ABSTRACT
The protonation state of the deazaflavin dependent nitroreductase (Ddn) enzyme bound cofactor F420 was investigated using UV-visible spectroscopy and computational simulations. The reduced cofactor F420H2 was determined to be present in its deprotonated state in the holoenzyme form. The mechanistic implications of these findings are discussed.
Subject(s)
Mycobacterium tuberculosis/enzymology , Nitroreductases/chemistry , Prodrugs/chemistry , Protons , Quinone Reductases/chemistry , Hydrogen-Ion Concentration , Models, Molecular , Molecular Conformation , Molecular Structure , Nitroreductases/metabolism , Prodrugs/metabolismABSTRACT
The low temperature magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectra of Cu(II) doped Cs(2)ZrCl(6) are reported. The Cu(II) ion is incorporated as the square planar copper tetrachloride ion, CuCl(4) (2-), which substitutes at the Zr(IV) site in the Cs(2)ZrCl(6) lattice, with a complete absence of axial coordination. Both the EPR and MCD show highly resolved spectra from which it is possible to determine the superhyperfine coupling constants and excited state geometries respectively. The Franck-Condon intensity patterns suggest that there is a substantial relaxation of the host lattice about the impurity ion. For the lowest energy (2)B(1g)(x(2)-y(2))-->(2)B(2g)(xy) transition, both the magnetic dipole allowed electronic origin as well as vibronic false origins are observed. The high resolution of the spectra allowed the accurate determination of the odd parity vibrations that are active in the spectra. The opposite sign of the MCD of the two components of the (2)E(g)(xz,yz) excited state allows this splitting to be determined for the first time. Accurate and unambiguous spectral parameters for the CuCl(4) (2-) ion are important as it has become a benchmark transition metal complex for theoretical electronic structure calculations.
Subject(s)
Copper/chemistry , Electrons , Absorption , Calibration , Circular Dichroism , Electron Spin Resonance Spectroscopy , Ligands , Magnetics , Sensitivity and Specificity , TemperatureABSTRACT
The spectral and geometric trends of Ln(trensal) complexes (H(3)trensal = 2,2',2' '-tris(salicylideneimino)triethylamine) along the lanthanide series are analyzed. Low-temperature polarized absorption and luminescence spectra are reported for nine of the complexes with transitions suitable for analysis. Both the angular and radial geometry variations as a function of the lanthanide ion are quantified. The structural parameters are related to the trend in the ligand field found from an analysis of the f-f transitions. The ligand-field analysis is fitted globally across the whole series accounting for the contraction of the f orbitals as a function of atomic number. This study establishes the utility of describing the ligand field of f electrons within the one-electron operator approach of the angular overlap model.