Critical micellar concentration

Detergents are indispensable in the isolation of integral membrane proteins from biological membranes to study their intrinsic structural and functional properties. Solubilization involves a number of intermediary states that can be studied by a variety of physicochemical and kinetic methods ; it usually starts by destabilization of the lipid component of the membranes, a process that is accompanied by a transition of detergent binding by the membrane from a noncooperative to a cooperative interaction already below the critical micellar concentration (CMC). This leads to the formation of membrane fragments of proteins and lipids with detergent-shielded edges. In the final stage of solubilization membrane proteins are present as protomers, with the membrane inserted sectors covered by detergent. We consider in detail the nature of this interaction and conclude that in general binding as a monolayer ring, rather than as a micelle, is the most probable mechanism. This mode of interaction is supported by neutron diffraction investigations on the disposition of detergent in 3-D crystals of membrane proteins. Finally, we briefly discuss the use of techniques such as analytical ultracentrifugation, size exclusion chromatography, and mass spectrometry relevant for the structural investigation of detergent solubilized membrane proteins. ß

Thioflavin T is a benzothiazole dye that exhibits enhanced fluorescence upon binding to amyloid fibrils and is commonly used to diagnose amyloid fibrils, both ex vivo and in vitro. In aqueous solutions, thioflavin T was found to exist as micelles at concentrations commonly used to monitor fibrils by fluorescence assay ($10-20 lM). Specific conductivity changes were measured at varying concentration of thioflavin T and the critical micellar concentration was calculated to be 4.0 ± 0.5 lM. Interestingly, changes in the fluorescence excitation and emission of thioflavin T were also dependent on the micelle formation. The thioflavin T micelles of 3 nm diameter were directly visualized using atomic force microscopy, and bound thioflavin T micelles were observed along the fibril length for representative fibrils. Increasing concentration of thioflavin T above the critical micellar concentration shows increased numbers of micelles bound along the length of the amyloid fibrils. Thioflavin T micelles were disrupted at low pH as observed by atomic force microscopy and fluorescence enhancement upon binding of thioflavin T to amyloid fibrils also reduced by several-fold upon decreasing the pH to below 3. This suggests that positive charge on the thioflavin T molecule has a role in its micelle formation that then bind the amyloid fibrils. Our data suggests that the micelles of thioflavin T bind amyloid fibrils leading to enhancement of fluorescence emission.

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to selfassociate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug^membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug^membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

We have determined the in vitro and in vivo cellular distribution of the antineoplastic agent paclitaxel (Taxol) in human blood and the influence of Cremophor EL (CrEL), the vehicle used for i.v. drug administration. In the absence of CrEL, the blood:plasma concentration ratio was 1.07 ؎ 0.004 (mean ؎ SD). The addition of CrEL at concentrations corresponding to peak plasma levels achieved after the administration of paclitaxel (175 mg/m 2 i.v. over a 3-h period; i.e., 0.50%) resulted in a significant decrease in the concentration ratio (0.690 ؎ 0.005; P < 0.05). Kinetic experiments revealed that this effect was caused by reduced erythrocyte uptake of paclitaxel by polyoxyethyleneglycerol triricinoleate, the major compound present in CrEL. Using equilibrium dialysis, it was shown that the affinity of paclitaxel for tested matrices was (in decreasing order) CrEL > plasma > human serum albumin, with CrEL present at or above the critical micellar concentration (ϳ0.01%). Our findings in the present study demonstrate a profound alteration of paclitaxel accumulation in erythrocytes caused by a trapping of the compound in CrEL micelles, thereby reducing the free drug fraction available for cellular partitioning. It is proposed that the nonlinearity of paclitaxel plasma disposition in patients reported previously should be reevaluated prospectively by measuring the free drug fractions and whole blood:plasma concentration ratios.

Haemolysis has been used as an initial selection criterion for the primary isolation of surfactant-producing bacteria. Only 37 of 492 strains of different origins had haemolytic activity. These 37 strains, together with 49 non-haemolytic ones chosen at random, were studied for surface activity. Only five strains, all of them haemolytic, tested positive. Haemolysis and biosurfactant-production are thus probably associated.

The critical micellar concentration (cmc) of both ionic and non-ionic surfactants can be conveniently determined from the measurements of UV absorption of pyrene in surfactant solution. The results on a number of surfactants have agreed with that realized from pyrene fluorescence measurements as well as that obtained following conductometric, tensiometric and calorimetric methods. The absorbance vs [surfactant] profiles for all the major UV spectral peaks of pyrene have been found to be sigmoidal in nature which were analyzed according to Sigmoidal–Boltzmann equation (SBE) to evaluate the cmcs of the studied surfactants. The difference between the initial and the final asymptotes (aiai and afaf, respectively) of the sigmoidal profile, Δa=(af−ai)Δa=(af−ai) and the slope of the sigmoid, SsigSsig have been observed to depend on the type of the surfactant. The Δa has shown a linear correlation with the ratio of the fluorescence intensities of the first and the third vibronic peaks, I1/I3I1/I3 of pyrene which is considered as a measure of the environmental polarity (herein micellar interior) of the probe (pyrene). Thus, Δa values have the prospect for use as another index for the estimation of polarity of micellar interior.

