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The food-colouring dye tartrazine is a significant additive and in the same time a biologically active material. Thermal behaviour of trisodium (4E)-5-oxo-1-(4-sulphonatophenyl)-4-[(4-sulphonatophenyl)hydrazono]-3-pyrazole carboxylate, tartrazine or E102 as it is also known, was studied in relation with the physical, chemical, thermal and biophysical (interaction with proteins, antioxidant and phytotoxicity) properties. Tartrazine structure and microstructure have been determined by X-ray diffraction and scanning electron microscopy investigations. Tartrazine has a monoclinic crystalline structure (space group C2/c). Electronic transitions and atomic bonds behaviour in molecules and fluorescent excitation of the compound have been identified by spectroscopic methods: Fourier-transformed infrared, UV–Vis, atomic fluorescence and Raman spectroscopies. Tartrazine absorbs in the visible region at 436.36 nm and shows laser fluorescence of all its elements. Chemical (acidity) and optical properties (refractive index and electric susceptibility) were determined for different concentrations on a sensitive range of temperatures. Thermal analysis measurements of tartrazine revealed thermal stability until 200 °C in air, while in the inert environment (argon) the stability is increased to 300 °C. Biological and biophysical activities and properties of tartrazine have been evidenced through its interaction with animal proteins, comparison with the standard gallic acid and phytotoxicity towards wheat strains/roots, when several concentrations of tartrazine solutions were used. Tartrazine has moderate biological activity when interacting with proteins, obtained antioxidant activity above a threshold concentration of 0.25% and presents plant growth phytotoxicity.

Seven new complexes of 2-pyridyl ketone Schiff bases N,N′-bis-(pyridin-2-yl-benziliden)-propan-1,3-diamine (bpbpd) and N,N′-bis-[1-(pyridin-2-yl)-etiliden]-propan-1,3-diamine (bpepd) with Co(II), Ni(II), Zn(II) and Cd(II) nitrates and perchlorates were synthesized and investigated using elemental analysis, spectroscopic techniques (IR and UV–Vis–NIR) as well as magnetic and conductometric measurements. The structure of a cadmium(II) complex was accomplished by single-crystal X-ray diffraction. The Schiff base ligands act as NNNN tetradentate ligands coordinating through pyridine nitrogens and azomethine nitrogens to transition metal ions. The metal ions are six-coordinate for Co(II) and Ni(II), four-coordinate in the case of Zn(II) and eight-coordinate for Cd(II) ions. The coordination sphere of cobalt and nickel complexes is completed by two water molecules, resulting a distorted octahedron. In the case of zinc(II) complexes has been proposed a distorted tetrahedral geometry. The Cd(II) ions are surrounded by a tetradentate Schiff base ligand and two bidentate nitrate anions, leading to a dodecahedral coordination environment. Thermal decomposition of these compounds is a multistage process. Generally, water elimination occurs in the first step and the decomposition of nitrate groups and organic ligands in the next stages. The last step of decomposition for all complexes is strong exothermic and corresponds to oxidative combustion of the Schiff base ligand.