Synthesis and antimicrobial activity of a series of optically active quaternary ammonium salts derived from phenylalanine

We synthesized nine quaternary ammonium compounds (QUATs) starting from phenylalanine, N-alkyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromides, which were prepared as optically pure substances. Five compounds were prepared as S-enantiomers and four compounds as R-enantiomers. These compounds were evaluated by their activities against bacteria and fungi. Three microbial strains were used in the study: the gram-negative bacteria Escherichia coli, the gram-positive bacteria Staphylococcus aureus and the fungi Candida albicans. The activities were expressed as minimum bactericidal or fungicidal concentrations (MBC). The most active compounds were (2S)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide and (2R)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide, with MBC values exceeding those of commercial benzalkoniumbromide (BAB) used as standard. The relationships between structure and biological activity of the tested QUATs were quantified by the bilinear model (QSAR) and are discussed.     

Surfactants with an amide group "spacer": Synthesis of 3-(acylaminopropyl)trimethylammonium chlorides and their aggregation in aqueous solutions

The cationic surfactants RCONH(CH2)3N+(CH3)3Cl-, where RCO = C10, C12, C14, and C16, respectively, have been synthesized by reacting the appropriate carboxylic acids with 3-N,N-dimethylamino-1-propylamine, followed by dehydration of the ammonium salt produced. Reaction of the intermediates obtained (RCONH(CH2)3N(CH3)2) with methyl iodide, followed by chloride/iodide ion-exchange furnished the surfactants. Their adsorption and aggregation in aqueous solutions have been studied by surface tension, conductivity, EMF, static light scattering and FTIR. Additional information on the micellar structure was secured from effects of the medium on the 1H NMR chemical shifts and 2D ROESY spectra. Increasing the length of the acyl moiety increased the micelle aggregation number, and decreased the minimum area/surfactant molecule at the solution/air interface, the critical micelle concentration, and the degree of dissociation of the counter-ion. Gibbs free energies of adsorption at the solution/air interface and of micelle formation were calculated, and compared to those of 2-(acylaminoethyl)trimethylammonium chloride; alkyl trimethylammonium chloride; and benzyl(3-acylaminopropyl)dimethylammonium chloride surfactants. For both processes (adsorption and micellization), contributions of the CH2 groups in the hydrophobic tail and of the head-group to DeltaG0 were calculated. The former contribution was found to be similar to those of other cationic surfactants, whereas the latter one is more negative than those of 2-(acylaminoethyl)trimethylammonium chlorides and trimethylammonium chlorides. This is attributed to a combination of increased hydrophobicity of the head-group, and (direct- or water-mediated) intermolecular hydrogen-bonding of aggregated monomers, via the amide group. FTIR and NMR results indicated that the amide group lies at the micellar interface.     

Forces between glass surfaces in mixed cationic-zwitterionic surfactant systems

We report atomic force microscopy (AFM) measurements of the forces between borosilicate glass solids in aqueous mixtures of cationic and zwitterionic surfactants. These forces are used to determine the adsorption of the surfactant as a function of the separation between the interfaces (proximal adsorption) through the application of a Maxwell relation. In the absence of cationic surfactant, the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) undergoes little adsorption to glass at concentrations up to about 2/3 critical micelle concentration (cmc). In addition, DDAPS does not have much effect on the forces over the same concentration range. In contrast, the cationic surfactant dodecylpyridinium chloride (DPC) does adsorb to glass and does affect the force between glass surfaces at concentrations much lower than the cmc. In the presence of a small amount of DPC (0.05 mM = cmc/300), the net force between the glass surfaces is quite sensitive to the solution concentration of DDAPS. A model-independent thermodynamic argument is used to show that the surface excess of DDAPS depends on the separation between the glass interfaces when the cationic surfactant is present and that the surface excess of the cationic surfactant is more sensitive to interfacial separation in the presence of the zwitterionic surfactant. The change in adsorption of the zwitterionic surfactant is explained in terms of an intermolecular coupling between the long-range electrostatic force acting on the cationic surfactant and the short-range hydrophobic interaction between the alkyl chains on the cationic and zwitterionic surfactants. The adsorptions of cationic and zwitterionic surfactants in mixtures were measured independently and simultaneously by attenuated total internal reflection infrared spectroscopy (ATR-IR). The adsorption of the zwitterionic surfactant is enhanced by the presence of a small amount of cationic surfactant.     

