Josip Požar

Fluorescent phenanthridine-based calix[4]arene derivatives: synthesis and thermodynamic and computational studies of their complexation with alkali-metal cations

New fluorescent calix[4]arene derivatives 1, 2, and 3 were synthesized by introducing phenanthridine moieties at a lower calixarene rim. It was shown that due to the prominent fluorescence of compounds 1 and 3, they could be considered as potential sensitive fluorimetric cation sensors. Complexation of the prepared compounds with alkali-metal cations was studied at 25 °C in acetonitrile–dichloromethane and methanol–dichloromethane solvent mixtures (φ = 0.5) by means of fluorimetric, spectrophotometric, potentiometric, and microcalorimetric titrations as well as NMR spectroscopy. The stability constants of the corresponding complexes were determined, as were the enthalpies and entropies of the complexation reactions. In addition, equilibrium constants of ion-pairing reactions between alkali-metal cations and several anions in the solvents used were measured conductometrically. It was found that the cation-binding affinity of ligand 1 with four phenanthridine subunits was much higher than that of 2 and 3, with the complex stabilities in all cases being significantly lower in methanol–dichloromethane mixture compared to that in acetonitrile–dichloromethane. These findings were thoroughly discussed by taking into account the determined thermodynamic complexation data, structural properties of the ligand and free and complexed cations, as well as the solvation abilities of the solvents examined. The conclusions made in that way were corroborated by the results of the molecular dynamics simulations of the systems studied. An attempt to get an insight into the possible structures of the alkali-metal cation complexes with ligand 1 was made by carrying out the corresponding density functional theory calculations.

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na+ cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL+ complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL+ stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.

Protonacijske ravnoteže linearnih homopolikiselina

Polielektroliti su polimerni spojevi čiji su monomeri u otopinama, odnosno u taljevinama, električki nabijeni.1–23 Najjednostavniji polielektroliti sastoje se od identičnih monomernih podjedinica koje sadržavaju funkcijske skupine (nosioce električkog naboja) povezane u lanac. Takvi spojevi poznati su i pod nazivom linearni homopolielektroliti.1–23 Ukoliko polimerni lanci sadržavaju više različitih funkcijskih skupina, polielektroliti se nazivaju heteropolielektrolitima.