The effect of the water-soluble UV-absorbing substance (UVAS) extracted from the marine red alga Porphyra yezoensis Ueda on UV-dependent thymine photodimer production was investigated. The T<>T pyrimidine-pyrimidone 6-4 dimer and the cyclobutane cis-syn T<>T 5-6 dimer produced by UV irradiation with a xenon lamp were analyzed by reverse-phase high-performance liquid chromatography. Although the dimer production was reduced when the irradiation was filtered through a UVAS solution, it decreased more when thymine was mixed with UVAS. Furthermore, UVAS inhibited the degradation of UV-irradiated thymine. The inhibitory effect of UVAS was significantly greater than that of exogenously added adenine or guanine, which forms complementary base pairs with thymine. These data suggest that in addition to its filtering effect against UV radiation, UVAS also protects thymine by a direct molecule-to-molecule energy transfer process. The protective function of UVAS against UV irradiation is advantageous for this alga under strong UV irradiation.
Np(V) / Stability constants / Complex formation / Carboxylic acid / Hydroxy acid
AbstractThe stability constants of Np(V) complexes with a series of aliphatic and aromatic carboxylates, including hydroxycarboxylates, hydroxydicarboxylates, dicarboxylates and pyridinecarboxylates have been obtained in 1.0 M NaC10 4 by a solvent extraction method using thenoyltrifluoroacetone and 1,10-phenanthroline in isoamyl alcohol. Stabilities of these complexes are discussed in terms of their structures and ligand basicities.with those obtained by different methods, we have checked various factors in the extraction procedure and evaluated the reliability of the method for determining the stability constants of Np(V) complexés. The result has shown that the data are more reliable by the back-extraction procedure than the usual forwardextraction procedure used in our earliest study [2], This paper deals with the reexamination of the extraction procedure and more comprehensive study on the complexation of Np(V) with aliphatic and aromatic carboxylates including hydroxymonocarboxylates, hydroxypolycarboxylates, dicarboxylates and pyridinecarboxylates.
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