A. B. Mirgorodskaya

Catalysis of nucleophilic substitution reactions in supramolecular systems

The factors determining the catalytic effect of supramolecular systems on the nucleophilic substitution reactions are analyzed. The role of the structural and phase transitions of nanoaggregates in the catalytic mechanism are determined. The substrate specificity is shown for different structures of the supramolecular composition.

Gemini surfactant-nonionic polymer mixed micellar systems

Tensiometry, dynamic light scattering, and optical spectrophotometry are employed to quantitatively characterize the aggregation behavior of a gemini (dicationic) surfactant in aqueous solutions in the presence of poly(ethylene glycol) with a molecular mass of 20000 Da or a Pluronic F127 block copolymer with a molecular mass of 12600 Da. It is shown that the formation of surfactant-polymer mixed aggregates decreases the positive surface potential of gemini surfactant micelles and is one of the main reasons for weakening of the micellar catalytic effect in hydrolysis of carboxylic acid esters.

Design of supramolecular biomimetic catalysts of high substrate specificity by noncovalent self-assembly of calix[4]arenes with amphiphilic and polymeric amines.

Supramolecular biomimetic catalysts of high substrate specificity are developed based on amphiphilic oxyethylated calix[4]arene bearing iso-nonyl fragments at the upper rim and hexadeca(ethylene glycol) fragments at lower rim (9CO16), and amines of amphiphilic or polymeric nature. Two critical concentrations determined by tensiometry and dye solubilization methods are probably reflect the onset of association process and transition from bimodal to monomodal size distribution revealed by the dynamic light scattering method. Amine components used may form aggregates as well, which is mediated by hydrophobic effect due to occurrence of long-chain alkyl tails. The micellar rate effect of the designed systems toward the cleavage of carboxylic acid ester is shown to be contributed by the formation of mixed aggregates with the reactive functional groups, as well as by the pKa shift of the amine and the character of the distribution of reagents in functional micelles. In the case of long-chain primary amines, an inversion of micellar rate effect (catalysis to inhibition) occurs upon transferring from the less hydrophobic substrate, p-nitrophenyl acetate, to the more hydrophobic analogs, p-nitrophenyl laurate and p-nitrophenyl caprinate. The opposite effect (inhibition of the reaction of p-nitrophenyl acetate and the acceleration of the process of hydrophobic analogs) was observed in systems based on polyethyleneimine.

Role of surface potential in the catalytic action of micelles of cationic surfactants with a hydroxyalkyl fragment in the head group

The surface potential in aqueous micellar solutions of a series of cetyltrialkylammonium bromides containing a hydroxyalkyl fragment in the head group was determined with a spectral probe (p-nitrophenol). It was found that the catalytic effect exerted by these surfactants in solution on the base hydrolysis of carboxylic acid esters is determined by two factors. First, the charged nucleophile is concentrated at the micelle surface. Second, hydrogen bonding of the substrate with the hydroxyalkyl substituents results in its activation.

Solubilizing and catalytic properties of supramolecular systems based on gemini surfactants

Quantitative parameters characterizing the aggregation behavior of dicationic surfactants of the 12-s-12 type in aqueous solutions were determined: critical micelle concentrations, aggregation numbers, and surface potentials. The effects of the spacer length of the surfactants on their solubilizing effect with respect to hydrophobic (dye Orange OT) and water-soluble (p-nitrophenol) spectral probes and on their ability to shift acid-base equilibria were studied. The kinetics of alkaline hydrolysis of p-nitrophenyl acetate and p-nitrophenyl caprinate in 12-s-12 solutions was studied by spectrophotometry. A correlation between the micellar catalytic effect and the surface potential of micelles was established. The pronounced substrate specificity was revealed: the maximum acceleration of hydrolysis is observed in solutions of 12-6-12, attaining 1760 times for p-nitrophenyl caprinate.

Geminal alkylammonium surfactants: Aggregation properties and catalytic activity

Geminal alkylammonium surfactants containing a hexamethylene spacer show a specific behavior, namely, a catalytic effect at low concentrations of the detergent in the system. The critical micellization concentrations of these surfactants are by an order of magnitude lower than those of the related surfactants with one hydrophobic fragment. The effect exerted on the hydrolysis of carboxylic acid esters by micellar structural rearrangements induced by addition of a supporting electrolyte is determined.

Solubility and hydrolytic stability of indomethacin in aqueous micellar solutions

The solubility of the indomethacin drug in aqueous micellar solutions of a series of dicationic surfactants was characterized by spectrophotometry. The use of these surfactants can significantly increase the indomethacin content in aqueous solutions without destruction of the drug. The increase in the solubility can be explained by the multifactorial mechanism of the influence of micelles involving the solubilization of the drug and its binding with surfactants due to electrostatic and specific interactions. The use of dicationic surfactants in alkaline solutions was shown to markedly accelerate the hydrolytic cleavage of indomethacin. The highest catalytic effect is observed for N,N´-(hexane-1,6-diyl)bis(2-hydroxyethyl)(methyl)(cetyl)ammonium dibromide: a 1200-fold increase in the reaction rate of alkaline hydrolysis of the drug.

Effect of surfactant micelles on solubility and spectral characteristics of 2,2’-bibenzimidazole

The solubilization capacity of surfactants of different types was quantitatively characterized by spectrophotometry toward 2,2’-bibenzimidazole (BBI), whose derivatives possess a wide range of pharmacological activity. 2,2’-Bibenzimidazole solubilized by sodium dodecyl sulfate micelles is characterized by a high molar absorption coefficient (9400 mol−1 L cm−1) at the absorbance maximum (342 nm at pH 4–10), which may serve as a basis for the development of procedures for analytical monitoring of the BBI content in aqueous solutions and biosystems. The ability of surfactants to enhance the solubility of BBI in water and, as a consequence, to increase its bioavailability in the series sodium dodecyl sulfate < cetyltrimethylammonium bromide < Tween-80.

Aggregation behavior, anticorrosion effect, and antimicrobial activity of alkylmethylmorpholinium bromides

Quaternary ammonium derivatives containing a morpholinium moiety in the head group and exhibiting micelle-forming activity have been synthesized and characterized. These compounds exhibit poly-functional properties: they efficiently inhibit hydrogen sulfide and combined (H2S and CO2) corrosion of steel, are characterized by strong bactericidal activity against sulfate-reducing bacteria, and possess pronounced bacteriostatic and fungistatic effects.

Dicationic surfactant based catalytic systems for alkaline hydrolysis of phosphonic acid esters

Use of aqueous micellar solutions of dicationic surfactants with the general formula [R(CH3)2N(CH2)6N(CH3)2R]2+2Br− (R = n-C10H21 to n-C16H33) as the reaction medium for the alkaline hydrolysis of phosphonic acid esters has revealed a strong catalytic effect of the surfactants, which can increase the reaction rate by two orders of magnitude. This effect depends on the surfactant structure, shows itself at low surfactant concentrations, and is substrate-specific. The effect of the micelles on the phosphonate hydrolysis rate is largely determined by the hydrophobicity factor.