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ABSTRACT: The association behaviors of single-chain surfactant dodecyltrimethylammonium bromide (DTAB) with double hydrophilic block co-polymers poly(ethylene glycol)-b-poly(sodium glutamate) (PEG(113)-PGlu(50) or PEG(113)-PGlu(100)) were investigated using isothermal titration microcalorimetry, cryogenic transmission electron microscopy, circular dichroism, ζ potential, and particle size measurements. The electrostatic interaction between DTAB and the oppositely charged carboxylate groups of PEG-PGlu induces the formation of super-amphiphiles, which further self-assemble into ordered aggregates. Dependent upon the charge ratios between DTAB and the glutamic acid residue of the co-polymer, the mixture solutions can change from transparent to opalescent without precipitation. Dependent upon the chain length of the PGlu block, the mixture of DTAB and PEG-PGlu diblocks can form two different aggregates at their corresponding electroneutral point. Spherical and rod-like aggregates are formed in the PEG(113)-PGlu(50)/DTAB mixture, while the vesicular aggregates are observed in the PEG(113)-PGlu(100)/DTAB mixture solution. Because the PEG(113)-PGlu(100)/DTAB super-amphiphile has more hydrophobic components than that of the PEG(113)-PGlu(50)/DTAB super-amphiphile, the former prefers forming the ordered aggregates with higher curvature, such as spherical and rod aggregates, but the latter prefers forming vesicular aggregates with lower curvature.
Langmuir 10/2012; · 4.19 Impact Factor
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ABSTRACT: Effects of calcium ions on the solubility and aggregation behavior of an anionic sulfonate gemini surfactant 1,3-bis(N-dodecyl-N-propylsulfonate sodium)-propane (12-3-12(SO(3))(2)) have been studied in aqueous solution. Compared with single-chain surfactant sodium dodecylsulfate, 12-3-12(SO(3))(2) shows much better performance to the hardness tolerance with calcium ions. Moreover aggregates of the Ca(2+)/12-3-12(SO(3))(2) complexes in clear solutions influence the morphologies of the precipitates. At 12-3-12(SO(3))(2) concentrations lower than 1.5 mM, the small spherical micelles of Ca(2+)/12-3-12(SO(3))(2) in clear solutions generate precipitates of solid particles owing to complexation of surfactant monomers with Ca(2+). At 12-3-12(SO(3))(2) concentrations higher than 1.5mM, the Ca(2+)/12-3-12(SO(3))(2) complexes transform into large compact spherical aggregates and then into long wormlike micelles. These large aggregates are well dispersed in aqueous solutions and efficiently complex calcium ions. In particular, long wormlike micelles are entangled with each other at 100.0 mM CaCl(2) and 100.0 mM 12-3-12(SO(3))(2) exhibiting viscoelastic properties. In addition, the stacking of long wormlike micelles produces precipitates with ordered fibrillar structures. This work reveals that such anionic sulfonate gemini surfactants are better candidates than single-chain surfactants in applications with high hardness levels, and the ordered aggregate structures may have potential applications in materials science.
Journal of Colloid and Interface Science 05/2012; 381(1):83-8. · 3.07 Impact Factor
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ABSTRACT: Two peptide-amphiphiles (PAs), 2C(12)-Lys-Aβ(12-17) and C(12)-Aβ(11-17)-C(12), were constructed with two alkyl chains attached to a key fragment of amyloid β-peptide (Aβ(11-17)) at different positions. The two alkyl chains of 2C(12)-Lys-Aβ(12-17) were attached to the same terminus of Aβ(12-17), while the two alkyl chains of C(12)-Aβ(11-17)-C(12) were separately attached to each terminus of Aβ(11-17). The self-assembly behavior of both the PAs in aqueous solutions was studied at 25 °C and at pHs 3.0, 4.5, 8.5, and 11.0, focusing on the effects of the attached positions of hydrophobic chains to Aβ(11-17) and the net charge quantity of the Aβ(11-17) headgroup. Cryogenic transmission electron microscopy and atomic force microscopy show that 2C(12)-Lys-Aβ(12-17) self-assembles into long stable fibrils over the entire pH range, while C(12)-Aβ(11-17)-C(12) forms short twisted ribbons and lamellae by adjusting pHs. The above fibrils, ribbons, and lamellae are generated by the lateral association of nanofibrils. Circular dichroism spectroscopy suggests the formation of β-sheet structure with twist and disorder to different extents in the aggregates of both the PAs. Some of the C(12)-Aβ(11-17)-C(12) molecules adopt turn conformation with the weakly charged peptide sequence, and the Fourier transform infrared spectroscopy indicates that the turn content increases with the pH increase. This work provides additional basis for the manipulations of the PA's nanostructures and will lead to the development of tunable nanostructure materials.
