Sugar Headgroup Research Articles

Alkyl-glycoside surfactants in the synthesis of mesoporous silica films

Alkyl glycosides were used as templating surfactants in the sol–gel processing of thin silica films. The sols were made from a prehydrolyzed silicate solution with the addition of a glucoside or a maltoside surfactant. The sol–gel–xerogel transitions and the silica–sugar interactions were studied by IR ATR spectroscopy. The siloxane condensation rate in the silica/glycoside sol was considerably reduced compared to a pure silica system due to hydrogen bonding interactions between the silanols and the sugar head groups. Thin films were deposited on silicon wafers and characterized by IR transmission, X-ray diffraction and TEM analysis. The size of the sugar head group had a large influence on the type of the mesophases formed. The use of the glucoside surfactant only resulted in temperature unstable lamellar phases, whereas the maltosides at low concentrations assembled in curved mesophases that were stable to template removal by extraction or calcination.

Another new family of “extended” glucidoamphiphiles. Synthesis and surfactant properties for different sugar head groups and spacer arm lengths

AbstractFollowing a new four‐step route, we prepared a family of “extended” glucidoamphiphiles from D‐glucose, D‐galactose, and xylitol in which the n‐dodecyl chain is attached to the glucidic moiety by the linkage Z=O‐Et‐O‐Et‐O‐(α‐PP‐O‐)n′ where‐O‐(α‐PP‐O‐)n is a poly‐(α‐propyloxy) commercial oligomeric mixture (with average length n=6, 10, and 14). This amphiphilic behavior study showed that (i) the glucose derivative exhibits water solubility and hydrophilic‐lipophilic balance values that are close to those found for the glucose compound with Z=‐O‐(α‐PP‐O‐)n (without the Et‐O‐Et group), (ii) all these compounds are more strongly hydrophilic than the corresponding glucidic derivatives with Z=O, (iii) the increase of the poly‐(α‐propyloxy) chain length from ñ=6 to ñ=14 tends to reduce the hydrophilicity slightly.

Sugar-Based Surfactants: Adsorption and Micelle Formation of Sodium Methyl 2-Acylamido-2-deoxy-6-O-sulfo-d-glucopyranosides

Aggregation in aqueous solutions of sodium methyl 2-acylamido-2-deoxy-6-O-sulfo-d-glucopyranoside surfactants has been studied, where the acyl group is octanoyl, dodecanoyl, or hexadecanoyl. Critical micelle concentration, cmc, minimum area per surfactant at the air/solution interface, σ, degree of counterion dissociation, αmic, and thermodynamic parameters (Gibbs free energy, enthalpy, and entropy) of adsorption and/or micellization were calculated from surface tension and conductance measurements. Static and quasi-elastic light scattering measurements were employed to obtain micellar weight-average molecular weight, aggregation number, Nagg, and hydrodynamic radius. Finally, the fluorescence spectrum of solubilized pyrene was employed for determination of micellar polarity. The similarities between these aminoglucose-based surfactants and simple anionic ones include decrease of cmc and of αmic and increase of Nagg as a function of increasing the chain length of the hydrophobic group. Compared to simple anionic surfactants, the sugar-based counterparts showed more favorable free energies of adsorption and micellization, higher Nagg, and larger σ. These differences are explained on the basis of the attractive interactions between the voluminous sugar headgroups.

Flocculation Transitions of Weakly Charged Oil-in-Water Emulsions Stabilized by Different Surfactants

This study concerns dodecane-in-water emulsions stabilized primarily by a range of nonionic surfactants. The emulsions are stable with respect to coalescence and Ostwald ripening but unstable with respect to flocculation and creaming. Sharp and reversible transitions between a flocculated state and a nonflocculated state can be induced by the addition of small mole fractions of either the anionic surfactant sodium octadecyl sulfate or the cationic surfactant octadecyl trimethylammonium bromide and were measured as a function of NaCl concentration. The flocculation transitions are modeled in terms of three types of colloidal forces: a short-range repulsion modeled as a “hard wall”, van der Waals attraction, and electrostatic repulsion. The flocculation transition is taken to correspond to the ionic surfactant concentration for which the maximum in disjoining pressure equals the capillary pressure of the drops. Comparison of calculated and experimental results shows reasonable agreement for emulsions stabilized by n-decyl-β-d-glucoside and 1-O-n-decyl-d,l-xylitol. Emulsions stabilized by n-decyl-N-methylglucamide and n-dodecyl octaoxyethylene and n-hexadecyl 20-oxyethylene glycol ethers (C12E8 and C16E20) reveal a significant negative charge on the drop surfaces in the absence of added ionic surfactant. Additionally, we find that the surface charging of the surfactants with sugar headgroups by addition of charged surfactants is correctly predicted from the concentration of added ionic surfactant with the assumption that the ionic surfactant distributes equally between the emulsion surface monolayer and the micelles present in the continuous phase. For C12E8 and C16E20, the added ionic surfactant is found to distribute preferentially to the emulsion surfaces.

