Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

In this paper we report the effect of dicationic ‘gemini’ surfactants (CH₃)₂C₁₆H₃₃N⁺? (CH₂)_m? N⁺C₁₆H₃₃(CH₃)₂, 2Br^? (where m = 4, 5, 6) on the reaction of ninhydrin with DL ‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k_ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k_ψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in ¹H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.     

Facile controlled synthesis of micro/nanostructure MCrO4 (M = Ba, Pb) by using Gemini surfactant C12-PEG-C12 as a soft template

Gemini surfactants, double sodium α-sulfonic polyethylene glycol laurate (abbreviated C₁₂-PEG-C₁₂), were prepared and applied as soft templates in the controlled synthesis of BaCrO₄ and PbCrO₄ micro/nanocrystals. The template effects were investigated by adjusting the length of the spacer, using PEG400 and PEG4000, of the Gemini surfactant. The results indicated that the size and morphology of BaCrO₄ and PbCrO₄ micro/nanocrystals varied with the change in spacer length of C₁₂-PEG-C₁₂, suggesting that the different lengths of the polyethylene glycol group spacers in the Gemini surfactants played a key role in determining the size and shape of the MCrO₄ micro/nanoparticles. The dynamic process of the formation of the novel morphology BaCrO₄ crystals showed that the morphology grew from a round-bar polyhedron, to regular polyhedron, to approximate octahedron to a uniform pistachio nut shape. The growth mechanism of the BaCrO₄ micro/nanocrystals was explained that C₁₂-PEG-C₁₂ had a greater interfacial adsorption and would effectively control the shape evolution during the crystal growth, while PbCrO₄ could be explained that the Gemini surfactants can undergo liquid-crystalline phase transitions with long channels providing a soft template effect and derived the nanorods formation. Room temperature fluorescence spectra were studied and these showed that the pistachio-shaped BaCrO₄ microcrystals and PbCrO₄ nanorods possess photoactive luminescence properties with emission peaks at 470 and 549 nm, respectively.     

Flow birefringence and stress optical law of viscoelastic solutions of cationic surfactants and sodium salicylate

The optical and rheological properties of different viscoelastic solutions of surfactant are studied in order to gather experimental data used to calculate the value of the stress optical coefficient C. Three surfactants of the same family (CTAB) have been chosen; they differ by the length of the hydrocarbon chain; it concerns the dodecyltrimethylammonium bromide (C₁₅H₃₄BrN or DoTAB), the myristyltrimethylammonium bromide (C₁₇H₃₈BrN or MyTAB), and the hexadecyltrimethylammonium bromide (C₁₉H₄₂BrN or CTAB). Different parameters like the temperature of the solution and the salinity of the solvent have been made to vary. Flow birefringence experiments and rheological measurements are performed on these solutions in order to study the dependence of the extinction angle , of the birefringence intensity and of the shear stress with the shear rate . These data are used to check the stress optical law which turns out to be valid in a wide range of shear rates. The stress optical coefficient C is then computed: it is found to vary with the salinity of the solvent and the temperature of the solution for a given surfactant. Then, for all solutions of this work the variations of C are related to the variations of the polarizability anisotropy and the persistence length. Received: 18 February 1998 / Revised: 23 June 1998 / Accepted: 22 July 1998     

The wettability of poly(tetrafluoroethylene) by aqueous solutions of ternary surfactant mixtures

Contact angle measurements on poly(tetrafluoroethylene) (PTFE) surface were carried out for the systems containing ternary mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100) and Triton X-165 (TX165). The aqueous solution of ternary surfactant mixtures were prepared by adding the third surfactant to the binary mixture of the surfactants where the synergetic effect in the reduction of the surface tension of water was determined, to compare the influence of the third surfactants on the values of surface tension of this binary mixture and the values of the contact angle on PTFE. The obtained results and calculations indicate that the ternary mixtures of CTAB + TX165 (αCTAB = 0.2, γ_LV = 60 and 50 mN/m) + TX100 (C = 10⁻⁸ to 10⁻² M) have the biggest efficiency of the reduction of contact angle of water on PTFE in comparison to aqueous solutions of the single surfactants and their binary and ternary mixtures. Also in the case of all studied ternary mixtures of surfactants at concentrations of the bulk phase corresponding to unsaturated monolayer at water-air interface the adsorption of surfactants at PTFE-water interface is different than that at water-air interface, but is the same at concentrations near the critical micelle concentration (CMC). Thus the linear dependences between γ_LV cos θ − γ_LV and cos θ − 1/γ_LV, in the range of concentration studied for all systems confirm the same adsorption at two interfaces only at C near the CMC.     

