On Trans-Resveratrol in Aqueous Solutions

A thermodynamic study on aqueous solutions of trans -Resveratrol (3,5,4′-trihydroxy- trans -stilbene) at 25.00 ± 0.02 °C, in 0.5 mol·dm −3 NaCl, has been conducted. The protolysis equilibria and the complex formation between trans -Resveratrol and a metal(II), namely Mn 2+ and Cu 2+ , have been investigated. The experimental method consists of potentiometric, spectrophotometric (absorption and emission) acid–base titrations. The pH range investigated is 2.5 ≤ pH ≤ 13 for the binary system, while for the ternary system it is 2.5 ≤ pH ≤ 6. The results of the graphical and numerical methods adopted indicate, for all the systems investigated, the formation of a predominant Me(II)– trans -Resveratrol mononuclear complex. UV–Vis absorption spectra and desorption/ionization time of flight mass spectra show the occurrence of hydrolytic species exhibiting a higher molecular weight than the Resveratrol molecule, becoming more evident as the pH and the time increased. Moreover, high performance liquid chromatography analysis and infrared spectroscopy of aqueous cis / trans -Resveratrol solutions upon excitation at 300 nm have highlighted a highly fluorescent compound, with absorption maximum at 250 nm, and a blue shift in the fluorescence emission that have not previously been reported.