Dextran fatty acid esters as polymeric surfactants with low hemolytic activity

Practically all low molecular weight surfactants show hemolytic activities. Aside of this serious disadvantage almost all low molecular weight solubilizers cause considerable side effects, particularly during or after parenteral application. Polymeric surfactants, however, usually show no or only very little hemolytic effects. They therefore are supposed not to be able to penetrate neither into cellular or erythrocyte walls nor into phospholipid bilayers, resp., similar bilayer membranes due to their large molecular size. Therefore no decay of biological bilayers should be expected with polymeric surfactants. The only pharmaceutically widely used polymeric surfactants are at the moment polyoxyethylene-polyoxypropylene block copolymers (poloxamers (INN), Pluronicsr̀ and Pluriolsr̀). Unfortunately they have only poor solubility capacities. In order to find better solubilizing polymeric surfactants, some water soluble dextran fatty acid esters (Ref. 1) were synthesized and tested with respect to their solubilisation capacity and hemolytic activity. Usually the hemolytic activity is tested by standard methods using purified animal or human erythrocyte suspensions. As erythrocytes also contain a relatively high amount of lactose dehydrogenase (LDH), we studied the suitability of the highly sensitive, and in the medical diagnostic well known LDH test, as a supplemental hemolytic determination method (Ref. 2). The advantage of this test is, that there is no need of the time consuming purification and standardization as it is required with the erythrocytes' suspension. It can be performed with original blood and without costly preparations at all. The synthesized dextran fatty acid esters proved themselves as very little hemolytic and, compared with the polyoxyethylene-polyoxypropylene block copolymers, they show improved solubilisation capacities.     

Effects of double-chained cationic surfactants n-dimethyldialkylammoniums on skin permeation of benzoic acid through excised guinea pig dorsal skin: comparison of their enhancement effects with hemolytic effects on erythrocytes

We examined the effects of the double-chained cationic surfactants dimethyidialkylammoniums (CH3)2N+ (CnH(2n+1))2 on the permeation of benzoic acid through excised guinea pig dorsal skin. Among five dimethyldialkylammoniums tested (n=10-18), dimethyldidecylammonium (n=10) had dose-dependent enhancement effects at concentrations of more than 20 microM. Compared with the marked enhancement effects of dimethyldialkylammoniums with relatively shorter alkyl chains, those of long-chain dimethyldialkylammoniums (n=16, 18) were much less. We compared the enhancement effects of these cationic surfactants on skin permeation with their hemolytic effects on guinea pig erythrocytes. Their enhancement effects corresponded to their hemolytic activity. The findings suggest that dimethyldialkylammoniums with relatively shorter alkyl chains, which form either vesicles with looser molecular packing or micelles and appear to be present as surfactant monomers in higher ratios than those with longer alkyl chains, favor the interaction with skin. Their enhancement mechanism is possibly similar to that of single-chained cationic surfactants.     

Detection of bioactive surfactants in aqueous solutions on the basis of H2O2-voltammetry

The voltammetric determination of surfactants at the hanging mercury drop electrode in aqueous solutions is described, based on the shift of the peak potential deltaEp or the increase of the peak height deltaip of the electroreduction of hydrogen peroxide or of the second oxygen reduction step, with increasing concentration of surfactants. Although the selectivity of this method is rather limited, it could be utilized, e.g., for monitoring the absence (or presence) or for the determination of the contents of specified surfactants by comparing the obtained deltaip (deltaEp) signal with the reference state of the system or with that of a selected reference surface active substance. As model surfactants n-octanol, tetrabutylammonium chloride and sodium dodecylbenzenesulfonate were used, the regular adsorption behavior of which is well known. The method was successfully applied to control the presence of a commercial detergent in water for rinsing bottles for infusion solutions.     

The synthesis and properties of homologous series of surfactants containing the pyrrolidinium head group with hydroxyethyl moiety

The surface activity, micelle formation, and solubilization ability towards hydrophobic compounds were estimated for the series of new cationic surfactants belonging to the type of 1-alkyl-1-(2-hydroxyethyl)pyrrolidinium bromides. The presence of 2-hydroxyethyl group in these surfactants leads to the twofold increase in their micelle-forming ability as compared to unsubstituted analogs. The critical micelle concentration for the investigated series of pyrrolidinium surfactants is lower at the same hydrophobicity than that for the analogs belonging to the alkylpyridinium, alkylimidazolium, and alkylmorpholinium types. The data acquired for the studied surfactants on their solubilization ability, antimicrobial activity, and hemolytic efficiency indicate their prospective applications to encapsulate hydrophobic biologically active molecules and as the promising bactericidal agents.

