Hyperextended amphiphiles. Bilayer formation from single-tailed compounds

Synthesis, Characteristics and Application of Novel Non-Ionic Gemini Surfactants as Reverse Micellar Systems for Encapsulation of Some Aromatic α-Amino Acids in n-Hexane

Non-ionic carbohydrate based gemini surfactants with rigid aromatic spacer CH2-Ar-CH2, which carry two hydrophobic tails of different tail lengths (C12, C14 and C16) and two sugar moiety polar head groups were synthesized and their reverse micellar behavior for solubilization of some aromatic α-amino acids viz. histidine (His), phenylalanine (Phy), tyrosine (Tyr) and tryptophan (Trp) in n-hexane were studied by spectroscopic analysis. The head group of these gemini surfactants consists of sugar moiety connected to C-6 of tertiary amines. Amino acids form complexes in order of His > Phy > Tyr > Trp, and in all cases it was found that the D-enantiomers solubilize better in comparison to the L-enantiomers. Moreover, more hydrophobic surfactants i.-e. surfactants with longer hydrocarbon tails show greater complex formation tendency towards D- and L-enantiomers of aromatic α-amino acids.

Novel Carbohydrate Based Non-Ionic Gemini Surfactants with Flexible Spacer as Reverse Micellar Systems for Encapsulation of D- and L-Enantiomers of Some Aromatic α-Amino Acids in n-Hexane

Novel non-ionic gemini surfactants derived from carbohydrate carrying two hydrophobic tails with varying tail length of C12, C14 and C16, two sugar moiety as head groups, and an α-(CH2)6-flexible spacer have been synthesized. The head group of these gemini surfactants consists of sugar moiety connected to C-6 of tertiary amines. These gemini amphiphiles were explored as reverse micellar systems for encapsulation of some D- and L-enantiomers of aromatic α-amino acids i.e. histidine (His), phenylalanine (Phe), tyrosine (Tyr) and tryptophan (Trp) in n-hexane in the absence of water. It is found that these amino acids are encapsulated in the order of His > Phe > Tyr > Trp, and it is also observed that in almost all cases the D-enantiomers were better encapsulated as compared to the L-enantiomers. In all cases, encapsulation of D- and L-enantiomers of aromatic α-amino acids increased with increase of the hydrophobic chain length of the gemini surfactants.

pH responsive vesicles with tunable size formed by single-tailed surfactants with a dendritic headgroup

Vesicles of variable sizes are obtained by changing pH with single-tailed dendritic surfactants.

Micellar Encapsulation of Some Polycyclic Aromatic Hydrocarbons by Glucose Derived Non-Ionic Gemini Surfactants in Aqueous Medium

Novel glucose-based non-ionic gemini surfactants consisting of two sugar head groups, two hydrophobic tails having chain length of C8, C10, C12, C14, C16, C18 and –CH2-C6H4-CH2– as a rigid spacer were synthesized and investigated for their micellar encapsulation properties. The head groups of the geminis consist of glucose entities (with reducing function blocked in cyclic acetal group) connected through C-6 to tertiary amines. These surfactants were explored for micellar encapsulation of some polynuclear aromatic hydrocarbons (PAHs) viz. fluorene, anthracene, triptycene and pyrene in 20% ethanol–water mixture. Micellar studies revealed that PAHs were encapsulated in the sequence fluorene > anthracene > triptycene > pyrene and the better efficiency of gemini surfactant was dependent on longer alkyl tail but lesser HLB value.

The Micelle-to-Vesicle Phase Transition in Dilute Aqueous Solution from Undecylamine Induced by Metal(II) ion (Cu2+)

A metal(II) ion (Cu2+)-induced vesicle phase was prepared from a mixture of n-undecylamine and CuCl2 in aqueous solution. Cu2+-ligand coordination with n-undecylamine results in the formation of molecular bilayers because Cu2+ can firmly bind to the amine groups of n-undecylamine which reduced the area of the head-group. In this system, no counterions in aqueous solution exist because of the Cu2+-ligand coordination, and the bilayer membranes are not shielded by salts. The vesicles were determined by transmission electron microscopy (TEM) images and dynamic light scattering (DLS) measurements.

