A new complex of 1-hexadecyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide (cationic surfactant with a bicyclic head group) with palladium dichloride (1:1) was synthesized. The spectral properties of the metal complex, as well as the aggregation and solubilizing ability in DMSO—water mixture (50:50, v/v) were studied by IR and 1 H NMR spectroscopies, tensiometry, conductometry, potentiometry, dynamic and electrophoretic light scattering, and spectrophotometry (solubilization of hydrophobic dye Orange OT). It was found that the aggregation parameters and solubilizing activity of the system depend on the amphiphile content and on the colloidal state of the solution. High antimicrobial activity against Gram-positive (including antibiotic-resistant) strains, low hemolytic activity, and a reduced cytotoxic effect on the WI-38 normal human fetal lung cell line and the Chang liver normal human hepatocyte cell line was established.

The aggregation behavior, solubilization effect, and catalytic activity of hexadecylpiperidinium surfactants (including ones functionalized with hydroxyl substituents) have been investigated. The kinetics of hydrolytic cleavage of the irreversible cholinesterase inhibitor ethyl p-nitrophenyl ethylphosphonate (armine) in the micellar solutions of these surfactants has been studied using spectrophotometry. It has been shown that the micellar catalytic effect increases in the following order: methyl(hexadecyl)piperidinium bromide < methyl(hexadecyl)-3-hydroxypiperidinium bromide < hexadecyl(2-hydroxyethyl)piperidinium bromide < 2-hydroxyethyl-4-hydroxypiperidinium bromide. The acceleration observed can be as high as almost two orders of magnitude.

A homologous series of cationic surfactants with a pyrrolidinium head group containing a hydroxyethyl moiety was studied for the solubilization of nonsteroidal anti-inflammatory drugs, indomethacin and meloxicam, and the antioxidant quercetin. For indomethacin, the solubilization capacity linearly increases with increasing number of carbon atoms in the alkyl chain. In the case of quercetin and meloxicam, the solubilization capacity passes through a maximum for the hexadecyl derivative. The possibility of solubilization by premicellar surfactant aggregates was shown for indomethacin and meloxicam.

The aggregation behavior of mixed micellar solutions of cationic hexadecylpiperidinium surfactants and nonionic surfactant Tween 80 is studied. The critical micelle concentration is determined by varying the component ratios, and a negative deviation from the ideal mixing model can be observed (synergistic effect). The adsorption parameters and surface potential of mixed micelles are estimated. The solubilizing effect individual and mixed compositions have on such hydrophobic biologically active compounds as bioflavonoid quercetin and systemic fungicide carboxin is characterized quantitatively via spectrophotometry.

The forming and study of cationic surfactant/polyelectrolyte (PE) polymer colloid systems has been done at different concentrations of an amphiphilic compound and fixed polymer concentration. An imidazolium amphiphilic compound with a tetradecyl radical (IA-14) served as the surfactant; polyacrylic acid (PAA) characterized by a molecular weight of 1800 Da was used as component of the polymer. The aggregation characteristics of the systems have been examined via tensiometry, conductometry and fluorescence spectroscopy. It is shown that introducing of polyelectrolyte initiates the formation of polymer colloid complexes (PCC) at a 50 times lower concentration than the one required for an individual IA-14 system. Dynamic light scattering analysis has shown that the values of the hydrodynamic parameters of PCC lied in the range of 100–120 nm and did not depend on the concentration of the PE or the surfactant. It has been estimated via electrophoretic light scattering that electrostatic interactions make the main contribution to the formation of complexes.

Spectrophotometry has been employed to study the effect of metal-containing micellar systems of alkylated 1,4-diazabicyclo[2,2,2]octane complexes with Cu(II) and La(III) nitrates on the solubility of an antifungal drug, griseofulvin. The solubilization capacity of the aggregates of the metal complexes with respect to griseofulvin is 2 times as high as that of the ligand and up to two to three times as high as that of cetyltrimethylammonium bromide and its mixtures with corresponding inorganic salts. UV spectroscopy and dynamic light scattering studies have shown that the presence of the solubilizate causes alterations in the aggregation characteristics of the amphiphilic compounds, namely, a decrease in the aggregation threshold and variations in the sizes of the associates.

The catalytic activity of supramolecular systems based on the complexes of 1-alkyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide (Alk = CnH2n+ 1, n = 16, 18) with lanthanum nitrate in the reaction of hydrolytic decomposition of 4-nitrophenyl-O-alkylchloromethylphosphonates (Alk = CnH2n+ 1, n = 4, 6) was demonstrated. It was found that the reaction was accelerated due to the formation of nanoscale aggregates of various sizes and types (small micelles and larger supramolecular structures), which effectively bind the reagents. The binding constants of phosphonates with aggregates are greater than three or four orders of magnitude. The catalytic activity of the metal complex systems manifested itself at a lower amphiphile concentration in solution, as compared with that of ligands.

