KOH catalysed preparation of activated carbon aerogels for dye adsorption

Surfactants prevent the irreversible aggregation of partially refolded proteins, and they are also known to assist in protein refolding. A novel approach to protein refolding that utilizes a pair of low molecular weight folding assistants, a detergent and cyclodextrin, was proposed by Rozema and Gellman (D. Rozema, S.H. Gellman, J. Am. Chem. Soc. 117 (1995) 2373). We report the refolding of bovine serum albumin (BSA) assisted by these artificial chaperones, utilizing gemini surfactants for the first time. A combination of cationic gemini surfactants, bis(cetyldimethylammonium)pentane dibromide (C(16)H(33)(CH(3))(2)N(+)-(CH(2))(5)-N(+)(CH(3))(2)C(16)H(33)·2Br(-) designated as G5 and bis(cetyldimethylammonium)hexane dibromide (C(16)H(33)(CH(3))(2)N(+)-(CH(2))(6)-N(+)(CH(3))(2)C(16)H(33)·2Br(-) designated as G6 and cyclodextrins, was used to refold guanidinium chloride (GdCl) denatured BSA in the artificial chaperone assisted two step method. The single chain cationic surfactant cetyltrimethylammonium bromide (CTAB) was used for comparative studies. The studies were carried out in an aqueous medium at pH 7.0 using circular dichroism, dynamic light scattering and ANS binding studies. The denatured BSA was found to get refolded by very small concentrations of gemini surfactant at which the single chain counterpart was found to be ineffective. Different from the single chain surfactant, the gemini surfactants exhibit much stronger electrostatic and hydrophobic interactions with the protein and are thus effective at much lower concentrations. Based on the present study it is expected that gemini surfactants may prove useful in the protein refolding operations and may thus be effectively employed to circumvent the problem of misfolding and aggregation.     

Syntheses of 1-alkyl-1,2,4-triazoles and the formation of quaternary 1-alkyl-4-polyfluoroalkyl-1,2,4-triazolium salts leading to ionic liquids

1,2,4-triazole was alkylated (alkyl = methyl, butyl, heptyl, decyl) at N-1 in >90% isolated yields. The resulting 1-alkyl triazoles were quaternized at N-4 in >98% isolated yields using fluorinated alkyl halides with >98% isolated yields, under neat reaction conditions at 100-120 degrees C to form N1-CH(3)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-triazolium (Taz) iodide (m = 1, 6), N1-C(4)H(9)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-Taz iodide (m = 1, 4, 6), N1-C(7)H(15)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-Taz iodide (m = 1, 4, 6), N1-C(10)H(21)-N4-(CH(2))(2)C(m)F(2)(m)(+1)-Taz iodide (m = 1, 4), and N1-C(n)H(2)(n )(+ 1)-N4-(CH(2))(2)F-Taz bromide (n = 4, 7, 10). Single-crystal X-ray analyses confirmed the structure of [1-CH(3)-4-CH(2)CH(2)CF(3)-Taz](+)I(-). It crystallized in the orthorhombic space group Pccn, and the unit cell dimensions were a = 13.8289(9) A, b = 17.3603(11) A, c = 9.0587(6) A (alpha = beta = gamma = 90 degrees ). Metathesis of these polyfluoroalkyl-substituted triazolium halides with other salts led to the formation of quaternary compounds, some of which comprise ionic liquids, namely, [R(R(f))-Taz](+)Y(-) (Y = NTf(2), BF(4), PF(6), and OTf), in good isolated yields without the need for further purification: N1-CH(3)-N4-(CH(2))(2)C(m)F(2)(m)( +) (1)-Taz Y (m = 1, 6; Y = NTf(2)), N1-C(4)H(9)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-Taz Y (m = 1, 4, 6; Y = NTf(2)), N1- C(7)H(15)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-Taz Y (m = 1, 4, 6; Y = NTf(2)), N1-C(10)H(21)-N4-(CH(2))(2)C(m)F(2)(m)(+1)-Taz Y (n = 1, 4; Y = NTf(2)), N1-C(n)H(2)(n )(+ 1)-N4-(CH(2))(2)F-Taz Y (n = 7, 10; Y = NTf(2)), N1-C(10)H(21)-N4-(CH(2))(2)F-TazY (Y = OTf), N1-C(7)H(15)-N4-(CH(2))(2)F-TazY (Y = BF(4)), N1-C(4)H(9)-N4-(CH(2))(2)C(m)F(2)(m) (+ 1)-Taz Y (m = 4, 6; Y = PF(6)), N1-C(7)H(15)-N4-(CH(2))(2)C(4)F(9)-Taz Y (Y = PF(6)), N1-C(4)H(9)-N4-(CH(2))(2)C(m)F(2)(m)(+ 1)-Taz Y (m = 4, 6; Y = OTf). All new compounds were characterized by (1)H, (19)F, and (13)C NMR and MS spectra and elemental analyses. T(g)s and T(m)s of ionic liquids were determined by DSC.     

