Micellization of dissymmetric cationic gemini surfactants and their interaction with dimyristoylphosphatidylcholine vesicles

Improved Green Synthesis and Crystal Structures of Symmetrical Cationic Gemini Surfactants

Gemini surfactants are composed of two hydrocarbon tails with corresponding polar headgroups, linked via a covalent spacer. The synthesis of these surfactants is a very active area of research due to their application as catalysts and other applied areas of study. The modification of green microwave techniques developed in our research on ionic liquids has resulted in the significant improvement of the synthesis of N,N'-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide (m-s-m type) symmetrical gemini surfactants. This approach utilizes a remarkably more economical, green, and sustainable methodology for the production of symmetrical gemini surfactants that can be utilized in numerous commercial applications. The improved synthetic approach of these gemini surfactants has led to the characterization of their crystalline packing for the first time ever using X-ray crystallographic analysis.

Synthesis, surface activities and aggregation properties of asymmetric Gemini surfactants

A series of Gemini surfactants with an asymmetric structure (PKO 15-3(OH)-n; n = 12, 14 and 16) were synthesized through a simple two-step reaction consisting of a ring-opening reaction followed by a quaternization reaction. The surface tension measurements indicated that the surface activities of PKO 15-3(OH)-n were higher than those of traditional single-chain and symmetrical Gemini surfactants. The thermodynamic parameters obtained from electrical conductivity measurements showed that the micellization processes of PKO 15-3(OH)-n were spontaneous and entropy-driven. Transmission electron microscopy and dynamic light scattering measurements confirmed that PKO 15-3(OH)-n molecules with a higher asymmetric degree could form vesicles, in which surfactant molecules were interdigitated side-by-side in the vesicle membrane. The obtained results are not in accordance with those calculated from the critical packing theory, which can further complement the theory.

Colloidal Stabilization of Sodium Dilauraminocystine for Selective Nanoparticle-Nanoparticle Interactions: Their Screening and Extraction by Iron Oxide Magnetic Nanoparticles

Nanoparticle-nanoparticle (NP-NP) interactions between Au and Ag NPs were studied by using sodium dilauraminocystine (SDLC)- and Gemini surfactant-stabilized NPs to demonstrate the unique NP surface adsorption behavior of SDLC in controlling and mimicking such interactions in complex mixtures. They were significantly affected by the spacer as well as the polymeric nature of the head group of Gemini surfactants. A longer spacer impeded while a polymeric head group facilitated the interactions. The Au-Ag NPs interactions in an aqueous phase were also controlled by placing surface-active magnetic NPs at an aqueous-air interface, which interacted with either or both kinds of interacting NPs in an aqueous phase and reduced their ability to interact with each other. On the other hand, water-soluble zwitterionic magnetic NPs proved to be excellent extractants of both Au and Ag NPs from the aqueous phase. Extraction efficiency depended on the strength of interactions between the water-soluble magnetic NPs and aqueous-solubilized Au and/or Ag NPs.

Partition and Solubilization of Phospholipid Vesicles by Noncovalently Constructed Oligomeric-like Surfactants

This work has investigated the interaction of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles with oligomeric surfactants noncovalently formed by sodium dodecyl sulfate (SDS) and a series of polyamines, 1,3-diaminopropane (PDA), triamine, spermidine, and spermine. The partition coefficients (P) of these surfactants between lipid bilayers and the aqueous phase are measured by isothermal titration microcalorimetry (ITC), showing that the P value increases and the Gibbs free energy of the partition becomes more negative with increasing oligomerization degree of the surfactants. This changing trend is similar to that of synthetic oligomeric surfactants regardless of the charge properties, suggesting that the polyamine and SDS molecules interact with the DOPC bilayer simultaneously. Meanwhile, the DOPC solubilization by these surfactants is evaluated by the effective surfactant-to-lipid molar ratios for the onset (R_e^sat) and end (R_e^sol) of the solubilization process, which are determined from the phase boundaries obtained by ITC, turbidity, and dynamic light scattering measurements. With the increment of oligomerization degree, the R_e^sat and R_e^sol values increase anomalously and are much larger than those of the synthetic surfactants with the same oligomerization degree, suggesting that noncovalently constructed oligomeric surfactants exhibit lower solubilization ability to phospholipid vesicles than the corresponding covalent oligomeric surfactants. Therefore, the noncovalently constructed oligomeric-like surfactants facilitate strong partition but weak solubilization to phospholipid vesicles, which may provide a useful strategy to mildly adjust the permeation and fluidity of phospholipid vesicles with solubilization delay.