     

Ultrasonic nebulization in aqueous solutions and the role of interfacial adsorption dynamics in surfactant enrichment

High-density micron-sized aerosols from liquid surfaces were generated using an ultrasonic (frequency = 1056 kHz) nebulization technique in the absence and presence of a number of surfactants. The surfactants included cationic surfactants, cetylpyridinium chloride and dodecylpyridinium chloride, and anionic surfactants, sodium dodecylbenzenesulfonate and sodium benzenesulfonate. The nebulization process generated aerosols of a narrow size distribution with a number mean diameter of about 3.4 mum, which is close to the theoretical value suggested by the Lang Equation. The aerosol droplets are enriched in surfactant as a consequence of the large interfacial area. The enrichment factor varied for different surfactants, depending on their surface activity. The extent of enrichment can be related to the rate of mass transfer of surfactant to the liquid surface. Surface concentrations of between 15 and 30% of the equilibrium value are observed, indicating turbulent mass transfer is the rate limiting step.     

Detection of bioactive surfactants in aqueous solutions on the basis of H2O2-voltammetry

The voltammetric determination of surfactants at the hanging mercury drop electrode in aqueous solutions is described, based on the shift of the peak potential ΔE_P or the increase of the peak height Δi_P of the electroreduction of hydrogen peroxide or of the second oxygen reduction step, with increasing concentration of surfactants. Although the selectivity of this method is rather limited, it could be utilized, e.g., for monitoring the absence (or presence) or for the determination of the contents of specified surfactants by comparing the obtained Δi_P (ΔE_P) signal with the reference state of the system or with that of ¶a selected reference surface active substance. As model surfactants n-octanol, tetrabutylammonium chloride and sodium dodecylbenzenesulfonate were used, the regular adsorption behavior of which is well known. The method was successfully applied to control the presence of a commercial detergent in water for rinsing bottles for infusion solutions.     

Interactions of novel, nonhemolytic surfactants with phospholipid vesicles

PEG-12-acyloxystearates constitute a novel class of pharmaceutical solubilizers and are synthesized from polyethylene glycol and 12-hydroxystearic acid, which has been esterified with a second acyl chain. The hemolytic activity of these surfactants decreases drastically with increasing pendant acyloxy chain length, and surfactants with an acyloxy chain of 14 carbon atoms or more are essentially nonhemolytic. In this paper, the interactions of PEG-12-acyloxystearates (acyloxy chain lengths ranging from 8 to 16 carbon atoms) with phosphatidylcholine vesicles, used as a model system for erythrocyte membranes, were studied in search of an explanation for the large variations in hemolytic activity. Surfactant-induced alterations of membrane permeability were investigated by studying the leakage of vesicle-entrapped calcein. It was found that all of the surfactants within the series interact with the vesicle membranes and cause slow leakage at elevated surfactant concentrations, but with large variations in leakage kinetics. The initial leakage rate decreases rapidly with increasing pendant acyloxy chain length. After prolonged incubation, on the other hand, the leakage is not a simple function of acyloxy chain length. The effect of the surfactants on membrane integrity was also investigated by turbidity measurements and cryo-transmission electron microscopy. At a surfactant/lipid molar ratio of 0.4, the vesicle membranes are saturated with surfactant. When the surfactant/lipid molar ratio is further increased, the vesicle membranes are progressively solubilized into mixed micelles. The rate of this process decreases strongly with increasing acyloxy chain length. When comparing the results of the different experiments, it can be concluded that there is no membrane permeabilization below saturation of the vesicle membranes. The large variations in the kinetics suggest that several steps are involved in the mechanism of leakage induced by PEG-12-acyloxystearates and that their relative rates vary with acyloxy chain length. The slow kinetics may in part be explained by the low critical micelle concentrations (CMCs) exhibited by the surfactants. The CMCs were found to be in the range of 0.003-0.025 microM.     

