EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE (EXAFS) STUDIES OF HYDROXO(OXO)IRON AGGREGATES AND MINERALS, AND A CRITIQUE OF THEIR USE AS MODELSFOR FERRITIN

Structural models for the hydroxo(oxo)iron core of ferritin include ex tended mineral structures and cluster systems such as [Fe11O6(OH)(6)(O (2)CPh)(15)] (= Fe-11 and two clusters that crystallise in the same la ttice (compound 1), namely, mu(3)-OH)(6)(mu(2)-OH)(10)(heidi)(8)(H2O)( 12)](3+) and u(3)-OH)(6)(mu(2)-OH)(8)(heidi)(10)(H2O)(12)](1+). The su itability of these systems as models for the structure of the core of ferritin has been tested by comparing their Fr K-edge EXAFS and X-ray crystallographic results with the Ee K-edge EXAFS data on horse spleen ferritin. The interpretative procedure for the EXAFS analysis was opt imised by using the X-ray crystallographic data for compound 1 as a ba sis. This protocol was then used to interpret the Fe K-edge EXAFS spec tra of alpha- and gamma-Fe(O)OH and to reinterpret that previously rec orded for horse spleen ferritin. The published Fe It-edge EXAFS data o n Fr-11 were also considered. The Fe ... Fe distances provide a clear indication of the nature of the hydroxo(oxo)iron assembly, It was foun d that the iron-iron interactions are the most reliable guide. Cluster s are shown to be mure appropriate than infinite lattices as structura l models for the core of ferritin.