Aggregation properties of supralong-chain surfactants with double or triple quaternary ammonium head groups

Double or triple quaternary ammonium head groups were designed to improve the solubility of supralong alkyl chain surfactants. In the surfactant head group, quaternary ammonium groups are connected by an ethylene spacer. Micellar shapes of divalent surfactants [C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 2Br(-): C(n)-2Am (n=18, 20, and 22)] and trivalent surfactants [C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 3Br(-): C(n)-3Am (n=18, 20, and 22)] were studied in aqueous solutions by means of dynamic light scattering (DLS) and transmission electron microscopy (TEM). Changes in the surfactant concentration have a small influence on the apparent hydrodynamic radii (r(h)) of the molecular aggregates in both surfactant series. Average values of r(h) of aggregates are 60-90 nm for C(n)-2Am (n=18, 20, and 22) and 2-40 nm for C(n)-3Am (n=18, 20, and 22). TEM micrographs showed that aggregates of C(n)-2Am (n=18, 20, and 22) typically formed rod-like micelles. In contrast, trivalent surfactants of C(n)-3Am (n=18, 20, and 22) formed spherical (C(18)-3Am) or ellipsoidal micelles (C(20)-3Am and C(22)-3Am). Moreover, the degree of micellar counterion binding for these surfactants was determined by using a bromide ion-selective electrode, which indicated relatively high values (0.8-0.9) for C(n)-2Am (n=18, 20, and 22) and more common values (0.5-0.8) for C(n)-3Am (n=18, 20, and 22). The size of the aggregates is closely related to the degree of counterion binding.

Efficient preparation of liposomes encapsulating food materials using lecithins by a mechanochemical method

In order to evaluate to the feasibility of using lecithins for nanocapsules including functional food materials, liposomes were prepared from different commercially available lecithins (SLP-WHITE, SLP-PC70 and PL30S) by the Bangham method, and their physicochemical properties were examined by using a confocal laser scanning microscopy (CLSM) and the measurements of trapping efficiency. There was little difference in the trapping efficiency among the three types of liposomes. In all cases, the trapping efficiency clearly increased with an increase of the lecithin concentration up to 10 wt % , and the maximum efficiency reached at approximately 15%. CLSM observation showed the particle size of liposomes prepared from SLP-WHITE is significantly smaller than that prepared from other lecithins. In addition, liposomal solution prepared from SLP-WHITE remained well dispersed for at least 30 days, while two other liposomal solutions showed a phase separation due to aggregation and/or fusion of liposomes. These results indicated that SLP-WHITE is the most appropriate for the preparation of stable liposomes with well dispersed among the lecithins tested. SLP-WHITE liposomes were then prepared by the mechanochemical method using a homogenizer and microfluidizer, aiming at improving the preparation efficiency and liposome stability. The particle size of the prepared SLP-WHITE liposomes decreased with increasing inlet pressure and the number of processed cycles, and reached between 73 and 123 nm based on the measurement using dynamic light scattering. Moreover, freeze-fracture transmission electron microscopy revealed that the prepared liposomes are small unilamellar vesicles (SUV) with a diameter of approximately 100 nm. The extract of Curcuma longa Linn. (Ukon), which contains curcumins as a functional food material, was then subjected to the mechanochemical method with SLP-WHITE to give liposomes including the functional materials. Interestingly, the trapping efficiency of the liposomes for curcumins was found to reach over 85%. From these results, the present mechanochemical method is very likely to allow us to efficiently prepare stable and functional liposomes from the low-cost lecithin. The method may thus have a potential for manufacturing practical nanocapsules, which serves as a novel carrier of functional food materials.

