Julia E. Morozova

Crystal violet dye in complexes with amphiphilic anionic calix[4]resorcinarenes: binding by aggregates and individual molecules.

Here, we report on a systematic study of six calix[4]resorcinarene macrocycles bearing eight carboxylic groups on the upper rim and four different lower rim substituents that are either aliphatic (2, 4, and 5) or alkylaromatic (1, 3, and 6). The macrocycles were studied in their individual aqueous solutions and in the presence of triphenylmethane dye crystal violet. It was found that binding of crystal violet with aggregated macrocycles shields it from the bulk of solution, preventing its discoloration under basic conditions and electrochemical reduction on the glassy carbon electrode. Most efficient shielding, reducing the rate of discoloration more than 173 times, as compared to solution with no macrocycle, was achieved with 6 forming aggregates of average 72 molecules in 0.1 mM solutions.

Influence of amidoammonium calix[4]resorcinarenes on methyl orange protolytic equilibrium: supramolecular indicator systems

Here, we report on the study of cationic amidoammonium calix[4]resorcinarenes 1–5 of various lipophilicity capable of binding acid–base indicator methyl orange (MO). We identified the contributions of macrocycle aggregation and conformational mobility in the binding of MO. The effective pKa values of bound MO systematically decrease as the size and the packing density of the aggregates increase with an increase in calixresorcinarene lipophilicity. Consideration of a series of macrocycles clearly shows that large aggregates form most stable complexes, binding guests not on individual level but as aggregates. It was found that the most stable MO complex with 5 is formed due to electrostatic binding with ammonium groups of the macrocycle and incapsulation of MO in a hydrophobic layer of the aggregates. We have shown that competitive binding of MO and cationic surfactants by aggregates of 5 is suitable for visual/spectrophotometric detection of colourless anionic substrates.

Investigation of tetramethylenesulfonated calix[4]resorcinarene interactions with azo dyes in aqueous solution.

The interaction of a macrocycles aggregates with a guest molecule has special interest due to the double role, both of macrocycle cavity and self-associates, in the binding of the guests. Here, we report on the interactions of nonaggregated methyl-substituted (SCA1) and aggregated penthyl-substituted (SCA2) tetramethylenesulfonated calix[4]resorcinarenes with pH indicators methyl yellow (MY) and methyl orange (MO) in aqueous solutions. It was found that the pH of aqueous solutions of SCA1 and SCA2 depends on their concentration; besides, variation of the concentration of SCA1 and SCA2 results in a shift of the absorption maxima and of pH-sensitive azo dyes. Association of the marocycles with azo dyes was demonstrated to follow a proton-transfer mechanism accompanied by protonation of the dyes; it was found that excess of the macrocycle in solution with the universal buffer background shifts the pK(a) values and stabilizes the protonated form of the dyes. Consideration of interactions of small dye molecules with large molecular associates, containing both individual and multimolecule binding sites, gives a closer approximation of synthetic biomimetics to their natural prototypes.

Nanoconjugates of a calixresorcinarene derivative with methoxy poly(ethylene glycol) fragments for drug encapsulation

In order to obtain a non-toxic amphiphilic calixresorcinarene capable to form nanoconjugates for drug encapsulation, tetraundecylcalixresorcinarene functionalized by methoxy poly(ethylene glycol) chains has been synthesized. The macrocycle obtained is characterized by low hemotoxicity. In aqueous solution it forms nanoassociates that are able to encapsulate organic substrates of different hydrophobicity, including drugs (doxorubicin, naproxen, ibuprofen, quercetin). The micelles of the macrocycle slowed down the release of the hydrophilic substrates in vitro. In physiological sodium chloride solution and phosphate-buffered saline, the micelles of the macrocycle acquire thermoresponsive properties and exhibit a temperature-controlled release of doxorubicin in vitro. The combination of the low toxicity and the encapsulation properties of the obtained calixresorcinarene–mPEG conjugate shows promising potential for the use as a supramolecular drug-delivery system.