Inter- and Intramolecular Proton Transfer in an Isolated (Cytosine-Guanine)H+ Pair: Direct Evidence from IRMPD Spectroscopy

A. CRUZ ORTIZ; R. A. JARA-TORO; J. P. ARANGUREN; D. SCUDERI; G. A. PINO *

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2022 vol. 126 p. 1402 - 1411

1089-5639

The collision-induced dissociation of the protonated cytosine−guaninepair was studied using tandem mass spectrometry (MS3) coupled to infrared multiple photon dissociation spectroscopy with the free electron laser at Orsay (CLIO) to determine the structure of the CH+ and GH+ ionic fragments. The results were rationalized with the help of electronic structure calculations at the density functional theory level with the B3LYP/6-311++G(3df,2p) method. Several tautomers of each fragment were identified for the first time, some of which were previously predicted by other authors. In addition, two unexpected and minor tautomers were also found: cytosine keto-imino [CKI(1,2,3,4)H+] and guanine keto-amino [GKA(1,3,7)H+]. These results highlight the importance of the DNA base tautomerization assisted by inter- and intramolecular proton or hydrogen transfer within the protonated pairs.