The spore photoproduct lyase repairs the 5S- and not the 5R-configured spore photoproduct DNA lesion

The spore photoproduct lyase is a Fe-S/AdoMet DNA repair enzyme, which directly repairs spore lesions, induced by UV irradiation of spores, using an unknown radical mechanism. The air sensitive radical SAM enzyme was for the first time challenged with synthetically pure substrates. It was found that the enzyme recognizes a synthetic 5S-configured spore lesion without the central phosphodiester bond. The 5R-configured lesion is in contrast to current belief not a substrate.     

The high-frequency stark effect in the balmer lineD-alpha

The calculation of the emission lineD _α under the influence of a linearly polarizedrf-field (the oscillation frequency is equal to 34.8 GHz, the electric field amplitude is of the order 200 kV/m) delivers satellites on both sides of the main peak. Deviations from symmetry with respect to the average wavelength of the central line originate from the fine structure: the entire satellite structure is slightly shifted (～ 1 pm) to the red and the intensity of the blue satellite is about 15% higher than that of the red one. The numerical analysis has incorporated also the Zeeman effect by a static magnetic field (140 mT) parallel to therf-electric field as well as Doppler broadening on account of the temperature of the deuterium atoms which amounts to 1000 K. The comparison of measured and calculated line shapes allows to determine therf-electric field strength with an accuracy of about 5%.     

Measurement of the ground state hyperfine splitting in207Pb II

The ground state hyperfine splitting of simply ionized lead has been determined using pulsed laser excitation of electrodynamically confined ions. We obtain ΔV(6P_1/2)=12.85(10) GHz     

The photosensitizing effect of the photoproduct of protoporphyrin IX

The photodynamic effect of a photoproduct of protoporphyrin IX (PpIX) induced by 5-aminolevulinic acid (ALA) was investigated in WiDr cells, a human adenocarcinoma cell line. The fluorescence excitation and emission spectra of PpIX and the photoproduct were measured. After 1, 3 or 5 min exposure of the ALA-incubated cells to 140 mW/cm² light at 635 nm, the photoproduct — the chlorin photoprotoporphyrin (Ppp), had an emission band around 670 nm. The Ppp excitation peak at 670 nm is well separated from the PpIX peak at 635 nm. The outcome of photodynamic therapy (PDT) was determined by measuring intracellular fluorescence intensity of propidium iodide (PI) 2 h following PDT and methylene blue (MB) staining 24 h following PDT. A significant increase in the fluorescence intensity of PI was noted when the ALA-loaded cells were exposed to 670 nm light after exposure to 635 nm, indicating enhanced cell membrane inactivation induced by the photodynamic action of the photoproduct. However, the fraction of the cells that survived following the same treatment as measured by MB staining was not significantly affected based on an analysis of variance. The fluorescence of PpIX decayed significantly during 635 nm light exposure. Exposure to light at 670 nm does not lead to any photodegradation of PpIX. The fluorescence of Ppp was bleached during 670 nm light exposure. Exposure of Ppp at 670 nm gives no PpIX back. Thus, the phototransformation of PpIX to Ppp is probably not a reversible process.     

The stark effect in condensed aromatic hydrocarbons

The changes in the static electric polarizability upon transition to excited singlet states are measured by perturbing the absorption spectrum with an intense (10⁶ V/cm) electric field. Observations of the Stark effect in a polystyrene matrix are reported for a series of substituted anthracenes, a group of condensed aromatic hydrocarbons and a substituted hexatriene.     

The transition time for the ground state hyperfine splitting of209Bi82+

The lifetime of the excited hyperfine state of the ground state level of²⁰⁹Bi⁸²⁺ is calculated. The result of (Bi⁸²⁺)=400.09 s still exhibits a discrepancy to the experimental value ^ex=351(16) s of about 14%.     

Dipole moment of cis-glyoxal in the 1B1 electronic state from static and modulated stark spectroscopy

The Stark effect on the ¹B₁ - ¹A₁ transition of cis-glyoxal near 487.5 nm is investigated. The effect arises from interaction between appropriate pairs of accidentally degenerate rotational levels. By using static and modulated electric fiels a value of 2.3 ± 0.5 D for the dipole moment along the b-axis of the molecule in the ¹B₁ state is obtained.     

On the origin of the splitting of the second maximum in the radial distribution function of amorphous solids

The splitting of the second maximum of the radial distribution function of an irregular atomic packing is regarded as an indication of the amorphous state of a substance. This paper describes the splitting-forming atomic configurations using Delaunay simplices, representing chains of elementary configurations. It is shown that the splitting is formed of chains in which all simplices are nearly regular tetrahedra and quartoctahedra. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 1, pp. 78–88, January–February, 1997.     