On the hydrophobic chains effect on critical micelle concentration of cationic gemini surfactants using molecular connectivity indices

The influence of the structure of hydrophobic tail chains on the critical micelle concentration of cationic gemini surfactants, using only the molecular connectivity indices, has been investigated in this work. The best model obtained shows that the relationship between the logarithm of critical micelle concentration and the alkyl chains length is parabolic. The formula has been derived for compounds with the same head groups and the same, medium length, spacer but with various hydrocarbon tail chains. Good-quality QSPR model obtained can be used to predict the critical micelle concentration value of structurally similar gemini surfactants as well as to design the structure of the hydrophobic tail chains to obtain new molecules more active in micelle formation.

Graphic abstract

Thermodynamic insights and molecular environments into catanionic surfactant systems: Influence of chain length and molar ratio

HYPOTHESIS

Imidazolium-based Ionic liquids as new generation cationic surfactants can provide designable alkyl chain length. In the catanionic surfactant systems, the alkyl chain lengths and molar ratios can greatly influence the interactions such as electrostatic and hydrophobic interaction. The variation in these interactions has a significant effect on the molecular environments of the self-assembly structure, and this process is always accompanied by the transition of aggregates and release or consumption of heat. Hence, it is of interest to study the relationship between intermolecular interactions, molecular environments, self-assembly structure and the change in energy of system in the catanionic surfactant mixed systems.

EXPERIMENTS

The enthalpy change ΔH of titrations the imidazolium-based into SDS micelle solution was studied to characterize the heat by using isothermal titration calorimetry (ITC) during the transitions of the aggregate structures. The corresponding self-assembly structure was monitored via cryogenic transmission electron microscopy (cryo-TEM). Employing proton magnetic resonance (¹H NMR), we focus on the interactions between imidazolium-based ILs and SDS based on the variations in the molecular environments of aggregates.

FINDINGS

Of these imidazolium-based ionic liquids/SDS system, the 1-octyl-3-methylimidazolium ([OMIM]Cl)/SDS system shows several features such as intense energy absorption and releasing processes, which indicate the formation of high entanglement wormlike micelles and vesicles. This is related to the formation of self-adjusting state between the SDS and [OMIM]Cl molecules due to the balance between the electrostatic interaction and hydrophobic interaction. Varying the alkyl chain length appears to cause significant differences to the molecular environments. From the molecular environments, three different models about the polarity of the catanionic surfactant molecules are used to explain the balance of the intermolecular interactions.

Partition of Glutamic Acid-Based Single-Chain and Gemini Amphiphiles into Phospholipid Membranes

Understanding the interactions of amphiphile molecules with biological membranes is very important to many practical applications. Amino acid amphiphiles are a kind of mild surfactants and have many unique performances. However, their interactions with phospholipid membranes have scarcely been studied. This work has studied the interactions of glutamic acid-based gemini amphiphile C₁₂(Glu)₂C₁₂ and single-chain amphiphile C₁₂Glu with the model biomembrane formed by the phospholipid 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC). The partition coefficients of C₁₂(Glu)₂C₁₂ and C₁₂Glu into the DOPC vesicles were derived from the observed enthalpy curves obtained by isothermal titration calorimetry at temperatures of 25.0 and 37.0 °C, and pHs of 5.6 and 7.4, corresponding to the skin surface and human physiological conditions. The results from cryogenic transmission electron microscopy, dynamic light scattering, and zeta potential measurements show that the amphiphile molecules form different aggregates, which make the amphiphile molecules exhibit different partition abilities to the DOPC vesicles. For C₁₂Glu, the molecules form shorter wormlike micelles with a lower surface charge at all the pHs and temperatures used, and the partition coefficient of C₁₂Glu into the DOPC vesicles does not change with temperature and pH. Differently, the C₁₂(Glu)₂C₁₂ molecules form fibers with a larger negative charge and belts with a smaller negative charge at pHs 7.4 and 5.6, respectively, no matter what temperature is used. As a result, the partitions of C₁₂(Glu)₂C₁₂ into the DOPC vesicles are markedly different at these two pH values, and the belts at pH 7.4 exhibit a stronger partition ability than the fibrils at pH 5.6. Moreover, at any temperature and pH, C₁₂(Glu)₂C₁₂ shows a stronger partition ability than C₁₂Glu. This work can help to understand the relationship between the molecular structure and aggregate structure of amino acid amphiphiles and their partition abilities into the biomembranes.

