Redox-Active Bis-Cyclometalated Iridium(III) Complex as a DNA Photo-Cleaving Agent.

The development of new photoactive metal complexes that can trigger oxidative damages to the genetic material is of great interest. In the present paper, we describe the detailed study of a highly photo-oxidant iridium(III) complex that triggers photoinduced electron transfer (PET) with purine DNA bases. The PET has been studied by luminescence and laser flash photolysis experiments. From plasmid DNA agarose gel electrophoresis experiments, we demonstrated the high ability of the iridium complex to induce strand breaks upon light irradiation. Reactive oxygen species (ROS)-specific scavengers and stabilizers were employed to identify that the photocleavage process, the results of which infer singlet oxygen and hydrogen peroxide as the predominant species. To the best of our knowledge, the present work represents one of the few study for highly photo-oxidant bis-cyclometalated iridium(III) complex toward DNA.

Disulfuryl Dichloride ClSO2 OSO2 Cl: A Conformation and Polymorphism Chameleon.

Disulfuryl dichloride ClSO2 OSO2 Cl was characterized by vibrational spectroscopy in the gaseous and liquid phase as well as in the Ar-matrix. By varying the temperature, certain bands could be assigned to several conformers. Gas-phase electron diffraction revealed a dominance of the anti-conformer at ambient temperature. The same conformation was found in the solid state. Via the in situ technique for crystallization, not less than four different modifications were identified. Among these different modifications, the structural parameters of the molecules remain relatively constant, but the aggregation pattern changes. Although the molecules aggregate by chlorine⋅⋅⋅oxygen contacts in each modification, the geometrical parameters of these interaction show significant differences and were evaluated and are in part inconsistent with the halogen bonding concept.

New Acridine-Based Tridentate Ligand for Ruthenium(II): Coordination with a Twist.

A new tridentate ligand based on acridine has been synthetized. The central acridine heterocycle bears two pyridine coordinating units at positions 4 and 5. The terdentate 2,7-di- tert-butyl-4,5-di(pyridin-2-yl)acridine (dtdpa) was then coordinated to a ruthenium(II) cation. The corresponding homoleptic complex could only be obtained where both ligands coordinate to the ruthenium in a fac fashion. Thus, a heteroleptic compound (2) was constructed in combination with a terpyridine ligand in order to constrain the ligand to adopt a mer geometry. Such a coordination imposes a dramatic twist on the acridine heterocycle, resulting in an unexpected photophysical behavior. The electrochemical and photophysical properties of both complexes were studied, and the molecular structure of 2 was determined by X-ray diffraction. The two compounds absorb at low energy wavelengths, and a very weak luminescence is detected only for complex 2 in the near-infrared region.

Preparation and Properties of Chlorosulfuryl Chloroformate, ClC(O)OSO2Cl.

The novel chlorosulfuryl chloroformate, ClC(O)OSO2Cl, was prepared by the reaction of CCl4 and SO3. Alternatively, the compound was obtained from the direct insertion reaction of SO3 to Cl2C═O. The latter reaction constitutes also a confirmation of the proposed mechanism for the former one. Density functional theory and MP2 theoretical approximations predict the existence of two conformers, syn-gauche and syn-anti, depending on the value adopted by the dihedral angles ϕ(Cl-C-O-S) and ϕ(C-O-S-Cl). The structure of the syn-gauche conformer was determined by gas-phase electron diffraction (GED). The existence of the syn-anti conformer can be neither confirmed nor excluded by the GED experiment. Vibrational spectra (vapor-phase and argon-matrix Fourier transform infrared and liquid Fourier transform Raman) were interpreted by an equilibrium mixture between both conformers.

Ultrafast charge transfer excited state dynamics in trifluoromethyl-substituted iridium(iii) complexes.

Time-resolved spectroscopy was exploited to gain new insights into the nature and dynamics of charge transfer excited states of bis-cyclometalated Ir(iii) complexes. We showed that its dynamics is strongly influenced by the nature of the diimine ligand due to the existence of a ligand-ligand charge transfer process in the picosecond timescale. All the results are supported by DFT/TD-DFT calculations and spectroelectrochemistry.

Ionic fragmentation mechanisms of 2,2,2-trifluoroethanol following excitation with synchrotron radiation.

