Micellar nanocontainers based on cationic surfactants with a pyrrolidinium head group for increasing drug bioavailability

Russian Chemical Bulletin - A homologous series of cationic surfactants with a pyrrolidinium head group containing a hydroxyethyl moiety was studied for the solubilization of nonsteroidal...     

Magnetic effects in hydroperoxide decomposition in mixed micelles with cationic surfactants

The retardation effect of oxygen and external magnetic field on the yield of radicals in hydroperoxide decomposition in catalytic nanoreactors was discovered. Mixed reverse micelles formed by the cationic surfactants (Surf) and hydroperoxide {mLOOH...nSurf} play the role of nanoreactors. Similar effects of oxygen and external magnetic field (60–150 mT) on the yield of radicals are observed in the catalytic decomposition of hydroperoxide in the presence of acetylcholine. It is noteworthy that the retardation effect of the magnetic field decreases in the presence of paramagnetic particles such as oxygen and relatively stable radicals.     

Effect of head group size, temperature and counterion specificity on cationic micelles

The critical micelle concentration (cmc) and ionisation degree (α), of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltripropylammonium bromide (CTPABr) and cetyltripropylammonium chloride (CTPACl) have been measured over a narrow temperature range at 2 degree intervals using electrical conductivity. CTPACl and CTPABr are very soluble in water and were measured in the temperature range 275.15-323.15K. The Krafft temperatures for CTABr and for CTACl are 293.15K and 284.15K, respectively and established a lower temperature limit for our studies on these two surfactants. The cmc vs temperature curves have a smooth minimum near room temperature and α linearly increases with temperature. The changes of cmc and α with temperature are smaller than those associated with the modification of head group size or counterion nature. Using these results, basic thermodynamic quantities associated with the phenomena of micellization have been evaluated. Thermodynamic properties of the surfactant solutions were discussed in terms of temperature dependence of the free energy, enthalpy and entropy of micellization. A close similarity between the effects of change in temperature on protein folding and micellization process appears from the data.     

Aqueous behaviour of cationic surfactants containing a cleavable group

The aggregation behaviour of two novel cationic RAFT agents (transfer surfactants); N,N-dimethyl-N-(4-(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium bromide (PCDBAB) and N-(4-((((dodecylthio)-carbonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium bromide (DCTBAB) in diluted solutions have been investigated by surface tension, conductimetry and microcalorimetry measurements. The thermodynamic parameters i.e. the critical micelle concentration (cmc), the degree of micelle ionization (alpha), the head group surface area (a 0), Delta H mic, Delta G mic and T Delta S mic are reported at 303 K. The thermodynamic parameters have been compared to those of the conventional surfactant cetyltrimethylammonium bromide (CTAB) in order to specify structural relationships. The obtained results have been discussed considering the hydrophobic behaviour of the S-C=S- linkage and the specific interactions that arise from the introduction of the benzene ring into the hydrophobic part.     

Mixed micelles of series of monomeric and dimeric cationic, zwitterionic, and unequal twin-tail cationic surfactants with sugar surfactants: a fluorescence study

Steady state fluorescence measurements have been carried out for binary mixtures of a series of monomeric cationic (MC), zwitterionic (ZI), dimeric cationic (DC), and twin-tail cationic (TC) surfactants with sugar (beta-C8G and beta-C12G) over the whole mole fraction range using pyrene as fluorescence probe. The cmc values thus determined for all the binary mixtures have been further evaluated using the regular solution theory. The various micellar parameters, such as micelle mole fraction (X1), regular solution interaction parameter (beta), micropolarity, and mean micelle aggregation number (Nagg), have been determined for all these series of mixtures. Variation in all these micellar parameters demonstrates that mixed micelles of these surfactants with beta-C8G are mostly synergistic in nature and the synergism increases with the increase in hydrophobicity of the cosurfactant in each case. The mixtures of beta-C12G with various cosurfactants do not show this behavior and instead of it, they show an increase in antagonism with the increase in hydrophobicity of cosurfactants. This discrepancy has been attributed to a large difference in hydrophobicity between beta-C8G and beta-C12G, and the chain folding of the latter is considered to be the reason for the antagonism.     

