Sugar-based Surfactants Research Articles

A comparative study of sugar-based surfactants for the solubilization of phosphatidylcholine vesicles

The solubilization of small unilamellar vesicles of egg phosphatidylcholine (PC) by a series of sugar-head surfactants was investigated. The experiments consisted of recording turbidity at 25°C, during continuous addition of surfactant solutions to PC vesicles of different initial concentrations. Surfactant-to-phospholipid molar ratios in the molecular aggregates [Surf/PC] ag as well as the surfactant concentrations in the aqueous phase [Surf] bulk were determined at the total micellization stage. The values of [Surf/PC] ag varied over a factor often, from 0.44 to 5.20, pointing out a significant variability of the solubilizing properties of the sugar derivatives. This was more likely due to the headgroup conformation of the surfactants rather than to their water-solubility.

Characterization of Mixed Micelles of SDS and a Sugar-Based Nonionic Surfactant as a Variable Reaction Medium

Time-resolved fluorescence quenching (TRFQ), electron paramagnetic resonance (EPR), and small-angle neutron scattering (SANS) are employed to characterize mixed micelles of sodium dodecyl sulfate (SDS) and the nonionic sugar-based surfactant dodecylmalono-bis-N-methylglucamide (DBNMG) as a reaction medium. Interpretation of the results from the three methods are constrained to fit the classical model of a hydrocarbon core surrounded by a polar shell. As measured by TRFQ, at 45 °C, the aggregation numbers increase from 48 for pure SDS to a maximum of 63 at 36 mole percent DBNMG and decrease again to 49 for pure DBNMG. The aggregation numbers of the pure DBNMG increase from 33 at 21° Ct o 49 at 45°C. SANS results of the pure DBNMG are interpreted by fixing the aggregation number at 49 (from TRFQ) and allowing the polar shell thickness to vary as a fitting parameter, yielding a value of 5.8 A at 45 °C. EPR, utilizing a hydrophobic spin probe, is used to measure the nonempirical polarity index, H(25 °C), of the polar shell. H(25 °C) is defined to be the ratio of molar concentration of OH dipoles in a solvent or solvent mixture to that in water at 25 °C; thus, both water and the sugar headgroups contribute. By fixing the volume in the polar shell inaccessible to water due to the presence of SDS (127 A 3 ) and DBNMG (580 A 3 ), theoretical values of H(25 °C) are computed, the result depending only on the number of OH bonds in DBNMG available to interact with the spin probe. A constant average value of 7.4 OH bonds out of a maximum possible number of 10 reproduces the measured values over the full range of mixed micelle compositions. At 45 °C, the microviscosity of the polar shell, as deduced from the rotational correlation time of the spin probe, varies from 2.79 ( 0.05 cP for pure SDS to 13.1 ( 0.2 cP for pure DBNMG departing only slightly from a linear dependence on the mole fraction of DBNMG. The uncertainties in the viscosity are the standard deviations in 10 measurements and therefore represent the uncertainty in the relative values of the viscosity. The viscosity decreases from 32 ( 4c P at 21°C to 13.1 ( 0.2 cP at 45 °C for pure DBNMG micelles. These viscosities are used to show that the quenching rate constant of pyrene by dimethyl benzophenone, measured by TRFQ, follows the Stokes-Einstein-Smolukhovsky equation with a quenching probability of P ) 0.5 whether the mixed micelle composition is changed at constant temperature or if the temperature is varied in pure DBNMG. The volume of the polar shell enters into the formulation because the effective concentration of the quencher depends on that volume; however, the quenching rates are not correlated with volume alone.