Gaseous 2,2,2-trifluoroethanol (TFE) is excited with synchrotron radiation between 10 and 1000 eV and the ejected electrons and positive ions are detected in coincidence. In the valence-electron energy region, the most abundant species is CH2 OH(+) . Other fragments, including ions produced by atomic rearrangements, are also detected; the most abundant are COH(+) , CFH2 (+) and CF2 H2 (+) . The energies of electronic transitions from C 1 s, O 1 s and F 1 s orbitals to vacant molecular orbitals are determined. A site-specific C 1 s excitation is observed. The photofragmentation mechanisms after the excitation of core-shell electrons are inferred from analysis of the shape and slope of the coincidence between two charged fragments in the bi-dimensional coincidence spectra. The spectra are dominated by islands that correspond to the coincidence of H(+) with several charged fragments. One of the most important channels leads to the formation of CH2 OH(+) and CF3 (+) in a concerted mechanism.

Photofragmentation Mechanisms of Chlorosulfonyl Isocyanate, ClSO2NCO, Excited with Synchrotron Radiation between 12 and 550 eV.

The unimolecular photofragmentation mechanisms of chlorosulfonyl isocyanate, ClSO2NCO, excited with tunable synchrotron radiation between 12 and 550 eV, were investigated by means of time-of-flight (TOF) coincidence techniques. The main fragmentation mechanism after single ionization, produced by irradiation of an effusive beam of the sample with synchrotron light in the valence electron region, occurs through the breaking of the Cl-S single bond, giving a chloride radical and a SO2NCO(+) fragment. This mechanism contrasts with the one observed for the related FSO2NCO, in which the rupture of the S-N bond originates the FSO2(+) fragment. The energies of the shallow- (S 2p, Cl 2p, and S 2s) and core-shell (C 1s, N 1s, and O 1s) electrons were determined by X-ray absorption. Transitions between these shallow and core electrons to unoccupied molecular orbitals were also observed in the total ion yield (TIY) spectra. Fourteen different fragmentation mechanisms of the doubly charged parent ion, ClSO2NCO(2+), were inferred from the bidimensional photoelectron-photoion-photoion-coincidence (PEPIPICO) spectra. The rupture of the S-N bond can evolve to form NCO(+)/SO2(•+), NCO(+)/SO(•+), or S(•+)/NCO(+) pairs of ions. The Cl-S bond breaking originates different mechanisms, Cl(+)/SO(•+), Cl(+)/S(•+), CO(•+)/S(•+), O(•+)/SO(•+), O(•+)/Cl(+), O(•+)/S(•+), C(•+)/S(•+), and C(•+)/O(•+) pairs being detected in coincidence as the final species. Another three coincidence islands can only be explained with an initial atomic rearrangement forming ClNCO(2+), ONCO(2+), and ClCO(2+), as precursors of CO(•+)/Cl(+), O(•+)/CO(•+), and C(•+)/Cl(+) pairs, respectively. The formation of Cl(•) radical is deduced from several mechanisms.

Electronic properties of fluorosulfonyl isocyanate, FSO2NCO: a photoelectron spectroscopy and synchrotron photoionization study.

The electronic properties of fluorosulfonyl isocyanate, FSO2NCO, were investigated by means of photoelectron spectroscopy and synchrotron based techniques. The first ionization potential occurs at 12.3 eV and was attributed to the ejection of electrons formally located at the π NCO molecular orbital (MO), with a contribution from nonbonding orbitals at the oxygen atoms of the SO2 group. The proposed interpretation of the photoelectron spectrum is consistent with related molecules reported previously and also with the prediction of OVGF (outer valence green function) and P3 (partial third order) calculations. The energy of the inner- and core-shell electrons was determined using X-ray absorption, measuring the total ion yield spectra, and the resonances before each ionization threshold were interpreted in terms of transitions to vacant molecular orbitals. The ionic fragmentation mechanisms in the valence energy region were studied using time-of-flight mass spectrometry as a function of the energy of the incident radiation. At 13 eV the M(+) was the only ion detected in the photoion-photoelectron-coincidence spectrum, while the FSO2(+) fragment, formed through the breaking of the S-N single bond, appears as the most intense fragment for energies higher than 15 eV. The photoion-photoion-photoelectron-coincidence spectra, taken at the inner- and core-levels energy regions, revealed several different fragmentation pathways, being the most important ones secondary decay after deferred charge separation mechanisms leading to the formation of the O(+)/S(+) and C(+)/O(+) pairs.