Structure of Hydroxylated Galactocerebrosides from Myelin at the Air-Water Interface

Hydroxy-galactocerebrosides (mixed chain length, constituent of myelin membranes) from bovine brain are investigated as monolayers at the air-water interface with isotherms, fluorescence microscopy, x-ray reflectivity and grazing incidence diffraction. With grazing incidence diffraction a monoclinic tilted chain lattice is found in the condensed phase. According to x-ray reflectivity, the longest chains protrude above the chain lattice and roughen the lipid/air interface. On compressing the chain lattice, the correlation length increases by ∼65%; obviously, the sugar headgroups are flexible enough to allow for lattice deformation. With fluorescence experiments, small coexisting fluid and ordered domains are observed, and there is lipid dissolution into the subphase as well. The dissolved hydroxy-galactocerebroside molecules reenter on monolayer expansion. The electron density profiles derived from x-ray reflectometry (coherent superposition) show that the chain-ordering transition causes the molecules to grow into the subphase.

Trienoic fatty acids and plant tolerance of temperature

The biophysical reactions of light harvesting and electron transport during photosynthesis take place in a uniquely constructed bilayer, the thylakoid. In all photosynthetic eukaryotes, the complement of atypical glycerolipid molecules that form the foundation of this membrane are characterised by sugar head-groups and a very high level of unsaturation in the fatty acids that occupy the central portion of the thylakoid bilayer. alpha-linolenic (18:3) or a combination of 18:3 and hexadecatrienoic (16:3) acids typically account for approximately two-thirds of all thylakoid membrane fatty acids and over 90% of the fatty acids of monogalactosyl diacylglycerol, the major thylakoid lipid [1, 2]. The occurrence of trienoic fatty acids as a major component of the thylakoid membrane is especially remarkable since these fatty acids form highly reactive targets for active oxygen species and free radicals, which are often the by-products of oxygenic photosynthesis. Photosynthesis is one of the most temperature-sensitive functions of plant [3, 4]. There remains a widespread belief that these trienoic fatty acids might have some crucial role in plants to be of such universal occurrence, especially in photosynthesis tolerance of temperature [5].

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-Dependent Spectral Responses of Azobenzene Glycopyranoside Monolayers

Novel amphiphilic glycopyranosides containing an azobenzene chromophore and an amide−benzene auxochrome are synthesized. A sugar headgroup is attached to the auxochrome unit that links directly to azobenzene. The UV−vis spectral response of the monolayer to a change of the molecular area is found to depend on the chemical structure of the sugar unit, α-d-glucopyranose or α-d-galactopyranose. When spread on the water surface at large molecular areas, both compounds show π−π* long-wavelength peaks at around 460 nm. Upon compression of the films, the peaks for the glucopyranoside exhibits a red shift, whereas that for the galactopyranoside gives a blue shift. A reference compound having a carboxylic acid in place of the sugar unit produces a blue shift because of the formation of H-like aggregates. The pressure isotherm and a morphological study suggest that a similar aggregation is responsible for the blue shift due to the galactopyranoside. FTIR spectroscopy indicates that the amide group of the glucopyranoside contains mostly the −CN− resonance form. This resonance form increases the planarity of the azobenzene−amide−benzene units, resulting in the observed red shift. This study offers a basic chemical structure for systematic controls of dye aggregates by sugar.

