Investigation of the Cu binding site at [dCdG] and [CG] base pairs in the absence of a DNA backbone

We investigated the gas-phase nucleobases [CGH]+1, [Cu(CG)]+1, [Cu(CG–H)]+1, and nucleoside [Cu(dCdG)]+1 complexes using collision-induced dissociation (CID) MS/MS spectra. Two forms, the Watson–Crick complex form (cation–base–base) and an interstrand complex form (base–cation–base), were included in the analysis of the [cation–base pair] complex structures. The main cytosine loss dissociation channel of the [Cu(CG)]+1 complex was analyzed as the loss of an interstrand [Cu(CG)]+1 form instead of the Watson–Crick form. The −43 amu (CONH) and −68 amu (cytosine–CONH) loss fragments of the [Cu(CG–H)]+1 complex can be explained by the dissociation process of the interstrand [Cu(CG–H)]+1 form.