Transfer of MPEG19oo-DSPE from micellar phase to pre-formed liposomes imparts long in vivo circulation half-life to an otherwise rapidly cleared lipid composition. MPEG19oo-DSPE transfers efficiently and quickly in a time and temperature dependent manner. There is negligible content leakage and a strong correlation between assayed mol% MPEG19oo-DSPE, liposome diameter increase, and pharmacokinetic parameters such as distribution phase half-life. Since a biological attribute (liposome clearance rate) can be modified by the insertion process, it suggests a simple and economical way to impart sitespecific targeting to a variety of liposome delivery systems. This method is also a convenient way to measure the 'brush' thickness of such conjugates directly.

Methane hydrate equilibrium has been studied upon continuous heating of the water-hydrate-gas system within the temperature range of 275-300 K. This temperature range corresponds to equilibrium pressures of 3.15-55 MPa. The hydrate formation/dissociation experiments were carried out in a high-pressure reactor under isochoric conditions and with no agitation. A small amount of surfactant (0.02 wt% sodium dodecyl sulfate, SDS) was added to water to promote hydrate formation. It was demonstrated that SDS did not have any influence on the gas hydrate equilibrium, but increased drastically both the hydrate formation rate and the amount of water converted into hydrate, when compared with the experiments without surfactant. To understand and clarify the influence of SDS on hydrate formation, macroscopic observations of hydrate growth were carried out using gas propane as hydrate former in a fully transparent reactor. We observed that 10 −3 wt% SDS (230 times less than the Critical Micellar Concentration of SDS) were sufficient to prevent hydrate particles from agglomerating and forming a rigid hydrate film at the liquid-gas interface. In the presence of SDS, hydrates grew mainly on the reactor walls as a porous structure, which sucked the solution due to capillary forces. Hydrates grew with a high rate until about 97 wt% of the water present in the reactor was transformed into hydrate.

We have developed a method for producing sterically stabilized immunoliposomal drugs (SIL) readily applicable to à mix and match' combinatorial approach for the simple manufacture of a variety of ligand-targeted liposomal drugs. Ligands coupled to the terminus of polyethylene glycol (PEG) in micelles formed from PEG-lipid derivatives (mPEG 2000 -DSPE) could be transferred into preformed, drug-containing liposomes from the micelles in a temperature-and time-dependent manner. Antibody densities up to 100 W Wg antibody/W Wmol of phospholipid, and up to 3 mol% of mPEG 2000 -DSPE, could be simultaneously transferred from the ligand-coupled micelles into the liposomal outer monolayer with negligible drug leakage from liposomes during transfer and good stability in human plasma. Transfer of anti-CD19 into SIL resulted in a three-fold increase in binding of these liposomes to CD19 + human B cell lymphoma cells.

The formation of micelles of Tween-20 and Brij-35 as well as of SDS, Tween-20, and Brij-35 mixed in different proportions in aqueous medium has been physicochemically investigated. The critical micellar concentration (CMC), micellar aggregation number, counterion binding by micelles, micellar polarity, free energies of micellization and interfacial adsorption, and entropy of micellization have been evaluated by conductometric, tensiometric, and fluorimetric measurements. The solution composition has been found to have a complex say on the measured physicochemical parameters. The enthalpies of micellization of both Tween-20 ؉ Brij-35 and SDS ؉ Tween-20 ؉ Brij-35 mixed surfactant systems have been found to be negligibly small. Attempts to understand the properties of mixed micelles (composition, mutual synergism, component activity coefficients, and CMC) have been made with the help of the propositions of Clint, Rubingh, and Rubingh and Holland. The mixed binary and ternary systems can be adequately described by these theories.

We present results of a systematic experimental and theoretical investigation of the effect of urea on micellization, micellar growth, and phase separation of aqueous micellar solutions of the nonionic surfactant n-dodecyl hexaethylene oxide (CI2E6). The experimental studies, which cover a wide range of urea concentrations from 0 to 6 M, involve determinations of the critical micellar concentration (cmc), micellar shape and size as a function of temperature, and liquid-liquid phase separation coexistence curves. We find that the addition of urea significantly affects micellar solution properties. In particular, (i) the cmc increases, (ii) micellar size decreases, (iii) the "sphere-to-rod" shape transition temperature shifts to higher values, and (iv) the critical point, associated with the coexistence curve, shifts to a higher temperature and concentration. We also find that the measured coexistence curves, at 0, 2, 4, and 6 M urea concentrations, collapse onto a single universal curve when plotted in reduced coordinates. In addition, we find that plots of the mean micellar hydrodynamic radius, Rh, vs T, -T, where T, is the critical temperature and Tis the actual temperature, overlap for 0, 2,4, and 6 M urea concentrations, with the resulting universal curve exhibiting a pronounced break at a value of T, -T = 37 "C.

