In spite of the fact that these two molecules bear three
positively charged amino groups, ruthenium hexamine appears to be 3.5 times more efficient as inhibitor of the ribozyme than cobalt
hexamine. This result shows not only that the inhibition of CChMVd-
HHR self-cleavage is due to the positively-charged amino groups but also that it is metal-core dependent, suggesting that the ruthenium hexamine either can bind to an additional site(s) unreachable by the cobalt hexamine or binds to the same site(s) with a higher affinity.
It is interesting to relate this observation with that of a study of the
influence of the inner coordination sphere of cobalt and ruthenium
hexamine on their interaction with thymus DNA in solution. This
study showed that the hydrodynamic radius of ruthenium is much
larger than that of cobalt [Rh (Co3) = 65 ± 5 nm and Rh (Ru3) =
440 ± 30 nm] although the two compounds exert an identical global
influence on the structure of the macromolecule [30].