Studies of N-Dodecyllactobionamide, Maltose 6‘-O-Dodecanoate, and Octyl-β-glucoside with Surface Tension, Surface Force, and Wetting Techniques

Three different types of sugar surfactants, octyl-β-glucoside, maltose 6‘-O-dodecanoate, and N-dodecyllactobionamide have been investigated to examine the effect of the structure of the sugar headgroup on the adsorption to liquid/vapor and solid/liquid interfaces using a number of techniques (surface tension, surface force apparatus, MASIF, and wetting). It was found that all the surfactants form monolayers when adsorbed to a hydrophobic interface at high concentrations. Increased headgroup flexibility leads to the adsorption of higher amounts on both the liquid/vapor and solid/liquid interfaces, resulting in a higher van der Waals attraction between two such monolayers. Increased hydrogen bonding within layers of more flexible surfactants is suggested to explain this difference. The most flexible surfactant, N-dodecyllactobionamide, is the least efficient wetting agent with the highest γSL. The behavior of the receding contact angles indicates the importance of intralayer hydrogen bonds between larger an...

Alkyl polyglucoside microemulsion phase behavior

We review several key elements of alkyl polyglucoside (C mG n) microemulsion phase behavior. The low solubility of C mG n surfactants in oils such as alkanes makes producing C mG n microemulsions and subsequent study of their phase behavior difficult. Increasing the solubility of C mG n in oil is therefore helpful for the systematic study of C mG n-based microemulsion formulations. To this end, the role of cosurfactants in producing microemulsions with water, alkanes, and n-alkyl β- d-glucopyranosides is first discussed. Adding C 10βG 1 to mixtures of water–alkane–ethoxylated alcohol surfactants (C iE j) produces a region of the three-phase body (a ‘chimney’) that is independent of temperature; thus C mβG 1 are not completely soluble in the co-oil formed of alkane and C iE j at higher temperatures. Then, through a novel approach using oxygenated ether oils (C kOC 2OC k), microemulsions are formed with water, C kOC 2OC k, and C mβG 1 and the phase behavior studied as a function of temperature and composition. Increased C mβG 1 solubility in the more hydrophilic ether oils produces patterns of phase behavior in water–C kOC 2OC k–C mβG 1 mixtures that are identical to those observed in water–alkane–C iE j mixtures. Using the water–ether oil–C mβG 1 mixtures as a base case, the role of C mG n surfactant structure in setting C mG n microemulsion phase behavior is explored. The solubility of the α- d anomer (n-alkyl α- d-glucopyranosides, C mαG 1) in water is much less than that of the β- d surfactant, and these solubility boundaries extend to high surfactant and oil concentrations in water–C kOC 2OC k–C mαG 1 mixtures. Adding C mG 2 compounds to water–C kOC 2OC k–C mβG 1 mixtures shifts the phase behavior to high temperatures, again demonstrating the extreme hydrophilic nature of the sugar headgroup. Finally, adding small amounts of ionic alkyl sulfate surfactants to water–C kOC 2OC k–C mβG 1 mixtures dramatically reduces the total amount of surfactant needed to form a single-phase microemulsion.

Surface Activity and Critical Aggregation Concentration of Pure Sugar Esters with Different Sugar Headgroups

We have studied the surface properties of a series of enzymatically synthesized sugar monoesters of xylose, galactose, sucrose, and lactose with different hydrophobic chain lengths (C12–C16) and purified, chemically synthesized sucrose esters that, unlike the enzymatically synthesized samples, contain a mixture of isomers. Data obtained have been compared with those for dodecanoic glucoside and maltoside acetals, and also a commercial sucrose myristate. Nearly all of the sugar esters studied brought about a significant reduction of the surface tension of water (to 31.0–43.0 mN m−1). A reduction in the critical aggregation concentration (CAC) of the surfactants with increasing carbon chain length was observed. Surfactants with more hydrophilic headgroups exhibited higher CAC, though this trend was moderated by the alkyl chain length. Comparing the chemically synthesized sucrose esters with their enzymatically synthesized equivalents revealed only minor differences in the CAC and the surfactant efficiency, indicating that the exact point of esterification might not be critical for the surfactant's properties. The presence of 0.1 M NaCl, KCl, or CaCl2 did not significantly alter the surface behavior of the chemically synthesized esters, indicating the absence of surface-active species with charged headgroups.

