The effects of solventa nd temperature on the complexation of adamantyl mannoside with b-cyclodextrin and 6-O-monotosyl-6-deoxy-b-cyclodextrinw ere explored experimentally and by means of molecular dynamics simulations. Efficientb inding was observedo nly in hydrogenbondeds olvents, which indicated solvophobically driven complexation. Thes tability of the inclusion complex was considerably higheri na queous media. Ap ronouncedt emperature dependence of D r H * and D r S * ,r esulting in perfect enthalpy-entropy compensation, was observedi nw ater.The complexation thermodynamicsw as in line with classical rationale for the hydrophobic effect at lower temperatures and the nonclassical explanation at higher temperatures. This finding linked cyclodextrinc omplexation thermodynam-ics with insights regarding the effecto ft emperature on the hydration water structure. The complexation enthalpies and entropies were weakly dependent on temperature in organic media. The signs of D r H * and D r S * were in accordance with the nonclassicalh ydrophobic (solvophobic) effect.T he structures of the optimized product corresponded to those deduceds pectroscopically,a nd the calculated and experimentally obtained values of D r G * were in very good agreement. This investigation clearly demonstrated that solvophobically drivenf ormation of cyclodextrin complexes could be anticipated in structured solvents in general. However,u nlike in water, adamantane and the host cavity behaved solely as structure breakers in the organic media explored so far.[a] SE = standard error of the mean (N = 3o r4). Figure 6. Relative a) conformation and b) solvation contribution to the hydration enthalpies of reactantsand the complex over the studied temperature range.

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.

Cation complexation in water presents a unique challenge in calixarene chemistry, mostly due to the fact that a vast majority of calixarene-based cation receptors is not soluble in water or their solubility has been achieved by introducing functionalities capable of (de)protonation. Such an approach inevitably involves the presence of counterions which compete with target cations for the calixarene binding site, and also rather often requires the use of ion-containing buffer solutions in order to control the pH. Herein we devised a new strategy towards the solution of this problem, based on introducing carbohydrate units at the lower or upper rim of calix[4]arenes which comprise efficient cation binding sites. In this context, we prepared neutral, water-soluble receptors with secondary or tertiary amide coordinating groups, and studied their complexation with alkali metal cations in aqueous and methanol (for the comparison purpose) solutions. Complexation thermodynamics was quantitatively characterized by UV spectrometry and isothermal titration calorimetry, revealing that one of the prepared tertiary amide derivatives is capable of remarkably efficient (log K ≈ 5) and selective binding of sodium cations among alkali metal cations in water. Given the ease of the synthetic procedure used, and thus the variety of accessible analogues, this study can serve as a platform for the development of reagents for diverse purposes in aqueous media.

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More than a hundred years after the first studies of the photo-and thermochromism of o-hydroxy Schiff bases (imines), it is still an intriguing topic that fascinates several research groups around the world. The reasons for such behavior are still under investigation, and this work is a part of it. We report the solution-based and mechanochemical synthesis of four o-hydroxy imines derived from α-aminodiphenylmethane. The thermochromic properties were studied for the single crystal and polycrystalline samples of the imines. The supramolecular impact on the keto-enol tautomerism in the solid state was studied using SCXRD and NMR, while NMR spectroscopy was used for the solution state. All four imines are thermochromic, although the color changes of the single crystals are not as strong as of the polycrystalline samples. One of the imines shows negative thermochromism, and that one is in keto-amine tautomeric form, both in the solid state as in solution.