Aggregation behavior of p-n-alkylbenzamidinium chloride surfactants

The aggregation behavior of a novel class of surfactants, p-n-alkylbenzamidinium chlorides, has been investigated. The thermodynamics of aggregation of p-n-decylbenzamidinium chloride mixed with cationic and anionic cosurfactants has been studied using isothermal titration calorimetry. For mixtures of p-n-decylbenzamidinium chloride with n-alkyltrimethylammonium chlorides, the aggregation process is enthalpically more favorable than for the pure n-alkyltrimethylammonium chlorides, probably caused by diminished headgroup repulsion due to charge delocalization in the amidinium headgroup. A critical aggregation concentration between 3 and 4 mM has been extrapolated for p-n-decylbenzamidinium chloride at 40 degrees C, around two times lower than that of similar surfactants without charge delocalization in the headgroup and well comparable to that of similar surfactants with charge delocalization in the headgroup. In mixtures of p-n-decylbenzamidinium chloride with either sodium n-alkylsulfates or sodium dodecylbenzenesulfonate, evidence is found for the formation of bilayer aggregates by the pseudo-double-tailed catanionic surfactants composed of p-n-decylbenzamidinium and the anionic surfactant. These aggregates are solubilized to mixed micelles by excess free anionic surfactant at the measured critical aggregation concentration.     

Studies of mixed micelle formation between cationic gemini and cationic conventional surfactants

Mixed micellization of dimeric cationic surfactants tetramethylene-1,4-bis(hexadecyldimethylammonium bromide)(16-4-16), hexamethylene-1,6-bis(hexadecyldimethylammonium bromide) (16-6-16) with monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC), and tetradecyltrimethylammonium bromide (TTAB) have been studied by conductivity and steady-state fluorescence quenching techniques. The behavior of mixed systems, their compositions, and activities of the components have been analyzed in the light of Rubingh's regular solution theory. The results indicate synergism in the binary mixtures. Ideal and experimental critical micelle concentrations (i.e., cmc(*) and cmc) show nonideality, which is confirmed by beta values and activity coefficients. The micelle aggregation numbers (N(agg)), evaluated using steady-state fluorescence quenching at a total concentration of 2 mM for CTAB/16-4-16 or 16-6-16 and 5 mM for TTAB/16-4-16 or 16-6-16 systems, indicate that the contribution of conventional surfactants was always more than that of the geminis. The micropolarity, dielectric constant and binding constants (K(sv)) of mixed systems have also been evaluated from the ratios of respective peak intensities (I(1)/I(3) or I(0)/I(1)).     

Synthesis,Micellar and Surface Properties of Cationic Trisiloxane Surfactants with Different Siloxane Hydrophobic Groups

Three cationic trisiloxane surfactants, 1-methyl-1-[bis(trimethylsiloxy)methyl]silyl-propylpyrrolidinium chloride (Si₃pyCl), 1-methyl-1-[bis(triethylsiloxy)methyl]silyl-propylpyrrolidinium chloride (Et-Si₃pyCl), and 1-methyl-1-[bis(vinyldimethylsiloxy)methyl]silylpropylpyrrolidinium chloride (Vi-Si₃pyCl) were synthesized. The aggregation behavior of the trisiloxane surfactants with different siloxane hydrophobic groups in aqueous solution was investigated by surface tension and electrical conductivity measurements. The structures of hydrophobic groups of the trisiloxane surfactants can obviously influence their surface activities and thermodynamics. All the three cationic trisiloxane surfactants have excellent surface activity. Owing to the steric hindrance of hydrophobic groups, the CMC values increase following the order Et-Si₃PyCl?<?Vi-Si₃PyCl?<?Si₃PyCl. The \(\Delta G_{\text{m}}^{\text{o}}\) values increase in the order Et-Si₃PyCl?>?Vi-Si₃PyCl?>?Si₃PyCl, attributed to the decrease in the hydrophobic effect. The micellization processes of these surfactants are entropy-driven.     