Interglycolipid Membrane Interactions: pH-Dependent Aggregation of Nonionic Synthetic Glycolipid Vesicles

Large unilamellar vesicles composed of a nonionic synthetic glycolipid, 1,3-di-O-phytanyl-2-O-(β-D-maltotriosyl)glycerol exhibited a pH-dependent aggregation–disaggregation process; vesicle aggregation occurred in a lower pH region and vesicle disaggregation occurred in a higher pH region. This process was almost reversible and the aggregation threshold pH increased as NaCl concentration increased. Electrophoretic mobility measurements revealed that the glycolipid vesicles are negatively charged in the range pH 1.6–13. The change in ζ-potentials as functions of pH and NaCl concentration could be well described by the Gouy–Chapman expression of the surface charges with an assumption that the interfacial charges arise from the “adsorption” of OH− at the vesicle–water interface and the dissociation of hydroxyl groups of the sugar headgroup in a higher pH regime (>pH 10). The pH-dependent aggregation process was reasonably well described by the classical DLVO theory. Thus, the double-layer repulsive forces appear to be a major factor in stabilizing the glycolipid vesicle suspension.

Sugar fatty acid ester surfactants: Structure and ultimate aerobic biodegradability

AbstractUltimate aerobic biodegradabilities of an array of sugar ester surfactants were determined by International Standards Organisation method 7827, “Water Quality—Evaluation in an Aqueous Medium of the Aerobic Biodegradability of Organic Compounds, Method by Dissolved Organic Carbon” (1984). The surfactants were nonionic sugar esters with different‐sized sugar head groups (formed from glucose, sucrose, or raffinose) and different lengths and numbers of alkyl chains [formed from lauric (C12) or palmitic (C16) acid]. Analogous anionic sugar ester surfactants, formed by attaching an α‐sulfonyl group adjacent to the ester bond, and sugar esters with α‐alkyl substituents were also studied. It was found that variations in sugar head group size or in alkyl chain length and number do not significantly affect biodegradability. In contrast, the biodegradation rate of sugar esters with α‐sulfonyl or α‐alkyl groups, although sufficient for them to be classified as readily biodegradable, was dramatically reduced compared to that of the unsubstituted sugar esters. An understanding of the relationship between structure and biodegradability provided by the results of this study will aid the targeted design of readily biodegradable sugar ester surfactants for use in consumer products.

Modulation of Nanotube Formation by Structural Modifications of Sphingolipids

Galactosylceramides (GalCers) containing nervonoyl (24:1Δ15(cis)) acyl chains have the capacity to assemble into nanotubular microstructures in excess water (Kulkarni et al., 1995. Biophys. J. 69:1976–1986). To define the structural parameters that modulate nanotube formation, GalCer derivatives were synthesized that contained cis monounsaturated acyl chains with the formula X:1(X-9). X indicates the total acyl carbon number (24, 22, 20, or 18), and 1 indicates a single cis double bond, the location of which is designated by the superscript (X-9). Deep etching of freeze-fractured 24:1Δ15(cis) GalCer dispersions followed by replica production and transmission electron microscopic analysis confirmed nanotube morphology (25–30-nm diameter). Control experiments revealed that tubule formation was promoted by cooling through the main enthalpic phase transition coupled with repetitive freeze-thaw cycling. Imparting a negative charge to the sugar headgroup of 24:1Δ15GalCer via sulfate dramatically altered mesomorpholgy and resulted in myelinic-like, multilamellar structures. Removal of the sugar headgroup (24:1Δ15Cer) resulted in flattened cylindrical structures with a cochleate appearance. Compared to these large-scale changes in morphology, more subtle changes were induced by structural changes in the acyl chain of 24:1Δ15GalCer. 22:1Δ13GalCer dispersions consisted of long, smooth tubules (35–40-nm diameters) with a strong tendency to self-align into bundle-like aggregates. In contrast, the microstructures formed by 20:1Δ11GalCer resembled helical ribbons with a right-handed twist. Ribbon widths averaged 30–35nm, with helical pitches of 80–90nm. 18:1Δ9GalCer displayed a variety of morphologies, including large-diameter multilamellar cylinders and liposome-like structures, as well as stacked, plate-like arrays. The results are discussed within the context of current theories of lipid tubule formation.