Crystalline structures and mesomorphic properties of gemini diammonium surfactants with a pendant hydroxyl group

A series of homologous crystals of gemini diammonium surfactants (GDAS) containing one hydroxyl substituted methylene spacer are prepared. The crystal structures of these compounds, namely [C(n)H(2)(n)(+1)-N(+) (CH(3))(2)-CH(2)CH(OH)CH(2)-N(+)(CH(3))(2)-C(n)H(2)(n)(+1)], are determined by single-crystal X-ray diffraction techniques, in order to have a better understanding of the structure relation between the solid and the mesophase. The hydroxyl groups enhance the hydrogen bonding interaction between neighboring compounds, and therefore the packing of GDAS in the solid state is arranged to form a herringbone-like mode. To the best of our knowledge, this is the first GDAS crystal with a herringbone-like structure. Their mesomorphic properties are investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray powder diffraction, and rheological measurement. These compounds have relatively low melting points and form thermotropic mesophases over a broad temperature range, as compared to those without a hydroxyl substituted at the spacer. The rheological behavior of the smectic phases clearly reveals that hydrogen bonds exert a significant effect on the high values of moduli and viscosity. Moreover, the melting point and rheological parameters increase, conforming to the length of alkyl chains.     

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(14)H(29)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(14)H(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 (1)H 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.     

Investigation of complexes formed by interaction of cationic gemini surfactants with deoxyribonucleic acid

Cationic gemini surfactants, N,N-bis(dimethylalkyl)-alpha,omega-alkanediammonium dibromide [C(m)H(2m+1)(CH(3))(2)N(+)(CH(2))(s)N(+)(CH(3))(2)C(m)H(2m+1) x 2 Br(-), or m-s-m], have proven to be effective synthetic vectors for gene delivery (transfection). Complexes (lipoplexes) of gemini compounds, where m = 12, s = 3, 12 and m = 18 : 1(oleyl), s = 2, 3, 6, with DNA have been investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), zeta potential, atomic force microscopy (AFM) and circular dichroism (CD) techniques. The results show that lipoplex properties depend on the structural properties of the gemini surfactants, the presence of the helper lipid dioleoylphosphatidylethanolamine (DOPE), and the titration sequence. ITC data show that the interaction between DNA and gemini surfactants is endothermic and the observed enthalpy vs. charge ratio profile depends upon the titration sequence. Isoelectric points (IP) of lipoplex formation were estimated from the zeta potential measurements and show good agreement with the reaction endpoints (RP) obtained from ITC. DLS data indicate that DNA is condensed in the lipoplex. AFM images suggest that the lipoplex morphology changes from isolated globular-like aggregated particles to larger-size aggregates with great diversity in morphology. This change is further accentuated by the presence of DOPE in the lipoplexes. The results are interpreted in terms of some current models of lipoplex formation.     

The Adsorption of Gemini and Conventional Surfactants onto Some Soil Solids and the Removal of 2-Naphthol by the Soil Surfaces

The adsorption of two cationic gemini surfactants, [C(n)H(2n+1) N(+)(CH(3))(2)-CH(2)CH(2)](2).2Br(-), where n=12 and 14, on limestone, sand, and clay (Na-montmorillonite) from their aqueous solution in double-distilled water and the effect of this adsorption on the removal of 2-naphthol have been studied. Compared to those of conventional cationic surfactants with similar single hydrophilic and hydrophobic groups (C(n)H(2n+1)N(+)(CH(3))(3).Br(-), where n=12 and 14), the molar adsorptions of the gemini and the conventional surfactants on Na-montmorillonite are almost identical and very close to their cation exchange capacities. On sand and limestone, the molar adsorption of the cationic gemini surfactants is much larger than that of their corresponding conventional surfactants. Adsorption studies of the pollutants onto the three kinds of solids treated by either the gemini or the conventional surfactants show that the former are both more efficient and more effective at removing 2-naphthol from the aqueous phase. On all three soil solids, the addition of KBr increases the efficiency of the adsorption of both types of cationics and for most cases increases also the maximum amount adsorbed, but decreases slightly the efficiency of removal of 2-naphthol. On limestone, the anionic gemini adsorbs with one hydrophilic group oriented toward the Ca(2+) sites on the surface and its second hydrophilic group oriented toward the aqueous phase. The conventional anionic surfactant forms a double layer. The gemini anionic is more efficient and more effective than the conventional anionic in the removal of 2-naphathol from the aqueous phase. Both anionic conventional and gemini surfactants have no adsorption on sand. The adsorption mechanisms for all the surfactants on the three soil solid surfaces are discussed. Copyright 2001 Academic Press.     

