DAMAGE TO URACIL- AND ADENINE-CONTAINING BASES, NUCLEOSIDES, NUCLEOTIDES AND POLYNUCLEOTIDES: QUANTUM YIELDS ON IRRADIATION AT 193 AND 254 NM

Abstract Photoreactions, such as base release and decomposition of the base moiety, induced by either 20 ns laser pulses at 193 nm or continuous 254 nm irradiation, were studied for a series of uracil and adenine derivatives in neutral aqueous solution. The quantum yield of chromophore loss (φ) depends significantly on the nature of the nucleic acid constituent and the saturating gas (Ar, N₂O or O₂). In the case of polynucleotides the destruction of nucleotides was measured by high-performance liquid chromatography after hydrolysis; the quantum yields (φ) are comparable to those of chromophore loss or larger. The φ_cl and aφ_dn of 0.04–0.1 for poly(U) and poly(dU), obtained for both wavelengths of irradiation, are due to processes originating from the lowest excited singlet state, i.e. formation of photohydrates and photodimers, and a second part from photoionization using λ_irr= 193 nm. Irradiation at 193 nm effectively splits pyrimidine dimers and thus reverts them into monomers. The quantum yield for release of undamaged bases (φ_br) from nucleosides, nucleotides and polynucleotides upon irradiation at 254 nm is typically φ_br= (0.1–1) × 10^?4 Breakage of the N-glycosidic bond is significantly more efficient for λ_irr=193 nm, e.g. φ_br= 1.1 × 10^?3, 0.8 × 10^?3, 4.3 × 10^?3 and 0.5 × 10^?3 for poly(A), poly(dA), poly(U) and poly(dU) in Ar-saturated solution, respectively. Enhanced φ values for λ_irr= 193 nm, essentially for adenine and its derivatives, are caused by photo-processes that are initiated by photoionization.     

Na*(3p)-Formation under grazing scattering of Na+-ions at an Al(111) surface

Excited Na*(3p)-atoms are observed in grazing surface-collision experiments with Na⁺-beams. Such atoms can be formed beyond a certain threshold velocity via resonant electron transfer between atomic and metallic conduction band levels due to motion of the atom relative to the surface of the metal (“kinematic resonance”). This mechanism is studied here theoretically employing two different techniques: the nonperturbative “Coupled Angular Mode” (CAM) method and the approximate “Transfer Hamiltonian” (TH) method. The calculated Na*(3p)-populations agree well with recent experimental results. Moreover, the complete density matrix of the Na*(3p)-subspace has been computed with the TH-method for ion-energies between 10 and 300 keV.     

Sorption preconcentration in combined methods for the determination of noble metals

Combined methods for the determination of noble metals with the use of sorption preconcentration with complexing, anion-exchange, and other sorbents are reviewed. Characteristics of sorbents, techniques of sorption preconcentration, and techniques for the preparation of a concentrate for determination are considered. Features of instrumental methods for the determination of noble metals in the analysis of different materials are discussed. Examples of the use of sorption preconcentration in combined methods for the determination of noble metals are given from publications between 1996–2005.     

Precipitation of Titanium(IV) and Iron(III) Phosphates from Sulfuric Acid Solutions

Conditions for the precipitation of phosphates from solutions of titanium(IV) sulfate containing iron(III) were studied. The precipitation of components and the mechanism of the phase formation in the system under study were considered in relation to the TiO₂ : Fe₂O₃ ratio in the starting solution.     

Evaluation of an Economical Sunlamp that Emits a Near Solar UV Power Spectrum for Conducting Photoimmunological and Sunscreen Immune Protection Studies

Expense and inconvenience have restricted the use of the filtered xenon are lamp (solar simulator) as a UV source for conducting large-scale animal studies. Because sunscreen immunoprotective levels are significantly affected by the UV power spectrum of the source it is imperative that a solar simulating source be used for accurate measurements of sunscreen protection levels that are relevant to human UV exposures from sunlight. However, relatively inexpensive sunlamps, e. g. the UVA-340, that emit a UV power spectrum similar to that of a solar simulator are available. Unlike FS-type UVB sunlamps, which have a significant amount of effective immunosuppressive nonsolar UV energy at wavelengths below 295 nm, the immunosuppression effectiveness spectrum of UVA-340 sunlamps was nearly identical to that of a solar simulator. The purpose of this study was to evaluate this sunlamp for conducting photoimmunological and sunscreen immune protection studies. Groups of C3H mice were exposed to a range of UVA-340 sunlamp doses (0.25 KJ/m² to 20.0 KJ/m²) to establish a dose-response curve and determine the minimum immune suppression dose (MISD) for induction of local-type suppression of contact hypersensitivity (CH). The MISD, defined as the lowest UV dose given to produce ～50% suppression of the CH response in mice, was determined to be 1.0 kJ/m² for UVA-340 sunlamps. Immune protection tests on four marketed sunscreen lotions (sun protection factors [SPF] 4, 8, 15 and 30) were then conducted with UVA-340 sunlamps using MISD as the endpoint. The immune protection factors for these sunscreens were equivalent to the level of protection predicated by their labeled SPF. These results are similar to those we have previously obtained using a solar simulator. We conclude from these data that the immunosuppressive effects of UVA-340 sunlamps are similar to those of a solar simulator; however, further studies are needed to determine if UVA-340, or similar, sunlamps are a viable alternative to the solar simulator for conducting large-scale animal experiments that require a relevant UV solar spectrum.     

