Chemistry Reference
In-Depth Information
Figure 4.22
Representation of the helical structure of the [{(NH
3
)
2
Pt(9-MeA-N7)(9-MeHx-
N7)}Ag(NO
3
)(H
2
O)](ClO
4
)(NO
3
) coordination polymer
polymers the metal centres adopt square pyramidal geometry, however the details
of the metal-nucleobase binding are quite different. In the guanine-containing mate-
rial, {[Cu(
N7
- Et - G - en)(H
2
O)
2
]
2+
}
n
, N7-binding is observed, whereas in the adenine
derivative, {[CuCl(
N7,N3
- Et - A - en]
+
}
n
, both N7 and N3 atoms are bound to the
metal centre. This difference in coordination has a dramatic effect on the shape of
the polymer chains with essentially parallel guaninyl residues in the former case
compared to an interplanar angle of
74 ° for adjacent bases in the latter. The helical
arrangement of the former compound with a pitch of
∼
12 Å and Cu · · · Cu (Figure
4.23) distances around the periphery of the helical structure of 7.0 Å is similar to
metrical parameters in native duplex DNA and raises the interesting possibility of
metal-nucleobase polymers acting as antisense agents.
Srivantsan and coworkers have described the catalytic activity of nucleobase-
copper polymeric frameworks.
25
Studies pertaining to prebiotic catalysis and the
chemical origin of life have attracted considerable attention over the years.
26
In this
context, the possible assistance of mineral surfaces for biological polymerization
reactions has been pointed out.
27
It has been noted that Cu(II) ions assist the binding
of nucleotides to mineral surfaces. The structure of 9-(4-vinylbenzyl)adenine-copper
polymer, which shows the copper ions coordinated to N1 and N7 positions of
adenine (Figure 4.24), mimics the periodicity of single-stranded nucleic acids.
25
The cross-linking of the polymeric chains of this complex with ethyleneglycol
dimethacrylate or 1,4-divinylbenzene ensured its insolubility in aqueous solutions
and, therefore, allowed biological studies to be performed, which revealed that these
∼
