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Title:Measured Electron Spin Relaxation Rates in Frozen Solutions of Azurin, Vitamin-B12r, and Nitrosyl Ferrous Myoglobin
Author(s):Muench, Philip James
Doctoral Committee Chair(s):Stapleton, Harvey J.,
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, General
Abstract:Rates in frozen glycerin/water solutions at temperatures between 1.4 K and 20 K are reported for a copper-containing protein, azurin, and a cobalt-containing biomolecular complex, vitamin B$\sb{\rm 12r}$, the paramagnetic product of the photolysis of coenzyme B$\sb $. Results are interpreted in terms of a spectral dimensionality. Rates are also reported for nitrosyl ferrous myoglobin in frozen water solution, which exhibits a dominant one-phonon relaxation process up to 20 K and thus does not reveal spectral dimensionality.
The anomalous variation of rate with temperature observed in several iron-containing proteins is not conspicuous here. In a model two-phonon mechanism of relaxation, temperature dependence is fixed by a spectral dimensionality, m, which specifies the variation of vibrational density of states with frequency $\rho$($\nu$) $\propto$ $\nu\sp{\rm m-1}$ and is named in analogy with the Debye density of states in 1-, 2-, and 3-dimensional crystals.
At sufficiently high temperatures, a non-resonant two-phonon process (Raman) should dominate the relaxation of a paramagnetic ion unless low-lying (under $\sp{\sim}$70 cm$\sp{-1}$) electronic states are present, as in many rare earths and in high spin ferric complexes, including many ferric proteins. The temperature dependence of the Raman rate for a Kramers ion (odd number of electrons) is T$\sp{\rm 3+2m}$ if temperature is sufficiently lower than $\Theta$ = h$\nu\sb{\rm max}$/k, the Debye temperature. The values of m from relaxation data on frozen solutions of a protein have sometimes been dependent upon solvent conditions. The maximum values of m for heme proteins, iron-sulfur proteins, and one copper-and-iron-containing protein, have ranged from about 1.3 to 1.8.
Pulse saturation/recovery was used. The recoveries were not exponential, but rates were estimated from semilogarithmic displays of signals or from numerical fitting. The temperature dependence of the rates for azurin between 1.5 K and 22 K can be fit with a spectral dimensionality of 3 and a rather low Debye temperature near 69 K, in contrast to iron proteins.
Relaxation of vitamin B$\sb{\rm 12r}$ differed between samples, indicating varied photolysis or freezing. The Raman relaxation was well fit by a simple power law in temperature, but the values of m varied from 1.14 to 1.48 between samples.
Issue Date:1987
Description:120 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
Other Identifier(s):(UMI)AAI8803143
Date Available in IDEALS:2015-05-13
Date Deposited:1987

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