含酰胺基Gemini阳离子表面活性剂的合成及性能

以棕榈酸、N,N-二甲基丙二胺、环氧氯丙烷和脂肪胺为原料合成了一系列Gemini阳离子表面活性剂.用红外光谱、质谱对产品进行了结构分析,并对产品性能进行了测定.结果表明:所合成的Gemini阳离子表面活性剂的临界胶束浓度低于传统阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)1-2个数量级;当浓度为1×10-3mol/...     

New piperidinium surfactants with a benzyl fragment in the head group: aggregation properties and the possibility of using to control plant pathogens

Russian Chemical Bulletin - New piperidinium surfactants with a benzyl fragment in the head group were synthesized and characterized. The critical micelle concentrations, degrees of binding of...     

Soluble complexes of sodium poly(isoprene-b-methacrylate) micelles with cationic surfactants in aqueous media

Water-soluble complexes between sodium poly(isoprene-b-methacrylate) (NaIMA) amphiphilic block copolymer micelles and two cationic surfactants with different hydrophobic tail lengths, namely, dodecyltrimethylammonium bromide (DTMAB) and octyltrimethylammonium bromide (OTMAB), were prepared by mixing individual aqueous solutions of block copolymers and surfactants. The complexes were characterized in terms of size, overall charge, and micropolarity by dynamic light scattering, zeta-potential measurements, and fluorescence spectroscopy. Properties of the systems were investigated as a function of surfactant concentration and surfactant type and state in the initial solutions, as well as temperature. Experiments reveal surfactant complexation at the coronal sodium poly(methacrylate) (NaMA) chains, followed by an increase in mass and a decrease in size of the micelles. Complexation of individual surfactant micelles was observed when the DTMAB concentration in the starting solutions was higher than the surfactant cmc. The complexes show a temperature dependence of their dimension due to the hydrophobic effect.     

Geometrical shape of micelles formed by cationic dimeric surfactants determined with small-angle neutron scattering

The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C(12)H(25)N(CH(3))(2)(CH(2))(s)N(CH(3))(2)C(12)H(25) (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 12-4-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 ≤ s ≤ 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 ≤ s ≤ 12.     

Antagonistic mixing behavior of cationic gemini surfactants and triblock polymers in mixed micelles

Conductance (kappa), pyrene fluorescence (I1/I3), cloud point (C(P)), and Krafft temperature (K(T)) measurements have been carried out for various dimethylene bis(alkyldimethylammonium bromide) (gemini) surfactants with different poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock polymers (TBP). From the kappa and I1/I3 studies, the critical micelle concentrations of mixed micelle formation between the gemini and TBP have been determined using regular solution theory. It has been observed that mixed micelle formation in all the binary mixtures of gemini+TBP occurs due to the unfavorable mixing, the magnitude of which decreases with increased hydrophobicity of the gemini component. The results are further supported by evaluating the mean micelle aggregation number and enthalpy of fusion from fluorescence and Krafft temperature measurements, respectively.     

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: the pH and spacer effect

Mixed micelle formation of binary cationic gemini (12-s-12, s=4, 6) and zwitterionic (N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.     

Local mobility of micelles of new cationic surfactants and their interactions with hydrophobically modified polyacrylamides

The local dynamics and organization of micelles of new long-chain cationic surfactants with saturated hydrocarbon fragments (from C₁₆ to C₂₂) are investigated via the EPR spin-probe technique. The local mobility of spin probes in the hydrocarbon core of a micelle changes insignificantly, while the order parameter noticeably increases with lengthening of the hydrocarbon fragment of the surfactant molecule. The specific features of the interaction of the surfactants with network junctions of the gels formed by two types of hydrophobically modified polyacrylamides??either containing charged groups (sodium acrylate) in the backbone or lacking these groups??are studied. In both cases, the local mobility of network junctions of the gel increases after the introduction of the surfactant (C₁₈). Moreover, for surfactant with a long alkyl group (C₂), the microscopic viscosity of the gel based on the uncharged polymer decreases, although the local mobility of the network junctions increases. Possible causes of the observed specific features are discussed.     

