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Xanthylium derivatives are curcumin analogs showing photochromic properties. Similarly, to anthocyanins, they follow the same multistate network of chemical species that are reversibly interconverted by external stimuli. In the present work, two new asymmetric monocarbonyl analogues of curcumin, 4-(4-hydroxy-3-metoxybenzylidene)-1,2,3,4-tetrahydroxanthylium chloride (compound 3) and 4-(4-hydroxybenzylidene)-6-methoxy-1,2,3,4-tetrahydroxanthylium chloride (compound 4) were synthesized, and their photochromic and biological properties were investigated. The UV-Vis spectroscopy and the direct and reverse pH-jumps studies confirmed the halochromic properties and the existence of different molecular species. A network of chemical reactions of these species was proposed. Furthermore, the antiproliferative properties of both compounds were evaluated using P19 murine embryocarcinoma cells and compared with each other. The results demonstrate that both new xanthylium derivatives modify the progression through the cell cycle of P19 cells, which translates into a significant antiproliferative effect. The effect of the methoxy group position is discussed and several checkpoint proteins are advanced as putative targets.

Six new bio-inspired flavylium salts were synthesized and investigated by a combined computational and experimental study for dye-sensitized solar cell applications. The compounds were characterized by FT–IR, UV–Vis, NMR spectroscopy, and LC–MS spectrometry techniques. The pH-dependent photochromic properties of the flavylium dyes were investigated through a UV–Vis spectroscopy study and revealed that they follow the same network of chemical reactions as anthocyanins upon pH changes. The structural and electronic properties of the dyes were investigated using density functional theory (DFT) and time-dependent density functional theory (TD–DFT). Geometry optimization calculation revealed that all dyes, regardless of the specie, flavylium cations or quinoidal bases, present a planar geometry. The photovoltaic performances of the dyes, in both flavylium and quinoidal base forms, were evaluated by the HOMO and LUMO energies and by calculating the light-harvesting efficiencies, the free energy change of electron injection, and the free energy change regeneration. The MO analysis showed that all dyes can inject electrons into the conduction band of the TiO2 upon excitation and that the redox couple can regenerate the oxidized dyes. The results obtained for the free energy change of electron injection suggest that the quinoidal bases should inject electrons into the semiconductor more efficiently than the flavylium cations. The values for the free energy change regeneration showed that the redox electrolyte can easily regenerate all dyes. Dipole moment analysis was also performed. DSSCs based on the dyes, in both flavylium and quinoidal base forms, were assembled, and their photovoltaic performances were evaluated by measuring the open-circuit voltage, the short circuit current density, the fill factor, and the energy conversion efficiency. Results obtained by both experimental and computational studies showed that the overall performances of the DSSCs with the quinoidal forms were better than those obtained with the flavylium cations dyes.

The widespread concerns about the environmental problems caused by conventional plastic food packaging and food waste led to a growing effort to develop active and intelligent systems produced from renewable biodegradable polymers for food packaging applications. Among intelligent systems, the most widely used are pH indicators, which are generally based on a pH-sensitive dye incorporated into a solid support. The objective of this study was to develop new intelligent systems based on renewable biodegradable polymers and a new bio-inspired pH-sensitive dye. The structure of the dye was elucidated through FT-IR and 1D and 2D NMR spectroscopic analyses. UV-VIS measurements of the dye solutions at various pH values proved their halochromic properties. Their toxicity was evaluated through theoretical calculations, and no toxicity risks were found. The new anthocyanidin was used for the development of biodegradable intelligent systems based on chitosan blends. The obtained polymeric films were characterized through UV-VIS and FT-IR spectroscopy. Their thermal properties were assessed through a thermogravimetric analysis, which showed a better stability of chitosan–PVA–dye and chitosan–starch–dye films compared to those of chitosan–cellulose–dye films and the dye itself. The films’ sensitivity to pH variations was evaluated through immersion in buffer solutions with pH values ranging from 2 to 12, and visible color changes were observed.

Anthocyanidins, the aglycons of anthocyanins, are known, beyond their function in plants, also as compounds with a wide range of biological and pharmacological activities, including cytostatic effect against various cancer cells. The nature and position of the substituents in the flavylium cation is essential for such biological properties, as well as the equilibrium between the multistate of the different chemical species that are generated by the flavylium cation, including quinoidal base, hemiketal, and cis- and trans-chalcones. In this work, eight new flavylium derivatives were synthesized, characterized for confirmation of the structure by FT-IR and 2D-NMR, and investigated in vitro as possible cytostatic compounds against HCT116 and HepG2 cancer cells. The most active two compounds were explored for their halochromic properties that can influence the biological activity and subjected to molecular encapsulation in β-cyclodextrin derivatives in order to increase their solubility in water and bioavailability. The anticancer effect was influenced by the position (6-, 7-, or 8-) of the methoxy group in the β-ring of the methoxy-4′-hydroxy-3′-methoxyflavylium cation, while the study of the halochromic properties revealed the important role played by the chalcone species of the pH-dependent multistate in both the uncomplexed and inclusion complex forms of these anthocyanidins.

The current work explores the potential for recycling unused or expired Midazolam (MID) drug, a benzodiazepine derivative, as an efficient corrosion inhibitor for copper in nitric acid solution. The technical advantage of recycling expired MID drug relates to the avoidance of organic inhibitor production costs and the reduction of disposal costs of the expired medication. A combination of electrochemical methods (potentiodynamic polarization and electrochemical impedance spectroscopy), weight loss, and quantum chemical calculation were used to assess the inhibition mechanism and efficiency of MID. It was found that inhibition efficiency increases with inhibitor concentration, reaching a highest value of 92.9% for a concentration of 10−4 M MID. MID was classified as a mixed-type inhibitor, showing a preferential cathodic suppression mechanism. The obtained values of −45.89 kJ mol−1 for the standard free energy of adsorption indicate that the inhibition mechanism is based on chemisorption of MID molecules on the copper surface, which obeys the Langmuir isotherm. Surface analysis using scanning electronic microscopy revealed that MID offers high protection against corrosion during both immersion and polarization tests. Molecular modelling and quantum chemical calculations indicated chemical interactions between MID molecules and the copper surface, as well as electrostatic interactions. The results obtained using the different techniques were in good agreement and highlight the effectiveness of MID in the corrosion inhibition of copper.