Molecular mechanism and thermodynamics study of plasmid DNA and cationic surfactants interactions

The molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants were investigated by isothermal titration calorimetry (ITC), dynamic light scattering, surface tension measurements, and UV spectroscopy. The cationic surfactants studied include benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The results indicate a critical aggregation concentration (cac) of a surfactant: above the cac the surfactant forms aggregates with plasmid DNA; below the cac, however, there is no detectable interaction between DNA and surfactant. Surfactants with longer hydrocarbon chains have smaller cac, indicating that hydrophobic interaction plays a key role in DNA-surfactant complexation. Moreover, an increase in ionic strength (I) increases the cac but decreases the critical micellization concentration (cmc). These opposite effects lead to a critical ionic strength (I(c)) at which cac = cmc; when I < I(c), cac < cmc; when I > I(c), DNA does not form complexes with surfactant micelles. In the interaction DNA exhibits a pseudophase property as the cac is a constant over a wide range of DNA concentrations. ITC data showed that the reaction is solely driven by entropy because both deltaH(o) (approximately 2-6 kJ mol(-1)) and deltaS(o) (approximately 70-110 J K(-1) mol(-1)) have positive values. In the complex, the molar ratio of DNA phosphate to surfactant is in the range of 0.63-1.05. The reaction forms sub-micrometer-sized primary particles; those aggregate at high surfactant concentrations. Taken together, the results led to an inference that there is no interaction between surfactant monomers and DNA molecules and demonstrated that DNA-cationic surfactant interactions are mediated by the hydrophobic interactions of surfactant molecules and counterion binding of DNA phosphates to the cationic surfactant aggregates.     

Spectrophotometric determination of cationic surfactants by formation of ternary complexes with Fe(III) and chrome azurol

An extraction-free spectrophotometric method for the determination of cationic surfactants, such as cetylpyridinium chloride, cetyltrimethylammonium bromide and zephiramine is proposed, which is based on the formation of ternary complexes with Fe(III) and chrome azurol S. The molar ratio of the complex is 2:1:1 (Fe(III):chrome azurol S: cationic surfactant). The method is simple, rapid and sensitive, giving an apparent molar absorptivity of 4.5×10⁴ L·mol^?1-cm^?1 and a linear range of 0.1–6.0 μmol/L cationic surfactants. The total cationic surfactant content can be determined directly in aqueous solutions by measuring the absorbance at 680 nm (pH 5.8). The method has been successfully applied to water samples.     

Interaction of Ionic Surfactants with a Hydrophobic Modified Thermosensitive Polymer

The interactions of a hydrophobic modified thermosensitive polymer poly(N-isopropylacrylamide)-ran-poly(methacrylic acid)-ran-poly(octadecyl acrylate) with five ionic surfactants, namely, sodium dodecyl sulfate (SDS), dodecayltrimethylaminium bromide (DTAB), 1,2-bis(dodecyldimethylammonio)- hexane dibromide (12-6-12), 1-dodecanaminium, N,N′-[(1,4-dioxo-1,4-butanediyl) bis(oxy-2,1-ethanediyl)] bis[N,N-dimethyl-, bromide] (12-su-12), and dodecanaminium, N, N′-[[(2E)-1,4-dioxo-2-butene-1, 4-diyl]bis(o-xy-2,1ethanediy-l)] bis[N,N-dimethyl-, bromide] (12-fo-12) were investigated by the static-steady fluorescence methods using crystal violet and pyrene as the probes. It was found that the SDS interacted with the polymer driven by the hydrophobic interaction, while the cationic surfactants first entered the core of the polymer micelle through the hydrophobic interaction then the corona area of the polymer micelle through the hydrophobic and static electrical interactions. Measurements of the transmittances of the polymer/surfactants/PBS mixtures at different temperatures showed that the SDS suppressed the phase transition of the system, while additions of the cationic surfactants into the polymer induced the phase transitions of the polymer complex systems first, then suppressed them after the minimum values of the lower critical phase transition temperatures (LPTT) was reached. It was also found that increase of the MAA content in the polymer could broaden the LPTT range adjusted by the cationic surfactants.      

Spectroscopic studies on the interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants

Bovine (BSA) and human (HSA) serum albumins are frequently used in biophysical and biochemical studies since they have a similar folding, a well known primary structure, and they have been associated with the binding of many different categories of small molecules. One important difference of BSA and HSA is the fact that bovine albumin has two tryptophan residues while human albumin has a unique tryptophan. In this work results are presented for the interaction of BSA and HSA with several ionic surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cethyltrimethylammonium chloride (CTAC) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonium-1-propanesulfonate (HPS), as monitored by fluorescence spectroscopy of intrinsic tryptophans and circular dichroism spectroscopy. On the interaction of all three surfactants with BSA, at low concentrations, a quenching of fluorescence takes place and Stern-Volmer analysis allowed to estimate their 'effective' association constants to the protein: for SDS, CTAC and HPS at pH 7.0 these constants are, respectively, (1.4+/-0.1) x 10(5) M(-1), (8.9+/-0.1) x 10(3) M(-1) and (1.4+/-0.1) x 10(4) M(-1). A blue shift of maximum emission is observed from 345 to 330 nm upon surfactant binding. Analysis of fluorescence emission spectra allowed to separate three species in solution which were associated to native protein, a surfactant protein complex and partially denatured protein. The binding at low surfactant concentrations follows a Hill plot model displaying positive cooperativity and a number of surfactant binding sites very close to the number of cationic or anionic residues present in the protein. Circular dichroism data corroborated the partial loss of secondary structure upon surfactant addition showing the high stability of serum albumin. The interaction of the surfactants with HSA showed an enhancement of fluorescence at low concentrations, opposite to the effect on BSA, consistent with the existence of a unique buried tryptophan residue in this protein with considerable static quenching in the native state. The effects of surfactants at low concentrations were very similar to those of myristic acid suggesting a non specific binding through hydrophobic interaction modulated by eletrostatic interactions. The changes in the vicinity of the tryptophan residues are discussed based on the recently published crystallographic structure of HSA myristate complex (S. Curry et al., Nat. Struct. Biol. 5 (1998) 827).     

壬基酚聚氧乙烯醚型Gemini季铵盐表面活性剂的合成 及其表面性质的研究

合成了系列壬基酚聚氧乙烯醚型Gemini季铵盐表面活性剂(GNPQA), 用核磁、红外和元素分析对它们的结构进行了表征, 考察了反应条件对转化率的影响, 并用表面张力法和稳态荧光探针法对GNPQA的表面性能及胶束聚集数(N)进行了研究. 结果表明, 较优的反应条件: 反应时间为12 h, 反应温度为70 ℃, 反应原料摩尔比为n(双聚壬基酚聚氧乙烯醚)∶n(三乙胺)∶n(环氧氯丙烷)＝1∶1∶1; GNPQA的临界胶束浓度(CMC)值较相应的单体壬基酚聚氧乙烯醚型季铵盐表面活性剂(NPQA)降低了1～2个数量级, 显示了较高的表面活性; 当GNPQA溶液浓度为5～9倍CMC时, N值随浓度增大而线性增大; 随着氧乙烯(EO)单元数的增长, GNPQA的CMC和N值均逐渐减小; 结合GNPQA的表面性能参数和N值的变化规律, 探讨了这类表面活性剂表面及胶束聚集体的结构形态.     

Star-shaped trimeric quaternary ammonium bromide surfactants: adsorption and aggregation properties

Novel star-shaped trimeric surfactants consisting of three quaternary ammonium surfactants linked to a tris(2-aminoethyl)amine core were synthesized. Each ammonium had two methyls and a straight alkyl chain of 8, 10, 12, or 14 carbons. The adsorption and aggregation properties of these tris(N-alkyl-N,N-dimethyl-2-ammoniumethyl)amine bromides (3C(n)trisQ, in which n represents alkyl chain carbon number) were characterized by equilibrium and dynamic surface tension, rheology, small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. 3C(n)trisQ showed critical micelle concentrations (CMC) 1 order of magnitude lower than that of the corresponding gemini surfactants with an ethylene spacer and the corresponding monomeric surfactants. The logarithm of the CMC decreased linearly with increasing hydrocarbon chain length for 3C(n)trisQ. The slope of the line, which is well-known as Klevens equation, was larger than those of the monomeric and gemini surfactants; however, considering the total carbon number in the chains, the slope was shallower than the monomeric and was close to the gemini. Through the results such as surface tensions at the CMC (32-34 mN m(-1)) and the parameters of standard free energy, CMC/C(20) and pC(20), it was found that 3C(n)trisQ could adsorb densely at the air/water interface despite the strong electrostatic repulsion between multiple quaternary ammonium headgroups. Moreover, dynamic surface tension measurements showed that the kinetics of adsorption for 3C(n)trisQ to the air/water interface was slow because of their bulky structures. Furthermore, the results of rheology, SANS, and cryo-TEM determined that 3C(n)trisQ with n = 10 and 12 formed ellipsoidal micelles at low concentrations in solution and the structures transformed to threadlike micelles with very few branches for n = 12 as the concentration increased, but for n = 14 threadlike micelles formed at relatively low concentrations.     

