

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