Langmuir 02/2012; 28(7):3391-6. · 4.19 Impact Factor
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ABSTRACT: Branched alkylbenzenesulfonate gemini surfactants: sodium 6,6'-(propane-1,3-diylbis(oxy))bis(3-(2-propylpentyl)benzenesulfonate) (C8BC3C8B), sodium 6,6'-(propane-1,3-diylbis(oxy))bis(3-(3,5,5-trimethylhexyl)benzenesulfonate) (C9BC3C9B), and sodium 6,6'-(propane-1,3-diylbis(oxy))bis(3-(2,4,4-trimethylpentan-2-yl)benzenesulfonate) (T-C8BC3C8B) have been synthesized. Their interfacial activity and aggregation behavior in aqueous solution were studied by surface/interface tension measurement, electrical conductivity, isothermal titration microcalorimetry, (1)H NMR spectroscopy, dynamic light scattering, steady-state fluorescence and cryogenic transmission electron microscopy. The critical aggregation concentration (CAC) and the minimum average surface area/molecule (A(min)) decrease with the decrease of the branching factor, i.e., in the order of T-C8BC3C8B, C8BC3C8B and C9BC3C9B. Moreover, alkyl side chain branches generate much more significant increases in CAC and A(min) for the gemini surfactants than single-chain surfactants. However, the branching factor does not change the air/water surface tension at CAC regularly. Instead, the air/water surface tension decreases with the increase of the carbon number of the hydrocarbon chains. In addition, it is noted that the branched gemini surfactants display high efficiency in reducing toluene/water interfacial tension. Interestingly, the increase in the branching factor leads to much more endothermic enthalpy of aggregation. All these three surfactants form spherical vesicles in aqueous solution and may present a parallel-displaced structure with a directional arrangement of the benzene ring in the vesicles.
Journal of Colloid and Interface Science 10/2011; 362(2):406-14. · 3.07 Impact Factor
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ABSTRACT: A star-shaped hexameric quaternary ammonium surfactant (PAHB), bearing six hydrophobic chains and six charged hydrophilic headgroups connected by an amide-type spacer group, was synthesized. The self-assembly behavior of the surfactant in aqueous solution was studied by surface tension, electrical conductivity, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, and NMR techniques. The results reveal that there are two critical aggregate concentrations during the process of aggregation, namely C(1) and C(2). The aggregate transitions are proved to be caused by the changes of the surfactant configuration through hydrophobic interaction among the hydrocarbon chains. Below C(1), PAHB may present a star-shaped molecular configuration due to intramolecular electrostatic repulsion among the charged headgroups, and large aggregates with network-like structure are observed. Between C(1) and C(2), the hydrophobic interaction among the hydrophobic chains may become stronger to make the hydrophobic chains of the PAHB molecules curve back and pack more closely, and then the network-like aggregates transfer to large spherical aggregates of ∼100 nm. Beyond C(2), the hydrophobic interaction may become strong enough to cause the PAHB molecular configuration to turn into a pyramid-like shape, resulting in the transition of the spherical large aggregates to spherical micelles of ∼10 nm. Interestingly, the PAHB displays high emulsification ability to linear fatty alkyls even at very low concentration.
