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

Abstract

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 H 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.

Synthesis of Fluorescent Diphenylantracene-Based Calix[4]arene Derivatives and their Complexation with Alkali Metal Cations

“…This is in accordance with previously reported results involving calix [4]arene derivatives in this solvent as well as in pure methanol [11,19,21] and can be attributed to particularly strong cation solvation with this alcohol. [74] The addition of Na + or K + salt solutions to the solution of compound L2 caused a small increase in the absorbance with the appearance of several isosbestic points, pointing to the equilibrium between two spectrally active species, namely the free ligand and the complexed ligand (Figures S16 and S17, Supporting Information).…”

“…This is the inclusion of the solvent molecule into the hydrophobic calixarene cavity of the ligand and especially of the complex formed [21,22,24,26,27] whereby the particularly favorable interaction between the acetonitrile methyl protons and the electron rich aromatic rings can be realized. In order to explore such a possibility in the studied MeCN/CH2Cl2 mixture, the molecular dynamics simulations of the ligand and its alkali metal complexes were performed.…”

“…[4,[17][18][19][20][21][22][23][24][25] In this context, the inclusion of solvent molecules in the macrocycle hydrophobic cavity can play an important role in the cation hosting. [20][21][22]24,26,27] The extent of complexation reactions in non-aqueous solvents can also be significantly affected by the process of ion pairing. [4,11] Among the vast variety of calixarene derivatives, those bearing suitable binding sites as well fluorescent functionalities (e.g.…”

The Role of Triazole and Glucose Moieties in Alkali Metal Cation Complexation by Lower-Rim Tertiary-Amide Calix[4]arene Derivatives

“…Due to the pronounced orientation of alcohol molecule dipoles around high-charge-density Li + , its desolvation is particularly entropically beneficial and enthalpically demanding [32], which is clearly reflected in the corresponding ∆ r H • and ∆ r S • values. As already mentioned, the peak affinity was observed for Na + , which is best suited to the size of the binding site [3,10,15,33]. In accordance, its complexation was the most enthalpically favored.…”

“…The calixarenes are a class of macrocyclic compounds that can serve as a proof of point [1][2][3][4][5][6]. Their stiff frame and the possibility of both upper-and lower-rim functionalization have led to preparation of exceptional ligands for charged and neutral species in a range of media but very rarely in water [7][8][9][10][11][12][13][14][15][16]. With the aim of overcoming this obstacle, we have recently introduced a new class of water-soluble glycocalixarenes designed for efficient hosting of first-group cations [16].…”