A Dinuclear Mercury(II)-Mediated Base Pair in DNA.

The first dinuclear metal-mediated base pair containing divalent metal ions has been prepared. A combination of the neutral bis(monodentate) purine derivative 1,N6 -ethenoadenine (ϵA), which preferentially binds two metal ions with a parallel alignment of the N-M bonds, and the canonical nucleobase thymine (T), which readily deprotonates in the presence of HgII and thereby partially compensates the charge accumulation due to the two closely spaced divalent metal ions, yields the dinuclear T-HgII2 -ϵA base pair. This metal-mediated base pair stabilizes the DNA oligonucleotide duplex as shown by an increase of 8 °C in its melting temperature. Formation of the base pair was demonstrated by temperature-dependent UV spectroscopy as well as by titration experiments monitored by UV and CD spectroscopy.