An electrosprayed water/methanol solution of guanosine and Cu(NO3)(2) was observed to give rise to gas-phase copper complexed ions of [CuLn](center dot 2+), [CuL(MeOH)(n) ](center dot 2+), and [CuG(n)(NO3)](center dot+), as well as the ions [L](center dot+), [L + H](+), [G](center dot+), and [G + H](+) (L guanosine, G = guanine). The Collision-Induced Dissociation (CID) of [CuL3](center dot 2+) and [CuL(MeOH)(n)](center dot 2+) (n 2, 3) generates guanosine radical cations [L](center dot+), while dimeric guanosine (center dot 2+) radical cations [L-2](center dot+)](center dot+) are generated in the dissociation of [CuL4](center dot 2+). Protonated guanosine [L + H](+) is one of the main products in the primary dissociation of [CuL2](center dot 2+), while the dissociation of the higher-order [CuG(2)](center dot 2+) produces the [G](center dot+) radical cation. The guanosine dimer radical cation, [L-2](center dot+) presumably arises from the interaction of two guanosine molecules via proton and hydrogen bonding and is observed to dissociate into [L + H](+) and [L -H](center dot) at low energies. We propose that the first two ligands bind strongly with Cu(II) through N7 and 06 to form a [CuL2](center dot 2+) complex with a four-coordinated planar structure and that a third ligand binds loosely with copper to form [CuL3] (center dot 2+). Additional ligation observed in the formation of [CuLn](center dot 2+) (n <= 6) ions is presumed to occur by hydrogen bonding. The ribose group of guanosine appears to play an important role in the stabilization of the doubly charged Cu-guanosine complex and in intraligand proton transfer upon CID. The molecular radical cations [L](center dot+) observed in the ESI-MS spectrum at low declustering potentials originate primarily from [CuL(MeOH)(2,3)](center dot 2+) complexes which can dissociate more easily than [CuL3](center dot 2+).