Sugar-based anionic surfactants: synthesis and micelle formation of sodium methyl 2-acylamido-2-deoxy-6- O-sulfo- d-glucopyranosides

The following sequence of reactions has been employed to synthesize the title anionic surfactants: where R=C 7H 15 ( 3a); C 11H 23 ( 3b); and C 15H 31 ( 3c), respectively, and Py refers to pyridine. Aggregation of the surfactants synthesized (predominantly α anomers) in water was studied at 40 °C by conductivity measurements. Increasing the chain length of R decreases the critical micelle concentration (CMC) and the degree of counter-ion dissociation. The dependence of the Gibbs free energy of micellization and CMC on the length of R is similar to other ionic surfactants, but the head-group, i.e., the sulfated sugar moiety is less hydrophilic than the structurally related group (OCH 2CH 2) 2OSO 3 −Na +, most probably because of intermolecular H-bonding in the micellar pseudo-phase

Physicochemical Properties of a Ternary System Based on Medium Chain Triglycerides/Water/Mixed Nonionic Sugar-Based Surfactants

Equal ratios of medium chainlength triglycerides and water were emulsified with 5% w/w of mixed nonionic surfactants with various hydrophilic-lipophilic balance (HLB) values. The HLB numbers ranged from 15 to 6.6. Emulsifiers with HLB numbers 15, 14.2, 13.3, and 12.5 produced low viscosity milk-like liquid, 11.6, 10.8, 10, and 9.1 produced cream, 8.3 and 7.4 produced paste like consistency, and 6.6 produced a coarse emulsion. The effects of HLB on stability, particle size, and rheological properties were studied. Emulsifiers with intermediate HLB numbers produced emulsions that are stable for 30 days at room temperature but a thin layer of oil on top of the emulsion was observed at 45°C. The thin oil layer can be redispersed with mild agitation without loss of stability. Emulsifiers with high and low HLB number (15, 14.2, 13.3, 6.6) produced emulsions that were unstable at both storage conditions. The stability of the emulsions correlate well with the particle size. The curve flow plot for most of the emulsions fit the Herschel Bulkley model. They exhibit a pseudoplastic type behavior. Emulsifiers with different HLB numbers also affect the shear stress at zero shear, τ0, and the yield value, τ.

Sugar-based tertiary amino gemini surfactants with a vesicle-to-micelle transition in the endosomal pH range mediate efficient transfection in vitro.

Novel reduced sugar gemini amphiphiles linked through their tertiary amino head groups via alkyl spacers of 4 or 6 carbons, and with varying (unsaturated) alkyl tail lengths of 12--18, have been synthesized and tested for transfection in vitro in an adherent Chinese hamster ovary cell line (CHO-K1). Transfection efficiencies peaked at 2.7 times that of the commercial standard Lipofectamine Plus/2000 for pure solutions of the compound bearing unsaturated (oleyl) alkyl tails. For those compounds bearing saturated alkyl tails, transfection efficiency peaked at a tail length of 16, at a level similar to Lipofectamine Plus/2000. All of the amphiphiles formed bilayer vesicles at physiological pH. Some of the amino groups at the surface were protonated, and vesicles therefore bore a positive charge. Increased protonation with reduced pH resulted in greatly increased monomer solubility and a morphology change from vesicle to micelle at characteristic pH values, dependent on the tail length. For the compounds promoting high transfection efficiency, this characteristic pH was within the range found in the endosomal compartment (7.4--4.0). Formation of mixed micelles between gemini surfactant and membrane phospholipids at reduced pH may therefore provide a method of endosome rupture and subsequent escape of entrapped DNA, thus discarding the need for extra fusogenic or endosomolytic agents. The positive charge on the vesicles at physiological pH drives the colloidal association with DNA. Small angle X-ray scattering measurements indicate that lamellar aggregates are formed, which have a d spacing of 48--54 A. Preliminary differential scanning calorimetric measurements suggest that reduction of pH causes a disordering of the hydrocarbon region of the DNA-surfactant complex.