The ground state tunneling splitting of malonaldehyde: accurate full dimensional quantum dynamics calculations

Benchmark calculations of the tunneling splitting in malonaldehyde using the full dimensional potential proposed by Yagi et al. are reported. Two exact quantum dynamics methods are used: the multiconfigurational time-dependent Hartree (MCTDH) approach and the diffusion Monte Carlo based projection operator imaginary time spectral evolution (POITSE) method. A ground state tunneling splitting of 25.7+/-0.3 cm(-1) is calculated using POITSE. The MCTDH computation yields 25 cm(-1) converged to about 10% accuracy. These rigorous results are used to evaluate the accuracy of approximate dynamical approaches, e.g., the instanton theory.     

On the spin-orbit splitting of CuCl2 in its 2 Pi g ground state

The spin-orbit splitting of CuCl(2) in its ground X(2)Pi(g) state remains an unknown or, at best, poorly defined quantity. The electronic spectrum of CuCl(2) has been studied by Fourier transform resolved, laser-induced fluorescence between 602 and 587 nm, in an attempt to identify transitions to the upper spin component of the ground state. In order to provide a well-defined excitation process, the sample was cooled to rotational temperatures of about 10 K in a free-jet expansion. Observations from just two rotationally perturbed levels in the upper electronic state, one for (63)Cu(35)Cl(2) and the other for (65)Cu(35)Cl(37)Cl, have revealed an additional feature about 482 cm(-1) above the (2)Pi(3/2) state. The effective rotational constants associated with these levels (0.066 20 cm(-1) for (63)Cu(35)Cl(2)) are significantly larger than those for the ground (2)Pi(3/2) state (0.058 13 cm(-1)). Analysis of this feature as the (2)Pi(1/2) component leads to a value of -482.9 cm(-1) for the spin-orbit coupling constant A and of -0.0846 cm(-1) for the lambda-doubling parameter (p+2q) for (63)Cu(35)Cl(2). Several other previously unobserved levels are also identified within 2000 cm(-1) of the ground state. Many of these also have anomalously large rotational constants.     

The second-order stark effect on the 1B2u electronic origin of tetracene and pentacene in p-terphenyl

The electric field induced shift of the electronic origin of the lowest B_2u singlet state of tetracene and pentacene in p-terphenyl at 1.8°K has been measured. From this shift we calculate the difference in polarizability of this state and the ground state along the long molecular axis to be 4.5 ± 0.5 ų for tetracene and 19.8 ± 1.0 ų for pentacene (F_c′ = 0.505 F_eff). The ratio of these tensor elements (Δα)_zz for pentacene and tetracene is found to be 4.4 ± 0.6 and is independent of the local field approximation.     

A calculation of the spin-orbit splitting of the X 2Π state of NO

Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X ² state of NO has been calculated using various potentials. Experimentally W (² _3/2) –W (² _1/2) is known to be 122 cm^–1. Using an unscreened nuclear field we find a value of 328 cm^–1. Inclusion of screening due to electronic repulsions reduces this value to 283 cm^–1. Agreement with the experimental value may be obtained by reducing the orbital exponents in the 2 molecular orbital by 30% over the value given by Slater's rules.

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Zusammenfassung Die Spin-Bahn-Aufspaltung des X ² -Zustandes von NO wurde mit verschiedenen Potentialen unter Verwendung der SCF LCAO MOs von Brion, Moser und Yamazaki berechnet. Der experimentelle Wert für W (² _3/2) –W (² _1/2) beträgt 122 cm^–1. Die Rechnung mittels eines reinen Kernfeldes liefert den Wert 328 cm^–1 und unter Einschluß der Abschirmung durch die Elektronen 283 cm^–1. Übereinstimmung mit dem experimentellen Wert läßt sich erzielen, wenn man den Exponenten des 2-Zustandes 30% kleiner als nach den Slater Regeln macht.

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Résumé Avec les orbitals moléculaires SCF LCAO de Brion, Moses et Yamazaki, nous avons calculé le dédoublement spin-orbitale de l'état X ² de NO. La valeur expérimentale W (² _3/2) –W (² _1/2) est 122 cm^–1. Dans un champ nucléaire «sans écran» on trouve 328 cm^–1. L'inclu-sion de l'effet d'écran dû aux répulsions interélectroniques réduit cette valeur à 283 cm^–1. La valeur expérimentale s'obtient, si l'on réduit de 30% les exposants d'après Slater dans l'orbi-tale moléculaire 2.