Shamrock surfactants: synthesis and characterization

Two types of a new class of surfactants with three headgroups, which possess the general structure 1, have been prepared. Within structure 1, a central headgroup is connected to two flanking headgroups by hydrocarbon chains. The term "shamrock" is used to describe surfactants of structure 1, denoting their triple-headed character and reflecting the fact that shamrocks have leaflets in groups of three. The major lipophilic character of shamrock surfactants is provided by the two hydrocarbon chains linking the three headgroups and not by long-chain alkyl groups appended to the linking hydrocarbon chains or the headgroups. The new surfactants are 2a (2,2,15,15,28,28-hexamethyl-2,15,28-triazonianonacosane triiodide), 2b (2,2,15,15,28,28-hexamethyl-2,15,28-triazonianonacosane trichloride), 3a (O,O'-di-[10-(N,N,N-tripropylammonio)decyl]phosphorodithioate bromide), and 3b (O,O'-di-[10-(N,N,N-tributylammonio)decyl]phosphorodithioate bromide). Compound 14 (2,2,9,9,16,16-hexamethyl-2,9,16-triazoniaheptadecane triiodide) was prepared for comparison with 2a. Surfactants 2 and 3 were characterized in water by measurement of their Krafft temperatures and critical aggregation concentrations, and their aggregates were studied by 1H NMR spectroscopy, dynamic laser light scattering, and phase-contrast optical microscopy. Aqueous 2b was also studied by cryo-etch high-resolution scanning electron microscopy, which revealed irregularly shaped cells containing a complex matrix of surfactant. Coacervates were observed by optical microscopy upon the hydration of 2 and 3.

Spontaneous formation of vesicles and chiral self-assemblies of sodium N-(4-dodecyloxybenzoyl)-L-valinate in water

A novel N-acylamino acid surfactant, sodium N-(4-dodecyloxybenzoyl)-L-valinate (SDLV), has been synthesized. The aggregation behavior of the surfactant in aqueous solution has been studied by surface tension, fluorescence probe, microscopy, and dynamic light scattering (DLS) techniques. The amphiphile has a very low critical aggregation concentration (cac). These studies have suggested formation of large bilayer structures in water. The mean apparent hydrodynamic radius, RH, of the self-assemblies in dilute aqueous solution obtained from DLS measurements confirmed formation of large aggregates. The FT-IR spectra of the amphiphile have indicated strong intermolecular amide hydrogen bonding in the self-assemblies in aqueous solution. The microenvironment of the fluorescence probes is highly nonpolar and viscous in nature. The circular dichroism (CD) spectra of SDLV were recorded in water and in a 1:1 water-methanol mixture. The CD spectra have indicated the presence of chiral aggregates in aqueous solution above the cac. The microstructure of the aggregates has been studied by use of optical and transmission electron microscopy. Both types of micrographs have shown the presence of a variety of morphologies including giant spherical vesicles, tubules, twisted ribbons, and helical strands in aqueous solutions.

Fusion of Vesicles in Manganese Complex of a Single-Chain Schiff Base Amphiphile—3-Cyano-N-Benzylidene Hexadecylamine

A single-chain amphiphile containing a rigid Schiff base segment, 3-cyano-N-benzylidene hexadecylamine (CNBHB) in the polar head group was synthesized and studied for its vesicle-forming properties. The dependence of the aggregation behavior of the vesicles as such and in the presence of manganese ions were studied as a function of temperature using differential scanning calorimetry and turbidity measurements. Transmission electron microscopy (TEM) was used to analyze the morphology of the vesicles, showed interesting features with fusion of regular structures, and were quite stable. In the presence of manganese ions, fusion of vesicles takes place. This could be due to the metal ions that are bound to the surface of the vesicles that cause a partial destruction of the hydration shell on the surface of the vesicles. The reduction in the hydration force could thus be responsible for the fusion.