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The crystal structure of 5-azacytosine was proposed by the X-ray diffraction pattern of the compound and the performed Rietveld analysis. The crystal structure solutions were achieved with the simulated annealing procedure. The model molecule for the procedure was taken from the BLYP/aug-cc-pVDZ optimization of the N1(H) oxo-amino tautomer of the compound. The refined unit cell parameters are: a = 12.82916 Å, b = 9.47282 Å, c = 3.66363 Å, and space group P212121. The studied excited-state reaction paths of the H-detachment processes of two oxo-amino tautomers show a possibility for mutual phototransformation of the two oxo-amino tautomers: N1(H) and N5(H). The driven states of this photoreaction are the 1nσ* and 1πσ* excited states. [ABSTRACT FROM AUTHOR]

In the present paper the main trends in the principal chemical parameters and the phytoplankton communities in the close coastal area arediscussed, aimed at evaluating the present ecological state of the environment and water quality in comparison with historical data. The results reveal a decrease in the content of PO4 and Si, while there is no apparent trend in the N-NO3 variability. In seasonal terms a change in the minima and maxima of some parametersis evident, and a seasonal dynamic closer to the natural annual cycle in the Black Sea. A decrease in the average annual phytoplankton biomass is established, especially pronounced during the summer period.The results suggest a positive sign of evolution of the environmental characteristics of the coastal zone, which should be treated rathertentatively due to the still high level of nutrients and the capacity of the ecosystem to produce and maintain high phytoplankton biomass. [ABSTRACT FROM AUTHOR]