Mixed micelles formed by cetyl pyridinium chloride (CPC), Tween-40, and Brij-56 mixed in different proportions in an aqueous medium have been physicochemically studied in detail using tensiometric, conductometric, and fluorimetric techniques. The critical micellar concentration (CMC), free energies of micellization and interfacial adsorption, counterion binding, micellar aggregation number, and micellar polarity have been determined. To understand the CMC, composition, mutual synergism, and component activity coefficients of the mixed micelles, the theories and equations of Clint, Motomura, Rubingh, Rubingh and Holland, and Sarmoria, Puvvada, and Blankschtein have been used. Such studies on binary and ternary combinations are limited. C 2001 Academic Press

The localisation of the xanthophyll neoxanthin within the structure of the major light harvesting complex (LHCII) of higher plants has been investigated by site-directed mutagenesis and spectroscopic methods. Mutation analysis performed on pigment binding sites in different helix domains leads to selective loss of neoxanthin for mutations on helix C thus localising this pigment between the helix C and helix A/B domains. Recombinant proteins binding two lutein molecules per polypeptide but lacking neoxanthin have been used in order to determine the contribution of neoxanthin to the absorption and linear dichroism spectra. The data were used to derive the orientation of the neoxanthin transition moment, lying in the polyene chain, which was thus determined to form an angle of 57 þ 1.5³ with respect to the normal to the membrane plane where the protein is inserted. On the basis of these results we propose a model for the localisation of the carotenoid site in the LHCII structure which is still unresolved.

The complexes of horse myoglobin (Mb) with the anionic surfactant sodium dodecyl sulfate (SDS), and with the cationic surfactants cetyltrimethylammonium chloride (CTAC) and decyltrimethylammonium bromide (DeTAB), have been studied by a combination of surface tension measurements and optical spectroscopy, including heme absorption and aromatic amino acid fluorescence. SDS interacts in a monomeric form with Mb, which suggests the existence of a specific binding site for SDS, and induces the formation of a hexacoordinated Mb heme, possibly involving the distal histidine. Fluorescence spectra display an increase of tryptophan emission. Both effects point to an increased protein flexibility. SDS micelles induce both the appearance of two more heme species, one of which has the features of free heme, and protein unfolding. Mb/CTAC complexes display a very different behavior. CTAC monomers have no effect on the absorption spectra, and only a slight effect on the fluorescence spectra, whereas the formation of CTAC aggregates on the protein strongly affects both absorption and fluorescence. Mb/DeTAB complexes behave in a very similar way as Mb/CTAC complexes. The surface activity of the different Mb/surfactant complexes, as well as the interactions between the surfactants and Mb, are discussed on the basis of their structural properties.

Measuring the stability of integrated membrane proteins under equilibrium conditions is hampered by the nature of the proteins' amphiphilic environment. While intrinsic fluorescence is a useful probe for structural changes in water-soluble proteins, the fluorescence of membrane proteins is sensitive to changes in lipid and detergent composition. As an attempt to overcome this problem, I present a kinetic analysis of the folding of a membrane protein, disulfide bond reducing protein B (DsbB), in a mixed micelle system consisting of varying molar ratios of sodium dodecyl sulfate (SDS) and dodecyl maltoside (DM). This analysis incorporates both folding and unfolding rates, making it possible to determine both the stability of the native state and the process by which the protein folds. Refolding and unfolding occur on the second to millisecond timescale and involve only one relaxation phase, when monitored by conventional stopped-flow. The kinetic data indicate that denaturation occurs around 0.3 mole fraction of SDS, in agreement with CD analysis and acrylamide quenching data. The rate constants have been fit to a three-state folding scheme involving the SDS-denatured state, the native state and an unfolding intermediate that accumulates only under unfolding conditions at high mole fractions of SDS. The stability of DsbB is around 4.4 kcal/mol in DM, and this is halved upon reduction of the two periplasmic disulfide bonds, and is sensitive to mutagenesis. With the caveat that kinetic data are always open to alternative interpretations, time-resolved studies in mixed micelles provide a useful approach to measure membrane protein stability over a wide range of concentrations of SDS and DM, as well as a framework for the future characterization of the DsbB folding mechanism.

The wet granulation process is sensitive to changes in product properties and process variables. The optimal process and formulation are based on the knowledge of the granule growth mechanisms and of the effects of product properties and process variables. This paper presents the study of wet granulation of microcrystalline cellulose powder, MCC (Avicel PH101) using high-shear mixer granulator. It aims at understanding the effect of operating parameters (impeller rotational speed, liquid binder flow ate) and of physicochemical properties (viscosity, wettability) of a binder solution on solid particles surfaces, on the agglomeration kinetics. The experiments are carried out with water, aqueous solutions of sodium carboxymethylcellulose, polyvinylpyrrolidone, hydroxypropylméthylcellulose or a non ionic surfactant oxo-C 10 C 6 at a critical micellar concentration. Concerning the process variables the experimental results show that an optimal interval of impeller speed operation exists ranging from 150 to 200 rpm for granule growth. Below, an uncontrollable agglomerate size and localised over-wetting occur, and above granule breakage occurs. Increasing the liquid binder flow rate reduces the extension of the non growth regime, but does not affect the granule mean size. The effect of the physicochemical properties is evaluated using a modified capillary viscous number, Ca′, that we define as the ratio between the viscous forces (μ L U) and the work of adhesion W a = γ L (1 + cosθ). For Ca′ b 1, the viscosity of the solution does not significantly affect the granulation process. The dominant forces in the granulation process are the interfacial forces since increasing the work of adhesion enhances the growth kinetics. For Ca′ N 1.6, the viscous forces predominate and control the granule growth.

