Infrared Multiple Photon Dissociation (IRMPD) Spectroscopy of H and Ag mediated Cytosine-Guanine base pair: Structure and reactivity

ANDRES F. CRUZ ORTIZ ; GUSTAVO A. PINO; MATIAS BERDAKIN

Mendoza, capital

Congreso; International Meeting On Photodynamics and related aspects; 2016

Universidad de Quilmes y Universidad Nacional de La Pla

Infrared Multiple Photon Dissociation (IRMPD) Spectroscopy of H+and Ag+ mediatedCytosine-Guanine base pair: Structure and reactivityAndres F. Cruz Ortiz, Matías Berdakin and Gustavo A. PinoINFIQC (UNC-CONICET), Dpto. de Fisicoquímica, Fac. de Ciencias Químicas, CentroLáser de Ciencias Moleculares, Universidad Nacional de Córdoba, Ciudad Universitaria,Pabellón Argentina, 5000 Córdoba, Argentina.The study of the interaction of DNA bases with metal cations and/or proton hasaroused the interest of the scientific community, in order to understand the intrinsicproperties that result from the formation and stabilization of noncanonical base pairs. Theformation of these noncanonical base pairs can lead to important changes affecting thestructure of DNA and also can present potential applications in materials science [1].In this work we present the results of experimental and theoretical studies of thestructure of the pairs which occur between cytosine (C) and guanine (G) mediated by aproton (C-H+-G) and the Ag+cation (C-Ag+-G).The ionic complexes (C-H+-G) and (C-Ag+-G) were generated in a electrosprayionization (ESI) source of a high resolution tandem mass spectrometer, FT-ICR. The ionswere isolated and the vibrational spectrum was obtained by Infrared MultiphotonDissociation (IRMPD) spectroscopy with the Free Electron Laser at the University of ParisSud (CLIO) in Orsay ? France and an OPO source couple to a CO2 laser.The optimized geometry of the various isomers, their relative energies, theirvibrational fequencies and the anharmonic corrections were performed at the DFT levelwith the B3LYP and M06-2X functionals, with the basis set 6-311G++ (d, p) for the C, H,N, and O and the effective core potential SDD [2] for Ag atom implemented in the packagesoftware Gaussian 09 [3].The calculations showed that in both pairs the most stable isomer is a Hoogsteentype. In addition, the IR spectra calculated for these isomers satisfactory fit theexperimental spectra.In the case of the pair C-Ag+-G, the cation Ag+is found equidistant from bothbases, forming a structure fairly rigid and the calculated vibrational frequencies fit very wellthe experimental values, when the scaling factors suggested in bibliography for eachfunctional are applied.In the case of the pair C-H+-G, the local minimum indicates that H+is preferablybonded to the cytosine (C). However, this H+is mobile and at room temperature isdelocalized between the two bases, because the energy barrier for this process is foundbelow the energy of the system. This generates a big change in the vibrational frequenciesof those modes that are coupled to the movement of this H+. It was found that thesefrequencies are better fitted when no scaling factors are applied to the calculated oneswith both functionals. On the contrary, the frequencies of those modes that are not coupledto the movement of the H+are fitted by scaled calculated frequencies.[1]. N. C. Seeman, Nature 2003, 421, 427.[2]. Andrea, D.; Haussermann, U.; Dolg, M.; Stoll, M.; Preuss, H.Energy-Adjustedab Initio Pseudopotentials for the Second and Third Row Transition Elements.Theor. Chim. Acta. 1990, 77, 123−141.[3]. Gaussian, Inc.: Wallingford, CT, 2009.