Metal-mediated base pairs represent a powerful tool for the site-specific functionlization of nucleic acids with metal ions. The development of applications of the metal-modified nucleic acids will depend on the availability of structural information on these double helices. We present here the NMR solution structure of a self-complementary DNA oligonucleotide with three consecutive imidazole nucleotides in its centre. In the absence of transition-metal ions, a hairpin structure is adopted with the artifical nucleotides forming the loop. In the presence of Ag(I) ions, a duplex comprising three imidazoleAg+-imidazole base pairs is formed. Direct proof for the formation of metal-mediated base pairs was obtained from (1)
AbstractMetal-mediated base pairs represent a powerful tool for the site-specific functionalization of nucleic acids with metal ions. The development of applications of the metal-modified nucleic acids will depend on the availability of structural information on these double helices. We present here the NMR solution structure of a self-complementary DNA oligonucleotide with three consecutive imidazole nucleotides in its centre: In the absence of transition metal ions, a hairpin structure is adopted with the artificial nucleotides forming the loop. In the presence of silver(I) ions, a duplex comprising three imidazole-Ag + -imidazole base pairs is formed.Direct proof for the formation of metal-mediated base pairs was obtained from 1 J( 15 N, 107/109 Ag) couplings upon incorporation of 15 N-labelled imidazole. The duplex adopts a B-type conformation with only minor deviations in the region of the artificial base pairs. This structure represents the first example of a metal-modified nucleic acid with a continuous stretch of metal-mediated base pairs.3 Nucleic acids such as DNA are becoming increasingly popular as versatile building blocks in nanobiotechnology as a result of their superb, predictable self-assembling properties and the high rigidity of their double helices on the nanoscale. 1 Their applicability can be extended even further by the introduction of functional groups such as metal ions. One recently established method for the site-specific functionalization of nucleic acids with metal ions is based on the use of metal-mediated base pairs. 2-5 Such base pairs comprise natural or artificial nucleobases and rely on coordinative bonds to a central metal ion instead of (or in addition to) hydrogen bonds. Depending on the choice of nucleosides, metal ions, and oligonucleotide sequence, a plethora of metal-modified double helices can be generated. Even if focussing only on the use of artificial nucleosides, examples exist for DNA duplexes containing one or two metal-mediated base pairs interspersed between natural ones, 6-8 DNA double helices with continuous stretches of metalated base pairs, 9-11 and DNA duplexes with different metalmediated base pairs at pre-defined positions. 12 When including also metal-mediated base pairs from natural nucleosides, 13-15 even more combinations can ...