Dicationic Gemini Research Articles

A complex and de-complex strategy to ordered mesoporous Ce0.5Zr0.5O2 with comprehensive pilot scale performances

Synthesis of ordered mesoporous ceria-zirconia (CeO2–ZrO2, M-CZ) solid solution in water-based conditions have challenged scientists for a long time due to the extremely different chemical properties of cerium and zirconium cations. This study discuss the synthesis of highly ordered mesoporous Ce0.5Zr0.5O2 solid solution in aqueous solution through a new complex and de-complex method using di-cationic Gemini as the template. The method takes advantage of the coordinative capability of citric acid (CA) to allow the coexistence of inorganic resources in mild basic solutions and uses the strong oxidic capability of H2O2 to precipitate Ce and Zr cations homogeneously. Through this strategy, the combination between inorganic–organic groups in aqueous solution was avoided, whereas coordination between inorganic–organic species was realized. Mechanisms show that the formation of peroxycarboxylic groups (–COOOH) from the reaction between metal-CA molecular and hydroxyl radical (OH) was the key process. Meso-scale micelles were formed during hydrothermal treatment, while hexagonally arranged pores with narrow size distribution were obtained in the calcination procedure. The surface area of the calcined product was 228 m2 g−1 with a pore volume of 0.7 cm3 g−1, whereas oxygen storage capacity was 652 μmol g−1. The M-CZ product illustrated fairly good pilot-scale three-way catalytic (TWC) performances thanks to the thin pore walls in the mesostructures. A complete (100%) conversion of CO and NOy at 340 °C was detected in the engine pedestal tests. The complex and de-complex strategy may provide a new route for the preparation of ordered mesoporous composite oxides.

Study of the interactions in dicationic gemini–anionic conventional mixed surfactant systems in the viewpoint of regular solution theory

In the present study, the influence of the hydrocarbon chain length of gemini surfactants on the process of micellization in mixed surfactant systems was investigated. Experiments were carried out with alkyldiyl-α, ω-bis(tetradecyldimethylammonium bromide) (m-4-m) dicationic gemini (m=14, 16)/anionic sodium dodecylbenzene sulfonate (SDBS) mixed surfactant systems in different ratios. The critical micelle concentration (cmc) values of binary mixtures of surfactants were evaluated using surface tension measurements. Results showed that mixtures of the SDBS with gemini surfactants possessed significant deviations from ideal behavior (attractive interactions). The application of the regular solution theory (RST) to experimental data yielded the interaction parameter at mixed micelles (β) and air–water interface (βσ), indicating an attractive interaction and reflecting the synergistic behavior in both the systems. The experimental mole fraction (X1) was found to be lower than the ideal mole fraction (X1ideal), the mole fractions of SDBS for both systems, provided that mixed micelles were more occupied by SDBS. In addition, the micelle aggregation number (Nagg) increased with an increase in the length of the hydrophobic tail. The micropolarity and binding constant (Ksv) values of various combinations were determined from the ratio of intensity (I1/I3) of peaks of pyrene fluorescence emission spectrum and its quenching.

Study of the Interaction Between Promazine Hydrochloride and Surfactant (Conventional/Gemini) Mixtures at Different Temperatures

In the present paper, the micellization of an amphiphilic drug, promazine hydrochloride, and gemini surfactants (16-s-16) with s = 4–6 and the monomeric hexadecyltrimethylammonium bromide (CTAB) counterparts has been examined conductometrically in the pure and mixed states in aqueous solutions at different compositions and temperatures (298.15–308.15 K). Dicationic gemini surfactants provide much better environment for the micellization behavior than the corresponding monocationic counterpart CTAB. The critical micelle concentration (cmc) values are lower than the cmc for ideal mixing, cmc id, suggesting attractive interactions between the two components in mixed micelles. The micellar mole fractions of surfactants, evaluated by different models, show greater contributions of surfactants in mixed micelles and increase with increasing concentrations of these surfactants. The negative values of β suggest synergism in the mixtures, which is highly beneficial as it reduces the total amount of surfactants required in a particular application, leading to reductions of cost and environmental impact. Activity coefficients (f 1 and f 2) are always less than unity showing nonideality in the systems. The data have been also used for evaluation of thermodynamic parameters.