Aggregation behavior of p-n-alkylbenzamidinium chloride surfactants

The aggregation behavior of a novel class of surfactants, p-n-alkylbenzamidinium chlorides, has been investigated. The thermodynamics of aggregation of p-n-decylbenzamidinium chloride mixed with cationic and anionic cosurfactants has been studied using isothermal titration calorimetry. For mixtures of p-n-decylbenzamidinium chloride with n-alkyltrimethylammonium chlorides, the aggregation process is enthalpically more favorable than for the pure n-alkyltrimethylammonium chlorides, probably caused by diminished headgroup repulsion due to charge delocalization in the amidinium headgroup. A critical aggregation concentration between 3 and 4 mM has been extrapolated for p-n-decylbenzamidinium chloride at 40 degrees C, around two times lower than that of similar surfactants without charge delocalization in the headgroup and well comparable to that of similar surfactants with charge delocalization in the headgroup. In mixtures of p-n-decylbenzamidinium chloride with either sodium n-alkylsulfates or sodium dodecylbenzenesulfonate, evidence is found for the formation of bilayer aggregates by the pseudo-double-tailed catanionic surfactants composed of p-n-decylbenzamidinium and the anionic surfactant. These aggregates are solubilized to mixed micelles by excess free anionic surfactant at the measured critical aggregation concentration.     

The effect of selected surfactants on the structure of a bicellar system (DMPC/DHPC) studied by SAXS

The stabilizing or disturbing effect of different surfactants on the bicellar phase of phospholipids significantly depends on their type. The effect of different surfactants on the bicellar structure made of a mixture of phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1,2-dihexanoyl-sn-glycero-3-phospho-choline (DMPC/DHPC) has been studied by the small angle scattering of synchrotron radiation. The study has been performed for three surfactants: dodecyldimethyl-(hexyloxymethyl)ammonium chloride, n-undecylammonium chloride and t-octylphenoxypolyethoxyethanol (Triton X-100) introduced into a bicellar solution of DMPC/DHPC (2.8:1). The bicellar phase has been disturbed in the shortest time in the presence of dodecyldimethyl-(hexyloxymethyl)ammonium chloride in this system a transition from the bicellar to lamellar structure has been directly visible. The changes have been less pronounced in the presence of undecylammonium chloride and practically not noted in the presence of Triton X-100.     

Effect of surfactants on the chemiluminescence of acridinium dimethylphenyl ester labels and their conjugates

Chemiluminescent acridinium dimethylphenyl esters, containing two methyl groups flanking the phenolic ester bond, display excellent chemiluminescence stability and are used as labels in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of the cationic surfactant cetyltrimethylammonium chloride. Under these conditions, light emission is rapid and is complete in <5 s. In the present study we examined the effect of various surfactants on light emission from acridinium dimethylphenyl ester labels and their conjugates containing hydrophilic linkers derived either from hexa(ethylene)glycol or a sulfobetaine zwitterion. Sulfobetaine zwitterions are very polar and incorporation of these functional groups in acridinium dimethyphenyl esters and their conjugates represents a new approach to improving the aqueous solubility of these chemiluminescent labels. Our results indicate that in general, surfactants affect light emission from these labels and their conjugates by two discrete mechanisms. Cationic surfactants, but not anionic or non-ionic surfactants, accelerate overall light emission kinetics and a more modest effect is observed with zwitterionic surfactants. Surfactants also enhance total light output and the magnitude of this enhancement is maximal for cationic surfactants and a sulfobetaine zwitterionic surfactant. These observations are the first to clearly delineate the role of the surfactant on the chemiluminescence reaction pathway of acridinium esters and can be rationalized based on known effects of surfactant aggregates on bimolecular and unimolecular reactions.     

Separation of phenols from aqueous micellar solutions by cloud point extraction

The cloud point technique was used to recover phenol, 4-methylphenol, and 4-nitrophenol from aqueous solutions using oxyethylated methyl dodecanoates as nonionic surfactants. Oxyethylated methyl dodecanoates are convenient nonionic surfactants for such separations. Their cloud points can be easily modified by a change in surfactant hydrophilicity or by the addition of a second nonionic surfactant and/or an electrolyte. The use of the hydrophile lipophile balance is preferred to model the cloud point of oxyethylated methyl dodecanoates and their mixtures with other surfactants. The composition of the surfactant-rich phase depends on electrolyte type and the overheating. The phase can contain only 5-15% of water. Recovery of phenols changes in the order 4-nitrophenol >4-methylphenol > phenol and is increased in the presence of sodium chloride. The presence of salting-out electrolytes is preferred both to decrease the cloud point and to increase the efficiency of extraction.     