Langmuir 08/2011; 27(17):10570-9. · 4.19 Impact Factor
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ABSTRACT: We report a finding that not only the micelles but also the premicellar aggregates of a star-like tetrameric quaternary ammonium surfactant PATC can disassemble and clear mature β-amyloid Aβ(1-40) fibrils in aqueous solution. Different from other surfactants, PATC self-assembles into network-like aggregates below its critical micelle concentration (CMC). The strong self-assembly ability of PATC even below its CMC enables PATC to disaggregate the Aβ(1-40) fibrils far below the charge neutralization point of the Aβ(1-40) with PATC. There may be two key features of the fibril disassembly induced by the surfactant. First, the positively charged surfactant molecules bind with the negatively charged Aβ(1-40) fibrils through electrostatic interaction. Second, the self-assembly of the surfactant molecules bound onto the Aβ(1-40) fibrils disaggregate the fibrils, and the surfactant molecules form mixed aggregates with the Aβ(1-40) molecules. The result reveals a structural approach of constructing efficient disassembly agents to mature β-amyloid fibrils.
Langmuir 03/2011; 27(8):4551-6. · 4.19 Impact Factor
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ABSTRACT: Gemini surfactants are constructed by two hydrophobic chains and two polar/ionic head groups covalently connected by a spacer group at the level of the head groups. Gemini surfactants possess unique structural variations and display special aggregate transitions. Their aggregation ability and aggregate structures can be more effectively adjusted through changing their molecular structures compared with the corresponding monomeric surfactants. Moreover, gemini surfactants exhibit special and useful properties while interacting with polymers and biomacromolecules. Their strong self-aggregation ability can be applied to effectively influence the aggregation behavior of both polymers and biomacromolecules. This short review is focused on the performances of gemini surfactants in aqueous solutions investigated in the last few years, and summarizes the effects of molecular structures on aggregation behavior of gemini surfactants in aqueous solution as well as the interaction of gemini surfactants with polymers and biomacromolecules respectively.
Physical Chemistry Chemical Physics 02/2011; 13(6):1939-56. · 3.57 Impact Factor
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The Journal of Physical Chemistry C. 11/2010; 114:21270-21276.
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Chemistry 10/2010; 16(44):13053-7. · 5.93 Impact Factor
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ABSTRACT: Rapid and sensitive methods to detect proteins and protein denaturation have become increasingly needful in the field of proteomics, medical diagnostics, and biology. In this paper, we have reported the synthesis of a new cationic water-soluble conjugated polymer that contains fluorene and diene moieties in the backbone (PFDE) for protein identification by sensing an array of PFDE solutions in different ionic strengths using the linear discriminant analysis technique (LDA). The PFDE can form complexes with proteins by electrostatic and/or hydrophobic interactions and exhibits different fluorescence response. Three main factors contribute to the fluorescence response of PFDE, namely, the net charge density on the protein surface, the hydrophobic nature of the protein, and the metalloprotein characteristics. The denaturation of proteins can also be detected using PFDE as a fluorescent probe. The interactions between PFDE and proteins were also studied by dynamic light scattering (DLS) and isothermal titration microcalorimetry (ITC) techniques. In contrast to other methods based on conjugated polymers, the synthesis of a series of quencher or dye-labeled acceptors or protein substrates has been avoided in our method, which significantly reduces the cost and the synthetic complexity. Our method provides promising applications on protein identification and denaturation detection in a simple, fast, and label-free manner based on non-specific interaction-induced perturbation of PFDE fluorescence response.
Chemistry - An Asian Journal 09/2010; 5(12):2524-9. · 4.50 Impact Factor
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ABSTRACT: The accumulation of a peptide of 38-43 amino acids, in the form of fibrillar plaques, was one of the essential reasons for Alzheimer's disease (AD). Discovering an agent that is able to disassemble and clear disease-associated Abeta peptide fibrils from the brains of AD patients would have critical implications not only in understanding the dynamic process of peptide aggregation but also in the development of therapeutic strategies for AD. This study reported a new finding that cationic gemini surfactant C(12)C(6)C(12)Br(2) micelles can effectively disassemble the Abeta(1-40) fibrils in vitro. Systematic comparisons with other surfactants using ThT fluorescence, AFM, and FTIR techniques suggested that the disassembly effectiveness of gemini surfactant micelles arises from their special molecular structure (i.e., positively bicharged head and twin hydrophobic chains). To track the disassembly process, systematic cryoTEM characterization was also done, which suggested a three-stage disassembly process: (i) Spherical micelles are first absorbed onto the Abeta fibrils because of attractive electrostatic interaction. (ii) Elongated fibrils then disintegrate into short pieces and form nanoscopic aggregates via synergistic hydrophobic and electrostatic interactions. (iii) Finally, complete disaggregation of fibrils and dynamic reassembly result in the formation of peptide/surfactant complexes.