Understanding the effect of alkyl chains of gemini cations on the physicochemical and cellular properties of polyurethane micelles

Cationic gemini quaternary ammonium (GQA) has been used as a cell internalization promoter to improve the permeability of the cell membrane and enhance the cellular uptake. However, the effect of the alkyl chain length on the cellular properties of nanocarriers has not been elucidated yet. In this study, we developed a series of polyurethane micelles containing GQAs with various alkyl chain lengths. The alteration of the gemini alkyl chain length was found to change the distribution of GQA surfactants in the micellar structure and affect the surface charge exposure, stability, and the protein absorption properties of nanocarriers. Moreover, we also clarified the role of the alkyl chain length in tumor cell internalization and macrophage uptake of polyurethane micelles. This work provides a new understanding on the effect of the GQA alkyl chain length on the physicochemical and biological properties of nanomedicines, and offers guidance on the rational design of effective drug delivery systems where the issue of functional group exposure at the micellar surface should be considered.

Self-Assembly and Functions of Star-Shaped Oligomeric Surfactants

Oligomeric surfactants consist of three or more amphiphilic moieties which are connected by spacer groups covalently at the level of headgroups. It provides a possible route to bridge the gap from conventional single-chain surfactants to polymeric surfactants and leads to many profound improvements in the properties of surfactants in aqueous solution and at the air/water and water/solid interfaces. Generally, oligomeric surfactants are categorized into linear, ring-like, and star-shaped on the basis of the topological structures of their spacer groups, and their aggregation behavior strongly depends on the resultant topological structures. In recent years, we studied trimeric, tetrameric, and hexameric surfactants with a star-shaped spacer which spreads from a central site of elemental nitrogen or carbon, and their charged headgroups connect with each other through the spacers. It has been found that both the nature of spacer groups and the degree of oligomerization show important influences on the self-assembly of oligomeric surfactants and provide great possibilities in fabricating various surfactant aggregate morphologies by adjusting the molecule conformations. The unique self-assembly behavior endows them with superior physicochemical properties and potential applications. This feature article summarizes the development of star-shaped oligomeric surfactants, including self-assembly at the air/water and water/solid interfaces, self-assembly in aqueous solution, and their functions. We expect that this review could provide a comprehensive understanding of the structure-property relationship and various potential applications of star-shaped oligomeric surfactants and offer additional motivation for their future research.

Asymmetric cationic gemini surfactants: an improved synthetic procedure and the micellar and surface properties of a homologous series in the presence of simple salts

The micellar and morphological properties of symmetric, cationic gemini surfactants have been well studied in the literature as a function of nature and type of the spacer group and the length and type of hydrophobic chain. In this paper, we have examined the effects of tail asymmetry on the properties of a series of cationic surfactants, the N-alkyl-1-N′-alkyl-2-N,N,N′,N′-tetramethyldiammonium dibromide. A novel synthetic method is used to prepare a series of these surfactants and the consequences of asymmetry on micellar properties are presented. This new method has been shown to be more efficient, with higher yields of the asymmetric surfactants than the yields of the accepted literature method. The critical micelle concentration values and the micelle sizes of the asymmetric gemini surfactants, 12-4-12, 12-4-10, 12-4-8, and 12-4-6 gemini surfactants, were obtained from conductivity and dynamic light scattering. With increasing chain asymmetry, the size of the micelle increased due to the formation of loose micelles. The addition of NaCl and Na2SO4 to the surfactant solutions increased the aggregate size, and this effect was more pronounced with increasing salt concentrations. These results are interpreted in terms of the effect these ions have on the “compactness” of the micelle structure.