Self-assembly of symmetrical and dissymmetrical dicationic surfactants in the solid phase and in solution

The effect of the spacer structure (linear, cyclic, bicyclic) and dissymmetry of alkyl fragment in a series of dicationic gemini surfactants on the ability to form thermotropic liquid crystals and on the micellar properties was studied. Transitions crystal-thermotropic liquid crystals-isotropic solution were studied using differential scanning calorimetry and optical microscopy. The self-diffusion coefficients of micelles and monomers of the dicationic dialkyl derivatives of 1,4-diazabicyclo[2.2.2]octane in water were determined by pulsed field gradient NMR spectroscopy. The effect of the surfactant structure on the values of critical micelle concentrations, hydrodynamic radii, and aggregation numbers of micelles was analyzed.

Influence of cationic gemini and conventional CTAB on the interaction of [Cr(III)-Gly-Tyr]2+ complex with ninhydrin

The kinetics of reaction between ninhydrin and [Cr(III)-Gly-Tyr]2+ complex have been studied spectrophotometrically in aqueous and aqueous–micellar media of CTAB and geminis (16-s-16, s=4, 5, 6) at 353K and pH 5.0. The reaction follows first- and fractional-order kinetics with respect to [Cr(III)-Gly-Tyr]2+ and [ninhydrin], respectively, both in the absence and presence of micelles. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is nearly 4-fold. The catalytic role of [CTAB] can be related to the extent of incorporation or association of the [Cr(III)-Gly-Tyr]2+ and ninhydrin into the micelles. Dicationic gemini surfactants provide much better environment for the reaction as compared to the corresponding monocationic counterpart CTAB. Also, whereas typical rate constant (kΨ) increase and leveling-off regions, just like CTAB, are observed with the geminis, the latter produce a third region of increasing kΨ at higher concentrations. The results obtained in micellar media are explained in terms of the pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton and Romsted). The kinetic data have been used to evaluate the micellar binding constants KS for [Cr(III)-Gly-Tyr]2+complex and KN for ninhydrin.

Micellization Studies of Dicationic Gemini Surfactants (m‐2‐m Type) in the Presence of Various Counter‐ and Co‐Ions

AbstractSalts have the ability to influence the water activity and self‐association of ionic micelles. In the present case, gemini surfactants; ethanediyl‐α,ω‐bis(dimethyl alkyl ammonium bromide) (referred to as m‐2‐m, m = 10, 12, 14) are synthesized and their micellization study in aqueous medium in presence of monovalent inorganic (NaBr, NaNO3, NaCl, KCl, LiCl) and organic salts (NaTos, NaBenz, NaSal) at 303 K is systematically investigated by conductometric and tensiometric methods. All the salts have the tendency to lower the critical micelle concentration of the surfactants. The effect of inorganic salts on the micellization properties has been found to obey the Hofmeister series. Organic salts reduce the CMC more effectively as compared to inorganic salts. The theoretical models of Rubingh and Rosen have been used to compare the results and obtain the interaction parameters, minimum area per molecule, surface excess, mixed micelle composition, activity coefficients and free energies of micellization/adsorption.

Nanocarriers from dicationic bis-imidazolium amphiphiles and their interaction with anionic drugs.

Dicationic gemini surfactants based on bis-imidazolium salts with bromide counterions were synthesized and shown to self-assemble into micellar-type structures in aqueous solution. The solubilisation capability of these micelles for anionic drugs (valproate) indicates their great potential as drug nanocarriers. A range of physicochemical techniques including surface tension, fluorescence spectroscopy, small-angle neutron scattering (SANS) and pulsed-gradient spin-echo nuclear magnetic resonance (PGSE-NMR) have been used to determine the nanocarrier (micelle) structure and to quantify the interaction of the drug with the nanocarrier. The insights gained here, structural activity relationships such as hydrophobic dependence of the CMC and drug binding isotherms, will allow for a rational optimization of molecular structure.

Effect of dicationic gemini surfactants 16–s‐16 (s = 4, 5, 6) on the ninhydrin‐dipeptide (glycyl‐tyrosine) reaction

AbstractThe effect of dicationic gemini surfactants H33C16(CH3)2N+‐(CH2)s‐N+(CH3)2 C16H33, 2Br− (s= 4, 5, 6) on the reaction of a dipeptide glycyl–tyrosine (Gly–Tyr) with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Tyr] and [ninhydrin]. The gemini surfactant micellar media are comparatively more effective than their single chain–single head counterpart cetyltrimethylammonium bromide (CTAB) micelles. Whereas typical rate constant (kΨ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produces a third region of increasing kΨ at higher concentrations. This subsequent increase is ascribed to the change in the micellar morphology of the geminis. The pseudophase model of micelles was used to quantitatively analyze the kΨ − [gemini] data, wherein the micellar‐binding constants KS for [Gly–Tyr] and KN for ninhydrin were evaluated. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 800–809, 2012