In this review, a comprehensive and illustrative survey is made of the regioselective synthesis of esters of sugars and related compounds using lipases. The main emphasis has been given to the screening and use of commercially available lipases for the enzymatic esterification of neutral monosaccharides, disaccharides, sugar alcohols and their selected ether and ester derivatives. The effect of solvents and solubilizing agents in improving the yields of the resultant sugar fatty acid esters has been incorporated. Further, solvent-free esterification with molten fatty acids, use of ionic liquids and microwave radiations for improvement in the methodology have also been discussed. Copyright © 2006 Society of Chemical Industry

An overview is given on the physicochemical properties of bacterial glycopolymers, i.e., pure oligo-and polysaccharides as well as glycolipids. Data from analysis of the chemical and physicochemical properties of various sugar polymers are summarized. Furthermore, data are presented on the thorough characterization of the most important class of bacterial glycopolymers, the lipopolysaccharides (LPS). These data comprise the chemical characterization, the gel to liquid crystalline phase transition behaviour of their acyl chains, the ultrastructural studies of their morphology, and the investigation of the types of aggregate structures present above the critical micellar concentration (CMC). Furthermore, the relevance of these data with respect to an understanding of the various biological effects elicited by LPS is discussed. #

Science is the attempt to make the chaotic diversity of our sense-experience to a logically unified system of thought. A sound theoretical basis and a rational physicochemical understanding based on experimental findings lead to a proper understanding of a topic. Colloid chemistry strengthened its footing by the extensive studies on gold sols by Michael Faraday in 1850s, however, the term ''colloid'' was coined by Thomas Graham in 1861. Historically, the Stone Age paintings in the Lascaux cave in France and the written records of Egyptian pharaohs were produced with stabilized colloid pigments. The part of colloid science dealing with amphiphilic molecules is so diverse on its own that it is dealt in a separate branch called the ''association colloid''. A key development in the study of association colloids was the observation by James McBain that the osmotic pressure of salts of alkali metal fatty acid displayed a pronounced break in the concentration beyond a specific characteristic concentration, after which the osmotic coefficient remained almost constant . McBain attributed this fact to the self-association of these molecules among themselves (McBain, 1913 in solution. Here, we are providing a molecular as well as thermodynamic approach toward the micellization process.

Cells of Actinobacillus actinomycetemcomitans, a gram-negative pathogen responsible for an aggressive form of juvenile periodontitis, form tenaciously adherent biofilms on solid surfaces. The bacteria produce long fibrils of bundled pili, which are required for adherence. Mutations in flp-1, which encodes the major subunit of the pili, or any of seven downstream tad genes (tadABCDEFG) cause defects in fibril production, autoaggregation, and tenacious adherence. We proposed that the tad genes specify part of a novel secretion system for the assembly and transport of Flp pili. The predicted amino acid sequence of TadA (426 amino acids, 47,140 Da) contains motifs for nucleotide binding and hydrolysis common among secretion NTP hydrolase (NTPase) proteins. In addition, the tadA gene is the first representative of a distinct subfamily of potential type IV secretion NTPase genes. Here we report studies on the function of TadA. The tadA gene was altered to express a modified version of TadA that has the 11-residue epitope (T7-TAG) fused to its C terminus. The TadA-T7 protein was indistinguishable from the wild type in its ability to complement the fibril and adherence defects of A. actinomycetemcomitans tadA mutants. Although TadA is not predicted to have a transmembrane domain, the protein was localized to the inner membrane and cytoplasmic fractions of A. actinomycetemcomitans cells, indicating a possible peripheral association with the inner membrane. TadA-T7 was purified and found to hydrolyze ATP in vitro. The ATPase activity is stimulated by Triton X-100, with maximal stimulation at the critical micellar concentration. TadA-T7 forms multimers that are stable during sodium dodecyl sulfatepolyacrylamide gel electrophoresis in nonreducing conditions, and electron microscopy revealed that TadA-T7 can form structures closely resembling the hexameric rings of other type IV secretion NTPases. Site-directed mutagenesis was used to substitute Ala and Gln residues for the conserved Lys residue of the Walker A box for nucleotide binding. Both mutants were found to be defective in their ability to complement tadA mutants. We suggest that the ATPase activity of TadA is required to energize the assembly or secretion of Flp pili for tight adherence of A. actinomycetemcomitans.

In the present work, we studied the ability of thymol to affect the organization of model membranes and the activity of an intrinsic membrane protein, the GABA A receptor (GABA A -R). In this last aspect, we tried to elucidate if the action mechanism of this terpene at the molecular level, involves its binding to the receptor protein, changes in the organization of the receptor molecular environment, or both. The self-aggregation of thymol in water with a critical micellar concentration (CMC) ∼ = 4 M and its ability to penetrate in monomolecular layers of soybean phosphatidylcholine (sPC) at the air-water interface, even at surface pressures above the equilibrium, lateral pressure of natural bilayers were demonstrated. Thymol affected the self-aggregation of Triton X-100 and the topology of sPC vesicles. It also increased the polarity of the membrane environment sensed by the electrochromic dye merocyanine. A dipolar moment of 1.341 Debye was calculated from its energy-minimized structure. Its effect on the binding of [ 3 H]-flunitrazepam ([ 3 H]-FNZ) to chick brain synaptosomal membranes changed qualitatively from a tendency to the inhibition to a clear activatory regime, up on changing the phase state of the terpene (from a monomeric to a self-aggregated state). Above its CMC, thymol increased the affinity of the binding of [ 3 H]-FNZ (K d-control = 2.9, K d-thymol = 1.7 nM) without changing the receptor density (B max-control = 910, B max-thymol = 895 fmol/mg protein). The activatory effect of thymol on the binding of [ 3 H]-FNZ was observed even in the presence of the allosteric activator gamma-aminobutyric acid (GABA) at a concentration of maximal activity, and was blocked by the GABA antagonist bicuculline. Changes in the dipolar arrangement and in the molecular packing of GABA A -R environment are discussed as possible mediators of the action mechanism of thymol.

