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Abstract— The photodestruction of purine free base used as a model for the purine bases in DNA has been studied in order to better understand the effect of UV light on these molecules. Photodestruction yields have been determined in glassy aqueous solutions at 77 K and at room temperature at different pH's. The yield decreases in the order of 0.04, 0.01, 0.001 in 8 M NaOH, 8 M NaCIO4 and 6 M H3 PO4 , respectively, while at room temperature the highest destruction yield is 0.005 for the unbuffered neutral solution. These yields have been determined by measuring the initial decrease in the purine absorption maximum as a function of irradiation time. During the illumination stable photoproducts, as well as reactive intermediates, such as trapped electrons, radical anions and cations, are formed and have been characterized from their absorption spectra. The addition of triplet quenchers and an electron scavenger resulted in a decrease in the yield, implying the participation of the purine triplet state and a radical anion in the reactions leading to the photodestruction of purine. 相似文献
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I. Brandariz F. Arce X. L. Armesto F. Penedo M. Sastre de Vicente 《Monatshefte für Chemie / Chemical Monthly》1993,124(3):249-257
Summary A systematic study of the dependence of acid-base stoichiometric constants on the ionic strength has been carried out for the aminoacidL-valine in ClK and BrK solutions. The observed dependence has been interpreted by using Guggenheim, Scatchard and Pitzer models for the activity coefficients of the species involved in the equilibria.
Die Abhängigkeit von Gleichgewichtskonstanten desL-Valin von der Ionenstärke entsprechend den Modellen von Guggenheim, Scatchard und Pitzer
Zusammenfassung Es wurde anL-Valin in KCl- und KBr-Lösungen eine systematische Studie der Abhängigkeit der Säure-Base-Stöchiometrie von der Ionenstärke durchgeführt. Die beobachteten Abhängigkeiten wurden aufgrund der nach den Modellen von Guggenheim, Scatchard und Pitzer erhaltenen Aktivitätskoeffizienten der an den Gleichgewichten beteiligten Spezies interpretiert.相似文献
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The flash photolysis of purine in acetonitrile and in water at different pH was studied. The transients produced on flash excitation of degassed aqueous solutions have been identified as the triplet excited state, the hydrated electron, a purine radical cation and radical anion on the basis of quenching experiments and comparison to transients observed in low temperature photolysis. 相似文献
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Summary We consider the problem of studying the behaviour of the eigenvalues associated with spline functions with equally spaced knots. We show that they are
wherem is the order of the spline andn, the number of knots.This result is of particular interest to prove optimality properties of the Generalized Cross-Validation Method and had been conjectured by Craven and Wahba in a recent paper. 相似文献
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Alfonsina E. Andreatta Eva Rodil Alberto Arce Ana Soto 《Journal of solution chemistry》2014,43(2):404-420
New experimental surface tension data have been provided at 283.15, 298.15, 313.15 K and atmospheric pressure for binary mixtures of 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide and 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with the alcohols: methanol, ethanol, 1-propanol, 2-propanol, l-butanol and 1-pentanol. The experimental results show that the surface tensions of these mixtures depend systematically on the alkyl chain length of the ionic liquid and alcohol, composition and temperature. Surface tension changes on mixing have been calculated and adequately fitted by the Redlich–Kister polynomial equation. The adjustable parameters and the standard deviations between experimental and calculated values are reported. 相似文献
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José Manuel Cordero Edurne Alonso-Morán Roberto Nuño-Solinis Juan F. Orueta Regina Sauto Arce 《European Journal of Operational Research》2015
This paper uses a fully nonparametric approach to estimate efficiency measures for primary care units incorporating the effect of (exogenous) environmental factors. This methodology allows us to account for different types of variables (continuous and discrete) describing the main characteristics of patients served by those providers. In addition, we use an extension of this nonparametric approach to deal with the presence of undesirable outputs in data, represented by the rates of hospitalization for ambulatory care sensitive condition (ACSC). The empirical results show that all the exogenous variables considered have a significant and negative effect on efficiency estimates. 相似文献
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