Reaction of 3′,5′-di-O-acetyl-2′-deoxyguansoine with hypobromous acid

AbstractHypobromous acid (HOBr) is formed by eosinophil peroxidase and myeloperoxidase in the presence of H2O2, Cl−, and Br− in the host defense system of humans, protecting against invading bacteria. However, the formed HOBr may cause damage to DNA and its components in the host. When a guanine nucleoside (3′,5′-di-O-acetyl-2′-deoxyguansoine) was treated with HOBr at pH 7.4, spiroiminodihydantoin, guanidinohydantoin/iminoallantoin, dehydro-iminoallantoin, diimino-imidazole, amino-imidazolone, and diamino-oxazolone nucleosides were generated in addition to an 8-bromoguanine nucleoside. The major products were spiroiminodihydantoin under neutral conditions and guanidinohydantoin/iminoallantoin under mildly acidic conditions. All the products were formed in the reaction with HOCl in the presence of Br−. These products were also produced by eosinophil peroxidase or myeloperoxidase in the presence of H2O2, Cl−, and Br−. The results suggest that the products other than 8-bromoguanine may also have importance for mutagenesis by the reaction of HOBr with guanine residues in nucleotides and DNA

Generation of sub-17 fs vacuum ultraviolet pulses at 133 nm using cascaded four-wave mixing through filamentation in Ne.

The sixth harmonic (6ω, 133 nm) of a Ti:sapphire laser is generated using cascaded four-wave mixing in filamentation propagation of the fundamental (ω) and the second harmonic (2ω) pulses through Ne gas. The method provides the 6ω pulse energy higher than 5 nJ/pulse at 1 kHz and a pulse duration shorter than 17 fs without dispersion compensation

Time-resolved photoelectron imaging spectra from non-adiabatic molecular dynamics simulations

We present an efficient method for the simulation of time-resolved photoelectron imaging (TRPEI) spectra in polyatomic molecules. Our approach combines trajectory-based molecular dynamics that account for non-adiabatic effects using surface hopping, with an approximate treatment of the photoionization process using Dyson orbitals as initial and Coulomb waves as final electron states. The method has been implemented in the frame of linear response time-dependent density functional theory. As an illustration, we simulate time- and energy-resolved anisotropy maps for the furan molecule and compare them with recent experimental data [T. Fuji, Y.-I. Suzuki, T. Horio, T. Suzuki, R. Mitrić, U. Werner, and V. Bonačić-Koutecký, J. Chem. Phys.133, 234303 (2010)]. Our method can be generally used for the interpretation of TRPEI experiments allowing to shed light into the fundamental photochemical processes in complex molecules

Real-time detection of S(1D2) photofragments produced from the 1B2(1Σu+) state of CS2 by vacuum ultraviolet photoelectron imaging using 133 nm probe pulses

Ultrafast photodissociation dynamics from the 1B2(1Σu+) state of CS2 are studied by time-resolved photoelectron imaging using the fourth (4ω, 198 nm) and sixth (6ω, 133 nm) harmonics of a femtosecond Ti:sapphire laser. The 1B2 state of CS2 was prepared with the 4ω pulses, and subsequent dynamics were probed using the 6ω vacuum ultraviolet (VUV) pulses. The VUV pulses enabled real-time detection of S(1D2) photofragments, produced via CS2*(1B2(1Σu+)) → CS(X 1Σ+) + S(1D2). The photoionization signal of dissociating CS2*(1B2(1Σu+)) molecules starts to decrease at about 100 fs, while the S(1D2) fragments appear with a finite (ca. 400 fs) delay time after the pump pulse. Also discussed is the configuration interaction of the 1B2(1Σu+) state based on relative photoionization cross-sections to different cationic states

Shallow and deep trap states of solvated electrons in methanol and their formation, electronic excitation, and relaxation dynamics

We present condensed-phase first-principles molecular dynamics simulations to elucidate the presence of different electron trapping sites in liquid methanol and their roles in the formation, electronic transitions, and relaxation of solvated electrons (emet−) in methanol. Excess electrons injected into liquid methanol are most likely trapped by methyl groups, but rapidly diffuse to more stable trapping sites with dangling OH bonds. After localization at the sites with one free OH bond (1OH trapping sites), reorientation of other methanol molecules increases the OH coordination number and the trap depth, and ultimately four OH bonds become coordinated with the excess electrons under thermal conditions. The simulation identified four distinct trapping states with different OH coordination numbers. The simulation results also revealed that electronic transitions of emet− are primarily due to charge transfer between electron trapping sites (cavities) formed by OH and methyl groups, and that these transitions differ from hydrogenic electronic transitions involving aqueous solvated electrons (eaq−). Such charge transfer also explains the alkyl-chain-length dependence of the photoabsorption peak wavelength and the excited-state lifetime of solvated electrons in primary alcohols

Time- and Angle-Resolved Photoemission Spectroscopy of Hydrated Electrons Near a Liquid Water Surface

世界で初めて、溶液反応の超高速時間・角度分解光電子分光に成功 --溶液化学反応の機構解明に前進--. 京都大学プレスリリース. 2014-04-22.We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1, 4-diazabicyclo[2, 2, 2]octane and I− in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed

Time-resolved photoelectron spectroscopy of bulk liquids at ultra-low kinetic energy

Time-resolved photoelectron spectroscopy (TR-PES) of ultrafast dynamics in solution is presented. To measure the photoelectron kinetic energy distribution (PKED) that is free from inelastic scattering in solution, photoelectrons were generated with ultra-low kinetic energies (ULKE: <5 eV). Time constants of the elementary processes in the charge-transfer-to-solvent (CTTS) reaction from I− to bulk water were in excellent agreement with those obtained by transient absorption spectroscopy, demonstrating the bulk-sensitivity of TR-PES-ULKE. The analysis suggests that the CTTS reaction proceeds via two intermediates, and that 30% of the first intermediate and 70% of the second intermediate respectively are quenched by geminate recombination between the electron and the neutral iodine atom