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Mössbauer spectroscopic studies of the six‐coordinate heme—nitric oxide complex of iron(III) octaethylporphyrin N ‐methylimidazole, the first model of the nitrophorin—no complexes
Author(s) -
Schünemann Volker,
Benda Rüdiger,
Trautwein Alfred X.,
Walker F. Ann
Publication year - 2000
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.5680400103
Subject(s) - chemistry , quadrupole splitting , diamagnetism , hyperfine structure , mössbauer spectroscopy , electron paramagnetic resonance , crystallography , quadrupole , analytical chemistry (journal) , nuclear magnetic resonance , magnetic field , atomic physics , physics , quantum mechanics , chromatography
The NO, N ‐methylimidazole complex of isotopically enriched octaethylporphyrinatoiron(III) chloride, [OEP 57 Fe(NO)(N‐MeIm) + Cl − has been prepared in dimethylacetamide solution and studied by low‐temperature Mössbauer spectroscopy in the presence and absence of a magnetic field. This complex is a model for the Fe(III)‐NO complexes of the nitrophorins of the blood‐sucking insect, Rhodnius prolixus , where NO is released from the histidine‐coordinated ferrihemin center of each of the proteins upon the insect's injection of the saliva into the victim. The [OEPFe(NO)( N ‐MeIm)] + Cl − complex is EPR silent and behaves as a diamagnetic species, with quadrupole splitting Δ E Q = 1.64 mm s −1 , asymmetry parameter η = 0.4, isomer shift δ = 0.02 mm s −1 , and linewidth Γ= 0.3 mm s −1 . Two electron configurations, Fe(III)‐NO (low‐spin d 5 , strongly antiferromagnetically coupled to NO), or Fe(II)‐NO + (low‐spin d 6 , purely diamagnetic), are possible. Which is the actual configuration cannot be determined until detailed molecular calculations are carried out. The low‐spin OEPFe(III)‐bis‐ N ‐methylimidazole complex also present in this sample has EPR g‐values, quadrupole splitting, isomer shift, and hyperfine splittings typical of rhombic low‐spin ferriheme centers.