The influence of cholesterol on the generation of radicals in mixed reverse micelles of cationic surfactants with hydroperoxides

Cationic surfactants (S+) and acetylcholine (ACh), the most important neurotransmitter playing an essential role in the neuromuscular and cognitive activity of living beings, form mixed reverse micelles with hydroperoxides (ROOH) in organic media, where ROOH decay into free radicals is catalytically accelerated. Adding cholesterol (Chol, 30 mol.%) to pyridinium (СРВ) and cetyltimethylammonioum (СТАВ) bromides, reduces the radical generation rate in ROOH catalytic decay several times. However, a higher radical initiation rate is observed in the case of less ordered and larger ACh–ROOH reverse micelles. A Chol additive does not essentially affect the size of СТАВ and СРВ micelles with hydroperoxides but results in their decrease in the case of ACh–ROOH.

     

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: fluorescence and Krafft temperature studies

Pyrene fluorescence and Krafft temperature measurements have been carried out for various combinations of cationic gemini (m-2-m) with zwitterionic surfactants by changing the length of the hydrophobic tail over the whole mixing range. The results have been evaluated by using the regular solution theory. All the mixtures of cationic gemini+zwitterionic surfactants indicate the presence of synergistic interactions which largely decrease at higher hydrophobicity of both components. A greater amount of gemini component in the mixed micelles induces stronger synergism which reduces with the increase in the length of hydrophobic tail of the gemini component. The Krafft temperature measurements also indicate the presence of strong synergistic interactions, which decrease with increase in the length of hydrophobic tail of both components.     

Surface activities and thermodynamic properties of novel cationic surfactants with hydroxymethyl group

A new series of cationic surfactants, N–alkyl–N,N–dimethyl–N–(p–(hydroxymethyl) benzyl) ammonium chlorides (p-DHBA-m), were synthesized and the structures were characterized by ¹HNMR, ¹³CNMR, FT–IR and ESI–MS. The surface activities, thermodynamic properties and aggregation behaviors of p-DHBA-m in aqueous solutions were respectively studied by means of surface tension, isothermal titration calorimetry and steady-state fluorescence methods. Thermodynamic parameters show that the micellization is an entropy-driven process. According to the fluorescence quenching method, the micelle aggregation numbers (N_agg) of p-DHBA-m were calculated and found that the increase of temperature or the elongation of alkyl chain length could lead to the reduction of the N_agg, respectively.     

Decomposition of cumene hydroperoxide in the systems of normal and reverse micelles formed by cationic surfactants

Decomposition of cumene hydroperoxide into free radicals in aqueous and organic media in the presence of cationic surfactants at 37°C is studied by the method of inhibitors using quercetin as an acceptor of radicals. It is found that cationic surfactants catalyze the decomposition of cumene hydroperoxide into radicals, the catalytic effect in an organic medium being higher than that in an aqueous solution. Catalytic action of surfactants greatly depends on the counterion nature. Cetyltrimethylammonium chloride has the highest catalytic activity. Characteristics of surface activity of some cationic surfactants and hydroperoxides are obtained.     