Langmuir 12/2009; 26(3):1583-7. · 4.19 Impact Factor
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ABSTRACT: Dendrimers composed of G1 polyamidoamine branched with poly(propylene oxide) (PPO)-block-poly(ethylene oxide) (PEO) were synthesised for the first time. Surface tension results showed an increase in the critical aggregation concentration (cac) with PPO-b-PEO chain lengthening. The thermodynamic parameters associated with aggregate formation were determined by isothermal titration microcalorimetry, indicating that both the cac and the Gibbs free energy for aggregation (ΔG°) ascended as the amphiphilic chain length increased. The gain of entropy (ΔS°) was the main contribution to aggregation due to TΔS° being larger than the enthalpy (ΔH°). Aggregate morphology and size distribution were studied through transmission electron microscope and dynamic light scattering measurements. Furthermore, the relationship between PEO chain length and aggregation behaviour was discussed.
Supramolecular Chemistry 12/2009; 21(8):754-758. · 2.14 Impact Factor
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ABSTRACT: A star-shaped tetrameric quaternary ammonium surfactant PATC, which has four hydrophobic chains and charged hydrophilic headgroups connected by amide-type spacer group, has been synthesized in this work. Surface tension, electrical conductivity, ITC, DLS, and NMR have been used to investigate the relationship between its chemical structure and its aggregation properties. Interestingly, a large size distribution around 75 nm is observed below the critical micelle concentration (cmc) of PATC, and the large size distribution starts to decrease beyond the cmc and finally transfers to a small size distribution. It is proved that the large size premicellar aggregates may display network-like structure, and the size decrease beyond the cmc is the transition of the network-like aggregates to micelles. The possible reason is that intramolecular electrostatic repulsion among the charged headgroups below the cmc leads to a star-shaped molecular configuration, which may form the network-like aggregates through intermolecular hydrophobic interaction between hydrocarbon chains, while the hydrophobic effect becomes strong enough to turn the molecular configuration into pyramid-like shape beyond the cmc, which make the transition of network-like aggregates to micelles available.
Langmuir 11/2009; 26(1):28-33. · 4.19 Impact Factor
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ABSTRACT: The aggregation of amyloid beta-peptide (Abeta(1-40)) into fibrils is a key pathological process associated with Alzheimer's disease. This work has investigated the micellization process of biosurfactant surfactin and its effect on the aggregation behavior of Abeta(1-40). The results show that surfactin has strong self-assembly ability to form micelles and the micelles tend to form larger aggregates. Surfactin adopts a beta-turn conformation at low micelle concentration but a beta-sheet conformation at high micelle concentration. The effect of surfactin on the Abeta(1-40) aggregation behavior exhibits a strong concentration-dependent fashion. Below the critical micelle concentration of surfactin, the electrostatic binding of surfactin monomers on Abeta(1-40) causes Abeta(1-40) molecules to unfold. Assisted by the hydrophobic interaction among surfactin monomers on the Abeta(1-40) chain, the conformation of Abeta(1-40) transfers to the beta-sheet structure, which promotes the formation of fibrils. At low surfactin micelle concentration, besides the electrostatic force and hydrophobic interaction, hydrogen bonds formed between surfactin micelles and adjacent Abeta(1-40) peptide chains may promote the ordered organization of these Abeta(1-40) peptide chains, thus leading to the formation of beta-sheets and fibrils to a great extent. At high surfactin micelle concentration, the separating of Abeta(1-40) chains by the excessive surfactin micelles and the aggregation of the complexes of Abeta(1-40) with surfactin micelles inhibit the formation of beta-sheets and fibrils.