Syntheses of surfactants from oleochemical epoxides

Sugar-based surfactants were obtained in good yields (up to 100%) under mild conditions (70°C, methanol or mixtures of methanol and water) by ring-opening of terminal epoxides with aminopolyols, derived from glucose. Reaction of N-methyl glucamine with epoxides from even-numbered C4-C18 alpha-olefins or from terminal unsaturated fatty acid methyl esters leads to linear products, while corresponding reactions with N-dodecyl glucamine or glucamine yield surfactants with different Y-structures. Products obtained by conversion of omega-epoxy fatty acid methyl esters were saponificated with NaOH or hydrolyzed enzymatically to sodium salts or free acids respectively, which are amphoteric surfactants. Studies of the surfactants at different pH-values demonstrate different surface active properties in aqueous solutions. Critical micelle concentrations (c.m.c.) in a range between 2 and 500mg/l and surface tensions of 25-40mN/m were measured for several of the synthesized sugar-based surfactants. The ring-opening products are rather poor foamers, whereas some of the corresponding hydrobromides show good foaming properties.

Formation of model lipid bilayers at the silica-water interface by co-adsorption with non-ionic dodecyl maltoside surfactant.

This present article describes a new and simple method for preparing model lipid bilayers. Stable and reproducible surface layers were produced at silica surfaces by co- adsorbing lipid with surfactant at the silica surface from mixed micellar solutions. The adsorption was followed in situ by use of ellipsometry. The mixed micellar solution consisted of a lipid (L-alpha-dioleoyllecithin) and a non-ionic sugar-based surfactant (n-dodecyl-beta-maltoside). The latter showed, by itself, no affinity for the surface and could, therefore, easily be rinsed off the surface after the adsorption step. By first adsorbing from solutions with high lipid and surfactant concentrations and then, in succession, rinsing and re-adsorbing from solutions with lower lipid-surfactant concentrations, a dense-packed lipid bilayer was produced at the silica surface. The same result can be achieved in a one-step process where the rinsing, after adsorption from the concentrated solution, is performed very slowly. The thickness of the adsorbed lecithin bilayer after this treatment found was to be about 44 +/- 3 A, having a mean refractive index of 1.480 +/- 0.004. The calculated surface excess of lipids on silica was about 4.2 mg m(-2), giving an average area per lipid molecule in the two layers of 62 +/- 3 A2. The physical characteristic of the adsorbed bilayer is in good agreement with previously reported data on bulk and surface supported lipid bilayers. However, in contrast to previous investigations, we found no support for the presence of a thicker multi-molecular water layer located between the lipid layer and the solid substrate.

Stereochemical aspects of micellar properties of esterified glucoside surfactants in water: apparent molar volume, adiabatic compressibility, and aggregation number

The apparent molar volume and the apparent molar adiabatic compressibility of the sugar-based surfactants methyl 6-O-octanoyl-α-d-glucopyranoside (α-MOnG), methyl 6-O-octanoyl-β-d-glucopyranoside (β-MOnG), and octyl β-d-glucoside were measured over a wide concentration range. Also, the aggregation number of their micelles was determined from the Debye plot using static light scattering data. It was found that the micellar aggregation number for α-MOnG is 179 at 35 °C, which is 1.5 times larger than that for β-MOnG, suggesting that the anomerism of the head group influences the packing of the monomers during micelle formation.

Sugar-based Surfactants

Physico-chemical properties of sugar-based surfactants, such as alkyl glucosides, alkyl maltosides, sucrose monoalkanoates, and alkanoylglucosides, were reviewed with attention directed primarily to anomeric effects of the head group sugar. Phase behaviors of surfactant solid and surfactant-water 2-component systems for α-anomer of alkyl glucosides differed considerably from that of β-anomer. Chain length effects of the hydrophobic group on phase behavior of alkyl glucoside-water system were studied for β-anomers and a liquid-liquid phase separation region was confirmed to exist for decyl β-glucoside (0.1-17 wt%) but for octyl and nonyl β-glucoside. The growth of micelles of decyl β-glucoside would thus appear to be promoted by increse in surfactant concentration and micellar network structure was noted to form at above 17 wt% solution. The size and shape of micellar aggregates for octyl glucoside, dodecyl maltoside, and octanoylglucoside demonstrated significant anomeric effects.