Non-ionic surfactant based vesicles (niosomes) in drug delivery

The self assembly of non-ionic surfactants into vesicles was first reported in the seventies by researchers in the cosmetic industry. Since then a number of groups world wide have studied non-ionic surfactant vesicles (niosomes) with a view to evaluating their potential as drug carriers. This article presents a summary of the achievements in the field to date. Niosomes may be formed form a diverse array of amphiphiles bearing sugar, polyoxyethylene, polyglycerol, crown ether and amino acid hydrophilic head groups and these amphiphiles typically possess one to two hydrophobic alkyl, perfluoroalkyl or steroidal groups. The self assembly of surfactants into niosomes is governed not only by the nature of the surfactant but by the presence of membrane additives, the nature of the drug encapsulated and the actual method of preparation. Methods of niosome preparation and the number of different morphologies that have been identified are detailed. The influence of formulation factors on niosome stability is also examined as are methods to optimise drug loading. In vivo these systems have been evaluated as immunological adjuvants, anti-cancer/anti-infective drug targeting agents and carriers of anti-inflammatory drugs. Niosomes have also been used in diagnostic imaging. Efforts to achieve transdermal and ophthalmic drug delivery with some formulations are also discussed.

Amphiphilic and mesogenic carbohydrates IX. Perfluoroalkyl substituted monosaccharides: a new group of amphiphilic liquid crystals

The thermal properties of twelve 'single-tailed' carbohydrate-based liquid crystal materials which have a perfluoroalkyl chain (n-C4F9, n-C6F13, n-C8F17) linked to the polar sugar head group are described. All reported amphiphiles, the 6-deoxy-6-C-perfluorohexyl-L-altrose 1, the (5R)-xylopentoses 2, 3 and 4, the 5,6-dideoxy-6-C-perfluoroalkyl-D-glucofuranoses 5 and 6, the 2,3-O-perfluoroalkylidene-D-gulopyranoses 7, 8 and 9 and the 3,4-O-perfluoroalkylidene- D-altropyranoses 10 and 11 form mesophases of the smectic A type. Even a C4F9-chain (compounds 2, 7, and 10) is long enough to cause liquid crystalline behaviour.

Phase Equilibria and Equation of State of a Mixed Cationic Surfactant−Glycolipid Lamellar System

We establish experimentally the equation of state relating pressure and composition of a ternary model glycolipid/synthetic cationic surfactant/water system at room temperature. It is shown that an adhesion energy induced by the sugar headgroups is necessary to explain the presence of two distinct critical points that close two biphasic lamellar−lamellar zones. Between these two critical points, a turbid single-phase region is evidenced.

Temperature scanning simultaneous small- and wide-angle X-ray scattering studies on glycolipid vesicles: areas, expansion coefficients and hydration

The polymorphic behaviour of glycolipid model membranes has been characterized by monitoring simultaneously wide- and small angle synchrotron X-ray scattering as a function of temperature along with temperature scanning differential density (DSD) measurements. We estimated the area per lipid and calculated the total volume of the lipid, V T, which includes the hydration shell as well as the interlamellar water. This volume was compared with the partial specific volume of the lipid, v̄ obtained from the DSD studies. The difference was attributed to the presence of water between the lamellar stacks. On this basis estimates of the number of water molecules associated with the sugar head group were made. The main results can be summarized as follows: The average area occupied by two chains within the bilayer plane changes from about 37 Å 2 in the L C phase to about 57 Å 2 in the L α phase at the respective main transition temperatures of the lipids. In the gel phase at T 1/2 an area of about 42 Å 2 is required for two lipid chains. We found that the highly ordered L C phase of the glycolipids is nearly unhydrated, while in the L β phase about seven H 2O molecules and in the L α phase about 14 H 2O molecules are observed per sugar moiety. Hydration increases slightly with temperature in the L β phase. This can be derived from differences in the expansion coefficients of V T and v̄.

Phase equilibria of charged lamellar phases: Effect of adding surfactants with sugar headgroups on interbilayer repulsions

Phase equilibria of charged lamellar phases: Effect of adding surfactants with sugar headgroups on interbilayer repulsions

Synthesis of Cyclodextrin Derivatives Carrying Bio-Recognisable Saccharide Antennae

The use of coupling saccharide antenna onto cyclodextrins allows mobility for the biologically active galactose head group, and allows the recognition process by the lectin (KbCWL). This paper reports a chemical synthesis of β-CD derivatives using spacer arms 3, 4, 5, 6 and 9 carbon atoms. Preliminary results suggested that recognition is strongly dependent on the length of the spacer chain between the cyclodextrin and the sugar head group. © 1997 Elsevier Science Ltd.