Synthesis of Novel Fluorescent Cyclohexenone Derivatives and their Partitioning Study in Ionic Micellar Media

An approach is demonstrated toward the synthesis of four novel cyclohexenone derivatives (CDs) via a convenient route of Michael addition of ethyl acetoacetate. The molecular structures of CDs were confirmed by means of FT-IR, ¹H NMR, EIMS, UV and also by X-ray single crystal structure analysis. CDs are strongly fluorescent compounds and their fluorescent spectra exhibits intense violet fluorescence. To model the binding to biological membranes the behavior of CDs in micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic surfactant, sodium dodecylsulfate (SDS) has also been examined. The characteristics of partition and binding interactions of CDs with CTAB and SDS were investigated by UV-Visible and fluorescence spectroscopic techniques. Higher values of all mentioned interactions in case of CTAB, compared to SDS, indicate that there are greater interactions between the CDs and CTAB than with SDS.     

Spectroscopic characterization approach to study surfactants effect on ZnO2 nanoparticles synthesis by laser ablation process

Zinc peroxide nanoparticles having grain size less than 5 nm were synthesized using pulsed laser ablation in aqueous solution in the presence of different surfactants and solid zinc target in 3% H₂O₂. The effect of surfactants on the optical and structure of ZnO₂ was studied by applying different spectroscopic techniques. Structural properties and grain size of the synthesized nanoparticles were studied using XRD method. The presence of the cubic phase of zinc peroxide in all samples was confirmed with XRD, and the grain sizes were 4.7, 3.7, 3.3 and 2.8 nm in pure H₂O₂, and H₂O₂ mixed with SDS, CTAB and OGM respectively. For optical characterization, FTIR transmittance spectra of ZnO₂ nanoparticles prepared with and without surfactants show a characteristic ZnO₂ absorption at 435-445 cm⁻¹. FTIR spectrum revealed that the adsorbed surfactants on zinc peroxide disappeared in case of CTAB and OGM while it appears in case of SDS. This could be due to high critical micelles SDS concentration comparing with others which is attributed to the adsorption anionic nature of this surfactant. Both FTIR and UV-vis spectra show a red shift in the presence of SDS and blue shift in the presence of CTAB and OGM. The blue shift in the absorption edge indicates the quantum confinement property of nanoparticles. The zinc peroxide nanoparticles prepared in additives-free media was also characterized by Raman spectra which show the characteristic peaks at 830-840 and 420-440 cm⁻¹.     

Effect of surfactants on the degradation of perfluorooctanoic acid (PFOA) by ultrasonic (US) treatment

Perfluorooctanoic acid (C₇F₁₅COOH, PFOA) is an aqueous anionic surfactant and a persistent organic pollutant. It can be easily adsorbed onto the bubble-water interface and both mineralized and degraded by ultrasonic (US) cavitation at room temperature. The aim of this study is to investigate whether the effect of US on the degradation of PFOA in solution can be enhanced by the addition of surfactant. To achieve this aim, we first investigated the addition of a cationic (hexadecyl trimethyl ammonium bromide, CTAB), a nonionic (octyl phenol ethoxylate, TritonX-100), and an anionic (sodium dodecyl sulfate, SDS) surfactant. We found the addition of CTAB to have increased the degradation rate the most, followed by TritonX-100. SDS inhibited the degradation rate. We then conducted further experiments characterizing the removal efficiency of CTAB at varying surfactant concentrations and solution pHs. The removal efficiency of PFOA increased with CTAB concentration, with the efficiency reaching 79% after 120 min at 25 °C with a 0.12 mM CTAB dose.     