Systematic data on the aggregation behavior of novel 3-hydroxypiperidinium surfactants in aqueous solutions were obtained. The ability of the surfactants to solubilize hydrophobic compounds, including the Orange OT dye and biologically active flavonoid quercetin, was characterized. The maximally achieved limiting content of these substances in micellar solutions of 3-hydroxypiperidinium surfactants is by two to three times higher than that in solutions of their non-functionalized analogs. The solubility of quercetin depends on the pH of the medium, and the highest effect observed on going from water to micellar solutions of the studied surfactants reaches two orders of magnitude.

In this study, we report the relationship between structure, self-assembly behavior and antimicrobial activity of multicationic gemini surfactants and their successful use as stabilizers of a new liposomal formulation for transdermal drug delivery. New surfactants containing natural moiety 1,4-diazabicyclo[2.2.2]octane with four charges and two hydrophobic chains (n-Dabco-s-Dabco-n, where s = 2, 6, 12 and n = 12, 14, 16, 18) were synthesized. A linear dependence of the CMC decrease, with the increase of the number of carbon atoms in alkyl groups (slope 0.23) was shown. The aggregation numbers of n-Dabco-2-Dabco-n are smaller than 30 and they decrease with increasing alkyl chain length. This is in compliance with the larger surface area per n-Dabco-2-Dabco-n molecule. New liposomal formulations loading Rhodamine B phosphatidylcholine (with mean size about 100 nm and increased zeta potential from -7 +/- 2 mV to +55 +/- 2 mV) have been successfully stabilized by n-Dabco-s-Dabco-n surfactants. These formulations were designed to improve the bioavailability and skin permeation of loaded compound. The antibacterial activity of Dabco-surfactants was shown to be strongly affected by their structure (alkyl chain length and number of charged nitrogen). 12-Dabco-2-Dabco-12 was the most active (MIC = 0.48, 0.98 and 15.6 mu g/mL against S. aureus, B. cereus and E. coli, respectively) without hemolytic activity at 3.1 mu g/mL concentration. PC/14-Dabco-2-Dabco-14-liposomes were shown to be the best formulation, with the highest antibacterial activity against Sa (MIC = 7.8 mu g.mL(-1)) and lowest cytotoxicity (IC50 > 125). The modification of liposomes by Dabco-surfactants stabilizes the membrane of the vesicles, preventing the release of rhodamine B and impairing the penetration of the dye across Strat-M (R) membrane. Cellular uptake of rhodamine B-loaded PC/12-Dabco-2-Dabco-12-liposomes was also reported. This is the first example of cationic mixed liposomes containing Dabco-surfactants of potential interest for transdermal drug delivery.

The spectral, aggregation, and adsorption properties of amphiphilic metal complexes of alkylated N-methyl-D-glucamines and lanthanum nitrate and their mixture with hexadecyltrimethylammonium bromide were studied using IR, UV, and 1H NMR spectroscopy, tensiometry, potentiometry, and dynamic and electrophoretic light scattering. The parameters of aggregation and adsorption at the interface were determined and compared with the parameters of the ligands, ligand–inorganic salt mixtures, and traditional cationic surfactants.

The aggregation characteristics of cationic amphiphiles with a hexadecyl radical and a variable head group in aqueous solutions were evaluated and their adsorption parameters were calculated. A transition from ammonium to imidazolium head group makes micelle formation and adsorption thermodynamically favorable. The structure of the head group was shown to play key role in the ability of surfactant molecules to be embedded in the lipid bilayer. The ability of some amphiphiles to increase the membranotropic ability of the drugs metronidazole and chloramphenicol was demonstrated.

A supramolecular catalytic system for hydrolytic decomposition of toxic phosphorus acid esters has been obtained on the basis of a cationic surfactant with a morpholinium head group and sodium polystyrene sulfonate. Self-organization of the new binary catalytic system has been studied by tensiometry, conductometry, pH-metry, spectrophotometry, and dynamic and electrophoretic light scattering, and its aggregation thresholds have been determined. High solubilizing ability of the system with respect to a hydrophobic guest has been revealed. The morpholinium surfactant has been found to accelerate the hydrolysis of phosphonates up to 50 times in comparison to the reaction in water. The apparent hydrolysis rate constant in the presence of the polyelectrolyte decreases threefold due to reduction of the reactant binding constants.

The aggregation characteristics of binary systems based on a novel pyrrolidinium surfactant with the hexadecyl hydrocarbon tail and hydroxyethyl fragment at the nitrogen atom were studied in the presence of polyacrylic acid by a complex of physicochemical methods (tensiometry, conductometry, dynamic light scattering, fluorescence spectroscopy, and spectrophotometry). The formation of surfactant–polyelectrolyte complexes leads to a decrease in the concentration thresholds of aggregation by an order of magnitude to form aggregates ~70 nm in size was established by tensiometry and fluorimetry. The solubilization capacity of the formed mixed aggregates was tested using the Orange OT hydrophobic dye.