Two-sublattice ordering in titanium monoxide

The disordered and ordered structures of nonstoichiometric titanium monoxide Ti_xO_z≡TiO_y(y=z/x) containing structural vacancies simultaneously in the nonmetallic and metallic sublattices were studied. In the stoichiometry range from TiO_0.9 to TiO_1.1, an ordered monoclinic phase [space group C2/m (A12m/1)] of the Ti₅O₅ type is formed in the TiO_y monoxide at temperatures below 1300 K. The disorder-order TiO_y?Ti₅O₅ phase-transition channel involves Lifshitz {k₁₀} and non-Lifshitz {k₄} and {k₁₁} star rays. The ordering proceeds as a first-order phase transition with a decrease in the volume of the basal cubic lattice. The titanium and oxygen distribution functions in the metallic and nonmetallic sublattices of titanium monoxide are calculated. The domain of allowed values is determined for the long-range order parameter.     

Application of nonionic amphiphiles for increasing solubility in water of alkylated bibenzimidazole derivatives

Solubilization capacity of a number of nonionic micelle-forming compounds toward 2,2´-bibenzimidazole and its alkylated derivatives was determined by spectrophotometry. It was found that as the hydrophilic lipophilic balance of the studied amphiphiles grows, their solubilization effect toward 2,2´-bibenzimidazoles increases and reaches the highest value in the case of pluronic F127. The conversion of bibenzimidazoles to the cationic form induced by lowering the medium pH improves efficiency of the solubilizers.     

New amphiphilic multiheterocycle: Micelle-forming properties and effect on the reactivity of phosphorus acid esters

Supramolecular systems based on a novel tetracationic amphiphilic multiheterocycle have been studied by tensiometry, conductometry, pH-metry, spectrophotometry, and dynamic and electrophoretic light scattering. The critical micelle concentration of the system has been determined (0.4 mM), and the possibility of open and closed association models realization has been demonstrated. A high solubilizing ability of the aggregates toward hydrophobic guest species has been revealed. Micellar catalysts based on the new multiheterocycle have shown substrate specificity in the hydrolysis of phosphonates possessing different hydrophobicities.     

The reactivity of phosphonic esters in aqueous micellar solutions of cationic surfactants

The micellar effect of cationic surfactants in alkaline hydrolysis of O-alkyl-O-aryl-chloromethyl phosphonates involves a positive contribution of concentrating the reagents and a negative effect of the micellar environment due to a loss in the activation entropy. The reactivity of substrates in micelles depends on both electronic and hydrophobic characteristics of substituents in the aryl group.     

Control of the catalytic effect of cetyltrimethylammonium bromide micelles by the addition of background electrolyte and nonionic surfactant

The variation of the microscopic properties (surface potential, micropolarity, etc.) of the interface of cetyltrimethylammonium bromide micelles upon the addition of a background electrolyte or the nonionic surfactant Triton X-100 decreases the rates of ion-molecular reactions, namely, alkaline hydrolysis of carboxylic acid esters and tetracoordinate phosphorus acid esters, and results in the shift of acid-base equilibria. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1933–1940, October, 2007.     

Intermolecular association of Tilan with vinylpyrrolidone copolymers

The results of physicochemical studies of promising prolonging agents for Tilan antibiotic: polyvinylpyrrolidone and vinylpyrrolidone copolymers, are reported. The optimal component ratios of the drug formulation were determined by viscometry and conductometric titration. As determined by IR spectroscopy, the components are associated mainly via intermolecular hydrogen bonds.     

Nanoreactors based on amphiphilic uracilophanes: self-organization and reactivity study

New amphiphilic pyrimidinic macrocycles (APMs) with two (APM-1) and three (APM-2) decyl tails have been synthesized by quaternization of the bridged N. Complex examination of the APM-based systems with the help of tensiometry, conductometry, dynamic light scattering, and UV and NMR spectroscopy provides evidence for their aggregation. Calculations based on surface tension isotherms and on packing parameter considerations make it possible to assume a lamellar packing of macrocycles when aggregating. Marked differences in the aggregation behavior of APM-1 and APM-2 have been found. The additives of polyethylenimine (PEI) exert little influence on the critical micelle concentration (cmc) of APM-1, while in the APM-2/PEI systems there occurs a pronounced decrease in the cmc and also a ca. 2-fold decrease in the surface area per molecule. The APM-based assemblies are explored as nanoreactors for the hydrolysis of O-alkyl O-p-nitrophenyl (chloromethyl)phosphonates (alkyl = ethyl, hexyl). The kinetic study reveals a minor rate effect of the APM-1-based systems. In the APM-2-based systems an acceleration of the hydrolysis of both phosphonates occurs as compared to the uncatalyzed process. Within the APM-2 --> APM-2/PEI --> APM-2/PEI/La(III) series, due to the cooperative contributions of the supramolecular, polymer, and homogeneous catalysis, an increase in the catalytic effect is observed from 30 times to 3 orders of magnitude as compared to that of the basic hydrolysis of the substrates.     

Micellization properties and the catalytic effect of the aqueous cetyltrimethylammonium bromide-Triton X-100 binary system in nucleophilic substitution in esters of phosphorus acids

The aggregation properties and catalytic effect of the cetyltrimethylammonium bromide-Triton X-100 binary system in nucleophilic substitution in esters of phosphorus acids are studied in the region of normal micelles and oil/water microemulsions. In the presence of phenol, the dissociation of O-alkyl-O-para-nitrophenyl chloromethyl phosphonates is up to 200 times more rapid than the same reaction in water. The efficiency of catalysis depends on the molar ratio of the surfactants and is determined by several factors: concentration, changes in the microenvironment of the reactants, and the shift of the pK _a of phenol.     

Reactivity of phosphorus esters in supramolecular systems based on surfactants containing an uracil residue and polyethylenimine

The reactivity of phosphorus esters with different hydrophobicities was studied in aqueous solutions of cationic surfactants containing an uracil residue, as well as in binary systems based on polyethylenimine. Pronounced substrate specificity was revealed in all supramolecular systems examined; in particular, acceleration of the hydrolysis of more hydrophobic substrate and inhibition of the reaction with less hydrophobic analog were observed. Aggregation in the examined systems was confirmed by tensiometric and conductometric measurements. The aggregation threshold considerably decreased in going from monocationic amphiphile to more hydrophobic dicationic analog due to the presence in the latter of two additional alkyl radicals.     

Substrate specific nanoreactors based on pyrimidine-containing amphiphiles of various structures for cleavage of phosphonates

ABSTRACT

The series of novel pyrimidine-containing amphiphiles were examined as catalysts for cleavage of phosphonates having various hydrophobicities. Kinetic data showed marked substrate specificity of three different types (i) inhibition for both substrates, (ii) catalysis for more hydrophobic phosphonate and inhibition for less hydrophobic phosphonate, and (iii) catalysis for both substrates. The highest acceleration (more than 11 times in comparison with the reaction in the absence of amphiphile) has been reached in the case of dicationic amphiphile with three hydrophobic tails.