Reactivity studies of carbon,phosphorus and sulfur‐based acyl sites with tertiary oximes in gemini surfactants

Kinetic studies of the reactions of tertiary oximes (monoisonitroso acetone; MINA and butane 2,3 dione monooxime; BDMO) with some carboxylate (p‐nitrophenyl acetate and p‐nitrophenyl benzoate), phosphate (p‐nitrophenyl diphenyl phosphate and bis (2,4‐dinitrophenyl) phosphate) and sulfonate (p‐nitrophenyl p‐toluene sulphonate) esters in gemini surfactants have been conducted. The observed first‐order rate constant versus surfactant profiles show micelle‐assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. Experimental results showed that MINA exhibited better nucleophilic activity towards ester cleavage than BDMO. Pseudophase model has been applied in order to determine micellar second‐order rate constants and binding constants. Copyright © 2013 John Wiley & Sons, Ltd.     

Chemiluminescence of phthalhydrazide derivatives in organized media: Interactions with surfactants and cyclodextrins

The chemiluminescent oxidation of some phthalhydrazide derivatives, luminol (LUM), isoluminol (ISOL), N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and N-(6-aminohexyl)-N-ethylisoluminol (AHEI), has been carried out in micellar media and in the presence of natural cyclodextrins (CDs), using Co(II) as catalyst and H₂O₂ as oxidant. The cationic cetyltrimethylammonium bromide (CTAB) and, in a lesser extent, the anionic sodium dodecyl sulfate (SDS) produce quenching in the chemiluminescence (CL) of all the luminophores at concentrations above the cmc, whereas slight enhancements are attained with the non-ionic pentaethylene glycol monododecyl ether (C₁₂E₅). On the contrary, the incorporation of the CDs to the reaction produces a remarkable intensification of the CL. Binding of the luminophores to the macrocycles and the micelles has been studied by Pulsed-Gradient-Spin-Echo-NMR (PGSE-NMR) and fluorescence anisotropy. The cationic CTAB decreases the emission mainly due to charge compensation as a result of the association of the luminophores and the luminescent intermediates to the micelles. The presence of the alkyl substituents of ABEI and AHEI provides an additional hydrophobic contribution to the binding process. SDS quenches this reaction as the micelles retain Co(II) on their anionic layer. The protection and stabilization of these luminophores or their luminescent intermediates provided by the cavities of the CDs make this family of cyclic oligosaccharides much more suitable agents than the surfactants for enhancing the CL in aqueous media for this specific reaction.     

Sensing of Micellar Microenvironment with Dual Fluorescent Probe, Triazolylpyrene (TNDMBPy)

We report a dual fluorescent triazolylpyrene ( ^TNDMB Py) as an efficient fluorescent light-up probe of various micellar microenvironments. The absorption spectra of ^TNDMB Py in an aqueous solution of varying surfactant concentration, CTAB, SDS and TX-100 showed that as the surfactant concentration was increased the absorbance increased with no shift in wavelength maxima. The increase of absorbance in each surfactant solution with increase in surfactant concentration was due to the enhanced solubilization of ^TNDMB Py in surfactant solutions. Our investigations based on steady state and time resolved fluorescence techniques showed that the probe reports the microenvironment of ionic surfactant solutions (CTAB and SDS) via dual emission (LE and ICT) at low surfactant concentration. The ICT band showed a blue shifting pattern with enhanced intensity that disappeared as the concentration of surfactant increases (> 1 mM for CTAB and > 3 mM for SDS). In non-ionic surfactant (Triton X-100) solution, the fluorophore showed dual emission with dominant ICT behaviour over LE emission at low concentration (up to 0.35 mM). In reverse micelle we observed a blue shifted ICT band with no LE band with increasing molar concentration of water. We found 100 nm blue shifting when we moved from R?=?0 to R?=?7, where R is the molar ratio of water to TX-100 (R?=?[H2O]/[TX-100]). The blue shifting of ICT band is because of the movement of the probe from hydrophilic core to hydrophobic core (surface) of the reverse micelle. Thus from the steady-state fluorescence study it was observed that the ICT band of the probe, ^TNDMB Py was more influenced by the micellar environment in comparison to the LE band. This difference in behaviour of the fluorophore is probably because of varying extent of hydrophobic/hydrogen bonding interactions experienced by the probe and its relative disposition inside the various micellar nanocores.      

