Adsorption of oppositely charged polyelectrolyte/gemini surfactant mixtures at the air/water interface and the effects of NaBr: a surface tension study

The adsorption of mixed solutions containing an anionic polyelectrolyte, carboxymethylchitosan (CMCH), and cationic gemini surfactants, alkanediyl-bis-(dimethyldodecyl-ammonium bromide) (C₁₂-s-C₁₂, s?=?2, 6, 12), has been investigated by surface tension method. The oppositely charged polyelectrolyte and the surfactants co-adsorb at the surface to form highly surface-active complexes. Combining the surface tension data with the Gibbs equation, it is referred that the surface layers of the mixed solutions have the multi-level structure, which includes the sublayers beneath an outermost layer. The gemini surfactant spacer with different length takes different conformations in the surface layers. The salt (NaBr) effects on the adsorption of the mixtures have also been studied. The spacer length of C₁₂-s-C₁₂ influences the responses of CMCH/C₁₂-s-C₁₂ mixtures to the salt effects. The comprehensive salt effects depend on the competition between the salt-enhancing effect and the salt-weakening effect.     

疏水相互作用引起Gemini表面活性剂柔性联接链的弯曲

为了理解gemini表面活性剂柔性烷基联接链在自组织过程中的特殊作用,我们合成了三种gemini表面活性剂烷基-a,w-二（二-十二烷基甲基溴化铵）（记为2C12-s-2C12×2Br (s=3, 6, 8)）。2C12-s-2C12×2Br在水表面构成铺展膜后,由于每个分子带有4根烷烃链,它们形成了稠密的烷烃尾链层。增强的烷烃尾链与联接链间的疏水相互作用促使联接链弯曲朝向空气一端,可发生弯曲的联接链长度要小于吸附在水溶液表面上的gemini表面活性剂C12-s-C12×2Br,后者每个分子只有2根烷烃链。由此可见,增强的烷烃尾链与联接链间的疏水相互作用可以有效地促进联接链的弯曲。     

Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length

The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants with different spacer length ([C₁₂–s–C₁₂im]Br₂, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence measurements. The values of cmc, γ _cmc, Γ _max, A _min, π _cmc, pc₂₀ and cmc/pc₂₀ suggest that the shorter the spacer, the higher the surface activity of [C₁₂–s–C₁₂im]Br₂ is. The cmc and γ _cmc values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl < NaBr < NaI. The thermodynamic parameters of micellization (, , ) indicate that the micellization of [C₁₂–2–C₁₂im]Br₂ and [C₁₂–4–C₁₂im]Br₂ is entropy-driven, whereas aggregation of [C₁₂–6–C₁₂im]Br₂ is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of [C₁₂–s–C₁₂im]Br₂.     

Micellization of monomeric and dimeric (gemini) surfactants in polar nonaqueous-water-mixed solvents

Dimeric or gemini surfactants are novel surfactants that are finding a great deal of discussion in the academic and industrial arena. They consist of two hydrophobic chains and two polar head groups covalently linked by a spacer. Data on critical micelle concentration (cmc) and degree of counterion dissociation (α) are reported on bis-cationic C₁₆H₃₃N⁺(CH₃)₂–(CH₂)_s–N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻, referred to as 16-s-16, for spacer lengths s=4, 5, 6 in aqueous and in polar nonaqueous (1-propanol, 2-methoxyethanol or methyl cellosolve, dimethyl sulfoxide, acetonitrile)-water-mixed solvents. The behavior is compared with conventional monomeric surfactant cetyltrimethylammonium bromide (CTAB). Thermodynamic parameters are obtained from the temperature dependence of the cmc values. It is observed that micellization tendency of the surfactants decreases in the presence of polar nonaqueous solvents. However, detailed studies with dimethylsulfoxide (DMSO) show that the geminis nearly outclass the micellization-arresting property of this solvent. Also, within geminis, higher spacer length is found suitable for showing micellization even with high DMSO content (50% v/v). The implications of these results of gemini micellization may be useful in micellar catalysis in polar nonaqueous solvents.     

