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See detailElectronic spectroscopy of nucleic acids in the gas phase
Gabelica, Valérie ULg; Rosu, Frédéric ULg; Joly, Laure ULg et al

Conference (2010)

DNA polyanions trapped in a mass spectrometer undergo electron detachment following UV irradiation. Photodetachment is a single-photon process. Its efficiency depends on the nature of the DNA bases, the ... [more ▼]

DNA polyanions trapped in a mass spectrometer undergo electron detachment following UV irradiation. Photodetachment is a single-photon process. Its efficiency depends on the nature of the DNA bases, the ion's charge, and the excitation wavelength. Photodetachment can therefore be used to perform ion spectroscopy experiments, which probe electronic excitation within the initial charge state of the nucleic acids. Ion spectroscopy experiments on trapped nucleic acid cations and anions were performed from 4 to 20 eV using an OPO laser or using synchrotron radiation. Photoelectron spectroscopy experiments were also performed on multiply charged anions to probe direct detachment cross sections and electronic excitations within the final charge. The electronic spectra obtained from photodetachment integral cross sections show several resonances, provided that the photon energy is larger than the electron binding energy. We will also discuss whether the electronic spectra obtained via photodetachment can be used to probe gas phase ion structure. [less ▲]

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See detailZwitterionic i-motif structures are preserved in DNA negatively charged ions produced by electrospray mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Joly, Laure ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12

DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine ... [more ▼]

DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine) base pairs. Negatively charged ions of DNA i-motifs produced by electrospray mass spectrometry are therefore zwitterionic if the base pairing motif is preserved in the gas phase. Here we used IRMPD spectroscopy and ion mobility spectrometry to assess whether i-motif structures were preserved in the gas phase. We first investigated the IRMPD spectral signature of the tetramer [dC(6)](4), which can only be formed via C-H(+)-C base pairing, compared to the single strand dC(6). The IR signature of i-motif formation is an apparent broadening of the band at 1650 cm(-1). DFT calculations show this apparent broadening is actually due to blue-shifts of the NH(2) scissoring modes and red shifts of C[double bond, length as m-dash]O stretching modes. We then investigated the gas-phase conformations of the telomeric sequence d(CCCAAT)(3)CCC, that can form an intramolecular i-motif, by performing IRMPD spectroscopy and ion mobility spectrometry as a function of the charge state. We show that the negative ions of the lowest charge states correspond to a preserved i-motif structure. This is the first demonstration of the native extraction of solution-phase zwitterionic nucleic acids using negative electrospray ionization. [less ▲]

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