Sorption of 3-hydroxyflavone within channel type zeolites: the effect of confinement on copper(ii) complexation

New anti-cancer explorations based on metal ions

Due to the urgent demand for more anti-cancer methods, the new applications of metal ions in cancer have attracted increasing attention. Especially the three kinds of the new mode of cell death, including ferroptosis, calcicoptosis, and cuproptosis, are of great concern. Meanwhile, many metal ions have been found to induce cell death through different approaches, such as interfering with osmotic pressure, triggering biocatalysis, activating immune pathways, and generating the prooxidant effect. Therefore, varieties of new strategies based on the above approaches have been studied and applied for anti-cancer applications. Moreover, many contrast agents based on metal ions have gradually become the core components of the bioimaging technologies, such as MRI, CT, and fluorescence imaging, which exhibit guiding significance for cancer diagnosis. Besides, the new nano-theranostic platforms based on metal ions have experimentally shown efficient response to endogenous and exogenous stimuli, which realizes simultaneous cancer therapy and diagnosis through a more controlled nano-system. However, most metal-based agents have still been in the early stages, and controlled clinical trials are necessary to confirm or not the current expectations. This article will focus on these new explorations based on metal ions, hoping to provide some theoretical support for more anti-cancer ideas.

A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites

Salicylideneaniline (SA) sorbed in cation-exchanged M-ZSM-5 (M = H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Zn²⁺) zeolites was studied by spectroscopic techniques assisted by quantum-chemical calculations. The nature of extra-framework cations present in the zeolite void was found to affect the spectral signature of the sorbed SA molecule that points to the shift of tautomeric equilibrium between the enol and keto forms. Small size cations, such as H⁺ and Li⁺, stabilize a cis-keto SA tautomer along with a enol one in the zeolite structure. The calculations indicate that the sorbed cis-keto tautomer may have the dipole large enough to be considered as a zwitterion. New features appearing in the spectra with the increase of the cation size were attributed to the presence of trans-keto SA tautomer, which up to now has been observed only in time-resolved spectroscopic experiments. A strong interaction of the molecule with cations in Zn-ZSM-5 zeolite results in the chelation of enol SA with the divalent Zn²⁺ ions. The results of the study suggest that the tautomeric equilibrium of molecules belonging to the Schiff base family can be tuned by the confinement in the nanoporous materials via a choice of topology of zeolite framework and the nature of extra-framework cations.

Electronic Spectroscopies Combined with Quantum Chemistry Calculations: Study of the Interactions of 3-Hydroxyflavone with Copper Ions

The current study aims at obtaining a better understanding of the mechanisms involved in the complexation of copper ions by 3-hydroxyflavone (3HF), which is one of the most studied compounds of the flavonoid family. To achieve this goal, quantum chemistry calculations combined with electronic spectroscopies, including absorption, fluorescence emission, and excitation, have been used. The formation of successive complexes of stoichiometry (metal/ligand) 1:2, 1:1, and 3:2 has been highlighted. Even under acidic conditions (pH = 4.0), the α-hydroxy-keto function of the molecule presents a high complexing power with regard to copper ions, insofar as a stable complex of 1:2 stoichiometry is obtained with a large conditional stability constant (log β = 8.7). The formation of this predominant species induces a quenching of the dual fluorescence of 3HF, whereas the second complex of stoichiometry 1:1 presents a fluorescence emission.