SOME PROTEIN PROPERTIES IMPORTANT FOR ENZYME CATALYSIS - New Trends in Enzyme Catalysis and Biomimetic Chemical Reactions - page 153

the early 1970's (Likhtenshtein et al., 1972). The effectiveness of nitroxides and
paramagnetic metal complexes as relaxation reagents for protons has been widely
demonstrated for both static and dynamic systems (Wien et al., 1972; Syrtsova et al.,
1972, 1974; Lezina et al., 1976; Krugh, 1971; Likhtenshtein, 1976, 1993; Sletten et al.,
1983; Niccolai et al., 1984). In contrast to nitroxides, metal complexes and luminescence
chromophores show a certain preferred affinity towards some functional groups and
therefore their use is limited.
The proposed method is based upon the quantitative measurement of the contribution
of differently charged nitroxide probes to the spin-lattice relaxation rate of protons
in a particular molecule, followed by the calculation of local electrostatic potential using
the classical Debye equation (Likhtenshtein et al., 1999; Glaser et al., 2000). In parallel,
the theoretical calculation of potential distribution with the use of the MacSpartan Plus
1.0 program has been performed.
Apparent local electrostatic potential can be determined from the experimental
dependence of the proton spin-lattice relaxation rate on the concentration of the nitroxide
probes [R • ]

The ratio of experimental apparent rate constants (Hwang et al . ,

1975; Hwang and Freed, 1975) can be given as:

where in ambient temperature

and

where I is the ionic strength. Estimating I and using can now be

calculated from equation 4.6. Nitroxide radicals IV-VI of different charges