Kinetics of the hydroxylation of N-picryl-4-[4-(dimethylamino)styryl]pyridinium salts by molecular oxygen in acetonitrile

The reactions of N-picryl-4-[4-(dimethylamino)styryl]pyridinium salts with molecular oxygen in the presence of 4-[4-(dimethylamino)styryl]pyridine (DASP) in acetonitrile proceeds with the formation of DASP picrate. The reactions are first-order relative to the salt cation, molecular oxygen, and the catalyst (DASP). L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R, Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 286–289, September–October, 1998.     

Half-Projected and Projected Hartree-Fock Calculations for Singlet Ground States. i. four-Electron Atomic Systems

The half-projected Hartree-Fock function (HPHF ) for singlet states is defined as a linear combination of two Slater determinants, which contains only spin eigenfunctions with even quantum number. Using a self-consistent procedure based on the generalized Brillouin's theorem, the RHF , HPHF and PHF functions are deduced for the ground states of the Li^?, Be, B⁺, and C²⁺ systems, in a limited basis set. It is found that the HPHF function yields better energy values than the RHF function, very close to that of the PHF one. The HPHF scheme seems thus to be useful as a substitute for the PHF model, specially in the case of large electronic systems in which the latter method becomes unmanageable.     

Effects of temperature on styrene–methacrylonitrile copolymerization

The free-radical copolymerization of styrene and methacrylonitrile was studied in toluene solution at 60, 90, and 120°C. Copolymer composition was estimated from gas-chromatographic measurement of unreacted monomer concentrations. Reactions were carried to about 20% conversion to minimize analytical errors. Reactivity ratios were calculated by using an integrated form of the Mayo-Lewis simple copolymerization equation. Reactivity ratios were not sensitive to reaction temperature. The values at 90°C are r₁ = 0.41 (methacrylonitrile) and r₂ = 0.37 (styrene). The r₁ values are higher than those reported by other workers, presumably because of advantages in the present analytical technique and calculation method. The negligible temperature dependence of reactivity ratios is in accord with theory. If monomer pairs exhibit pronounced dependence of reactivity ratios on polymerization temperature, this may indicate a change in mode of placement of units in the polymer chain.     

Direkte fluorimetrische Bestimmung von 3,4-Benzpyren im w?\rigen Medium

Zusammenfassung Es wurde eine direkte Bestimmung des 3,4-Benzpyrens in wä\riger Lösung beschrieben, die auf der Löslichkeitserhöhung beruht, die das in Wasser schwer lösliche 3,4-Benzpyren durch Coffein erfährt. Es können so noch 4 ng/ml bei der angegebenen Standardisierung bestimmt werden. Bei der Direktbestimmung des 3,4-Benzpyrens im System Coffein-Wasser ist ein p_H >6,0 einzuhalten, da bei höheren Wasserstoffionenkonzentrationen die Fluorescenzintensität stark abnimmt.

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Direct fluorimetric determination of benzo(a)pyrene in aqueous medium

A method for the direct determination of benzo(a)pyrene in aqueous solution is based on the increase of its solubility by coffeine. 4 ng of benzo(a)pyrene/ml can be determined by the procedure described. In this direct determination in the system coffeine-water the p_H has to be adjusted to >6.0, as the fluorescence intensity considerably decreases with higher H⁺ concentrations.

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Eine ausführliche Darstellung findet sich in der Dissertation von G. Becker, Univ. Karlsruhe 1968.

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Die Messungen zu dieser Arbeit -wurden an dem Chemischen Untersuchungsamt für das Saarland, Saarbrücken, mit einem Spektralphotometer der Deutschen Forschungsgemeinschaft ausgeführt. Beiden Institutionen sind wir zu Dank verpflichtet.     

Platinum(II) Mono-N1-(2"-Tetrahydrofuranyl)-5-Fluorouracilate Complexes with Ammonia

The reaction between cis-[Pt(NH₃)₂Cl₂], N¹-(2"-tetrahydrofuranyl)-5-fluorouracil (HL), and NaOH (taken in a molar ratio of 1 : 1 : 1) or between cis-[Pt(NH₃)₂Cl₂], HL, and Ag₂O (taken in the molar ratio of 1 : 1 : 0.5) was used to synthesize complexes Ia (in the case of NaOH) or Ib (in the case of Ag₂O) with composition Pt(NH₃)₂LCl. The model complex [Pt(NH₃)₃L]NO₃ (II) was synthesized by the reaction between [Pt(NH₃)₃Cl]Cl, HL, AgNO₃, and Ag₂O (1 : 1 : 1 : 0.5). The obtained compounds were characterized by chemical analysis, chromatography, thermogravimetry, conductometry, potentiometry, IR, electronic, and NMR spectroscopies. Complexes Ia and Ib were found to have both similar and different properties. The structures of the compounds and the type of L^– coordination to platinum(II) were suggested. Cytotoxic properties of Iaand Ib were studied.