The effect of the spacer rigidity on the aggregation behavior of two ester-containing Gemini surfactants

Two Gemini surfactants with very similar structure but different spacer rigidity, namely 1-dodecanaminium,N,N'-[[(2E)-1,4-dioxo-2-butene-1,4-diyl]bis(oxy-2,1-ethanediyl)]bis[N,N-dimethyl-,bromide] (12-fo-12) and 1-dodecanaminium, N,N'-[(1,4-dioxo-1,4-butanediyl)bis(oxy-2,1-ethanediyl)] bis[N,N-dimethyl-, bromide] (12-su-12), and their monomeric counterpart 1-dodecanaminium, N-[2-(acetyloxy)ethyl]-N,N-dimethyl-, bromide (DTAAB) were synthesized and their aggregation behavior in aqueous solutions was studied by measurements of surface tension, conductivity, isothermal titration calorimetry, dynamic light scattering, and transmission electron microscopy. It was found that the Krafft point of 12-fo-12 was 18.6°C, significantly higher than that of 12-su-12 (7.6°C) and DTAAB (<0°C). The minimum surface areas per surfactant A(min) at the water-air interface of DTAAB, 12-su-12, and 12-fo-12 were determined. It was found that the value of A(min) of DTAAB was larger than half that of 12-su-12 but smaller than half that of 12-fo-12. The values of the degree of association β of the three surfactants were found to be in a sequence of DTAAB>12-su-12>12-fo-12, which was in accord with the sequence of the entropy of micellization. The enthalpies of micellization of the two Gemini surfactants were found to be more negative than double that of DTAAB, and 12-fo-12 had the most negative standard enthalpy of micellization. It was also found that 12-su-12 and DTAAB formed micelles in aqueous solutions, while 12-fo-12 could form micelles and vesicles dependent on the concentration.     

Adsorption and micelle formation of alkylammonium chloride-alkyltrimethylammonium chloride mixtures

The surface tension of the aqueous solutions of binary cationic surfactant mixtures of (1) dodecylammnonium chloride (DAC)-tetradecyltrimethylammonium chloride (TTAC), (2) decylammonium chloride (DeAC)-dodecyltrimethylammonium chloride (DTAC), and (3) DAC-DTAC was measured as a function of the total molality and composition of surfactants at 298.15 K. The compositions of surfactants in the adsorbed film and micelle were evaluated and the phase diagram of adsorption and that of micelle formation were constructed. Furthermore the excess Gibbs energies of adsorption and micelle formation were calculated to estimate the deviation from the corresponding ideal mixing. It was found that the surface and micelle are enriched in trimethylammonium salts in (1) and (2), while in ammonium salt in (3) compared to the bulk solution. On the other hand, the micelle is enriched in trimethylammonium salts compared to the surface at the critical micelle concentration (CMC) in all the systems. The miscibility of the surfactants was clarified from the standpoints of the structure of the head group and of the matching between the size of polar head group of surfactants and the difference in hydrocarbon chain length.     

表面活性剂与叶酸的相互作用及其对光氧化降解的影响

表面活性剂与有机小分子作用不仅能提高表面活性剂的聚集能力,还能提高小分子的溶解度、稳定性等应用性能,因此研究二者之间的相互作用机理对于促进表面活性剂的发展和实际应用具有重要意义。本工作提出了一种利用功能有机小分子调控表面活性剂聚集行为,进而提高不稳定小分子自身稳定性的新策略。利用表面张力、紫外可见吸收光谱、荧光光谱、动态光散射、等温滴定量热和核磁共振技术研究了在p H为7.0时,叶酸分别与十二烷基硫酸钠(SDS)、十二烷基三甲基溴化铵(DTAB)、季铵盐Gemini 12-6-12和季铵盐线性三聚12-3-12-3-12四种表面活性剂之间的相互作用及其导致的叶酸光氧化降解性能的变化,结果表明,阴离子表面活性剂SDS抑制叶酸光氧化降解的效率较低,而阳离子表面活性剂都能够显著抑制叶酸的光氧化降解,且随着表面活性剂寡聚度的增加,抑制效果增强,所需表面活性剂的浓度显著降低,寡聚表面活性剂12-3-12-3-12的抑制效率高达96%。     

Synthesis,Characterization, and Surface Properties of Cationic Gemini Surfactants

