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

Gas-phase interactions between Ba2+ 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-Canti ]+ isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba2+ 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…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 Ba2+ 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.