Comparison of oleyl and elaidyl isomer surfactant-counterion systems in drag reduction, rheological properties and nanostructure

Compared with quaternary ammonium cationic surfactants with saturated alkyl chains, quaternary ammonium cationic surfactants with one double-bond in their alkyl chains, when mixed with appropriate counterions (in certain molar concentration ratios, ξ), can reach much lower effective drag-reduction temperatures, while maintaining the upper drag-reduction temperature limit of the corresponding saturated drag reducing surfactant solutions. No previous study has compared the effects of cis- vs. trans-unsaturated alkyl hydrocarbon tail configurations (oleyl vs. elaidyl) trimethyl ammonium chloride cationic surfactants at different counterion/surfactant concentration ratios on micellar nanostructures, (1)H NMR spectra and on rheological and drag-reduction behavior of their solutions. Since neither pure oleyl (cis-) nor elaidyl (trans-) trimethyl ammonium chloride surfactants are commercially available, they were synthesized and their 5mM solutions with NaSal counterion at concentrations of 5mM, 7.5mM and 12.5mM were studied.     

Cationic Surfactants in Interfacial Synthesis of Linear Aromatic Polyester

Abstract

The polycondensation of terephthaloyl chloride and bisphenol A was used as a model reaction for the production of linear aromatic polyesters in stirred interfacial polymerization. The evaluation of several catalytic and surfactant additives to this system was based upon yields and intrinsic viscosities of the products obtained with both low and high concentrations of cationic surfactants of the quaternary ammonium type, of an anionic surfactant, and of a non-micelle forming quaternary ammonium salt. Although yields were similar in most cases, viscosity differences were marked. The highest intrinsic viscosities, hence highest degrees of polymerization, were found for preparations where cationic surfactant in excess of the critical micelle concentration was employed. Modes of action for such surfactants are suggested. The possibilities include, but are not limited to, solubilization of the product, solubilization of either or both monomers, emulsification of the liquid phases, catalytic phase transfer of one monomer, and micellar catalysis.     

Phospholipid Bilayer-Perturbing Properties Underlying Lysis Induced by pH-Sensitive Cationic Lysine-Based Surfactants in Biomembranes

Amino acid-based surfactants constitute an important class of natural surface-active biomolecules with an unpredictable number of industrial applications. To gain a better mechanistic understanding of surfactant-induced membrane destabilization, we assessed the phospholipid bilayer-perturbing properties of new cationic lysine-based surfactants. We used erythrocytes as biomembrane models to study the hemolytic activity of surfactants and their effects on cells' osmotic resistance and morphology, as well as on membrane fluidity and membrane protein profile with varying pH. The antihemolytic capacity of amphiphiles correlated negatively with the length of the alkyl chain. Anisotropy measurements showed that the pH-sensitive surfactants, with the positive charge on the α-amino group of lysine, significantly increased membrane fluidity at acidic conditions. SDS-PAGE analysis revealed that surfactants induced significant degradation of membrane proteins in hypo-osmotic medium and at pH 5.4. By scanning electron microscopy examinations, we corroborated the interaction of surfactants with lipid bilayer. We found that varying the surfactant chemical structure is a way to modulate the positioning of the molecule inside bilayer and, thus, the overall effect on the membrane. Our work showed that pH-sensitive lysine-based surfactants significantly disturb the lipid bilayer of biomembranes especially at acidic conditions, which suggests that these compounds are promising as a new class of multifunctional bioactive excipients for active intracellular drug delivery.     

Synthesis and Characterization of Optically Active Surfactants Derived from Phenylalanine and Leucine

Two optically active cationic surfactants, (2S)-N-hexadecyl-N, N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium chloride 1 and (2S)-N-hexadecyl-N,N-dimethyl-(1-hydroxy-4-methylpentyl)-2-ammonium chloride 2, have been selected and synthesized for use as enantioselective micellar catalysts in aqueous media. Their surface and aggregation behavior has been investigated at 298 K using surface tension and light scattering studies, which revealed that both molecules associate at low concentrations to produce micellar aggregates. Interestingly, although the area per molecule occupied by the surfactants at the air-water interface (43.6 ?(2) for 1 and 54.6 ?(2) for 2) is similar to that of related cationic surfactants, their aggregation number (23 for 1 and 19 for 2) is much smaller, perhaps reflecting the influence of the size or homochiral nature of the head group in the packing of the micelle. Copyright 2001 Academic Press.     