New pyridinium gemini surfactants have been synthesized by esterification of renewable fatty acids with mercaptoethanol furnishing respective esters (mercaptomethyl decanoate, mercaptomethyl dodecanoate, mercaptomethyl tetradecanoate, mercaptomethyl hexadecanoate) followed by their subsequent treatment with 4-dimethyl amino pyridine resulting in the formation of title gemini surfactants: 1-(5-(decanoyloxy)-2-hydroxypentyl)-4-((5-(decanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (9), 1-(5-(dodecanoyloxy)-2-hydroxypentyl)-4-((5-(dodecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (10), 1-(5-(tetradecanoyloxy)-2-hydroxypentyl)-4-((5-(tetradecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (11), and 1-(5-(hexadecanoyloxy)-2-hydroxypentyl)-4-((5-(hexadecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (12). Their identifications are based on infrared, ¹H NMR, ¹³C NMR, distortionless enhanced polarization transfer, co-relational spectroscopy (COSY), and mass spectral studies. Their surface active properties are also evaluated on the basis of surface tension and conductivity measurements. Thermal stability of these long chain cationic gemini surfactants have been measured by thermal gravimetric analysis under nitrogen atmosphere.     

Small-angle X-ray scattering and electron paramagnetic resonance study of the interaction of bovine serum albumin with ionic surfactants

Small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) techniques have been used to monitor the interaction of bovine serum albumin (BSA) with ionic surfactants such as anionic sodium dodecyl sulfate (SDS), zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonium-1-propane sulfonate (HPS), and cationic cethyltrimethylammonium chloride (CTAC) at pH 7.0. The SAXS results have shown that in the presence of 5 mM SDS and HPS the radius of gyration (Rg) almost does not change as compared to the BSA free-surfactant solution; its value is ca. 30 Angstroms. In the presence of 5 mM CTAC the SAXS data indicate the presence of a particle with a Rg of at least 63 Angstroms, suggesting that in this case, a kind of protein aggregation takes place. In the presence of SDS and HPS surfactants at concentrations above 10 mM, a characteristic broad peak in the region of 0.12-0.18 Angstroms(-1) indicates the presence of micelle-like aggregates in solution. The SAXS curves are consistent with the "pearl necklace" model, where micelle-like aggregates are randomly distributed around the polypeptide chain. EPR results using 5-DSA and 16-DSA spin labels show that in the presence of BSA the EPR spectra are composed of two label populations, one contacting the protein and a second one due to label localization in the micelles. Evidence is also obtained for a competition of the surfactants with the spin labels for the high-affinity binding sites of the stearic acid spin labels as monitored by changes in the fractions of the two label populations as the surfactant concentration is increased. The effect of SDS seems to be stronger in the sense that increased SDS concentration leads to a complete transfer of spin labels from close protein contact sites to micelles, while for HPS, a significant immobilization of probe apparently remains even at higher surfactant concentrations. These two techniques are quite useful since SAXS monitors the overall properties of the scattering particle, while EPR gives information on the dynamics inside this particle and associated with label localization and motion.     

Interactions between zwitterionic and conventional anionic and cationic surfactants

Critical micelle concentration (cmc) values have been determined for the mixed zwitterionic/anionic surfactant systems of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/sodium dodecyl sulfate (SDS), N-dodecyl-N,N-(dimethylammonio)butyrate (DDMAB)/SDS, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-08)/sodium octyl sulfate (SOS), and the zwitterionic/cationic systems of ZW3-12/dodecyltrimethylammonium bromide (DTAB), DDMAB/DTAB. Conductivity studies and nuclear magnetic resonance (NMR) spectroscopy were the methods employed for cmc determinations. The degree of nonideality of the interaction in the micelle (beta(m)), for each system, was determined according to Rubingh's nonideal solution theory. Evidence was found for the existence of strong interactions between zwitterionic and anionic surfactants in each of the zwitterionic/anionic systems. The ZW3-08/SOS and DDMAB/SDS systems behaved synergistically at all mole fractions studied while the ZW3-12/SDS system exhibited synergistic behavior above mole fractions of 0.30. Greater negative deviations from ideal behavior were demonstrated in the DDMAB/SDS system than in the other two zwitterionic/anionic systems. The zwitterionic/cationic systems of ZW3-12/DTAB and ZW3-08/OTAB displayed only slight deviations from ideal behavior, therefore indicating near ideal mixing.     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

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.