81276-93-9Relevant academic research and scientific papers
XAS investigations on the iron-zinc center of purple acid phosphatase from red kidney beans
Priggemeyer,Eggers-Borkenstein,Ahlers,Henkel,K?rner,Witzel,Nolting,Hermes,Krebs
, p. 1445 - 1454 (2008/10/08)
X-ray absorption measurements are used to study the iron-zinc center of purple acid phosphatase isolated from red kidney beans. XANES and EXAFS data were taken at the iron and the zinc K-edge of the native enzyme (pH 7) and of the enzyme after addition of phosphate at pH 7 and pH 4. In the native enzyme both the iron and zinc ions are coordinated by five O/N donor ligands. The first shell EXAFS data yield a model with 2.4 O/N at 1.91 ? + 2.6 N/O at 2.10 ? around the iron atom, and 3.4 N/O at 1.97 ? + 1.6 N/O at 2.08 ? around the zinc atom. An iron-zinc distance of 3.96 ? was determined. No evidence for a bridging oxo group (indicated by doxo ca. 1.8 ?) could be obtained. After addition of phosphate the iron edge shifts to lower and the Zn edge to higher energies. At pH 7 the coordination numbers of iron and zinc increase to six (2.4 N/O at 1.94 ? + 3.6 N/O at 2.12 ?, Fe K-edge, and 4.0 N/O at 1.98 ? + 2.0 N/O at 2.11 ?, Zn K-edge). Since the iron-zinc distance decreases by 0.28 ? to 3.68 ? we propose a bridging coordination mode of phosphate at pH 7. Lowering the pH value to 4 does not affect the binding of phosphate. The features of the higher shell peaks in the Fourier transformed spectra remain essentially unchanged and the iron-zinc distance is maintained (d(Fe-Zn) = 3.69 ?). The ligand atoms in the first shells, however, are more disordered, indicating the involvement of protonation equilibria in the first coordination spheres (2.8 N/O at 1.97 ? and 3.2 N/O at 2.19 ?, Fe K-edge, and 4.7 N/O at 2.05 ? and 1.3 N/O at 2.18 ?, Zn K-edge). These results are checked against structural data from XAS and crystallographic studies of a number of iron and zinc model complexes with mixed ligand environments and structural characteristics similar to those expected for the enzyme samples.
Catecholate and Phenolate Iron Complexes as Models for the Dioxygenases
Heistand, Robert H.,Lauffer, Randall B.,Fikrig, Erol,Que, Lawrence
, p. 2789 - 2796 (2007/10/02)
The syntheses and physical properties of a series of Fe(salen)X and Fe(saloph)X complexes where X is phenolate or catecholate are reported.Magnetic susceptibility measurements as well as electronic, infrared, and NMR spectra indicate that the catecholate in Fe(salen)catH behaves very much like a phenolate and is concluded to be monodentate in its coordination to the iron.The abstraction of a proton from Fe(salen)catH results in an anionic complex, (-), with markedly different properties; the catecholate in this complex is chelated.Both monodentate and chelated catecholate complexes are high-spin ferric, demonstrating that catecholate coordination to a bis(phenolato)iron(III) complex does not result in the reduction of the ferric center.This is in agreement with observations made on dioxygenase-substrate complexes.In addition, studies on a series of Fe(salen)X complexes where X is a phenolate, thiophenolate, benzoate, and catecholate show that the dominant salen-to-Fe(III) charge-transfer interaction is modulated by the coordination of these ligands.Comparisons with corresponding dioxygenase complexes show that the tyrosinate-to-iron(III) charge-transfer interactions are similarly affected, thus indicating that the salen ligand provides a reasonable approximation of the iron environment in the dioxygenases.