Structural transition of bifunctional surfactants

Abstract  The effect of primary alcohols (butanol to hexanol) and n-hexylamine on the micellar properties of solutions of alkanediyl-α,ω-bis(dimethylcetylammonium bromide) (16-s-16, with s = 5, 6) in the absence and presence of KBr was investigated by viscometric studies at 30 ± 0.1°C. The viscosities were determined using an Ubbelohde viscometer. The viscosity values exhibit the order s = 5 > 6, i.e., the gemini with short spacer produces the more viscous solution with hexanol > pentanol > butanol. The high viscosities observed in these systems are interpreted in terms of a micellar sphere to rod transition that takes place over a certain range of concentration of the surfactants with added salt or organic additives or both. Micellar growth was higher in case of C₆H₁₃OH when compared to C₆H₁₃NH₂. In the presence of C₆H₁₃NH₂, the relative viscosity becomes almost constant when the concentration of the additive is increased, which has also been discussed in terms of electrostatic and hydrophobic forces operating in the solution. The positive synergistic effects of additives also confirm pronounced micellar growth. Graphical abstract        

Surface properties, aggregation behavior and micellization thermodynamics of a class of gemini surfactants with ethyl ammonium headgroups

Cationic gemini surfactant homologues alkanediyl-α,ω-bis(dodecyldiethylammonium bromide), [C(12)H(25)(CH(3)CH(2))(2)N(CH(2))(S)N(CH(2)CH(3))(2)C(12)H(25)]Br(2) (where S=2, 4, 6, 8, 10, 12, 16, 20), referred to as C(12)C(S)C(12)(Et) were synthesized systematically. This paper focused on various properties of the above gemini surfactants in order to give a full understanding of this series of surfactants. The following points are covered: (1) surface properties, which include (i) effect of the spacer carbon number on the general properties and (ii) the effect of added NaBr on the general surface properties; (2) aggregation behavior in bulk solution, including (i) morphologies of above gemini surfactants classed as having short spacers, middle-length spacers and long spacers and (ii) superior vesicle stability against high NaBr concentration for the long spacer gemini surfactants; (3) thermodynamic properties during micellization and the effect of spacer carbon number on them; and (4) perspectives for the further use and application of these compounds.     

Surface tension study of cationic gemini surfactants binding to DNA

Binding of cationic gemini surfactants alkanediyl-a-ω-bis(dimethyldodecylammonium bromides) with variable polymethylene spacer length ranging from 2 to 12 methylene groups to DNA in NaBr solution is investigated utilizing the tensiometry method. A simple method is presented for calculating the number of surfactant molecules bound to DNA. The results are evaluated in terms of the gemini surfactant spacer length, showing that gemini molecules with either short spacers (2 methylene groups) or long spacers are most efficiently adsorbed to DNA. A weak adsorption to DNA was found for gemini molecules with a medium spacer length (6 methylene groups in the spacer). The binding properties of cationic gemini surfactants as a function of spacer length are consistent with the results obtained by other experimental methods (dynamic light scattering measurements, fluorescence spectroscopy), indicating identical adsorption behaviour of gemini molecules as a function of the spacer length.      

Ferric nitrate in the presence of catalytic amounts of KBr or NaBr: an efficient and homoselective catalytic media for the selective oxidation of sulfides to sulfoxides

Abstract  A mild, efficient, and highly selective oxidation method of sulfides to sulfoxides using Fe(NO₃)₃·9H₂O and catalytic amounts of KBr or NaBr in the presence of wet SiO₂ (50% w/w) has been developed. A variety of aliphatic and aromatic sulfides were selectively oxidized at room temperature in good to excellent yields. Graphical abstract        

Combining TXRF,FT-IR and GC–MS information for identification of inorganic and organic components in black pigments of rock art from Alero Hornillos 2 (Jujuy,Argentina)