Adsorption of Gemini and Conventional Cationic Surfactants onto Montmorillonite and the Removal of Some Pollutants by the Clay

The adsorption of a series of gemini surfactants, [C(n)H(2n+1)N(+) (CH(3))(2)-CH(2)CH(2)](2).2Br(-), where n = 10, 12, 14, and 16, on clay (Na-montmorillonite) from their aqueous solution in 0.01 M KBr and the effect of this adsorption on the removal of 2-naphthol and 4-chlorophenol have been studied. Compared to those of conventional cationic surfactants with similar single hydrophilic and hydrophobic groups (C(n)H(2n+1)N(+)(CH(3))(3).Br(-), where n = 10, 12, 14, and 16), the molar adsorptions of the gemini and conventional surfactants are almost identical. This indicates that only one of the hydrophilic groups in the gemini molecule is adsorbed onto the clay and that the second hydrophilic is presumably oriented toward the aqueous phase, in contrast to the adsorption of the conventional surfactants, where the hydrophobic group is oriented toward the aqueous phase. Stability studies on dispersions of clay treated with the two types of surfactants confirm this. The slight increase in the moles of surfactant to values above the CEC of the clay with an increase in the carbon number of the hydrophobic chain indicates that adsorption through hydrophobic group interaction occurs in addition to the major ion exchange. Adsorption studies of the pollutants onto the clay treated by either the gemini or the conventional surfactants show that the former are both more efficient and more effective at removing the pollutants from the aqueous phase. Copyright 2000 Academic Press.     

Mixed monolayers of Gemini surfactants and stearic acid at the air/water interface

The properties of mixed monolayers composed of the cationic Gemini surfactant ([C(18)H(37)(CH(3))(2)N(+)(CH(2))(3)N(+)(CH(3))(2)C(18)H(37)],2Br(+), abbreviated as 18-3-18,2Br(-1)) and stearic acid (SA) at the air/water interface were investigated by using a Langmuir film balance. The excess areas at the different mixed monolayer compositions were obtained and used to evaluate the miscibility and nonideality of mixing. Due to the electrostatic attractive interactions between 18-3-18,2Br(-1) and SA, the excess areas indicated negative deviations from ideal mixing. Moreover, 18-3-18,2Br(-1) and SA were miscible at the air/water interface, as was confirmed by atomic force microscopy (AFM) images of the LB films transferred onto mica substrates. The attenuated total reflectance (ATR) infrared spectra showed that SA in the mixed monolayers was ionized completely at a composition X(SA)=0.67 and formed a "cationic-anionic surfactant," i.e., the carboxylate, with 18-3-18,2Br(-1) owing to the electrostatic interaction between the head groups.     

Role of desorption kinetics in determining marangoni flows generated by using electrochemical methods and redox-active surfactants

We report quantitative measurements of Marangoni flows generated at the surfaces of aqueous solutions by using water-soluble redox-active surfactants in combination with electrochemical methods. These measurements are interpreted within the framework of a simple model that is based on lubrication theory and the proposition that the kinetics of the desorption of redox-active surfactants from the surfaces of aqueous solutions plays a central role in determining the strength of the Marangoni flow. The model predicts that the leading edge velocity of the Marangoni flow will decay exponentially with time and that the rate constant for the decay of the velocity can yield an estimate of the surfactant desorption rate constant. Good agreement between theory and experiments was found. By interpreting experimental measurements of electrochemically generated Marangoni flows within the framework of the model, we conclude that the desorption rate constant of the redox-active surfactant Fc(CH(2))(11)-N(+)(CH(3))(3)Br(-), where Fc is ferrocene, is 0.07 s(-)(1). We also conclude that the ionic strength of the aqueous solution has little effect on the desorption rate constant of the ferrocenyl surfactant.     