Production of biosurfactant by free and alginate-entrapped cells of Pseudomonas Xuorescens Migula 1895-DSMZ was investigated using olive oil as the sole carbon and energy source. Biosurfactant synthesis was followed by measuring surface tension and emulsifying index E24 over 5 days at ambient temperature and at neutral pH. DiVusional limitations in alginate beads aVected the kinetics of biosurfactant production when compared to that obtained with free cells culture. Nevertheless, the emulsion stability was improved and fewer by-products interfered with the biosurfactant activity. A decrease in pH down to 5 in the case of immobilized cells was observed during the Wrst 3 days, after which it returned to its initial value. The minimum values of surface tension were 30 and 35 dynes cm ¡1 achieved after 40 and 72 h with free and immobilized cells, respectively, while the corresponding maximum E24 values were 67 and 62%, respectively. After separation by acetone precipitation, the biosurfactant showed a rhamnolipid-type in nature, and had a good foaming and emulsifying activities. The critical micellar concen-tration was found to be 290 mg l ¡1 . The biosurfactant also showed good stability during exposure to high temperatures (up to 120°C for 15 min), to high salinity (10% NaCl) and to a wide range of pH (4-9).

Ultrafiltration experiments were carried out with tangential cell system. The permeate flux and rejection characteristics of SDS and nonylphenol ethoxylated C 9 H 19 C 6 H 4 (CH 2 CH 2 O) 5 CH 2 CH 2 OH (NPE) micellar solutions for a ceramic tubular membrane (zirconium oxide-Titanium oxide) were investigated. For both surfactants, micelle rejection increased with pressure and reached an asymptotic value at P = 250 kPa beyond which micellar rejection remained unchanged (∼+99%). This was explained in terms of concentration polarization occurring in the vicinity of the membrane-solution interface. Time dependence of the permeate surfactant concentration was also investigated. During the first 2 h of ultrafiltration, the surfactant concentration changed with time. Then a steady-state condition was reached and the permeate concentration remained invariant. This trend was attributed to a time-dependent gradual change of the state of packing of the micelles over the membrane surface. Cr 3+ rejection by SDS-NPE mixed micelles yielded high Cr 3+ rejection (+99.5%) at NPE molar fraction up to 0.2. Within this optimum composition and P = 250 kPa, unexpectedly high rejection (33.50%) was measured below the critical micellar concentration (cmc). This was considered as due to a high surfactant concentration in the vicinity of the membrane surface where micelles are present, although the retentate surfactant concentration is below the cmc. Above the cmc, high Cr 3+ rejections (+99%) were obtained. Interestingly, this rejection was found to be independent of the feed surfactant concentration within the range investigated in this study (3×cmc-30×cmc), suggesting that Cr 3+ rejection is not a function of the surfactant concentration in the bulk retentate solution but a function of the surfactant concentration nearby the membrane surface. The presence of NaCl in the feed surfactant solution showed a drastic adverse effect on Cr 3+ rejection by SDS-NPE micelles. .om (M. Aoudia). used to remove multivalent metal ions from aqueous streams . In this process, an anionic surfactant at a concentration higher than its critical micellar concentration (cmc) is added to the aqueous stream containing the dissolved solutes. The negatively charged micelles cause the cations to bind or adsorb at the micelle interface. The stream is then passed through an ultrafiltration membrane having pore sizes small 0376-7388/03/$ -see front matter

The effect of glycerol on the micellization of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and of the ethoxylated nonionic surfactant Brij 58 has been investigated by various experimental techniques. For both surfactants the critical micellar concentration (cmc), determined by surface tension measurements, is almost unaffected by the presence of glycerol in the mixture; only at high glycerol concentrations ( 20% w/w) does the cmc significantly increase. The area per surfactant molecule at the air-solution interface, A, increases with increasing glycerol weight percentage, w g . Fluorescence quenching measurements indicate that the presence of glycerol induces a lowering of the aggregation number of both surfactants. The glycerol intradiffusion coefficient has been measured by the pulsed-gradient spin-echo NMR technique as a function of glycerol content at constant surfactant concentration. It is almost unaffected by the presence of the surfactants, indicating that no direct glycerol-surfactant interaction occurs in the mixture. The surfactant intradiffusion coefficient has been also measured. In the case of CTAB, it increases with increasing glycerol concentration, a reflection of the decreased aggregation number. For Brij 58, in spite of the lowering of the aggregation number, the surfactant intradiffusion coefficient decreases with increasing glycerol concentration, suggesting an increase of the intermicellar interaction. The experimental evidence shows that for both surfactants the micellization is affected by the presence of glycerol through an indirect, solvent-mediated mechanism. In the case of CTAB, the main effect of glycerol is a lowering of the medium dielectric constant, which enhances the electrostatic interactions in solution. In the case of Brij 58, the results can be interpreted in terms of a salting-out effect according to which glycerol competes with the surfactant for water molecules, causing a dehydration of the surfactant ethoxylic headgroup.