Advances in the synthesis, molecular architectures and potential applications of gemini surfactants

Gemini surfactants have been the subject of intensive scrutiny by virtue of their unique combination of physical and chemical properties and being used in ordinary household objects to multifarious industrial processes. In this review, we summarize the recent developments of gemini surfactants, highlighting the classification of gemini surfactants based on the variation in headgroup polarity, flexibility/rigidity of spacer, hydrophobic alkyl chain and counterion along with potential applications of gemini surfactants, depicting the truly remarkable journey of gemini surfactants that has just come of age. We have focused on those objectives which will act as suitable candidates to take the field forward. The preceding information will permit us to estimate the effect of structural variation on the aggregation behavior of gemini surfactants for nanoscience and biological applications like antimicrobial, anti-fungal agent, better gene and drug delivery agent with low cytotoxicity and biodegradability, which makes them more advantageous for a number of technological processes and hence reduces the impact of these gemini surfactants on the environment.

Interactions of Phospholipid Vesicles with Cationic and Anionic Oligomeric Surfactants

This work studied the interactions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with cationic ammonium surfactants and anionic sulfate or sulfonate surfactants of different oligomeric degrees, including cationic monomeric DTAB, dimeric C₁₂C₃C₁₂Br₂, and trimeric DDAD as well as anionic monomeric SDS, dimeric C₁₂C₃C₁₂(SO₃)₂, and trimeric TED-(C₁₀SO₃Na)₃. The partition coefficient P of these surfactants between the DOPC vesicles and water was determined with isothermal titration microcalorimetry (ITC) by titrating concentrated DOPC solution into the monomer solution of these surfactants. It was found that the P value increases with the increase of the surfactant oligomeric degree. Moreover, the enthalpy change and the Gibbs free energy for the transition of these surfactants from water into the DOPC bilayer become more negative with increasing the oligomeric degree. Meanwhile, the calcein release experiment proves that the surfactant with a higher oligomeric degree shows stronger ability of changing the permeability of the DOPC vesicles. Furthermore, the solubilization of the DOPC vesicles by these oligomeric surfactants was studied by ITC, turbidity, and dynamic light scattering, and thus the phase boundaries for the surfactant/lipid mixtures have been determined. The critical surfactant to lipid ratios for the onset and end of the solubilization for the DOPC vesicles derived from the phase boundaries decrease remarkably with increasing the oligomeric degree. Overall, the surfactant with a larger oligomerization degree shows stronger ability in incorporating into the lipid bilayer, altering the membrane permeability and solubilizing lipid vesicles, which provides comprehensive understanding about the effects of structure and shape of oligomeric surfactant molecules on lipid-surfactant interactions.

Interactions of Cationic/Anionic Mixed Surfactant Aggregates with Phospholipid Vesicles and Their Skin Penetration Ability

This work studied the interactions of an oppositely charged surfactant mixture of oleyl bis(2-hydroxyethyl)methyl ammonium bromide (OHAB) and sodium dodecyl sulfate (SDS) with 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) vesicles as well as the penetration of the OHAB/SDS mixture through model skin, aimed at understanding the relationship between the ability of different surfactant aggregates in solubilizing phospholipid vesicles and their potential in irritating skin. By changing the molar fraction of OHAB (X_OHAB), five kinds of aggregates are constructed: OHAB and SDS separately form cationic and anionic small micelles, whereas the OHAB/SDS mixtures form cationic and anionic vesicles at X_OHAB = 0.30 and 0.70, respectively, and weakly charged vesicles at X_OHAB = 0.50. The mixtures have much lower critical micellar concentrations (CMCs) and much larger aggregates than either OHAB or SDS alone, and the CMC and the size of the OHAB/SDS vesicles decrease with the increase in X_OHAB. The phase diagrams indicate that the OHAB/SDS mixtures show much stronger ability in solubilizing the DOPC vesicles than individual OHAB and SDS and decrease in the order of X_OHAB = 0.30 > 0.50 > 0.70 ≫ 1.00 > 0. However, the ability of the surfactants in penetrating the model skin decreases reversely, and the penetration of the surfactants are significantly reduced by mixing. These results indicate that the surfactant mixture with a larger aggregate size and a smaller CMC value displays much stronger ability in solubilizing the DOPC vesicles but much weaker ability in penetrating the skin.

Synthesis and characterization of asymmetrical gemini surfactants

The effect of variation in the length of surfactant hydrocarbon tail groups was tested in a series of dissymmetric gemini surfactants.

