Relative Strand Orientation in a DNA Duplex Controls the Nuclearity of a Metal-Mediated Base Pair.

1,N6 -Ethenoadenine (ϵA) and cytosine (C) are able to form two different metal-mediated base pairs. When the glycosidic bonds are arranged in a cisoid manner (i.e., in antiparallel-stranded DNA), the ϵA:C mispair binds one AgI ion, leading to a mononuclear ϵA-AgI -C base pair that contains a synergistic hydrogen bond. In contrast, a transoid orientation of the glycosidic bonds (as found in parallel-stranded DNA) results in the formation of a dinuclear metal-mediated base pair ϵA-AgI2 -C.