Sodium dodecyl sulphate (SDS), a detergent that mimics some characteristics of biological membranes, has been found to a¡ect signi¢cantly ¢bril formation by a peptide from human complement receptor 1. In aqueous solution the peptide is unfolded but slowly aggregates to form ¢brils. In sub-micellar concentrations of SDS the peptide is initially K K-helical but converts rapidly to a L L-sheet structure and large quantities of ¢brils form. In SDS above the critical micellar concentration the peptide adopts a stable K K-helical structure and no ¢brils are observed. These ¢ndings demonstrate the sensitivity of ¢bril formation to solution conditions and suggest a possible role for membrane components in amyloid ¢bril formation in living systems.

From differential pulse voltammetry, DPV, it was determined the electrochemical behaviour of dopamine, DA, and ascorbic acid, AA, using a carbon paste electrode, CPE, with the surfactant sodium dodecyl sulfate, SDS, present at concentrations around the critical micellar concentration, CMC. It is shown that without SDS in solution, the oxidation peak potential of AA, E AA , and DA, E DA , completely overlap, however when [SDS] > CMC separation is possible between them (E AA − E DA = 238 mV). Moreover, at variance with other proposed systems, the DA potential peak becomes less positive than AA potential peak. Therefore, separation of signals allows selective determination of DA even when AA is present in the same solution. Optimization of the experimental conditions permitted to obtain a calibration plot for the DA in the presence of the AA, having a 0.01-0.2 mM linear range, a detection limit of 5 M and a 0.04812 A M −1 sensitivity. This new approach was used effectively to determine dopamine in real pharmaceuticals obtaining satisfactory results.

The influence of molecular characteristics on the mutual interaction between peptides and nonionic surfactants has been investigated by studying the effects of surfactants on amphiphilic, random copolymers of α-L-amino acids containing lysine residues as the hydrophilic parts. The hydrophobic residues were either phenylalanine or tyrosine. The peptide-surfactant interactions were studied by means of circular dichroism spectroscopy and binding isotherms, as well as by 1D and 2D NMR. The binding of surfactant to the peptides was found to be a cooperative process, appearing at surfactant concentrations just below the critical micellar concentration. However, a certain degree of peptide hydrophobicity is necessary to obtain an interaction with nonionic surfactant. When this prerequisite is fulfilled, the peptide mainly interacts with self-assembled, micelle-like surfactant aggregates formed onto the peptide chain. Therefore, the peptide-surfactant complex is best described in terms of a necklace model, with the peptide interacting primarily with the palisade region of the micelles via its hydrophobic side chains. The interaction yields an increased amount of α-helix conformation in the peptide. Surfactants that combine small headgroups with a propensity to form small, nearly spherical micelles were shown to give the largest increase in α-helix content.

The behaviour of N-hexadecanoylsphingosine (Cer16), N-hexanoylsphingosine (Cer6) and N-acetylsphingosine (Cer2) in aqueous media and in lipid-water systems, monolayers and bilayers has been comparatively examined using Langmuir balance and fluorescence techniques. Cer16 behaves as an insoluble non-swelling amphiphile, not partitioning into the air-water interface, thus not modifying the surface pressure of the aqueous solutions into which it is included. By contrast both Cer6 and Cer2 behave as soluble amphiphiles, up to approx. 100 AM. At low concentrations, they become oriented at the air-water interface, increasing surface pressure in a dose-dependent way up to ca. 5 AM bulk concentration. At higher concentrations, the excess ceramide forms micelles, critical micellar concentrations of both Cer6 and Cer2 being in the 5-6 AM range. When the air-water interface is occupied by a phospholipid, Cer2 and Cer6 become inserted in the phospholipid monolayer, causing a further increase in surface pressure. This increase is dose dependent, and reaches a plateau at ca. 2 AM ceramide bulk concentration. Both Cer2 and Cer6 become inserted in phospholipid monolayers with initial surface pressures of up to 43 and 46 mN m À1 , respectively, which ensures their capacity to become inserted into cell membranes whose monolayers are estimated to support a surface pressure of about 30 mN m À1 . Both Cer2 and Cer6, but not Cer16, had detergent-like properties, such as giving rise to phospholipidceramide mixed micelles, when added to phospholipid monolayers or bilayers. The short-chain ceramides form large aggregates and precipitate at concentrations above approx. 100 AM. These results are relevant in cell physiology studies in which short-and long-chain ceramides are sometimes used as equivalent molecules, in spite of their different biophysical behaviour. D

ABSTRACT Surfactant molecules in water above their critical micellar concentration (CMC) aggregate in spherical or elongated worm-like micelles (living polymers). Like shear-thickening polymer solutions, the apparent viscosity of some worm-like micellar solutions increases with the shear rate and/or the duration of shear. We present the first report of freeze-fracture experiments on worm-like micellar solutions which enables us to study the microscopic structure of unsheared and sheared micellar solutions. When unsheared, two different solutions appear as a network containing polydisperse water cells of diameter less than or equal to 3 microns. When these solutions are sheared they form a gel-like phase of entangled micelles which may also contain regions of aligned micelles as recently predicted( C.H. Liu and D.J. Pine, Phys. Rev. Lett. 77, 2121-2124 (1996)). Regions of aligned micelles probably have lower viscosity than the gel, suggesting that for the sheared system to flow it must maintain pockets of aligned micelles.