The miscibility of dodecyltrihydroxyethylammonium bromide with cationic, nonionic and anionic surfactants in mixed monolayers and micelles

In this paper were analyzed the surface properties of surfactants and the miscibility and interactions between components of adsorbed monolayers and micelles formed from mixed systems. The investigated compounds differ in the structure of the polar head and represented cationic (dodecyltrihydroxyethylammonium bromide—DTEAB, dodecyltrimethylammonium bromide DTMAB), anionic (sodium dodecyl sulfate—SDS), and nonionic (dodecyl-β-d-glucoside—DG) surfactant. The experiments were based on the measurements of the surface tension of the aqueous solutions of the investigated compounds and their mixtures (cationic/nonionic—DTEAB/DG, cationic/cationic—DTEAB/DTMAB and cationic/anionic—DTEAB/SDS). The composition of the mixed films and micelles as well as the free energies of mixing values, which are a measure of the molecular interactions, was calculated basing on the equations resulting from the Motomura theory. The obtained results indicate that all the investigated systems mix nonideally both in the monolayers and micelles. The magnitude of the deviations from ideal behavior is strongly dependent on the type of the investigated mixture and increases in the following order: DTEAB/DTMAB < DTEAB/DG  DTEAB/SDS.     

Thermodynamics of micellization of cationic surfactants in aqueous solutions: consequences of the presence of the 2-acylaminoethyl moiety in the surfactant head group

The enthalpies of micellization of the following surfactant series have been determined by calorimetry: benzyl (2-acylaminoethyl)dimethylammonium chlorides, RABzMe₂Cl, and alkyldimethylbenzylammonium chlorides, RBzMe₂Cl, where A, Bz and Me refer to amide, benzyl, and methyl groups, respectively and the acyl (for RABzMe₂Cl) and/or the alkyl (for RBzMe₂Cl) groups C₁₀, C₁₂, C₁₄, and C₁₆, respectively. For both series, the shapes of the calorimetric titration curves (enthalpograms) depend on the following micellar parameters: critical micelle concentration, aggregation number, and degree of counterion binding. The calorimetric-based critical micelle concentrations are in excellent agreement with those determined by conductivity. The Gibbs free energy, the enthalpy and the entropy of micellization were calculated, and divided into contributions from the CH₂ groups of the hydrophobic tail, and the terminal CH₃ plus head group of the surfactant. For both surfactant series, all thermodynamic parameters per CH₂ group were found to be similar, since their transfer (from bulk solution to the micelle) is independent of the surfactant head-group structure. The Gibbs free energy, the enthalpy, and the entropy of transfer of the head group of RABzMe₂Cl are more favorable than their counterparts for RBzMe₂Cl, because of direct and/or water mediated hygrogen bonding of the amide groups in the micelle.     

Interaction of poly(L-glutamic acid) with cationic surfactants carrying different head groups

Three cationic surfactants carrying a common hydrocarbon tail (dodecyl group) interact differently with fully ionized poly(L-glutamic acid)(PGA), depending on the type of their ionic head groups. Decrease of pH occurred in the order; dodecylammonium chloride (DAC) > dodecyldimethylammonium chloride (DDAC) > dodecyltrimethylammonium chloride (DTAC). The-helix of PGA was strongly induced by the addition of DAC and DDAC but weakly by DTAC. The induction was inhibited when NaCl concentration was greater than 0.05 M. In the solid state, proton transfer through hydrogen bonds from ionic heads of DDAC to carboxylate groups of the polypeptide was observed. Distortion of circular dichroism spectra occurred at high mixing ratios of surfactant to polymer, due to the aggregation of-helices, as confirmed by light scattering measurements and infrared absorption spectra.     

NMR studies of mixed cationic surfactants with similar tails and dissimilar bulky head groups

The mixed micelle formation by benzyldimethylhexadecylammonium chloride (BHDACl) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium choride (HPyCl) has been studied with the help of ¹H and ¹³C NMR studies influenced by both the head-group modifications as well as mutual hydrophobicity. The results showed that the mixed micelles of BHDACl+HPyBr and BHDACl+HPyCl mixtures are significantly affected by the steric factors originating from the bulkiness of the pyridinium head group of both cosurfactants in the stern layer. The result is that BHDACl+HPyBr and BHDACl+HPyCl mixed micelles are in the state of loose micellar arrangements rather than the mixed micelles of the BHDACl+HTAB mixture. A relative comparison between Br ^- and Cl ^- counterion effect suggests that the stronger binding ability of Br ^- than Cl ^-produces relatively compact mixed micelles.