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

The collision-induced dissociation of the protonated cytosine-guanine pair was studied using tandem mass spectrometry (MS) 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.

Guanine Tautomerism in Ionic Complexes with Ag Investigated by IRMPD Spectroscopy and Mass Spectrometry.

In this paper, we present the IRMPD spectra of three ionic complexes between guanine (G) and silver (Ag): [GAg-HO], [GAgG] produced in the electrospray ionization source of the mass spectrometer, and [GAg] produced by collision induced dissociation of the [GAgG] complex. On the basis of the comparison of theoretically calculated IR spectra, we show that there are two isomers of each complex containing two different keto-amino (KA) tautomers of G (GKA(1,9) and GKA(1,7)). The observed isomers are the most stable structures in aqueous solution, and their experimentally estimated relative populations are in better agreement with the calculated relative populations in solution than in the gas phase, both at 298 K.

Infrared Multiple Photon Dissociation Spectroscopy of Protonated Cyameluric Acid.

The present study reports the first structural characterization of protonated cyameluric acid ([CA + H]) in the gas phase, which paves the way for prospective bottom-up research on the condensed-phase chemistry of CA in the protonated form. A number of [CA + H] keto-enol isomers can a priori be produced as a result of protonation at available N and O positions of precursor neutral CA tautomers, yet ab initio computations predict different reduced [CA + H] isomer populations dominating the solution and gas phases that are involved in the ion generation process (i.e.

On the Interaction between Deprotonated Cytosine [C ] and Ba : Infrared Multiphoton Spectroscopy and Dynamics.

Gas-phase interactions between Ba and deprotonated cytosine (C ) were studied in [C Ba] and [C BaC] complexes by IRMPD spectroscopy coupled to tandem mass-spectrometry in combination with DFT calculations. For the [C BaC] complex only one [C KAN1O-Ba-C ] isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba that simultaneously interacts with keto-amino [C ] deprotonated on N1 and neutral keto-amino C.

UV Photofragmentation of Cold Cytosine-M Complexes (M: Na, K, Ag).

The UV photofragmentation spectra of cold cytosine-M complexes (M: Na, K, Ag) were recorded and analyzed through comparison with geometry optimizations and frequency calculations of the ground and excited states at the SCS-CC2/Def2-SVPD level of theory. While in all complexes, the ground state minimum geometry is planar ( symmetry), the ππ* state minimum geometry has the NH group slightly twisted and an out-of-plane metal cation. This was confirmed by comparing the simulated ππ* Franck-Condon spectra with the vibrationally resolved photofragmentation spectra of CytNa and CytK.

Fingerprints of Both Watson-Crick and Hoogsteen Isomers of the Isolated (Cytosine-Guanine)H Pair.

 Gas phase protonated guanine-cytosine (CGH) pair was generated using an electrospray ionization source from solutions at two different pH (5.8 and 3.2).