The immunosuppressive agent Cyclosporin A (CsA) has very poor solubility in water and, in consequence, non-aqueous formulations have been developed for its intravenous administration to treat patients with transplant rejection. In this article, aqueous micelle solutions of novel amphiphilic copolymers based on methoxy-poly(ethylene glycol) (MPEG) and hexyl-substituted poly(lactides) (hexPLA) were studied for possible incorporation and formulation of CsA, and for their biocompatibility towards novel pharmaceutical applications. Above the critical micellar concentration (CMC), MPEG-hexPLA block-copolymers selfassemble into unimodal micelles with diameters of around 30 nm, either unloaded or drug-loaded. The best shelf-life stability of these formulations was observed when stored at 4°C with a drug loss inferior to 7% after 1 year. The polymer and micelle toxicities were evaluated in vitro for three different cell lines and in vivo using the chick embryo chorioallantoic membrane (CAM) model. The hemolytic property was assessed using human blood samples. As the studies revealed, MPEG-hexPLAs are non-toxic and do not show hemolysis; the same was found for the comparable MPEG-PLAs, both as unimers below their CMC and as polymeric micelles up to copolymer concentrations of 20 mg/mL. At this concentration, CsA was efficiently incorporated into MPEG-hexPLA micelles up to 6 mg/mL, which corresponds to a 500-fold increase of its water solubility. The current recommended clinical concentration administered per infusion (0.5-2.5 mg/mL) can be easily achieved and requires four times less copolymer than with the oftenused Cremophor Ò EL surfactant. In this regard, MPEG-hexPLA micelle formulations can be an applicable formulation in transplant rejection treatments as an injectable CsA carrier system.

Background: Membrane proteins are privileged pharmaceutical targets for which the development of structure-based drug design is challenging. One underlying reason is the fact that detergents do not stabilize membrane domains as efficiently as natural lipids in membranes, often leading to a partial to complete loss of activity/stability during protein extraction and purification and preventing crystallization in an active conformation.

Reversible adsorption of non-ionic surfactants, such as alkyl (C Na E Np) or alkyl phenol polyoxyethylene glycol (C Na PE Np), occurs onto hydrophilic or polar solids below the critical micellar concentration (CMC). As shown in several experimental studies, all adsorption isotherms reach a plateau around the CMC. Generally speaking, the adsorption appears to be a cooperative process involving strong lateral interaction between surfactants and weak interaction with the solid surface. In the first part of this paper, an overview of some recent experimental studies of non-ionic adsorption layer is presented, including fluorescence spectroscopy, neutron scattering and atomic force microscopy. In the second part, a theoretical discussion of the aggregative adsorption process onto hydrophilic solid/water interface is presented. This last part will permit to raise some interesting questions concerning the role of the so-called 'normal interaction' (surfactant/solid interaction) to select the optimal surface aggregate curvature.

The interaction between complexes of plasmid DNA with cetyltrimethylammonium bromide (CTAB) and L929 fibroblasts was first examined using confocal microscopy. The complexes labeled with the DNA intercalator, YOYO-1, were found to be trapped onto the external face of the plasma membrane; a feature that may constitute a major limiting step in transfection. Moreover, since no cytotoxic effect appeared in these conditions, we further inferred that the CTAB molecules remained bound to the DNA. The interaction of the complexes with the membranes was best modeled with neutral vesicles. From anisotropy thermotropic curves of DPHpPC-labeled vesicles and fluorescence resonance energy transfer measurements between these vesicles and YOYO-labeled complexes, we evidenced that the binding of the complexes to the vesicle surface opened the micelle-like domains and unwound DNA. However, DNA was not released but remained stably bound via electrostatic interactions to the CTAB molecules incorporated in the external liposome leaflet. Consequently, the large diameter of the unwound plasmid DNA is likely the major factor that precludes its internalization into the cells by endocytosis. In contrast, anionic vesicles that mimic the cytoplasmic facing monolayer of the plasma membrane rapidly released DNA from the complex. This may explain the previously reported high transfection efficiency of DNA complexed with liposomes composed of neutral lipids and cationic surfactants, since the latter may destabilize the endosomal membrane and induce the release of DNA in the cytoplasm. ß

