5‐Mercuricytosine: An Organometallic Janus Nucleobase

Abstract

The base-pairing properties of 5-mercuricytosine have been explored at the monomer level by NMR titrations and at the oligonucleotide level by melting temperature measurements. The NMR studies revealed a relatively high affinity for guanine, hypoxanthine, and uridine, that is, bases that are deprotonated upon coordination of Hg(II) . Within an oligonucleotide duplex, 5-mercuricytosine formed Hg(II) -mediated base pairs with thymine and guanine. In the former case, the duplex formed was as stable as the respective duplex comprising solely Watson-Crick base pairs. Based on detailed thermodynamic analysis of the melting curves, the stabilization by the Hg(II) -mediated base pairs may be attributed to a comparatively low entropic penalty of hybridization.

1,8‐Dimercuri‐6‐Phenyl‐1H‐Carbazole as a Monofacial Dinuclear Organometallic Nucleobase

“…The highest melting temperature (53.6±0.4 °C), as well as the greatest stabilization by mercuration (+7.3 °C), were observed with duplex ON1 z‐Hg 2 ⋅ ON2 t . For reference, similar melting temperatures have been reported for respective duplexes incorporating a mononuclear Hg II ‐mediated 5‐mercuricytosine–thymine or a canonical thymine–adenine base pair in the middle of the chain (56.1 and 56.9 °C, respectively) . On the other hand, the stabilization relative to the unmercurated duplex ON1 z ⋅ ON2 t is similar to the value previously reported for parallel‐stranded duplexes incorporating a dinuclear Hg II ‐mediated base pair between 1,N 6 ‐ethenoadenine and thymine …”

“…The melting curves of all duplexes formed by the unmetallated oligonucleotide ON1 z were sigmoidal and monophasic. The melting temperatures (46–50 °C) were considerably higher than with respective unmodified duplexes incorporating a single mismatch in the middle of the chain (30–35 °C) . The relatively high stability of these duplexes is probably attributable to the large stacking surface of the 6‐phenyl‐1 H ‐carbazole base.…”

“…In each duplex, a modified nucleobase (6‐phenyl‐1 H ‐carbazole or 1,8‐dimercury‐6‐phenyl‐1 H ‐carbazole) was paired with either a canonical nucleobase (adenine, cytosine, guanine, or thymine) or an abasic site. Respective studies on unmodified duplexes of otherwise identical sequence, but having either cytosine or thymine in place of the modified residue have been reported previously …”

Concomitant Site‐Specific Incorporation of Silver(I) and Mercury(II) Ions into a DNA Duplex

“…Most recently, the first Cu I ‐mediated base pair stable in aqueous solution was reported . Based on such metal‐containing nucleic acids, several promising applications have been proposed and investigated, including charge transfer through DNA, DNA‐templated metal nanoparticle generation, DNA‐based hybrid catalysis, metal‐ion sensors, recognition of oligonucleotide sequences, metal‐responsive materials, and expansion of the genetic four letter code, to name just a few.…”

Artificial DNA Base Pairing Mediated by Diverse Metal Ions

“…58 5-Mercuricytosine forms not only a hydrogen-bonded base pair with guanine ( Figure 6b) but also Hg(II)-mediated base pairs with thymine (Figure 6c) or guanine. In the Hg(II)-mediated base pair, the HgC nucleoside adopts the syn conformation, and the deprotonated endocyclic nitrogen atom of the counter base (T) coordinates to the Hg 2+ ion.…”