EXAFS studies of binuclear iron complexes as models for hemerythrin and related proteins

Journal Article · Wed Sep 24 04:00:00 EDT 1986 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00240a040· OSTI ID:7129700

Hedman, B; Co, M S; Armstrong, W H; Hodgson, K O; Lippard, S J

There is increasing interest in oxo-bridged polyiron centers in biology. Binuclear units of this kind occur in hemerythrin, the marine invertebrate oxygen carrier, in ribonucleotide reductase, and in purple acid phosphatases. The reversible binding of dioxygen in hemerythrin has been postulated to occur where the bridging carboxylate groups are contributed from glutamate and aspartate residues of the protein. Following the synthesis of realistic model compounds for both oxidized and reduced forms of the hemerythrin iron core, as well as analogues of the former in which either the oxo bridge was protonated or the bridging carboxylate ligands were replaced by diphenylphosphate groups, they have been working to establish their relevance to the chemical and physical properties of the proteins. Previously, they showed close similarities between the molecular geometry, magnetic exchange interactions, and optical spectroscopic and vibrational properties of azidomethemerythrin and the model compounds (Fe/sub 2/O(O/sub 2/CCH/sub 3/)/sub 2/(HB(pz)/sub 3/)/sub 2/) and (Fe/sub 2/O-(O/sub 2/CCH/sub 3/)/sub 2/(TACN)/sub 2/)/sup 2 +/, where HB(pz)/sub 3//sup -/ = hydrotris(1-pyrazolyl)borate and TACN = 1,4,7-triazacyclononane. They now report the results of extended X-ray absorption fine structure (EXAFS) studies of these two complexes as well as the derivatives (Fe/sub 2/O)O/sub 2/P(OC/sub 6/H/sub 5/)/sub 2/)/sub 2/(HB(pz)/sub 3/)/sub 2/) and (Fe/sub 2/(OH)(O/sub 2/CCH/sub 3/)/sub 2/(HB(pz)/sub 3/)/sub 2/)/sup +/. This work addresses in well-defined model systems how sensitive EXAFS spectroscopy is to the important question of modulations in the iron-to-bridging oxygen and nonbonded, e.g. Fe...Fe or Fe...P, distances. Such geometric information is necessary to understand the oxygen binding reaction of hemerythrin as well as the structural biology of ribonucleotide reductase and purple acid phosphatase.

• Research Organization: Stanford Synchrotron Radiation Lab., CA
• OSTI ID: 7129700
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 25:20; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
550200 -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTROSCOPY
COMPLEXES
DATA
ELECTROMAGNETIC RADIATION
ENZYMES
EXPERIMENTAL DATA
INFORMATION
IONIZING RADIATIONS
IRON COMPLEXES
MATHEMATICAL MODELS
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDOREDUCTASES
OXYGEN COMPLEXES
RADIATIONS
SIMULATION
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
X RADIATION