Chemistry Reference
In-Depth Information
molecule might have some structural features that guide foreign molecules to the
heme pocket. The heme carboxylate, located at the gate of the entrance into the
heme pocket, may serve as the initial contact point for catalysis. With a Cu(
II
)Cyc moi-
ety of Cu(
II
)B-PS
MS/Ac
anchored to the heme carboxylate, the other Cu(
II
)Cyc can inter-
act with the peptide group of Gln(91)-Ser(92) or Ala(94)-Thr(95) without significant
steric strain, as examined with molecular mechanics computer programs.
3.3.4
Adducts giving Nuclease Activity to Polymers
Catalytic hydrolysis of DNA is much more challenging than that of RNA or peptides in
view of the ca. 10
8
-fold higher stability of DNA [56]. Most known synthetic catalysts for
DNA hydrolysis are metal complexes [57-59]. Although several metal complexes pro-
mote cleavage of supercoiled and open circular DNA and single- or double-stranded
oligodeoxyribonucleotides, hydrolytic cleavage of linear double-stranded polydeoxyri-
bonucleotides by metal complexes has seldom been observed. One successful report is
that for the dicerium complex
24
, which hydrolyzes a long linear DNA duplex [60].
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The Co(
III
)-complex of cyclen, Co(
III
)Cyc, is one of the most effective synthetic cat-
alysts discovered so far for the hydrolysis of supercoiled DNAs [59]. The hydrolytic
nature of DNA cleavage by the Co(
III
) complexes of polyamines including cyclen
has been well documented [57, 58]. The mechanism illustrated in
25
has been pro-
posed [57] for the catalytic action of the Co(
III
) complexes. Given the remarkable en-
hancement of proteolytic activity of Cu(
II
)Cyc upon attachment to PCD [49], we tested
the activity of Co(
III
)Cyc in phosphodiester hydrolysis to see if it is also enhanced
greatly upon attachment to PCD derivatives [61, 62].
25
