A. R. Ibragimova

Micellization and catalytic activity of the cetyltrimethylammonium bromide-Brij 97-water mixed micellar system.

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)-polyoxyethylene (10) oleyl ether, C(18)H(35)(OCH(2)CH(2))(10)OH (Brij 97)-water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter beta as -4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.

Self-assembling systems based on amphiphilic alkyltriphenylphosphonium bromides: Elucidation of the role of head group

A systematic study of the aggregation behavior of alkyltriphenylphosphonium bromides (TPPB-n; n=8, 10, 12, 14, 16, 18; here n is the number of carbon atoms in alkyl groups) in aqueous solutions has been carried out and compared with trimethyl ammonium bromides (TMAB-n). Critical micelle concentrations (cmcs) of TPPB-n and TMAB-n decrease with the number of carbon atoms with the slope parameter of ca.0.3. The low cmcs and effective solubilization power toward Orange OT indicate high micellization capacity of phosphonium surfactants. The low counterion binding parameter β is revealed for TPPB-10 and TPPB-12, while high counterion binding of ≥80% is observed for high TPPB-n homologs. Values of the surface potential ψ calculated on the basis of pK(a) shifts of p-nitrophenols is similar for both series and monotonously increase with alkyl chain length. Several points indicate non-monotonic changes within TPPB-n series. There are peculiarities of the tensiometry and solubilization plots for high homologs and above mentioned increases in counterion binding on transiting from low to high molecular weight surfactants. Differences in aggregation behavior between TPPB and TMAB series and between low and high homologs can be due to the specific structural character of the TPP(+) cation, which is supported by X-ray data.

Synthesis and photophysical properties of colloids fabricated by the layer-by-layer polyelectrolyte assembly onto Eu(III) complex as a core

The luminescent colloids have been synthesized through the layer-by-layer assembly of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) onto the luminescent core. The latter has been obtained by the reprecipitation of complex Eu[(TTA)(3)1] (where TTA(-) and 1 are thenoyltrifluoroacetonate and 2-(5-chlorophenyl-2-hydroxy)-2-phenylethenyl-bis-(2-methoxyphenyl)phosphine oxide, respectively) from organic solvent to aqueous solution. The variation of Eu(III) complexes indicates the role of the complex core in the development of such core-shell colloids. Complex Eu[(TTA)(3)1] is most convenient precursor of Eu-doped luminescent nanocomposites. The fluorometric measurements at each step of the layer-by-layer polyelectrolyte assembly onto Eu[(TTA)(3)1] core, at various pHs and additives reveal the quenching of Eu-centered luminescence as a result of the interfacial interaction of the core and the dye. The AFM images and electrochemical behavior of PSS-(PEI-PSS)(n)-Eu[(TTA)(3)1] colloids deposited on the surface indicate the stability of the polyelectrolyte multilayer in the dried state.

Structural, biocomplexation and gene delivery properties of hydroxyethylated gemini surfactants with varied spacer length.

Gemini surfactants with hexadecyl tails and hydroxyethylated head groups bridged with tetramethylene (G4), hexamethylene (G6) and dodecamethylene (G12) spacers were shown to self-assemble at the lower critical micelle concentration compared to their conventional m-s-m analogs. The lipoplex formation and the plasmid DNA transfer into different kinds of host cells were studied. In the case of eukaryotic cells, high transfection efficacy has been demonstrated for DNA-gemini complexes, which increased as follows: G6<G4<G12. Different activity series, i.e., G6>G4>G12 has been obtained in the case of transformation of bacterial cells with plasmid DNA-gemini complexes, mediated by electroporation technique. Solely G6 shows transformation efficacy exceeding the control result (uncomplexed DNA), while the inhibitory effect occurs for G4 and G12. Analysis of physico-chemical features of single surfactants and lipoplexes shows that compaction and condensation effects change as follows: G6<G4 ≤ G12, i.e., agree with the order of transfection efficacy, which is supported by membrane tropic properties of G12. On the other hand, gel retardation assay and docking study testify low electrostatic affinity in G12/DNA pair, thereby indicating that hydrophobic effect probably plays important role in the lipoplex formation. Two factors are assumed to be responsible for the inhibition effect of gemini in the case of transformation of bacterial cells. They are (i) an unfavorable influence of cationic surfactants on the electroporation procedure due to depressing the electrophoretic effect; and (ii) antibacterial activity of cationic surfactants that may cause the disruption of integrity of cell membranes.