Archaeological samples are complex in composition since they generally comprise a mixture of materials submitted to deterioration factors largely dependent on the environmental conditions. Therefore, the integration of analytical tools such as TXRF, FT-IR and GC–MS can maximize the amount of information provided by the sample. Recently, two black rock art samples of camelid figures at Alero Hornillos 2, an archaeological site located near the town of Susques (Jujuy Province, Argentina), were investigated. TXRF, selected for inorganic information, showed the presence of manganese and iron among other elements, consistent with an iron and manganese oxide as the black pigment. Aiming at the detection of any residual organic compounds, the samples were extracted with a chloroform–methanol mixture and the extracts were analyzed by FT-IR, showing the presence of bands attributable to lipids. Analysis by GC–MS of the carboxylic acid methyl esters prepared from the sample extracts, indicated that the main organic constituents were saturated (C_16:0 and C_18:0) fatty acids in relative abundance characteristic of degraded animal fat. The presence of minor C_15:0 and C_17:0 fatty acids and branched-chain iso-C_16:0 pointed to a ruminant animal source. Figure Rock art painting at Hornillos 2 Cave, Susques, Argentina     

Steady-state fluorescence investigations of aqueous binary mixtures of myristyl alcohol based bis-sulfosuccinate anionic gemini surfactant and effect of different conventional surfactants therein

The present research work is associated with the fluorescence investigations of binary aqueous mixed surfactants solutions of anionic bis-sulfosuccinate gemini surfactant (BSGSMA_1,8) and three different conventional surfactants—anionic viz. sodium dodecyl sulfate (SDS), cationic viz. cetyl trimethyl ammonium bromide (CTAB), and nonionic surfactant viz. Triton X 100. Steady-state fluorescence spectroscopy technique has been utilized to examine the micellization behavior of aqueous solution of pure myristyl alcohol-based BSGSMA_1,8 having flexible methylene chain [(CH₂)₈] as spacer group. Critical micelle concentration (CMC), aggregation number (N), and micropolarity of pure and mixed surfactants systems were explored during the investigations. The results revealed the best synergism behavior of prepared gemini BSGSMA_1,8 with SDS as compared to CTAB and Triton X 100. The maximum reduction in the value of pyrene intensity ratio (I₁/I₃) was observed for gemini and SDS mixed surfactant solution. On the other hand, the increased I₁/I₃ value of mixed gemini with Triton X 100 exhibited that mixed surfactant system of anionic gemini BSGSMA_1,8 with non-ionic Triton X 100 is not as compact as other mixed surfactant systems. Aggregation number increased and micropolarity decreased with increased concentration of gemini surfactants.     

Synthesis and monolayer film of a series of new twin-tailed gemini cationic surfactants at the air/water interface

A series of new dimeric surfactants, twin-tailed gemini surfactants, 2(12)-s-2(12), were successfully prepared and characterized, and their monolayer films investigated by the measurement of surface pressure-area (π-A) and surface pressure-time (π-t) isotherms at the air/water interface by a Langmuir film balance. Compared to their monomeric counterparts, their collapse pressure (γ_collapse) is smaller, whilst all the molecular area parameters are larger. The limited area (A_limited) and the initial area (A_initial) of these twin-tailed gemini surfactants change with increasing spacer length s, and the surface pressure decreases with increasing time. It was also found that the higher the initial surface pressure, the larger the attenuation.      

Adsorption and micellization of alkanediyl-bis(dimethyldodecylammonium bromide) in isopropyl myristate/aqueous system

The adsorption and the micellization of a series of cationic Gemini surfactants, alkanediyl-bis(dimethyldodecylammonium bromide), referred as 12-s-12, in the isopropyl myristate (IPM)/aqueous system have been investigated using interfacial tension measurements. These surfactants showed much stronger ability for their adsorption at the IPM/water interface and micellization in the water phase in comparison with the corresponding monomer, C₁₂TABr. The adsorption and micellization behavior of 12-s-12 was found to strongly depend on the length of spacer chain, which was comparable with those studied previously in the air/water system. Compared with the compounds with short spacer chain, the 12-s-12 having a long spacer chain (s?≥?12) showed complicated behavior for their adsorption and micellization due to the bending of the long spacer chain. Thus, the adsorption process could be divided into two stages. At the beginning stage, the adsorption was diffusion-only controlled and the long spacer chain had a free conformation on the interface. At the second stage, more 12-s-12 molecules crowd into the adsorption layer and forced the long spacer chain to bend strongly in order to make room for the new molecules. This resulted in more and more tight packing of the molecules on the interface and thus a quite large limiting dilational elasticity for 12-16-12 and 12-18-12. The addition of salt greatly promoted the adsorption and micellization of 12-s-12. The present results suggested that the 12-s-12 with s?≥?12 may be a good emulsifier to construct stable emulsion.     