     

Precise determination of the ground state hyperfine structure splitting of43Ca II

Within the framework of systematic hyperfine structure (hfs) investigation of titanium atom the hfs-splittings of 3d ³(² G)4s b ¹ G ₄ levels for two stable isotopes⁴⁷Ti and⁴⁹Ti have been studied. 5 hfs intervals for each isotope have been measured using ABMR-LIRF method (atomic beam magnetic resonance detected by laser induced resonance fluorescence) with an accuracy of about 300 Hz. TheJ-off-diagonal second order perturbation effects have been taken into account in the interpretation. Upper limit of the contributions from octupole and hexadecapole hyperfine structure interaction to hfs intervals of this level have been estimated to be about 400 Hz. However, for most of hfs intervals these contributions are almost within experimental error and in order to study such effects a more precise experimental method should be used.     

Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

We have measured the three hyperfine components of the spin—orbit split (²P_{$\text{3}\text{2}$} → ²P_{$\text{1}\text{2}$}) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm^?1), with the third line at 404.210 cm^?1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.     

Model studies of the (6-4) photoproduct photoreactivation: efficient photosensitized splitting of thymine oxetane units by covalently linked tryptophan in high polarity solvents

Three covalently linked tryptophan-thymine oxetane compounds used as a model of the (6-4) photolyase-substrate complex have been prepared. Under 290 nm light, efficient splitting of the thymine oxetane with aromatic carbonyl compounds gives the thymine monomer and the corresponding carbonyl compounds by the covalently linked tryptophan via an intramolecular electron transfer, and exhibits a strong solvent dependence: the quantum yield (Phi) is ca. 0.1 in dioxane, and near 0.3 in water. Electron transfer from the excited tryptophan residue to the oxetane unit is the origin of fluorescence quenching of the tryptophan residue, and is more efficient in strong polar solvents. The splitting efficiency of the oxetane radical anion within the tryptophan.+-oxetane.- species is also solvent-dependent, ranging from ca. 0.2 in dioxane to near 0.35 in water. Thus, the back electron transfer reaction in the charge-separated species would be suppressed in water, but is still a main factor causing low splitting efficiencies in the tryptophan-oxetane systems. In contrast to the tryptophan-oxetane system, fast nonradiation processes are the main causes of low efficiency in the flavin-oxetane system. Hence, nonradiative processes of the excited FADH-, rather than electron transfer to oxetane, may be an important factor for the low repair efficiency of (6-4) photolyase.     

Reaction of exciplex formation in the gas phase. The role of weak attractive interactions in the initial state

The reaction of molecular exciplex formation in the gas phase is treated within the framework of the Landau-Zener approximation, with the assumption that the initial state of the reaction has a potential energy curve including both repulsive and attractive interactions. It is found that the introduction of attractive interactions into the initial state (commonly treated as a repulsive state) leads, in the case of dipole-induced-dipole interaction, to a “reverse” temperature dependence of the exciplex formation rate constant.     

The dependence of the branching ratio in the F+HD reaction on the initial rotational state of HD

Both classical trajectory and quantal scattering calculations indicate that the branching ratio in the F+HD reaction varies considerably with the initial rotational state of HD. Information theory argues that this variation must be reflected in the distribution of the reaction products. Hence, given the (normalized) product distribution for each reaction path one should be able to predict the dependence of the branching ratio on the state of the reagents. The trajectory computations of Muckerman are used to illustrate the procedure. First the dynamic constraint is identified and then the reaction probability matrix is constructed. The determination (“synthesis”) of the matrix, in terms of the given constraint invokes information theory and, in particular, the procedure of maximising the entropy. The branching ratio is readily computed from the elements of the probability matrix. Very good agreement is obtained between the trajectory-computed and the synthetic branching ratio for all initial rotational states of HD.The F+HD reaction has three possible final arrangement channels (one nonreactive and two reactive ones) and is used to illustrate the structure of the reaction probability matrix and the associated entropy measures.     

Non-isothermal differential thermal analysis in the study of the initial state of the thermal decomposition of polynitroaromatic compounds in the condensed state

The activation energies, E, of the decomposition of picramide and its N-methyl-,N-ethyl-,N-n-propyl- and N-n-butyl-derivatives are determined by means of non-isothermal DTA, in its simple form, as well as by the Piloyan method. A relationship is found between the E values of the above-mentioned compounds and the published values of the moments of inertia of the corresponding n-alkyl groups. Taking into account data published previously, which were obtained by application of the Piloyan method in the DTA of polynitroaromates, it is concluded that by suitable selection of DTA measurement conditions, it is possible to record the early part of the exothermal decomposition of the above-mentioned compounds were no autocatalytic influence exists. Attention is also paid to the thermostability of the polynitroaromates due to their contact with the construction materials employed in the course of thermolysis.