A Spin-Probe Study of the Modification of the Hydration of SDS Micelles by Insertion of Sugar-Based Nonionic Surfactant Molecules

The spin-probe detected polarity index H(25 °C) of SDS micelles decreases linearly with the number of inserted sugar-based nonionic surfactant molecules. This decrease is interpreted as being due to the expulsion of water molecules by the sugar groups from the polar shell surrounding the hydrocarbon core of the dodecyl micelle. Employing the geometrical model described in the companion paper immediately preceding this work, the effective volume of water expulsion is found to be similar to the volume of the sugar groups after taking into account that the OH bonds of the sugar groups also contribute to the polarity index H(25 °C). The estimate of the hydration of pure SDS micelles as a function of their aggregation number from these studies with the spin probe 16 doxylstearic acid methyl ester is similar to that with 5 doxylstearic acid methyl ester. This confirms that both spin probes are located similarly in the polar shell.

Sugar-based surfactants for consumer products and technical applications

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Sugar-based surfactants for consumer products and technical applications

Sugar-based surfactants, such as sorbitan esters, sucrose esters, alkyl polyglycosides, and fatty acid glucamides gain increasing attention due to advantages with regard to performance, health of consumers, and environmental compatibility compared to some standard products. Sorbitan esters are well established products, which are mainly used as leather and textile auxiliaries or as emulsifiers for food at a volume of approx. 20,000 t/a. Sucrose esters are relatively hydrophobic products. The actual market size is estimated to be < 4,000 t/a – the main application being emulsifiers for food and cosmetics. Their use is still limited. Alkyl polyglycosides and fatty acid glucamides represent a perfect amphiphilic structure with excellent surface activity as well as solubility due to highly selective syntheses. For alkyl polyglycosides industrial processes have been developed in the past couple of years and a total capacity of ca. 80,000 t/a has been established. They are mainly used for cosmetic, manual dishwashing, and detergent applications. Fatty acid glucamides to date are exclusively used by one company in liquid and powdered detergents. The estimated production capacity is approx. 40,000 t/a. Comparable in their performance profile as co-surfactants, both products differ in their raw material base: whereas in the case of the fatty acid glucamides methylamine is incorporated in the product, alkyl polyglycosides are completely based on renewable resources. This, combined with very good performance and mildness, could be one reason why alkyl polyglycosides are the most successful sugar-based surfactants nowadays. Research to develop derivatives on this basis is still ongoing. Tenside auf Basis von Kohlenhydraten für Verbraucherprodukte und technische Anwendungen Tenside auf Basis von Kohlenhydraten, also Sorbitanester, Saccharoseester, Alkylpolyglycoside und Fettsäure-N-Methylglucamide, gewinnen aufgrund ihrer anwendungstechnischen Eigenschaften, ihrer relativ guten Umweltverträglichkeit und ausgezeichneten Hautmilde weiterhin an Interesse. Die selektive Funktionalisierung von Saccharose und Sorbitol zum Aufbau einer perfekten amphiphilen Struktur ist aufgrund der Polyfunktionalität der Moleküle in einfachen technischen Prozessen nicht zu realisieren. Die am Markt angebotenen Produkte enthalten deshalb unterschiedliche Mengen an Mono-, Di- und Triester und sind deshalb nur für bestimmte Anwendungen geeignet, z.B. als Nahrungsmittel- und Kosmetikemulgatoren oder im Falle der Sorbitanester auch in technischen Bereichen wie Explosivstoffen und in der Emulsionspolymerisation. Diese Produkttypen sind seit langer Zeit bekannt. Die geschätzten Produktionskapazitäten betragen für Sorbitanester ca. 20.000 t/Jahr und für Saccharoseester < 4.000 t/Jahr. Der ideale Rohstoff für selektive Derivatisierungen ist Glucose. Die Umsetzung mit Alkohol liefert Alkylglucoside, durch reduktive Aminierung mit Methylamin und anschließende Acylierung werden N-Methylglucamide hergestellt. Beide Produkte haben sich als hochwirksame Tenside in Wasch- und Reinigungsmitteln erwiesen. Für diese Einsatzgebiete werden die N-Methylglucamide gegenwärtig exklusiv von einem Wasch- und Reinigungsmittel-Hersteller eingesetzt (Produktionskapazität ca. 40.000 t/Jahr). Die Alkylglucoside (Produktionskapazität ca. 80.000 t/Jahr) sind darüber hinaus auch im Bereich der Kosmetikprodukte, als Hilfsstoffe in Pflanzenschutzformulierungen und als Tenside für industrielle Reiniger etabliert und können heute angesichts der jährlichen Produktionsmengen als das bedeutendste Zuckertensid bezeichnet werden.