Synthesis and surface properties of semi-fluorinated gemini surfactants with two reactive bromo pendant groups

This paper presents a series of semi-fluorinated gemini surfactants with two bromo pendant groups. It reviews the effect of the number of methylene units in the spacer group between the two hydrophilic quaternary ammonium heads. Critical micelle concentration (cmc) and free energy of micellization (ΔG(M)(0)) of the title surfactants, in aqueous solution, have been investigated as a function of the number n of carbon atoms in the hydrocarbon spacer. We have pointed out a different behaviour as compared to Gemini hydrocarbon homologues. In the present study, when the number of methylene units (n) in the spacer increases, the cmc first decreases and reaches an optimum for (n=6), then it increases linearly from n≥6. Variations of cmc have been interpreted in terms of conformation changes of the surfactant ion and progressive penetration of the alkyl chain spacer in the micelle hydrophobic core. In this series, the increase of the hydrophobicity seems not to favour the micellisation process as expected, probably impacted by the mutual phobicity of the perfluorinated tails and the hydrocarbon spacer. A minimum is reached for a spacer with six methylene units which seems to be the optimal conformation. The free energy of micellization (ΔG(M)(0)) confirm this tendency.     

C12-s-C12·2Br与低碳醇混合水溶液胶团化行为的温度效应和焓/熵补偿

季铵盐Gemini表面活性剂C12-s-C12·2Br(s=2,3,4,6)与丙醇、丁醇、戊醇、己醇混合水溶液的In(cmc)随温度升高而逐渐增大.计算所得热力学数据表明,C12-s-C12·2Br与醇混合胶团化过程服从熵驱动机理,也出现了焓/熵补偿现象.随着温度上升,熵驱动力增大,在指定温度时,醇分子烷烃链上碳原子数n增大使△Gm0值减小,胶团结构更加稳定;而增加s使值增大,胶团稳定性下降.     

Effect of the nature of the spacer on the aggregation properties of gemini surfactants in an aqueous solution

The aggregation properties of three dicationic quaternary ammonium gemini surfactants with the same structure, except the spacer group, diethyl ether, six methylene, and p-xylyl, have been studied using electrical conductivity and fluorescence. The critical micelle concentration (cmc) and the micelle aggregation number (N) were determined, and the micropolarity and the microviscosity of the micelle were characterized. The micelle ionization degree (alpha) was obtained by a combination of the electrical conductivity data and the micelle aggregation number. Furthermore, the Gibbs free energy of micellization (deltaGmic) was studied. These results have shown that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in an aqueous solution. A hydrophilic, flexible spacer prompts micelle formation, which leads to a smaller cmc, smaller alpha, larger N, and more negative deltaGmic. Meanwhile, the microviscosity study indicates that the gemini surfactant with a hydrophilic, flexible spacer forms a more closely packed micelle structure than the one with a hydrophobic, rigid spacer.     

Adsorption and thermodynamic properties of dissymmetric gemini imidazolium surfactants with different spacer length

A series of dissymmetric gemini imidazolium surfactants with different spacer length ([C_mC_sC_nim]Br₂, m + n = 24, m = 12, 14, 16, 18; s = 2, 4, 6) were synthesized and characterized by ¹H NMR and ESI-MS spectroscopy. Their adsorption and thermodynamic properties were investigated by the surface tension and electrical conductivity methods. Consequently, the surface activity parameters (cmc, γ_cmc, π_cmc, pC₂₀, cmc/C₂₀, Γ_max, A_min) and thermodynamic parameters (ΔG_m^θ, ΔH_m^θ, ΔS_m^θ) were obtained. The effects of the dissymmetry (m/n) and the spacer length (s) on the surface activity and micellization process of surfactants have been discussed in detail.     