Effect of Neutral Polymer on Critical Micelle Concentration of Cationic Gemini Surfactants in Aqueous Solutions

The interaction between three PEGs (polyethylene glycol) and gemini surfactants in aqueous solution has been studied using conductometry. The surfactants studied were dicationic dibromide gemini surfactants with different methylene spacer length, 16-s-16, where s = 4 to 6 methylene groups. The critical aggregation concentration (CAC), and critical micelle concentration concentration (CMC) were derived from conductometric titration curves. The thermodynamic parameters were evaluated where ΔGmic, ΔGagg, and ΔGtrans are found to be negative, confirming the feasibility of interaction.

Micellar growth of m-2-m type gemini surfactants (m=10, 12, 14) with higher chain length alcohols/amines (C6–C8) in the absence and presence of organic salts (sodium salicylate, sodium tosylate)

Abstract The micellar growth of dicationic gemini surfactants with the general formula CmH2m + 1(CH3)2 N+(CH2)2 N+(CH3)2CmH2m + 1, 2Br− as a function of alkyl chain length (m = 10, 12, 14) and effect of addition of alcohols (C6OH, C7OH, C8OH) and amines (C6NH2, C7NH2, C8NH2) in the absence and presence of organic salts (NaSal, NaTos) have been investigated by viscosity measurements at 30 °C. A simultaneous presence of organic salt and alcohol/amine induced aggregate morphologies in the gemini micellar systems by giving high viscosity values. As the chain length of the organic additive increases, the viscosity increases with increase in additive concentration and the extent of the effect followed the sequence: C6

Morphological Changes of Cationic Gemini Surfactants 14-s-14 (s=4,5,6) in the Presence of Additives

The effect of adding aliphatic alcohols (C4OH, C5OH, C6OH) and corresponding amines (C4NH2, C5NH2, C6NH2) on a series of dicationic gemini surfactants with the general formula C14H29(CH3)2N+–(CH2)s–N+(CH3)2C14H29, 2Br− (14-s-14; s=4,5,6), in the absence and presence of KNO3, has been studied by viscosity measurements at 303.15 K. As the chain length of the additive increased, the viscosity increased with increasing additive concentration and the extent of the effect followed the sequence: C6OH>C5OH>C4OH; C6NH2>C5NH2>C4NH2. The simultaneous presence of salt and additives showed an increase in ηr values due to a synergistic effect. However, for equal chain lengths in the additives, the effect was greater for the n-alcohols. The tendency for the micelles to grow from spherical to rod-like structures is mainly influenced by the spacer chain length. At 303.15 K, the micellar growth was more pronounced for the shorter spacer, i.e. s being 4, which can be interpreted in terms of the short spacer having a higher tendency for micellar growth. Contrary to the cationic geminis, no effect was observed with a conventional surfactant of equal chain length, TTAB, even in the presence of KNO3 at the same concentration used for the geminis.

Influence of the strong electrolyte on the aggregation behavior and catalytic properties of dicationic surfactants

The introduction of potassium chloride into an aqueous solution of dicationic (gemini) surfactants results in the partial neutralization of the surface charge of micelles, which is accompanied by an increase in their size, a decrease in the critical concentration of micelle formation, a decrease in the surface potential of the system, and a change in the micellar influence on the hydrolytic stability of solubilized carboxylic esters.

Synergism in cationic gemini – additive systems

A series of dicationic gemini surfactants with the general formula C16H33(CH3)2N+−(CH2)s−N+(CH3)2C16H33, 2Br− (where s = 4–6), designated as 16-s-16, were synthesised. Their interaction with organic additives: n-alcohols (C3H7OH, C7H15OH, C8H17OH) and the corresponding amines (C3H7NH2, C7H15NH2, C8H17NH2) in the absence and presence of KNO3 at 30°C was studied viscometrically to observe their effect on assembly formation and micellar transition. The simultaneous presence of KNO3 and organics induced rich aggregates morphologies in the gemini micellar systems by giving high viscosity values. On comparing the behaviour of the gemini surfactant series for a given alkyl chain length of the organic additive, the spacer is found to markedly influence the behaviour; shorter the spacer, earlier the sphere-to-rod transition. In the case of the conventional surfactant, CTAB, the concentration of KNO3 used with the geminis was insufficient to induce any transition.