The Journal of Physical Chemistry B 12/2008; 112(47):15195-201. · 3.70 Impact Factor
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ABSTRACT: The suspending behaviors of multiple-wall carbon nanotubes (MWNTs), including pristine MWNTs (p-MWNTs) and acid-mixture-treated MWNTs (MWNTCOOH), stabilized by cationic single-chain surfactant, dodecyltrimethylammonium bromide (DTAB), and cationic gemini surfactant hexyl-alpha,beta-bis(dodecyldimethylammonium bromide) (C 12C 6C 12Br 2) were studied systematically. The surfactant structure influences the suspendability of MWNTs dramatically as well as the surfactant adsorption behavior on the nanotubes. Although both the surfactants can disperse the MWNTs effectively, they actually show different stabilizing ability. DTAB is not capable of stabilizing these two MWNTs below critical micelle concentration (CMC). However, C 12C 6C 12Br 2 can suspend both the nanotubes effectively even well below its CMC. Moreover, the adsorption of these two surfactants reaches equilibrium at twice the CMC with the original MWNT concentration of 2 mg/mL, 2 mM for C 12C 6C 12Br 2, and 30 mM for DTAB. After the adsorption equilibrium, the maximum amounts of the two suspended MWNTs in C 12C 6C 12Br 2 solution are about twice as much as those in DTAB solution. The strong hydrophobic interaction among the C 12C 6C 12Br 2 molecules and between the C 12C 6C 12Br 2 molecules and the nanotubes as well as the high charge capacity of C 12C 6C 12Br 2 lead to its much stronger adsorption ability on the MWNTs and result in its superior stabilizing ability for the MWNTs in aqueous phase. The gemini surfactant provides a possibility to effectively stabilize the MWNTs in aqueous solutions even at very low surfactant concentration well below its CMC.
The Journal of Physical Chemistry B 07/2008; 112(24):7227-33. · 3.70 Impact Factor
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ABSTRACT: A series of anionic sulfonate gemini surfactants with the general structure of [(Cn H2n+1)(C3H6SO(-)3) NCsN(C3H6SO(-)3)(CnH2n+1)].2Na+ have been synthesized. While the spacer group Cs represents p-xylyl or (CH2)3, the surfactants are abbreviated as CnCpxCn(SO3)2 (n=8,10,12) or C12C3C12(SO3)2(n=12), respectively. A corresponding monomeric surfactant C12H25N(CH3)(C3H6SO(-)3).Na+(C12NSO3) has also been prepared. The aggregation behavior of these surfactants has been studied at pH 9.2 and ionic strength of 30 mM. The gemini surfactants exhibit stronger aggregation tendencies and much less endothermic enthalpy changes of micellization (DeltaH mic) compared with the monomeric surfactant. The critical micelle concentrations (CMC) of the gemini surfactants decrease with the increase of the hydrophobic chain length from C8CpxC8(SO3)2 to C10CpxC10(SO3)2, but the CMC values of C10CpxC10(SO3)2 and C12CpxC12(SO3)2 are very close. The DeltaH mic values vary from endothermic for C8CpxC8(SO3)2 to almost zero for C12CpxC12(SO3)2. Besides, vesicles are observed above the CMC for all these surfactants. The water-mediated intermolecular hydrogen bonding between the tertiary nitrogen groups may assist C12NSO3 and C12C3C12(SO3)2 in their vesicle formation, while the pi-pi interaction between aromatic rings should be another additional driving force for the vesicle formation of CnCpxCn(SO3)2. Meanwhile, the hydrogen bonding, pi-pi interaction, and strong hydrophobic interaction provide the possibility of a multilayer formation for C12CpxC12(SO3)2 and C12C3C12(SO3)2 at the air/water interface, which is a possible reason for the extremely small minimum area occupied per surfactant molecule at the air/water interface for these two gemini surfactants.
