Chemistry Reference
In-Depth Information
Figure 4.37
Schematic representation of H-bonding patterns involving cytosine.
Figure 4.38
Schematic representation of H-bonding patterns involving thymine/uracil.
Self-pairing of nucleobases requires hydrogen-bond interactions between edges
of different nucleobases: (i) minor groove edge, Hoogsteen and Watson- Crick edges
in purines; (ii) sugar and Watson-Crick edges in pyrimidines. Evidently, coordina-
tion of a metal to a nucleobase hinders the pairing of that site (edge), although the
pairing of other edges can be favoured, for example through p
K
a
alterations.
47- 53
A
graphic scheme of the existing self-pairing of metal-nucleobase complexes patterns
is depicted in Figures 4.37- 4.40 .
The dataset may be categorized from the viewpoint of the number, and loca-
tion, of coordinated metal ions. It is apparent that there is a wide variety of metal
ion binding modes to the different nucleobase sites (Table 4.1). For statistical reasons
5-MeC was considered as C, and
N
-alkylated bases as their unalkylated ones. The
format in Table 4.1 is as follows: the location (G, N1), for instance, corresponds with
21(13), where 21 is the number of examples containing a metal coordinated at the
N1 position of guanine and 13 is the number of molecules where N1 is the only
metal-coordinated position. The type of transition metal was not considered, but is
usually Pt, Pd, Ag, Cu or Hg.
As evident from Table 4.1, examples of metal ions bonded to all accessible
coordination sites of the different nucleobases have been found. Even endocyclic
carbon atoms, such as the C5 of cytosine
17
and uracil, and C8 of adenine
54
and
guanine,
55
can substitute their protons by metal ions.
Adenine can be considered the most versatile nucleobase, with many examples
of monometallated derivatives featuring binding at different sites. Guanine is an
extreme case, with 184 monometallated complexes found with N7-coordination and