Structure of the complex monolayer of gemini surfactant and DNA at the air/water interface

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.     

Effect of hydrocarbon structure of the headgroup on the thermodynamic properties of micellization of cationic gemini surfactants: an electrical conductivity study

A series of cationic gemini surfactants butanediyl-1,4-bis(dodecyldialkylammonium bromide), C(12)H(25)N(+)(C(m)H(2)(m)(+1))(2)C(4)H(8)N(+)(C(m)H(2)(m)(+1))(2)C(12)H(25)·2Br(-), where m=1, 2, 3, 4, referred to as C(12)C(4)C(12)(Me), C(12)C(4)C(12)(Et), C(12)C(4)C(12)(Pr), and C(12)C(4)C(12)(Bu), respectively, were synthesized, and their thermodynamic properties of micellization were studied by electrical conductivity measurements. There existed a minimum critical micelle concentration (cmc) in the curve of cmc versus temperature, and the temperature of the minimum of cmc (T(min)) increased with increasing the headgroup alkyl chain length. The values of log (cmc) depended linearly on carbon number of the alkyl chains, but that was not true for the carbon number of the headgroup substituents. The temperature dependence of cmc and degree of counterion association (β) were used to calculate the Gibbs free energy (Δ(mic)G°), enthalpies (Δ(mic)H°) and entropies (Δ(mic)S°) of micelle formation for these gemini surfactants, and well correlated enthalpy-entropy compensation was observed. The analyses showed C(12)C(4)C(12)(Me) and C(12)C(4)C(12)(Et) behaved similarly in terms of thermodynamics of micellization, but they behaved differently from C(12)C(4)C(12)(Pr) and C(12)C(4)C(12)(Bu), which could be ascribed to the hydrophobicity and the location of the headgroup alkyl chains in the aggregates. These initial results indicate the headgroup alkyl chain plays an important role in influencing the thermodynamic properties of gemini surfactants.     

1H NMR study on pre-micellization of quaternary ammonium gemini surfactants

Two quaternary ammonium Gemini surfactant series, 12-s-12, ([C(12)H(25)N+ (CH(3))(2)](2)(CH(2))(s).(2)Br(-)) and 14-s-14 ([C(14)H(29)N(+)(CH(3))(2)](2)(CH(2))(s).(2)Br(-)), where s = 2, 3, and 4, have been studied by the use of (1)H NMR in aqueous solution at concentrations below their critical micelle concentrations (CMC) at 25 degrees C. The appearance of a second set of peaks for the 14-s-14 series and the changes in chemical shifts, line widths, and line shapes of the 12-s-12 series with increasing concentration below the CMC are interpreted as evidence for the formation of premicelle aggregates (oligomers) that appear at approximately one-half their CMC values. Self-diffusion coefficients (D) and transverse relaxation times (T(2)) have also been detected and support the results obtained by (1)H NMR.     

