On the Interaction between Deprotonated Cytosine [C(-H)]-and Ba2+: Infrared Multiphoton Spectroscopy and Dynamics

Gas-phase interactions between Ba(2+)and deprotonated cytosine (C(-H)) were studied in [C(-H)Ba](+)and [C(-H)BaC](+)complexes by IRMPD spectroscopy coupled to tandem mass-spectrometry in combination with DFT calculations. For the [C(-H)BaC](+)complex only one [C((-H))KAN1O-Ba-C-anti](+)isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba(2+)that simultaneously interacts with keto-amino [C(-H)](-)deprotonated on N1 and neutral keto-amino C. Both moieties are in different planes as a consequence of an additional NH horizontal ellipsis O=C hydrogen bond between C and [C(-H)](-). A sequential IRMPD dynamics is observed in this complex. For the [C(-H)Ba](+)complex produced by electrospray ionization two isomers ([C((-H))KAN1OBa](+)and [C((-H))KAN3OBa](+)) were identified, in which Ba(2+)interacts simultaneously with the C=O group and the N1 or N3 atom of the keto-amino [C(-H)](-), respectively. A comparison with the related [C(-H)Pb](+)complex (J. Y. Salpin et al.,Chem. Phys. Chem.2014, 15, 2959-2971) is also presented.