Theoretical investigation of the phase behaviour of model ternary mixtures containing n-alkanes,perfluoro-n-alkanes,and perfluoroalkylalkane diblock surfactants

We have used the hetero-SAFT-VR approach developed by McCabe and collaborators [Mol. Phys. 104, 571 (2006)] to investigate the phase equilibria of a number of binary and ternary mixtures of n-alkanes, perfluoro-n-alkanes, and perfluoroalkylalkane diblock surfactants. We focused our work on the understanding of the microscopic conditions that control the phase behaviour of these mixtures, with a particular emphasis of the effect on the liquid–liquid separation and the stabilisation of n-alkane + perfluoro-n-alkane mixtures when a diblock surfactant is added. We used very simple molecular models for n-alkanes, and perfluoro-n-alkanes that describe the molecules as chains with tangentially bonded segments with molecular parameters taken from the literature. In the particular case of semifluorinated alkanes or SFA surfactants, we used an hetero-segmented diblock chain model where the parameters for the alkyl and perfluoroalkyl segments taken from the corresponding linear alkanes and perfluoroalkanes, as shown in our previous work [J. Phys. Chem. B 111, 2856 (2007)]. Our goal was to identify the main effects on the phase behaviour when different perfluoroalkylalkane surfactants are added to mixtures of n-alkanes and perfluoro-n-alkanes. We selected the n-heptane + perfluoromethane binary mixture, and studied the changes on the phase behaviour when a symmetric (same number of alkyl and perfluoroalkyl chemical groups) or an asymmetric (different number of alkyl and perfluoroalkyl chemical groups) diblock surfactants is added to the binary mixture. We have obtained the phase diagrams of a wide range of binary and ternary mixtures at different thermodynamic conditions. We have found a variety of interesting behaviours as we modify the alkyl or/and the perfluoroalkyl chain-length of the diblock surfactants: the usual changes in the vapour–liquid phase separation, changes in the type of phase diagrams (typically from type I to type V phase behaviour according to the Scott and Konynenburg classification), azeotropy, and Bancroft points. We noted that the main effect of adding a symmetric or an asymmetric surfactant to the n-heptane + perfluoromethane mixture is to stabilise the system, i.e. to decrease the two-phase (liquid–liquid) immiscibility region of the ternary diagram as the surfactant concentration is increased. This effect becomes larger as the chain length of the surfactant is increased, which is consistent with a higher number of alkyl–alkyl and perfluoroalkyl–perfluoroalkyl favourable interactions in the mixture.     

Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push-pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane-water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.     

Small angle neutron scattering study of mixed micelles of oppositely charged surfactants

Structures of mixed micelles of oppositely charged surfactants dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulphate (SDS) have been studied using small angle neutron scattering. The concentration of one of the components was kept fixed (0.3 M) and that of another varied in the range 0 to 0.1 M. The aggregation number and micellar size increase and fractional charge decreases dramatically with the addition of small amount of oppositely charged surfactant. The effect of addition of SDS on DTAB is significantly different from that of the addition of DTAB on SDS. The contrast variation SANS experiments using deuterated surfactant suggests the homogeneous mixing of two components in mixed micellar system.      

Functionalized surfactant mediated reactions of carboxylate,phosphate and sulphonate esters

Nucleophilic reactivity of some functionalized surfactants, i.e. quaternary pyridinium aldoximes towards the hydrolysis of p‐nitrophenyl acetate (PNPA), p‐nitrophenyl benzoate (PNPB), p‐nitrophenyldiphenyl phosphate (PNPDPP) and p‐nitrophenyl p‐toluene sulphonate (PNPTS) has been studied at pH 7.1 and 27 °C. Addition of functionalized surfactant to reaction medium causes progressive increase in the rate of hydrolysis and reaches a maximum and then decreases due to further addition of surfactant. An increase in the alkyl chain length of functionalized surfactants resulted in an increase in the first‐order rate constant. The apparent pK_a and CMC of functionalized surfactants have also been determined by spectrophotometric and conductometric methods, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Synergistic effects in mixed wormlike micelles of dimeric and single-chain cationic surfactants at high ionic strength

The mixed micellization between the cationic gemini surfactant [ C₁₂H₂₅( CH₃)₂N⁺( C₂H₄) N⁺( CH₃)₂ C₁₂H₂₅•2Br^-] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture. Received: 18 November 2002 / Accepted: 8 April 2003 / Published online: 27 May 2003 RID="a" ID="a"e-mail: candau@fresnel.u-strasbg.fr     

Aggregation Behavior of Monomeric Surfactants and a Gemini Cationic Surfactant by NMR and Computer Simulation Data

