Artificial DNA Directed toward Synthetic Metallofoldamers - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 321

Figure 9.16 (a) The imidazole and the 1,2,4-triazole base pairs as well as (b) the 1-deazaade-
nine-thymine base pair are all suited to incorporate Ag(I) ions into DNA double helices.

9.5.4 The Imidazole, Triazole and 1-Deazaadenine-Thymine Base Pairs

Aseriesofsimple N -glycosidic metal base pairs mainly coordinating Ag(I) ions were
reported by M uller and coworkers [33,42]. Figure 9.16a shows the structure of the imid-

€

azole (X N) base pairs and Figure 9.16b shows a hydrogen-

bonded base pair between thymine and 1-deazaadenine (in the so-called Hoogsteen bond-
ing mode) in which one of the two hydrogen bonds can be replaced by a Ag(I) ion.
Using three consecutive imidazole base pairs having the nitrogen donor positions
enriched in 15 N, NMR studies yielded the secondary structure depicted in Figure 9.17
[53]. The analysis revealed that the duplex adopts a right-handed helical structure show-
ing only minor deviations from the canonical B-type DNA conformation. Furthermore,
the 15 N-enrichement allowed an unambiguous allocation of the three Ag(I) ions coordi-
nated between the imidazole ligands, as seen by the observation of

¼ CH) and 1,2,4-triazole (X ¼

1 J ( 15 N, 107/109 Ag)

couplings.
Further noteworthy is the fact that, by using the 1-deazaadenine-Ag(I)-T base pair, the
longest stretch of stacked metal base pairs realized so far includes 19 Ag(I) ions, thus
reaching over almost two complete helical turns [54].

Figure 9.17 NMR structure of a B-DNA-like duplex containing three stacked Ag(I)-imidazole
base pairs.