Self-Aggregation, Antibacterial Activity, and Mildness of Cyclodextrin/Cationic Trimeric Surfactant Complexes

Despite efficacious antimicrobial activity, cationic oligomeric surfactants show strong skin irritation potential due to their larger cationic charge numbers and multiple hydrophobic chains. This work reports that the incorporation of α-, β-, and γ-CDs with different cavity sizes can effectively improve the mildness of cationic ammonium trimeric surfactant DTAD with a star-shaped spacer while maintaining its high antibacterial activity. On the basis of the different cavity sizes of CDs and the asymmetry in the spacer of DTAD, the CD/DTAD mixtures form α-CD@DTAD, 2α-CD@DTAD, β-CD@DTAD, and γ-CD@DTAD complexes. Compared to DTAD, these CD/DTAD complexes show much stronger self-assembly ability with much lower critical aggregation concentrations (CAC) and form more diverse aggregates with reduced zeta potential. Just above their CACs, the CD/DTAD complexes form vesicles or solid spherical aggregates of ∼50 nm and then transform into small micelles of ∼10 nm as the concentration increases. The strong self-assembly ability and the multiple sites of hydrogen bonds of the CD/DTAD complexes endow them with high antibacterial activity against E. coli, showing a very low minimum inhibitory concentration (2.22-2.48 μM) comparable to that of DTAD. In particular, the addition of CDs significantly reduces the abilities of DTAD in solubilizing zein (a skin model protein) and in binding with zein, and the mildness decreases in the order of 2α-CD@DTAD > β-CD@DTAD > γ-CD@DTAD > α-CD@DTAD. This tendency depends on their different self-assembling structures, and the formation of vesicles is approved to be in favor of the improvement of the mildness.

Solution Properties of Dissymmetric Sulfonate-type Anionic Gemini Surfactants

Dissymmetric and symmetric anionic gemini surfactants, N-alkyl-N'-alkyl-N,N'dipropanesulfonylethylenediamine (CmCnSul, where m and n represent alkyl chain lengths of m-n = 4-16, 6-14, 8-12, 10-10, and 12-12), were synthesized by two- or three-step reactions. Their physicochemical properties were characterized by equilibrium surface tension measurements, steady-state fluorescence spectroscopy of pyrene, and dynamic light scattering. The critical micelle concentration (CMC) of the dissymmetric surfactants C4C16Sul, C6C14Sul, and C8C12Sul was slightly lower than that of the symmetric surfactant C10C10Sul. The occupied area per molecule (A) of C8C12Sul was smaller than that of C10C10Sul, indicating that C8C12Sul has a high surface activity. However, the increase in the degree of dissymmetry from C8C12Sul to C6C14Sul and then to C4C16Sul resulted in high surface tension and large A. Based on the surface tension, the standard free energies of micellization (∆G°mic) and adsorption (∆G°ads), the efficiency of surface adsorption (pC20), and the effectiveness of surface adsorption (CMC/C20) were obtained. These parameters suggested that C8C12Sul formed micelles more readily than the other surfactants. The properties determined from the surface tension indicated that C8C12Sul's ability is intermediate between those of C10C10Sul and C12C12Sul. The pyrene fluorescence and dynamic light scattering results revealed that the micelle size depends on the longer of the two alkyl chains in dissymmetric surfactants.

Unique Phase Behaviors in the Gemini Surfactant/EAN Binary System: The Role of the Hydroxyl Group

The hydroxyl group in the spacer of a cationic Gemini surfactant (12-3OH-12) caused dramatic changes of the phase behaviors in a protic ionic liquid (EAN). Here, the effects of the hydroxyl group on micellization and lyotropic liquid crystal formation were investigated through the surface tension, small-angle X-ray scattering, polarized optical microscopy, and rheological measurements. With the hydroxyl group in the spacer, the critical micellization concentration of 12-3OH-12 was found to be lower than that of the homologue without hydroxyl (12-3-12) and the 12-3OH-12 molecules packed more densely at the air/EAN interface. It was then interesting to observe a coexistence of two separated phases at wide concentration and temperature ranges in this 12-3OH-12/EAN system. Such a micellar phase separation was rarely observed in the ionic surfactant binary system. With the increase of surfactant concentration, the reverse hexagonal and bicontinuous cubic phases appeared in sequence, whereas only a reverse hexagonal phase was found in 12-3-12/EAN system. But, the hexagonal phases formed with 12-3OH-12 exhibited lower viscoelasticity and thermostability than those observed in 12-3-12/EAN system. Such unique changes in phase behaviors of 12-3OH-12 were ascribed to their enhanced solvophilic interactions of 12-3OH-12 and relatively weak solvophobic interactions in EAN.