Structure and order of DODAB bilayers modulated by dicationic gemini surfactants

Cationic liposomes have been extensively studied from the experimental and theoretical standpoints, motivated both by their fundamental interest and by potential applications in drug delivery and gene therapy. However, a detailed understanding of the nature of interactions within mixed bilayers containing cationic gemini surfactants is still lacking. This work focuses on the structural and dynamic properties of DODAB membranes in the presence of dicationic gemini surfactants. A thermodynamic characterization of the phase transitions in the mixed systems has been carried out by differential scanning calorimetry, while insight into the molecular interactions in the bilayer has been provided by molecular dynamics. For this purpose, variations in the gemini spacer and tail length, as well as in the respective molar fraction, have been included in both experimental and simulation studies. The results indicate that the influence of cationic gemini surfactants upon the thermotropic behavior and degree of order of DODAB structures is controlled by a complex interplay between charge density, conformation and hydrophobic effects, for which a detailed rationale is provided.

Role of added counterions in the micellar growth of bisquaternary ammonium halide surfactant (14- s-14): 1H NMR and viscometric studies

The change in the morphology of a series of dicationic gemini surfactants C 14H 29(CH 3) 2N +−(CH 2) s −N +(CH 3) 2C 14H 29, 2Br − (14- s-14; s = 4–6) on their interaction with inorganic (KBr, KNO 3, KSCN) and organic salts (NaBenz, NaSal) have been thoroughly investigated by means of 1H NMR spectral analysis and the results are well supported by viscosity measurements. The presence of salt counterions results in structural transition (spherical to nonspherical) of gemini micelles in aqueous solution. With an increase in salt concentration all the three gemini surfactants showed changes in their aggregate morphology. This change is dependent on the nature and size of the added counterion. The effect of inorganic counterions on the micellar growth is observed to follow the Hofmeister series ( Br - < NO 3 - < SCN - ). The roles of organic counterions are discussed on the basis of probable solubilization sites of the substrate molecule in the gemini micelles, showing more growth in case of Sal − than Benz −. The results are confirmed in terms of the obtained values of chemical shift ( δ), line width at half height ( lw), and relative viscosity ( η r ). Also, the growth of micelles was most pronounced for the gemini surfactant with the shortest spacer ( s = 4). This was attributed to the unique molecular structure of gemini surfactant micelles having flexible polymethylene spacer chain linking the twin polar headgroups.

Structural variations in mesoporous materials with cubic Pm[formula omitted]n symmetry

The fine structural details of mesoporous materials possessing Pm 3 ¯ n symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity–windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity–windows. Results support that whilst attainment of Pm 3 ¯ n cubic packing is due to the overall surfactant geometry, the formation of cavity–windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.

Catalytic role of gemini surfactant micelles in the ninhydrin-L-isoleucine reaction

Effect of dicationic gemini surfactants C16H33(CH3)2N+-(CH2)s-N+(CH3)2C16H33, 2Br− (where s = 4, 5, 6) on the reaction of ninhydrin with L-isoleucine has been investigated spectrophotometrically as a function of [gemini], [L-isoleucine], [ninhydrin], and pH. The reaction follows first- and fractional-order kinetics, respectively, in [L-isoleucine] and [ninhydrin]. The gemini surfactant micellar media are found more effective for the reaction than their conventional monomeric counterpart CTAB. Furthermore, whereas typical rate constant (kψ) increase and leveling-off regions are observed with CTAB and geminis, the latter produce a third region of increasing kψ at concentrations ≥ 60 cmc’s. 1H NMR studies reveal that this unusual third-region effect of the geminis is due to changes in their micellar morphologies. Quantitative kinetic analysis has been performed on the basis of modified pseudo-phase model.