Hydrophilicity of Polar and Apolar Domains of Amphiphiles

The hydrophilicity of polar and apolar domains of various amphiphiles was systematically estimated for their homologues and analogues by measuring the molar adiabatic compressibility of an aqueous solution at infinite dilution. The homologues of protic alkyl H(CH(2))(n)-, perfluoroalkyl F(CF(2))(n)-, and alkylphenyl H(CH(2))(n)(C(6)H(5))- groups (n=0-10) were chosen to represent apolar hydrophobic domains. The polar hydrophilic domains tested were -SO(4)Na, -SO(3)Na, -COONH(4), -N(CH(3))(3)Br, N(C(m)H(2m+1))(4)Br (m=1-5), and -NH(CH(2))(n)SO(3) (n=3, 4) groups. Also tested were the tetraphenyl ionic compounds (C(6)H(5))(4)MX (M=B/X=Na, M=P/X=Cl, M=As/X=Cl) to study the effect of the ionic sign of the core atom across the tetraphenyl apolar shell, the polyethylene glycols H(OCH(2)CH(2))(m)OH (m=1-4) to study the role of apolar -CH(2)- units in the hydrophilic oxyethylene group, and the zwitterionic dimethylaminoalkylsulfonate (CH(3))(2)NH(CH(2))(n)SO(3) homologues to study the effect of intramolecular salt formation on the hydrophilicity of the zwitterion. The adiabatic compressibility of the solution was calculated from measurement of the sound velocity and density of solutions. The introduction of laboratory automation and the numerical control of the system improved the accuracies and efficiencies of the measurements a great deal. The range of the temperature scan was 0-40 degrees C with an effective accuracy of +/-0.001 degrees C and the concentration was automatically scanned down to far below the cmc of the surfactant. The hydrophilicity of various polar and apolar substances was estimated as the decrease of molar adiabatic compressibility of the aqueous solution with increased concentration of their homologues and analogues. The hydrophobic hydration of nonpolar substances was found to be very small at room temperature and was barely detected above 40 degrees C; however, it became large as the temperature was lowered and attained a maximum at 0 degrees C. The cationic charge of quaternary ammonium N(+)(C(n)H(2n+1))(4) was found to enhance the hydrophobic hydration of methylene groups located at a distance of 4 to 6 ? from the core nitrogen atom, while the terminal negative charge of the anionic surfactant R-SO(4)(-), R-SO(3)(-), or R-COO(-) was found to decrease the hydrophobic hydration of -CH(2)- units within the same range. The hydrophilicity of quaternary ammonium and the tetraphenyl ions should be synergistically given by both hydrophobic and ionic hydrations. The hydrophilicity of the perfluoromethylene unit -CF(2)- was found to have a value comparable to that of the protic methylene unit -CH(2)-. The hydrophobic hydration seems to offer a good measure of the hydrophilicity of apolar substances; however, it does not necessarily represent the "hydrophobicity" of the apolar segment when the "surface activity" of the amphiphile is concerned. Copyright 2000 Academic Press.     

Polymerizable cationic gemini surfactant

A polymerizable cationic gemini surfactant, [CH(2)=C(CH(3))COO(CH(2))(11)N(+)CH(3))(2)CH(2)](2).2Br(-), 1 has been synthesized and its basic interfacial properties were investigated (in water and in the presence of 0.05 M NaBr). For comparison, the properties of monomeric surfactant corresponding to 1, CH(2)=C(CH(3))COO(CH(2))(11)N(+)(CH(3))(3).Br(-), 2, were also investigated. Parameters studied include cmc (critical micelle concentration), C(20) (required to reduce the surface tension of the solvent by 20 mN/m), gamma(cmc) (the surface tension at the cmc), Gamma(cmc) (the maximum surface excess concentration at the air/water interface), A(min) (the minimum area per surfactant molecule at the air/water interface), and cmc/C(20) ratio (a measure of the tendency to form micelles relative to adsorb at the air/water interface). For the polymerizable gemini surfactant, 1, the methacryloxy groups at the terminal of each hydrophobic group in a molecule have no contact with the air/water interface in the monolayer, whereas for the corresponding monomeric surfactant, 2, the methacryloxy group contacts at the interface forming a looped configuration like a bolaamphiphile. Polymerized micelles of the gemini surfactant are fairly small monodisperse and spherical particles with a mean diameter of 3 nm.     

Giant brainlike aggregates from new fluorocarbon/hydrocarbon hybrid cationic surfactants

A rapid synthetic procedure in two steps from perfluoroalkylethyl iodide derivatives led to 18 novel ammonium type hybrid surfactants of the general formula: R(F)(CH(2))(2)S(CH(2))(2)N(+)(CH(3))(2)R(H)Br(-) (R(F) = C(4)F(9), C(6)F(13), C(8)F(17); R(H) = C(4)H(9), C(6)H(13), C(8)H(17), C(10)H(21), C(12)H(25), C(14)H(29)). These hybrid surfactants exhibited very low surface tension (from 16 to 25 mN/m) as well as low critical micellar concentration until 1.5 × 10(-5) mol/L. A special focus was made on aggregation phenomenon as giant multilamellar "brainlike" vesicles were observed via cryogenic scanning electron microscopy (cryoSEM) and transmission electron microscopy (TEM; with a contrast agent) suggesting a high encapsulation ability and a very important specific surface of these particular organizations.     

