SOME PROTEIN PROPERTIES IMPORTANT FOR ENZYME CATALYSIS - New Trends in Enzyme Catalysis and Biomimetic Chemical Reactions - page 154

have been used for studying electrostatic effects in the vicinity of definite protons in
specific molecules (Likhtenshtein et al., 1999).
As these radicals have similar chemical structures, they differ in the presence or
absence of a small-sized functional group in a ring position remote from the
paramagnetic nitroxide group. Therefore, it is obvious that they have very similar
paramagnetic parameters, affected by the spin-lattice relaxation, i.e. magnetic moment,
distance between radical and proton and the diffusion coefficients of the radicals
(Hwang and Freed, 1975; Alexandrov, 1975; Berdnikov et al., 1980). On the basis of the
analysis of molecular models for these radicals, we can suggest that they are comparable
for all radicals used in this study. The only marked difference expected for the radicals
is the value and sign of their electrostatic charge [0, -1 and +1] for the corresponding
radicals IV-VI. Accordingly, marked differences in the experimental data of and

were obtained (Fig. 4.3.).

Experimental data
The general conclusions from the referred study are as follows:
1. Proton nuclei located at different positions within the small molecules and amino
acids that were investigated exhibit similar degrees of spin-probe accessibility as shown
by the similar values of slope for these protons in the presence of the neutral
spin-probe IV. This experimental observation is consistent with the theoretical
estimation of spin-probe accessibility as studied by computer-assisted molecular
modeling of the various amino acid/spin-probe encounter complexes in our study.