Interaction of a Cationic Gemini Surfactant with DNA and with Sodium Poly(styrene sulphonate) at the Air/Water Interface: A Neutron Reflectometry Study

The interactions between a dicationic gemini surfactant with a six-hydrocarbon spacer (1,2-bis(dodecyldimethyl-ammonio)hexane dibromide, C12C6C12Br2) and anionic polyelectrolyte DNA or sodium (polystyrene sulfonate) (NaPSS) at the air/solution interface have been studied and compared using neutron reflectometry together with surface tension. In the presence of the dichained cationic gemini surfactant, DNA and NaPSS display very different adsorption behaviors. The DNA/gemini mixtures show adsorption behavior very similar to that of DNA/C12TAB mixtures, with enhanced surfactant adsorption at low concentrations and thick structured layers at higher concentrations. However, for the NaPSS/gemini mixtures the amount of gemini at the surface is reduced relative to that in the absence of NaPSS at concentrations below the cmc. These differences in adsorption behavior are attributed to differences in the molecular structure and flexibility of the two polyanions. NaPSS is relatively hydrophobic and flexible enough to form bulk-phase polymer-micelle complexes with the gemini surfactant at low surfactant concentrations, whereas the adsorption of surface complexes is much less favorable because the dications on the gemini would require adjacent bulky pendant charges on the NaPSS to be oriented toward the surface. This would force the NaPSS to bend significantly whereas it is more favorable for the NaPSS to adopt an extended conformation at the surface. Thus, surfactant is actually removed from the surface to form bulk-phase complexes. In contrast with NaPSS, DNA has a far more rigid structure, and the charges on the backbone are at fixed intervals, factors that make the formation of surface DNA-monomer complexes much more favorable than bulk-phase DNA-micelle complexes. Finally, a short-chain sample of NaPSS consisting of only five to six segments adsorbs very strongly at the surface with the gemini to form more extensive layered structures than have previously been observed, consisting of approximately five sublayers.

Segregation and Phase Transition in Mixed Lipid Films

Energy dispersion X-ray diffraction (EDXD) was applied to investigate the structure of partly dehydrated mixed films formed by the phospholipid dimyristoyl phosphatidylcoline (DMPC) and any of the three diastereomers of the dicationic gemini surfactant (2S,3S)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium) butane dibromide. As the surfactant to lipid molar ratio (R(S/L)) increases, the gemini monotonically solubilizes the lipid bilayer promoting the formation of a cubic phase of space group Pmn segregating from the residual lamellar phase of the lipid. Finally, at R(S/)(L) = 1, the phase transition is complete. The mixed film at the highest surfactant to lipid molar ratio (R(S/L) = 2.3) was hydrated by a vapor saturated atmosphere. At full hydration, a cubic to lamellar phase transition occurs. Coarse grain dynamic investigations, carried out as a function of both the surfactant to lipid molar ratio and the number of water molecules for amphiphile unit, allowed us to elucidate the structure of the emerging cubic phase and the hydration-induced structural pathway of the cubic to lamellar phase transition observed by EDXD.

Characterization of Mixed Monolayers of Phosphatidylcholine and a Dicationic Gemini Surfactant SS-1 with a Langmuir Balance: Effects Of DNA

Monolayers of a cationic gemini surfactant, 2,3-dimethoxy-1,4-bis( N-hexadecyl- N; N-dimethyl-ammonium)butane dibromide (abbreviated as SS-1) and its mixtures with 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) were studied using a Langmuir balance. More specifically, we measured the force-area ( π- A) curves and determined the elastic area compressibility modulus ( C s −1) as a function of lateral packing pressure and the mole fraction of the cationic lipid ( X SS-1), with and without DNA in the subphase. Both SS-1 and POPC exhibited smooth compression isotherms, indicating their monolayers to be in the liquid expanded state. Even low contents ( X SS-1 < 0.05) of SS-1 in a POPC monolayer condensed the film dramatically, up to 20% at 30 mN/m. This effect is suggested to reflect reorientation of the P −-N + dipole of the POPC headgroup. Accordingly, the magnitude of the condensing effect diminishes with X SS-1 and is not observed for mixed films of dioleoylglycerol and SS-1. Reorientation of the P −-N + dipole is further supported by the pronounced increase in monolayer dipole potential ψ due to SS-1. The presence of DNA in the subphase affected the mixed POPC/SS-1 monolayers differently depending on the constituent lipid stoichiometry as well as on the DNA/SS-1 charge ratio. At a DNA concentration of 0.63 μM (in base pairs) condensation of neat POPC monolayers was evident, and this effect remained up to X SS-1 < 0.5, corresponding to DNA/SS-1 charge ratio of 1.25. An expansion due to DNA, evident as an increase in Δ A/molecule, was observed at X SS-1 > 0.5. At a higher concentration of DNA (1.88 μM base pairs) in the subphase corresponding to DNA/SS-1 charge ratio of 3.75 at X SS-1 = 0.5, condensation was observed at all values of X SS-1.