Journal of Colloid and Interface Science 04/2008; 319(2):534-41. · 3.07 Impact Factor
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ABSTRACT: Modulation of the fibrillogenesis of amyloid peptide Abeta(1-40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) has been studied. Both UV-vis and AFM results show that C(12)C(6)C(12)Br(2) monomers can promote the fibrillogenesis of Abeta(1-40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Abeta(1-40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Abeta(1-40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Abeta(1-40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the alpha-helix to beta-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Abeta(1-40) aggregates also vary upon increasing C(12)C(6)C(12)Br(2) concentration.
The Journal of Physical Chemistry B 12/2007; 111(47):13436-43. · 3.70 Impact Factor
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ABSTRACT: Cationic surfactants N,N,N-trimethyl-10-(4-nitrophenoxy)decylammonium bromide (N10TAB) and N,N,N',N'-tetramethyl-N,N'-bis[10-(4-nitrophenoxy)decyl]-1,6-hexanediammonium dibromide (N10-6-10N), bearing aromatic nitrophenoxy groups in the ends of their hydrophobic chains, have been synthesized, and their self-assembling properties in aqueous solutions have been studied by conductivity, isothermal titration microcalorimetry, 1H NMR spectroscopy, and dynamic light scattering. Below the critical micelle concentration, N10-6-10N can form premicelles with 2 or 3 surfactant molecules. Beyond the critical micelle concentration, the two surfactants have strong self-aggregation ability and can form micelles of rather small size and with small aggregation numbers N, which are 30 +/- 3 for N10TAB and 20 +/- 2 for N10-6-10N, respectively. Also, the variations in 1H NMR signals at different surfactant concentrations provide the information on the environmental change of the surfactants upon their micellization progress. The most prominent phenomenon is the shielding effect of the aromatic groups over the protons in the aliphatic chains, implying that the nitrophenoxy groups partially insert into the micelles and face the several middle methylenes of the hydrophobic side chains.
The Journal of Physical Chemistry B 12/2007; 111(43):12439-46. · 3.70 Impact Factor
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ABSTRACT: The interaction of hydrophobically modified copolymers of acrylamide and acrylic acid, designated as PAM-C12-AA (X%) (X% indicates the percentage of acrylic acid unit and X = 5, 10, 20), with dimyristoylphosphatidylcholine (DMPC) vesicles has been studied. Complementary techniques including isothermal titration microcalorimetry (ITC), differential scanning calorimetry (DSC), turbidity measurement, calcein leakage measurement, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were used to get comprehensive information. The results show that PAM-C12-AA leads to solubilization of DMPC vesicles. There is a critical concentration (C(s)) for PAM-C12-AA to induce obvious vesicle disruption. This concentration is very close to the critical aggregation concentration (CAC) for the polymer self-aggregation. The Cs values are found to be similar for the three polymers. However, the disruption of DMPC vesicles induced by the polymers increases to a greater degree at higher AA fraction, owing to the increasing strength of interaction between the polymer and the lipid bilayer.
The Journal of Physical Chemistry B 09/2007; 111(34):10123-9. · 3.70 Impact Factor
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ABSTRACT: The adsorption of hydrophobically modified poly(acrylamide)-co-(acrylic acid), designated as PAM-C14-AA (x%) (x = 5, 10, 20, representing the mole percent of acrylic acid units), at an amino-functionalized silicon surface was studied. The effect of polymer charge density was determined by varying the acrylic acid content of the copolymer. Characteristics of the adsorbed layer were evaluated by atomic force microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy. The results showed that the adsorption behavior of PAM-C14-AA (x%) is influenced by the balance among the electrostatic, hydrogen-bonding, and hydrophobic interactions. Adjusting the solution pH and polymer charge density significantly affects the morphology and thickness of the adsorbed film. Furthermore, it was found that the adsorbed PAM-C14-AA undergoes conformational rearrangements when the surface is wetted by selected organic solvents. The resultant morphology and wettability of the films indicated that the different affinities of the solvents for different segments of PAM-C14-AA (x%) can be considered to be the possible cause of the conformational rearrangements of adsorbed polymer.
Langmuir 05/2007; 23(8):4279-85. · 4.19 Impact Factor
