Purple acid phosphatases (PAPs) are a group of heterovalent binuclear metalloenzymes that catalyze the hydrolysis of phosphomonoesters at acidic to neutral pH. While the metal ions are essential for catalysis, their precise roles are not fully understood. Here, the Fe(III)Ni(II) derivative of pig PAP (uteroferrin) was generated and its properties were compared with those of the native Fe(III)Fe(II) enzyme. The k cat of the Fe(III)Ni(II) derivative (approximately 60 s -1 ) is approximately 20% of that of native uteroferrin, and the Ni(II) uptake is considerably faster than the reconstitution of full enzymatic activity, suggesting a slow conformational change is required to attain optimal reactivity. An analysis of the pH dependence of the catalytic properties of Fe(III)Ni(II) uteroferrin indicates that the l-hydroxide is the likely nucleophile. Thus, the Ni(II) derivative employs a mechanism similar to that proposed for the Ga(III)Zn(II) derivative of uteroferrin, but different from that of the native enzyme, which uses a terminal Fe(III)-bound nucleophile to initiate catalysis. Binuclear Fe(III)Ni(II) biomimetics with coordination environments similar to the coordination environment of uteroferrin were generated to provide both experimental benchmarks (structural and spectroscopic) and further insight into the catalytic mechanism of hydrolysis. The data are consistent with a reaction mechanism employing an Fe(III)-bound terminal hydroxide as a nucleophile, similar to that proposed for native uteroferrin and various related isostructural biomimetics. Thus, only in the uteroferrin-catalyzed reaction are the precise details of the catalytic mechanism sensitive to the metal ion composition, illustrating the significance of the dynamic ligand environment in the protein active site for the optimization of the catalytic efficiency.

Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear Fe III M II center (M II = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a variety of phosphoric acid esters. The dinuclearhas recently been prepared and is found to closely mimic the coordination environment of the Fe III Zn II active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the Fe III center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted Fe III N 2 O 4 octahedron with a dominant tetragonal compression aligned along the μ-OH-Fe-O phenolate direction. To probe the role of the Fe-O phenolate bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (-CH 3 , -H, -Br, -NO 2 ) in the 5-position. The effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic structural information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order -NO 2 rBr rH rCH 3 when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k cat /k 0 ) is plotted against the Hammett parameter σ. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing -NO 2 and electron-donating -CH 3 groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups.

Modifying the porphyrinogen framework in lanthanide porphyrinogen complexes by trans-N,NЈ-dimethylation results in Sm II and Sm III derivatives that are remarkably simple in structure and formulation, and are amenable to highly controllable further reaction chemistry. The Sm II bis(tetrahydrofuran) adduct, Sm III chloride and bis(trimethylsilyl)amide

Articles you may be interested inAbsence of exchange interaction between localized magnetic moments and conduction-electrons in diluted Er3+ gold-nanoparticles J. Appl. Phys. 115, 17E128 (2014) The low temperature magnetic circular dichroism ͑MCD͒ and electron paramagnetic resonance ͑EPR͒ spectra of Cu͑II͒ doped Cs 2 ZrCl 6 are reported. The Cu͑II͒ ion is incorporated as the square planar copper tetrachloride ion, CuCl 4 2− , which substitutes at the Zr͑IV͒ 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 ͑xy͒ 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 , yz͒ 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.

The Cu(II) doped MgO system is known to display features indicating behavior intermediate between static and dynamic Jahn-Teller effects at low temperature. The system is interesting as there is a low barrier between equivalent Jahn-Teller distortions in the cubic host lattice. In order to study the geometry of the Cu(II) ion in this system, we have recorded the low temperature magnetic circular dichroism (MCD) and X-ray absorption fine structure (XAFS) spectra. The spectra have been interpreted in terms of the Cu(II) centers distorting the host lattice such that the CuO 6 center is a tetragonally elongated octahedron.