Aggregation morphologies of a series of heterogemini surfactants with a hydroxyl head group in aqueous solution

The aggregation behaviors of a series of heterogemini surfactants N,N-dimethyl-N-[3-(alkyloxy)-2-hydroxypropyl]-alkylammonium bromide, abbreviated as CmOhpNCn (m, n = 10, 8; 10, 14; 12, 8; 12, 10; 12, 12; 12, 14; 14, 8 and 14, 10), have been investigated in aqueous solution. Electric conductivity, steady-state and frequency sweep rheological measurements were adopted to study the micellar morphology affected by molecular structure, concentration and temperature, and a close relationship among them was established. Electric conductivity measurement results indicated that Krafft temperatures were mainly related to the total number of carbon atoms, while the CMC values were affected by the combined factors of alkyl chain length, degree of dissymmetry and hydroxyl head group. And some unusual values may come from the poor water solubility induced by the relatively long alkyl chain n. Dynamic rheological results and cryo-TEM images revealed various micellar behaviors of CmOhpNC8 affected by different combined factors. When m value was increased, the formation of quite long rodlike or wormlike micelles derived from the enhanced hydrophobility and hydrogen bonding. And the effect of concentration on aggregation behavior was similar to that of m value except for formation of micellar joints. With temperature increase, the decreased viscosity of C14OhpNC8 was due to formation of micellar joints and weakening of hydrogen bonding, which could be confirmed by dynamic light scattering (DLS). Furthermore, the C14OhpNC8 aggregates formed below the Krafft temperature were more likely to be affected by temperature at high concentrations.

Modelling of the Critical Micelle Concentration of Cationic Gemini Surfactants Using Molecular Connectivity Indices

Modelling of the critical micelle concentrations (cmc) using the molecular connectivity indices was performed for a set of 21 cationic gemini surfactants with medium-length spacers. The obtained model contains only the second-order Kier and Hall molecular connectivity index. It is suggested that the index ²χ includes some information about flexibility. The obtained model was used to predict log₁₀ cmc of other cationic gemini surfactants. The agreement between calculated and experimental values of log₁₀ cmc for the gemini surfactants that were not used in the correlation is very good.

Properties of sodium phosphate-hydroxy ethanolamide gemini surfactant synthesized from the seed oil of Luffa cylindrical

The production of surfactant from biological and renewable sources is important as this reduces environmental hazards since the products are highly biodegradable. Oil extracted from the seed of Luffa cylindrica using hexane in a soxhlet extractor was used in the synthesis of sodium phosphate-hydroxy ethanolamide via a simple reaction mechanism. The progress of the reaction was monitored and confirmed by FTIR, 1HNMR and 13CNMR. The process used gave a yield of 88.46% of sodium phosphate-hydroxy ethanolamide. The properties of this compound were compared with those of sodium dodecyl sulphate (SDS) used as a known reference surfactant. Important properties of sodium phosphate-hydroxy ethanolamide such as foam stability, wetting power and surface tension turned out superior to those of the known reference surfactant (SDS).

Effects of structure dissymmetry on aggregation behaviors of quaternary ammonium Gemini surfactants in a protic ionic liquid EAN

The aggregation behaviors of a series of dissymmetric cationic Gemini surfactants, [C(m)H(2m+1)(CH(3))(2)N(CH(2))(2)N(CH(3))(2)C(n)H(2n+1)]Br(2), designated as m-2-n (with a fixed m + n = 24, m = 16, 14, 12) have been investigated in a protic ionic liquid, ethylammonium nitrate (EAN). Surface tension, polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheological measurements are adopted to investigate the micellization and lyotropic liquid crystal (LLC) formation. The obtained results indicate that the structure dissymmetry plays an important role in aggregation process of m-2-n. With increasing degree of dissymmetry, the critical micellization concentration, the maximum reduction of solvent surface tension, and the minimum area occupied per surfactant molecule at the air/EAN interface all become smaller. The thermostability of formed LLCs is therefore improved because of the more compact molecules. These characteristics can be explained by the enhancement of solvophobic effect due to the increased structure dissymmetry of Gemini surfactants.