Supra-long chain surfactants with double or triple quaternary ammonium headgroups

Novel supra-long chain surfactants with double or triple quaternary ammonium salts (C(n)-2Am, C(n)-3Am, in which n represents a hydrocarbon chain length of 18, 20, and 22) were synthesized, and electrical conductivity and surface tension were used to characterize their properties depending on both the hydrocarbon chain length and number of hydrophilic groups. The Krafft temperatures decreased remarkably with an increase in the quaternary ammonium headgroups, resulting in a high solubility in water. The critical micelle concentration (cmc) increased with an increase in the number of quaternary ammonium moieties in the hydrophilic group, and the difference in the cmc was smaller for C(n)-2Am and C(n)-3Am than for C(n)-2Am and C(n)-Am of alkyltrimethylammonium bromide. The surface tension at the cmc was approximately 45 and 48 mN m(-1) for C(n)-2Am and C(n)-3Am with n=18-22, respectively. This indicated that the supra-long chain surfactants could not efficiently adsorb at the air/water interface and orient by themselves, as is known for conventional surfactants.     

Molecular aggregates of partially fluorinated quaternary ammonium salt gemini surfactants

The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (CnFC3-2-C3CnF, where n=4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmcx5 for n=4, 115 nm at the cmcx15 for n=6, and 62 nm at the cmcx30 for n=8, at 298.2 K. The shapes of CnFC3-2-C3CnF aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small aggregates (n=4), string-like aggregates (n=6), and vesicles (n=8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants.     

Studies of mixed surfactant solutions of cationic dimeric (gemini) surfactant with nonionic surfactant C12E6 in aqueous medium

The interaction between the alkanediyl-alpha,omega-type cationic gemini surfactant, [(C(16)H(33)N(+)(CH(3))(2)(CH(2))(4)N(+)(CH(3))(2)C(16)H(33))2Br(-)], 16-4-16 and the conventional nonionic surfactant [CH(3)(CH(2))(10)CH(2)(OCH(2)CH(2))(6)OH], C(12)E(6) in aqueous medium has been investigated. The critical micelle concentrations of different mixtures have been measured by surface tension using a du Nouy tensiometer in aqueous solution at different temperatures (303, 308, and 313 K). Maximum surface excess (Gamma(max)) and minimum area per molecule (A(min)) were evaluated from a surface tension vs log(10)C (C is concentration) plot. The cmc value of the mixture was used to compute beta(m), the interaction parameter. The beta(sigma), the interaction parameter at the monolayer air-water interface, was also calculated. We observed synergism in 16-4-16/C(12)E(6) system at all concentration ratios. The micelle aggregation number (N(agg)) has been measured using a steady state fluorescence quenching method at a total surfactant concentration approximately 2 mM at 25 degrees C. The micropolarity and the binding constant (K(sv)) of mixed systems were determined from the ratio of intensity of peaks (I(1)/I(3)) of the pyrene fluorescence emission spectrum. The micellar interiors were found to be reasonably polar. We also found, using Maeda's concept, that the chain-chain interactions are very important in this system.     

A new type of intermediate, C+(BCH3)11- <--> C(BCH3)11, in a Grob fragmentation coupled with intramolecular hydride transfer. A nonclassical carbocation ylide or a carbenoid?

In solvolysis of alkyl halides Hal-(CH(2))(n)-C(BCH(3))(11)(-) (n = 2, 5, 6, but not 3, 4, or 7) and protonation of alkenes CH(2)=CH-(CH(2))(n)(-)(2)-C(BCH(3))(11)(-) (n = 3, 6, 7, but not 4 or 5) carrying the icosahedral electrofuge -C(BCH(3))(11)(-) attached through its cage carbon atom, generation of incipient positive charge on C(alpha) (as shown in Scheme 1 in the article) leads to simultaneous cleavage of the C(beta)-C(BCH(3))(11)(-) bond. The products are a C(alpha)=C(beta) alkene and a postulated intermediate C(+)(BCH(3))(11)(-) <--> C(BCH(3))(11), trapped as the adduct Nu-C(BCH(3))(11)(-) by one of the nucleophiles (Nu(-)) present. The reaction kinetics is E1, first order in the haloalkylcarborane and zero order in [Nu(-)], and the elimination appears to be concerted, as in the usual E2 mechanism. The process is best viewed as a Grob fragmentation. The loss of the longer chains involves intrachain hydride transfer from the C(alpha)-H bond to an incipient carbocation on C(delta)(') or C(epsilon)(') via a five- or six-membered cyclic transition state, respectively. The electronic structure of the postulated intermediate is believed to lie between those of a nonclassical carbonium ylide C(+)(BCH(3))(11)(-) and a carbenoid C(BCH(3))(11) whose electronic ground state resembles the S(2) state of ordinary carbenes.     

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.