Interaction studies between europium and a surfactant cage “TAC8” by time-resolved laser-induced fluorescence

Time-resolved laser-induced fluorescence (TRLIF) has been used for interaction studies between europium(III) used as a fluorescent probe and a new micellar system (TAC8) of a “diblock” surfactant–cage molecule containing a cage (cyclam) as a complexation part linked to a sugar-based surfactant part. The effect of each constituent (cage and surfactant unit) as well the complete molecule on the europium fluorescence have been studied. By using the hypersensitive transition of europium, it was shown that the separate constituents, e.g. cyclam and surfactant, had little effect. On the other hand, the complexation constant between europium and TAC8 was close to 10 2 demonstrating that a synergetic effect is achieved with such a diblock surfactant–cage molecule.

Segregation of mixed micelles in the presence of polymers

The diffusion behaviour of an aqueous mixture of the sugar-based non-ionic surfactant dodecylmalono-bis-N-methylglucamide DBNMG and the anionic surfactant of similar tail length, sodium dodecyl sulfate SDS, are examined in the presence of 5 mass% gelatin; the results clearly show that there are two types of mixed micelle present in the system arising through competition between gelatin and the non-ionic micelle for the anionic surfactant.

Synthesis of new sugar-based surfactants having biological applications: key role of their self-association

Non-ionic surfactants based on sugars are of interest to both chemists and biochemists. They have potential pharmaceutical (biocompatible formulation) biochemical (extraction of membrane proteins) and medicinal applications; generally these derivatives are not readily synthesized as the starting sugars require protection. We present here routes, avoiding protection of the starting sugars, to new series of surfactants derived from lactose, glucose, gluconic or lactobionic acids. By changing the tail or the hydrophobic body bonded to the sugar heads, we have synthesized sugar-based amphiphilic compounds having (1) one chain, (2) one fluorinated chain, (3) a double chain or (4) two sugar heads (bolaamphiphilic compounds) All these compounds form aggregates in solution: direct, reverse micelles, or vesicles. Fluorinated molecules give gels in aqueous or non-aqueous media. Some of them are interesting products to extract membrane proteins or to formulate solution of hydrophobic acids to realize enzymatic reactions. Finally soluble analogs of Galcer possess activity against both HIV and Aspergillus fumigatus, a yeast responsible for opportunistic infections in AIDS patients.

FT-PGSE NMR Study of Mixed Micellization of an Anionic and a Sugar-Based Nonionic Surfactant

The interaction of a sugar-based nonionic surfactant (dodecylmalonobis(N-methylglucamide)) with an anionic surfactant of similar tail length (sodium dodecyl sulfate) has been studied by CORE PGSE N...

Electrolyte Effects on the Surface Tension and Micellization of n-Dodecyl β-d-Maltoside Solutions

Sugar-based surfactants such as polyglucosides are a relatively new class of nonionic surfactants portrayed to be suitable for high-salinity applications. To better utilize such surfactants, it is useful to elucidate the mechanisms of their interactions at various interfaces in the presence and absence of electrolytes and the reasons for their salt tolerance. In this work, the effect of various salts on the surface tension and critical micelle concentration of the nonionic surfactant n-dodecyl β-d-maltoside (DM) was studied. Interestingly, while the packing of DM molecules at the air−water interface was not affected by the nature of salt added, cations and anions were found to have markedly different effects on the surface activity and critical micelle concentration (cmc) of the surfactant. For the same cation Na+, the effect of anions decreases in the order F- > Cl- > SO42- > Br- > PO43- > citrate > I- > SCN-. For the same anion Cl-, the effect of cations follows the order K+ > Na+ > Rb+ > Li+ > Ca2+ > A...

