Investigation of dinuclear Mn (II) model complexes by multifrequency EPR spectroscopy and theoretical simulations /
Many hydrolase enzymes utilize a dinuclear metal center to catalyze chemical reactions. Most of the enzymes contain either Mg(II) or Zn(II) in their native state, but retain some activity when substituted with other divalent metals such as Mn(II). Manganese can be used as a paramagnetic probe to s...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731980791&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Many hydrolase enzymes utilize a dinuclear metal center to catalyze chemical reactions. Most of the enzymes contain either Mg(II) or Zn(II) in their native state, but retain some activity when substituted with other divalent metals such as Mn(II). Manganese can be used as a paramagnetic probe to study these enzymes. Dimanganese model complexes have been synthesized and studied by EPR spectroscopy in order to understand the spectral properties of this motif. In this work the model complex Mn₂(H₂O)(OAc)₄(tmeda)₂ was studied using variable temperature X and Q-band EPR spectroscopy. The EPR spectra showed evidence for an exchange coupled manganese center with J = -2.9 cm⁻¹. Analysis of the temperature dependence of the main spectral features revealed that the transitions originated from the S = 2 state of the coupled cluster. A computer program, DDPOWJHE which uses a full Hamiltonian approach to calculate EPR and ENDOR spectra, was used to simulate the main features of the X and Q-band EPR spectra. A good simulation was produced by the parameters: g = 2.00, A = 272 MHz and D₂ = -0.060 cm⁻¹. The value of the zero field splitting D₂ was larger than the value calculated using the point dipole approximation for this complex and was consistent with a previous study showing an inverse relationship between the zero field splitting and the internuclear distance of the two Mn(II) atoms. Possible evidence for a trinuclear complex of the form Mn₃(OAc)₆(tmeda)₂ was observed in the Q-band EPR and ESI mass spectra. The EPR spectrum of phosphotriesterase, an enzyme containing a dinuclear manganese active site, was examined using techniques developed during the study of inorganic complexes. Variable temperature X-band spectra of manganese substituted phosphotriesterase are reported. The observed transitions are assumed to result from the S = 2 level of the exchange-coupled system. A full spin Hamiltonian simulation of the X-band spectra revealed the zero-field splitting of the S = 2 state to be D₂ = -0.055 cm⁻¹ and E₂ = -0.0067 cm⁻¹. The exchange coupling constant of the coupled manganese system was found to be J = -2.75 [] 0.25 cm⁻¹. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xi, 138 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 117-122). |