Effect of the spacer length on the association and adsorption behavior of dissymmetric gemini surfactants

A series of dissymmetric gemini surfactants with the general formula [C12H25(CH3)2N(CH2)sN(CH3)2C14H29]Br2 designed as 12-s-14, where s=2, 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12-s-14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length.     

Micellization behavior of anionic gemini surfactants-templated manufacture of cerium oxide nanoparticles

A series of anionic gemini surfactants (GS) were synthesized from the reactant of N, N-dimethylaminoethanol (DMEA) with dicarboxylic acid diester (DADE), after the DADE was synthesized from pyromellitic dianhydride (PMDA) and fatty alcohol. Through rational design, benzene ring was introduced into the molecular structure to work as spacer group; carboxylic acid ammonium salt with hydroxyl as functional hydrophilic head group, and double-alkyl chain performed as hydrophobic tail chains. Then, surface active properties and micellization behavior were investigated respectively. It is found that these novel molecular structure dramatically improved the surface active properties, including critical micelle concentration (CMC: 10^?3?mol/L), surface tension (γ_min: 26.5?mN/m), conductivity and absorption at interface. Moreover, GS were able to form intermolecular hydrogen bonds, which, together with rigid spacer group, greatly affected the micellization behavior in bulk solution. More importantly, the self-assembly of aggregation with different morphologies can be controlled via adjustment to solution concentration or tail chain length. Finally, GS were applied as soft templates for the shape controllable synthesis of cerium oxide (CeO₂) nanoparticles, and CeO₂ nanoparticles in diverse shapes were eventually obtained and verified, such as dorayaki shape (double-pancake shape), rod-cluster shape, lamellar shape, butterfly shape and dendrite shape.     

Removal of Congo red dye by gemini surfactant C12-4-C12 · 2Br-modified chitosan hydrogel beads

In this paper, chitosan hydrogel beads were modified with gemini surfactant C₁₂-4-C₁₂ · 2Br and then used for the adsorption and removal of Congo red dye. The effects of pH, inorganic salt, temperature, shaking rate, and surfactant concentration were investigated in detail. The gemini surfactant concentration was the main factor, and the maximum adsorption amount was observed at 0.5% C₁₂-4-C₁₂ · 2Br. The Sips isotherm model fit well with the equilibrium experimental data, and the values of the heterogeneity factor (n) indicated heterogeneous adsorption. The adsorption kinetics was found to follow the pseudo-second-order rate model better than the pseudo-first-order rate model.     

Phosphorus heterocycles: synthesis,spectroscopic study and X-ray crystallography of some new diazaphosphorinanes

New diazaphosphorinanes with formula R=C₆H₅O (2), 4-CH₃-C₆H₄NH (3), 4-NO₂-C₆H₄NH (4), R=Cl (5), 4-CH₃-C₆H₄O (6), and C₆H₅NH (7) were synthesized and characterized by ¹H, ¹³C, ³¹P NMR and IR spectroscopy and elemental analysis. The crystal structures of compounds 1 and (8) were determined using X-ray crystallography. In these structures, the P=O bond is placed in an equatorial position and the aliphatic six-membered rings show chair conformations. These compounds form two-dimensional polymeric chains via intermolecular P=O…H–N hydrogen bonds. ¹H NMR spectrum of compound 1 shows a ddd splitting pattern for the coupling of H_equatorial proton with phosphorus atom, H_axial atom, and NH proton with a high-value ³ J(PNCH) coupling constant = 26.1 Hz. But, H_axial indicates a dd splitting pattern because of the coupling with H_equatorial and NH protons. ¹³C NMR spectra of compounds 5–7, indicated high values for ³ J(P,C)_aromatic = 11.9, 11.3 and 10.2 Hz due to the coupling of the aromatic carbon atom of naphthalene moiety with the phosphorus atom. ³¹P NMR spectra indicate that the δ(³¹P) of compounds 1–4 and 8 containing NH groups connected to the aliphatic carbon atoms appear downfield relative to those of compounds 5–7 that containing NH groups connected to the aromatic naphthalene group.

---

Graphical abstract