Neutron Reflection Study of a Double-Chained Sugar Surfactant

Neutron reflection and surface tension have been used to investigate the structural features exhibited at the air−liquid interface by an adsorbed layer of the sugar-based nonionic surfactant 7,7-bis[(1,2,3,4,5-pentahydroxyhexanamido)methyl]-n-tridecane. It consists of two glucamide headgroups and two C6H13 alkyl chains, i.e., (C6H13)2C(CH2NHCO(CHOH)4CH2OH)2, abbreviated to di(C6-Glu). Isotopic substitution was used to distinguish the chains of the surfactant from the headgroup and solvent distributions. The critical micelle concentration (CMC) was found to be (1.9 ± 0.1) × 10-3 M using surface tension measurements, and the latter also indicated that the surface properties were not affected by isotopic substitution. The specular reflection of neutrons has been used to determine the surface concentrations of skeletally deuterated di(C6-Glu) over the concentration range CMC/400 to 2CMC. The neutron measurements showed the area per molecule A at the CMC to be 66 ± 3 Å2, as compared with 60 ± 10 Å2 from surface tension measurements. The layer structure has been determined using three different isotopic contrasts at concentrations of CMC and CMC/400. The fit of a two-layer model shows that the total monolayer thickness decreases from 17.5 ± 1.5 Å at the CMC to 14.5 ± 1.5 Å at CMC/400, respectively. The kinematic approximation was used to fit the neutron data and an X-ray reflection profile. The most remarkable feature of the structure obtained is the apparent smoothness of the layer. The calculated roughness of the layer at the CMC is 9.7 Å2 which corresponds exactly to the value expected for capillary waves using the model of a pure liquid. At the CMC the molecule as a whole appears to be tilted about 35−40° away from the surface normal, but at CMC/400 the hydrocarbon chains are approximately normal to the surface while the gluconamide groups are strongly tilted.

Disjoining Pressure Measurements for Foam Films Stabilized by a Nonionic Sugar-Based Surfactant

Disjoining pressure isotherms for foam films made from a nonionic surfactant, octyl β-glucoside, are measured at different surfactant concentrations, ionic strengths, and solution pH values. Below the cmc an electrostatic double-layer repulsion is present and dominates the long-range interaction. The decay length of the forces agrees with the expected Debye length and the measured long-range interactions are consistent with solutions to the nonlinear Poisson−Boltzmann equation using constant charge conditions. The deduced surface charge densities increase with pH and ionic strength but decrease with increasing surfactant concentration. At, or just above, the cmc, surfactant covers the interface and suppresses the charge sufficiently to induce a transition from a common black film to a Newton black film. Ultimately, the film stability is determined by both surface forces and elasticity. Combining both, via an overall film tension, leads to a general expression for the film elasticity.

Non-ionic sugar-based surfactants: Self assembly and air/water interfacial activity

The air/water interfacial activity and self-assembly of the mono-dodecyl esters of glucose, sucrose, raffinose and stachyose have been investigated. These four non-ionic surfactants provide a series where the hydrocarbon chain length is invariant while the surfactant headgroup sequentially increases in size. The minimum area per surfactant molecule at the air/water interface increases smoothly with the sequential addition of galactose structural units, sucrose < raffinose < stachyose, but the galactose units appear not to lie in the plane of the interface. The free energy of micellization increases linearly with the number of galactose units. For binary surfactant/water systems, the glucose surfactant exists as hydrated crystals at relatively low temperatures and forms lamellar phases at high temperatures, i.e. an L β followed by an L α phase as the temperature is increased. At a low weight percentage of surfactant, the other three surfactants form isotropic micellar phases. At relatively higher weight percentages of surfactant, the sucrose surfactant forms hexagonal and L β phases, the raffinose surfactant forms discrete cubic micellar and hexagonal phases, and the stachyose surfactant begins to crystallize. At a very high weight percentage of surfactant, the sucrose, raffinose and stachyose surfactants exist as hydrated crystals. Most of the self-assembly behaviour in water can be readily explained in terms of the geometric packing constraints.