Catalytic Effect of Multicomponent Supramolecular Systems in Phosphoryl-Group Transfer Reactions

The catalytic effect of the cetyltrimethylammonium bromide–poly(ethylenimine)–water system in the hydrolysis reactions of phosphonic acid esters (an increase in the rate constant by three orders of magnitude) is due to the concentration of reactants in polymer–colloid complexes and changes in their microenvironments. The catalyst efficiency depends on the structures of substrates, surfactants, and polymers.

Supramolecular catalytic systems based on calix[4]resorcinarene for nucleophilic substitution in phosphorous acid esters

The aggregation and catalytic effect in the reaction of hydrolytic decomposition of phosphorous acid esters are studied for series of systems such as calixarene (CA)-sodium dodecyl sulfate (SDS), CA-poly(ethylene imine) (PEI), SDS-PEI, and CA-SDS-PEI. Using dynamic light scattering, sizes of aggregates are determined, cloud point is estimated, and catalytic effect is studied. Data obtained are consistent with the assumption of the joint aggregation in systems studied. The possibility of the passage from 20-fold inhibiting effect to the catalysis (higher than the order of magnitude) of studied reaction by the immobilization of anionic nanoaggregates (nanoreactors) on a catalytically active polymer matrix is demonstrated. The possibility of the passage from microheterogeneous to heterogeneous system and the separation of catalyst from the products are established.

Properties of a sodium dodecyl sulfate-Brij 35 binary micellar system and their effect on the alkaline hydrolysis of O-ethyl-O-p-nitrophenylchloromethylphosphonate

It is found that a sodium dodecyl sulfate-Brij 35 binary mixture inhibits the alkaline hydrolysis of O-ethyl-O-p-nitrophenylchloromethylphosphonate. Tensiometric data and variations in cloud point suggest the synergistic effect of the above surfactants caused by the formation of mixed micelles. The method of solvatochromic probe ET(30) shows that the micropolarity of a medium rises at the sites of localization of substrates solubilized in micelles with an increase in ionic surfactant fraction in mixed aggregates. Variations in micellization properties, micropolarity, and surface potential with the composition of the binary mixture of the surfactants influence the catalytic properties of mixed micelles with respect to the examined reaction.

Polyelectrolyte micro- and nanocapsules with varied shell permeability controlling the rate of esters hydrolysis

Two variants of layer-by-layer deposition of polyelectrolytes (polyacrylic acid and polyethyleneimine) for the encapsulation of low-molecular-weight hydrophobic substrates (carboxylic acid esters) were proposed. The spectrophotometric method was used to study the kinetics of alkaline hydrolysis of the esters by monitoring the permeability of microcapsule shells. The first procedure provides a preliminary microencapsulation of substrates into the carbonate matrix to form stable capsules 7–10 μm in size with a low wall permeability. According to the second procedure, the polyelectrolytes were adsorbed directly on the dispersed substrate. In this case, nanosized capsules are formed, whose permeability is controlled by the ultrasonic treatment and the number of deposited layers.

Influence of the medium self-organization on the catalytic activity of palladium nanoparticles stabilized by amphiphilic phosphonium salts in the Suzuki reaction

The influence of the aggregation properties of the medium on the catalytic activity of palladium nanoparticles stabilized by amphiphilic phosphonium salts was demonstrated for the Suzuki coupling of bromoarenes and phenylboronic acid.

The influence of the nature of surfactants and dispersion medium on the catalytic effect of reverse micellar systems

The catalytic effect of reverse micellar systems in alkaline hydrolysis of phosphonic acid esters is to a considerable extent determined by the structure of the substrate and surfactant and the nature of the oil phase but weakly depends on the surface potential of the aggregates. AOT-butanol-decane-water, sodium dodecyl sulfate-butanol-decane-water, and cetyltrimethylammonium bromide-butanol-decane-water microemulsions exhibit specific catalytic properties rather than catalytic properties intermediate between those of the surfactant-alkane-water and surfactant-alkanol-water three-component systems.