The potentiometric titration of surfactants and soaps using ion-selective electrodes

Summary Several quaternary ammonium halides have been evaluated for the precipitation titration of anionic surfactants and soaps. The titrants were hexadecyltrimethylammonium chloride and bromide, hexadecylpyridinium chloride, and diisobutylphenoxyethoxyethyl(dimethyl)benzylammonium chloride. Hexadecylpyridinium chloride yielded the highest precision and largest potentiometric break. Titrations were monitored with a commercically available fluoroborate ion-selective indicator electrode and a double-junction reference electrode. Commercially available perchlorate, nitrate, and calcium electrodes may also be used for emf monitoring. This obviates the need of preparing special liquid membrane or other electrodes mostly used heretofore in the potentiometric titration of surfactants and soaps. Electrophoresis purity reagent sodium dodecylsulfate is recommended for the standardization of the quaternary ammonium halides. The reverse titration, of cationic surfactants vs. standard sodium dodecylsulfate, is similarly feasible.Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore Laboratory under contract number W-7405-ENG-48.     

Binding of ionic surfactants to purified humic acid

The binding of organic contaminants to dissolved humic acids reduces the free concentration of the contaminants in the environment and also may cause changes to the solution properties of humic acids. Surfactants are a special class of contaminants that are introduced into the environment either through wastewater or by site-specific contamination. The amphiphilic nature of both surfactants and humic acids can easily lead to their mutual attraction and consequently affect the solution behavior of the humics. Binding of an anionic surfactant (sodium dodecyl sulfate, SDS) and two cationic surfactants (dodecyl- and cetylpyridinium chloride, DPC and CPC) to purified Aldrich humic acid (PAHA) is studied at pH values of 5, 7, and 10 in solutions with a 0.025 M ionic strength (I). Monomer concentrations of the surfactants are measured with a surfactant-selective electrode. At I = 0.025 M, no significant binding is observed between the anionic surfactant (SDS) and PAHA, whereas the two cationic surfactants (DPC, CPC) bind strongly to PAHA over the pH range investigated. The binding is due both to electrostatic and hydrophobic attraction. The initial affinity increases with increasing pH (i.e., negative charge of PAHA) and tail length of the surfactant. Binding reaches a pseudo-plateau value (2-5 mmol/g) when the charge associated with PAHA is neutralized by that of the bound surfactant molecules. The pseudo-plateau values for DPC and CPC are very similar and depend on the solution pH. The cationic surfactant-PAHA complexes precipitate when the charge neutralization point is reached. This occurs at approximately 10% of the critical micelle concentration or CMC. This type of phase separation commonly occurs during surfactant binding to oppositely charged polyelectrolytes. For CPC, the precipitation is complete, but in the case of DPC, a noticeable fraction of PAHA remains in solution. At very low CPC concentrations (less than 0.1% of the CMC), CPC binding to PAHA is cooperative. The investigated range of concentrations for DPC was too limited to reach a similar conclusion. The results of this study demonstrate that the fate of humic acids will be strongly affected by the presence of low cationic surfactant concentrations in aqueous environmental systems.     

EVALUATION OF A SERIES OF PERFLUOROALKYLATED SURFACTANTS DERIVED FROM TERTIARY AMINES: SURFACE PROPERTIES AND EMULSIFICATION OF FLUOROCARBONS

In view of their easy preparation, the physicochemical properties of a series of highly fluorinated cationic (ammonium salts), zwitterionic (carboxybetaines) or nonionic (amine oxide) surfactants derived from perfluoroalkylated tertiary amines were investigated. Their solubility in water, interfacial properties and the exceptionally low hemolytic activity of the zwitterionic series mark them out as potential surfactants or co-surfactants for the preparation of fluorocarbon emulsions and other preparations for biomedical use. Fine and moderately concentrated fluorocarbon emulsions (50 w/w% in fluorocarbon) could be obtained in some cases when they were used as the sole surfactant. However, none was found suitable for preparing concentrated emulsions (90 w/v% in fluorocarbon) and no appreciable stabilization was found when they were used as co-surfactants with egg yolk phospholipids.     

Extractive spectrophotometric determination of non-ionic surfactants in water

The solvent extraction of non-ionic surfactants with potassium chloride and tetrabromophenolphthalein ethyl ester potassium salt has been studied, and a method developed for determining trace amounts of non-ionic surfactants in water spectrophotometrically. Various non-ionic surfactants of general type RO(CH(2)CH(2)O)(n)H (where R is an alkyl or alkylphenyl group and n is the number-average degree of polymerization) are extracted quantitatively into o-dichlorobenzene from the water sample, and reacted in the organic phase with tetrabromophenolphthalein ethyl ester potassium salt to give a coloured product, the absorbance of which is measured at 620 nm.