Electron paramagnetic resonance of myoglobin and related ferrous complexes
Hendrich, Michael Paul
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Permalink
https://hdl.handle.net/2142/23909
Description
Title
Electron paramagnetic resonance of myoglobin and related ferrous complexes
Author(s)
Hendrich, Michael Paul
Issue Date
1988
Doctoral Committee Chair(s)
Debrunner, Peter G.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Electron paramagnetic resonance (EPR)
myoglobin
ferrous complexes
Language
en
Abstract
"Electron paramagnetic resonance spectra of myoglobin (Mb), the 02-storage protein of mammals, are reported for the first time. The EPR signals arise from the biologically active ferrous deoxyMb and photolyzed oxyMb, Mb""(2) complexes. Similar EPR signals were also discovered in photolyzed carbonmonoxy Mb, Mb*(CO), and from a model heme complex. The EPR signals in this work are from non-Kramers doublets which are not usually EPR active. These integer spin systems are nondegenerate in B = 0 and therefore split quadratically in B. In order to interpret the signals, a simulation program based on the spin Hamiltonian Illi = S·D·S + (3S.g.B was developed. The experimental EPR spectra are rather broad. and analysis shows that the components of the tensor D have to be distributed in order to explain the lineshapes. The EPR signals from Mb and Mb*(CO) could be simulated well with this model, but not the Mb*(02) signals. It is suggested that the Mb*(02) spectrum results from magnetic coupling between the iron spin S = 2 and 02 spin S = 1. The model was tested on single crystals of magnetically dilute ferrous fluosilicate and found to be satisfactory. In addition, EPR data and simulations are presented for two ferrous solution complexes. The findings disagree with a previous report, and a
iv
flaw in the simulation of field -swept spectra is discussed. Further characterization of the complexes with magnetic susceptibility supports the EPR analysis presented here.
The magnitude of the splitting of the non-Kramers doublet in zero magnetic field is crucial for observation of signals. The measurements were made using X (9 GHz) and Q (35 GHz) band microwave spectrometers and demonstrate the need for higher frequency measurements as only a fraction of the molecules give signals at 9 GHz.
The EPR spectra of high-spin ferrous complexes are shown to be quite sensitive to the iron environment. As with most transition metal complexes, the EPR signals are observed only at low temperatures (T < 77 K)."
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