Aggregation of decyltrimethylammonium bromide and cetyltrimethylammonium bromide (CTAB) in D₂O has been studied. Spin–lattice relaxation time and self-diffusion coefficient of surfactant molecules were measured at concentrations below and above surfactant critical micelle concentration. The aggregation properties of conventional surfactant, CTAB, examined by nuclear magnetic resonance (NMR) and molecular dynamic (MD) simulation, were compared with the properties of double-tail analog, N,N,N′,N′-tetramethyl-N,N′dihexadecyl-1,4-butan di-ammonium di-bromide (BCTA). Both NMR and computer simulation methods suggest that micellization is a stepwise process and the pre-micellar aggregates take place in a solution at concentration below critical micelle concentration. According to MD simulation Gemini surfactant, BCTA, forms worm-like micelles, whereas CTAB, which may be considered as its “monomer”, forms only elongated micelles.     

Facile fabrication of pomponlike microarchitectures of lanthanum molybdate via an ultrasound route

Pomponlike La₂(MoO₄)₃ microstructures assembled with single-crystalline nanoflakes have been facilely fabricated via a surfactant-assisted ultrasound route for the first time. Various synthesis conditions were examined, such as the surfactant concentration, the molecular structure of surfactants, and the pH value. The obtained pomponlike microstructures were characterized by X-ray diffraction (XRD), (field-emission) scanning electron microscopy [(FE)SEM], transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. It has been revealed that a minimum concentration of sodium dodecylsulfate (SDS) was required for the formation of pomponlike La₂(MoO₄)₃ microstructures. When the SDS concentration is above 0.02 mol L⁻¹, the pomponlike microstructures become more perfect, and the size is also increased with the increasing SDS concentration. Under the same sonication, similar pomponlike microstructures were obtained when a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used instead of the anionic surfactant SDS, indicating that the hydrophobic alkyl chains are an important factor for the formation of the pomponlike La₂(MoO₄)₃ microstructures. It is also found that the pomponlike La₂(MoO₄)₃ microstructures can only be obtained within an optimal pH range of 8.0–9.0 under sonication. Based on TEM, Fourier transform infrared spectroscopy (FT-IR) and solubilization experiment, a formation mechanism of pomponlike La₂(MoO₄)₃ microstructures was proposed, in which the collaborative action of surfactants and sonication plays a key role. Furthermore, the porosity of the pomponlike La₂(MoO₄)₃ microstructures were discussed.     

Structural and electrochemical properties of polythiophene

Polythiophenes (PTs) were prepared by chemical oxidative polymerization method in presence and absence of three different (cationic - CTAB, anionic - SDS and non-ionic - Triton X-100) surfactants using FeCl₃ as oxidant. The prepared PTs were characterized by FT-IR, UV-Vis, XRD, SEM and cyclic voltammetry studies. The FT-IR spectra inferred the polymerization of thiophene and elucidate the corresponding functional groups of PTs. Our results on the UV-Vis spectra demonstrate the n−π* electronic transition of the conjugated molecules. Further the red shift in the absorption peak confirms the longer conjugation length of PTs. The amorphous nature of the PTs was inferred from the XRD pattern. The PTs prepared with surfactant exhibited different morphology compared to PT prepared without surfactant. The specific capacitances (SC) of the prepared PTs were calculated using cyclic voltammetry technique, the PT prepared with TRITRON X-100 exhibited higher SC of 117 F/g compared to SC of surfactant free PT (78 F/g). Hence, the PTs prepared with surfactants were found to be suitable electrode materials for redox supercapacitors.     

Aggregation and microenvironmental properties of gemini and conventional mixed surfactants systems: A fluorometric study

Aggregation behavior of cationic gemini (hexanediyl-1,5-bis(dimethylcettylammonium bromide) (16-5-16)) surfactant with conventional single chain surfactants cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied with the help of fluorescence measurements. Fluorescence probe is a proficient technique for examining the surfactant-surfactant interaction and aggregation. The micelle aggregation number (N _agg) was measured using steady-state fluorescence quenching method. The micelle aggregation numbers of binary combinations fall between those of constituent surfactants. The micropolarity (I ₁/I ₃), binding constant (K _sv) and dielectric constant (D _exp) of mixed systems were determined from the ratio of peaks intensity in the pyrene fluorescence spectrum. The I ₁/I ₃ values were found to be more than >1, showing more polar environment around pyrene in the mixed micelle as compared to the pure micelles.