Response of an environment-sensitive intramolecular charge transfer probe towards solubilization of liposome membranes by a non-ionic detergent: association and dissociation kinetics

The present report describes an endeavor to follow the solubilization of DMPC and DMPG liposome membranes by a non-ionic detergent Triton X-100 on the lexicon of environment-sensitive intramolecular charge transfer (ICT) photophysics of an extrinsic molecular probe 5-(4-dimethylamino-phenyl)-penta-2, 4-dienoic acid methyl ester (DPDAME). The prospective applicability of the probe to function as a reporter for detergent-sequestered solubilization of liposome membranes is argued on the basis of comparison of the spectral properties of the probe in various environments. Fluorescence anisotropy study delineates the degree of motional restriction imposed on the probe in different microheterogeneous assemblies. The kinetics of association of the probe with the liposome membranes and the dissociation kinetics of TX-100-sequestered solubilization process of the liposomes have been monitored by the stopped-flow fluorescence technique and the results are rationalized in relevance to fluorescence anisotropy study.

Responsive wormlike micelles from dynamic covalent surfactants

Dynamic covalent chemistry is a powerful tool for the construction of adaptive and stimulus-responsive nanosystems. Here we report on the spontaneous formation of dynamic covalent wormlike micelles from imine-based gemini surfactants, formed upon mixing aqueous solutions of two complementary non-surface-active precursors. Resulting from the reversibility of the dynamic covalent imine bond, the wormlike micelles can be switched between an isotropic solution and the assembled state, triggered by pH and temperature. Thermodynamic modeling of the reaction equilibria shows that, although mixtures of single- and double-tailed surfactants are formed, it is mainly the double-tailed surfactant that assembles into the wormlike micelles.

Aggregation behavior of gemini surfactants and their interaction with macromolecules in aqueous solution

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.

Dissymmetric gemini surfactants generated by disulfide exchange in mixed micelles

We found the generation of dissymmetric gemini surfactants from symmetric ones in aqueous micelle solutions of gemini surfactants with a spacer containing disulfide linkage. The equilibrium was attained during 5 h incubation at 25 degrees C with 1:2 ratio of symmetric to dissymmetric ones when the total concentrations were sufficiently high compared with monomer concentrations. The generation of dissymmetric form is attributed to the disulfide exchange between the spacer chains, which occurs in the mixed micelles of gemini surfactants with different hydrocarbon chains. The pseudo-phase separation model for micellization was successfully used to predict not only the cmc of binary and ternary mixtures composed of symmetric and dissymmetric gemini surfactants but also the monomer concentrations after the equilibrium. Reversibility of the disulfide exchange was ascertained by the generation of symmetric gemini surfactants from dissymmetric ones.

A survey of the year 2007 literature on applications of isothermal titration calorimetry

Elucidation of the energetic principles of binding affinity and specificity is a central task in many branches of current sciences: biology, medicine, pharmacology, chemistry, material sciences, etc. In biomedical research, integral approaches combining structural information with in-solution biophysical data have proved to be a powerful way toward understanding the physical basis of vital cellular phenomena. Isothermal titration calorimetry (ITC) is a valuable experimental tool facilitating quantification of the thermodynamic parameters that characterize recognition processes involving biomacromolecules. The method provides access to all relevant thermodynamic information by performing a few experiments. In particular, ITC experiments allow to by-pass tedious and (rarely precise) procedures aimed at determining the changes in enthalpy and entropy upon binding by van't Hoff analysis. Notwithstanding limitations, ITC has now the reputation of being the "gold standard" and ITC data are widely used to validate theoretical predictions of thermodynamic parameters, as well as to benchmark the results of novel binding assays. In this paper, we discuss several publications from 2007 reporting ITC results. The focus is on applications in biologically oriented fields. We do not intend a comprehensive coverage of all newly accumulated information. Rather, we emphasize work which has captured our attention with originality and far-reaching analysis, or else has provided ideas for expanding the potential of the method.