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[Display omitted] • Alkannin and shikonin are enantiomeric red natural dyes of Japanese origin. • SERS analysis of alkannin and shikonin at neutral and acid pH shows differences in the spectra of both dyes. • Vibrational analysis of alkannin and shikonin were performed aided by DFT methods, allowing the assignment of the experimental bands. • Marker bands were proposed for both dyes to allow discrimination between them. • The red dye shikonin was detected for the first time in a dyed paper sample. Alkannin is the main coloring matter of Alkanet, a natural red dye extracted from the root of Alkanna tinctoria L. Shikonin, the optical isomer of alkannin, is extracted from Lithospermum erythrorhizon. As both red dyes are only slightly soluble in water, the application of ordinary Raman spectroscopy is limited. Thus, Surface-enhanced Raman spectroscopy (SERS) can be successfully applied to the study of the red dyes solutions. Solid alkannin and shikonin were characterized by ordinary Raman spectroscopy. Density Functional Theory (DFT) methods were used to calculate the Raman spectrum of the dyes and to assign the experimental Raman bands to their vibrational normal modes. Different pH conditions were tested in order to determine the optimal conditions for the SERS detection of alkannin and shikonin. Based on the previous results, a perpendicular orientation of the red dyes on the Ag substrate was deducted. Finally, shikonin was identify by SERS spectroscopy in a dyed paper sample from an 8th century handscroll from Japan. [ABSTRACT FROM AUTHOR]

The formation of hydroxynitrofluoranthene (OHNF) via photochemical reactions of 2-nitrofluoranthene (2-NF) was demonstrated using a UV irradiation system. The photoreaction of 2-NF in acetonitrile/water (3/1, v/v) gave a product that was hydroxynitro-substituted. Moreover, we detected an OHNF isomer, which was found in the 2-NF photoreaction products, in soluble organic fractions of ambient airborne particles collected in Kanazawa, Japan. The atmospheric concentration of the OHNF isomer was estimated to be less than 2 fmol m−3, which was comparable to that of 1-hydroxy-3-nitropyrene, but lower than that of 1-hydroxy-6-nitropyrene by a factor of 10. The results suggests that atmospheric OHNF is partly formed via secondary formation processes, i.e., photochemical reactions of 2-NF appear to have a significant effect on the occurrence of OHNF in the atmosphere. [ABSTRACT FROM PUBLISHER]