Ingenierie & Architerctures Macromoleculaires (IAM) team belongs to Gerhardt of Montpellier (ICGM) and has many activities that many focus on the synthesis and characterization and original macromolecules in four topics: ''Controlled Radical (Co)polymerization'', ''Heterochemistry'' (P, Si, F chemistries), ''Clean Process'', ''Green Chemistry and Sustainable Development'' (see ). In the field of Fluorine Chemistry, main interests focus on the radical reactions and macromolecular engineering ranging from the synthesis of organofluorinated synthons or monomers to the design of macromolecular fluorinated architectures such as block, alternated, and graft copolymers, and this wide range of topics is rather unique. Main methodologies are: (i) the telomerization of commercially available fluorinated alkenes (such as vinylidene fluoride, 3,3,3-trifluoropropene, chlorotrifluoroethylene, trifluoroethylene) and synthesized fluoromonomers have been extensively investigated in the presence of numerous chain transfer agents and reviewed in a book (Ref. ); (ii) radical copolymerization of these above fluorinated alkenes with functional commercially or synthesized comonomers (see Chem. Rev. 109 (2009), 6632-6686), with efforts made in the design of specific comonomers to favour the copolymerization also involving concept of acceptor-donor copolymerization; (iii) the controlled radical (co)polymerization of these fluoroalkenes (see Ref. [38]). Further interests are the characterizations (spectroscopic, thermal, surface, or rheological) and applications dealing with surfactants (Ref. ), high performance elastomers, coatings, optics, nanofillers/fluoropolymers composites, or energy-relative activities such as fuel cell membranes (protonic, alkaline, or quasianhydrous), polymer electrolytes for lithium batteries, piezoelectrical and photovoltaic (co)polymers.

~ Surfactanis carrying either a hydrocarbon or a fluorocarbon alkyl ckain have been synthesized. The pol~, head was ekl/el tris(hydroxyiuethyl)acrylanlidomethane @HAM), telonlerized Tt|AM, or a glycosylaied THAM nlok.ty. The aqueous solubility of some of these molecules was increased by oxidb'hlg to a null'oxide the lhioether function lhat associates their hydrophobic and hydropkilic moieties. In all cases, the critical lnicellar concentration ~ ~l,,, i)rhicil)all) , dc:termhled b) die length and chemical ulattlre of the alkyl dlain. The usefulness of these surfaclanis in handlhlg hllegral illeinbrane proteins in solution has been examined using, as lest materials chloroplast lkyhtkoid illelnbralleS lind tile photosynthetic conlplex cytochl'ome b4t] In keeping with earlier observations in oilier systelns, 110110 of the fluorinated surl'actants was able to solubilize thylakoid illenlbraiics. Transfei to a solulioil of fluorinated surl'aclant of ht~f complexes thai had been solubilized and purified in the presence of a classical detergent usually restllted in aggregation and precipitation of the protein, while most homologous molecules with hydrocarbon chahls did keep the ht~/'conlplex soluble, qg'o of the fluorinated surfactants, however, proved able to maintain the bql'complex waler-soluble, intact, and enzymatically active. Because of their lilnitcd affinily lk~r lipid alkyl chahls and oiker hydrocarbon surfaces, fluorinated snrfaclalllS appear ;is potentially illteresling tools for tile sitidy of nlenlbrane proichlx IMi do not stand well eXpOSUI'O tO classical delel'genls 1(0 Socidd fran~'aise de biochimie el biologic lnolik'ulaire / Elsevier, Paris). nienlllnine protdns / detergents I Iluorhulted surfactan|s / cytochronic bof A CIi3-(CH~)I I" B CF3-(CF~)5-,,, J _ .... J < n > cm~" (raM) 7 0. i-0.2 7 0.3 Scheme I. Tdomers wilh D7~fi = 7.

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) have been studied in different aqueous micellar environments using steady-state and time-resolved emission spectroscopy. The charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift, along with an enhancement in the fluorescence intensity in all the micellar media. This is associated with an increase in the fluorescence anisotropy (r), which suggests that the fluorophore molecule experiences motionally restricted environments upon binding with the micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the fluorescing moiety does not penetrate into the core of the micellar units; rather it binds at the micelle-water interfacial region. The binding constant and free energy change during probe-micelle binding have been evaluated from relevant fluorescence data. Light has been thrown on the mode of action of urea on micelle bound probes. The results are interpreted in terms of the model that urea displaces water molecules from the micellar interface and the consequent destabilization leads to the expulsion of the probe molecules from the interfacial region. Polarity and viscosity of the microenvironments around the probe have been determined in the micellar systems.

The recently reported amphiphilic chelate, (Gd(EPTPAC16)(H2O)) 2� , forms supramolecular aggregates in aqueous solution by self-assembly of the monomers with a relaxometrically determined critical micellar concentration (CMC) of 0.34 mM. The effect of sonication on the aggregate size was characterized by dynamic light scattering and relaxometry, indicating the presence of premicellar aggregates and an overall decrease in aggregate size and

We used cryo-electron tomography to visualize Rous Sarcoma Virus, the prototypic alpharetrovirus. Its polyprotein Gag assembles into spherical procapsids, concomitant with budding. In maturation, Gag is dissected into its matrix (MA), capsid (CA) and nucleocapsid (NC) moieties. CA reassembles into cores housing the viral RNA and replication enzymes. Evidence suggests that a correctly formed core is essential for infectivity. The virions in our data set range from ~ 105 to ~ 175 nm in diameter. Their cores are highly polymorphic. We observe angular cores, including some that are distinctively "coffin-shaped" for which we propose a novel fullerene geometry; cores with continuous curvature including, rarely, fullerene cones; and tubular cores. Angular cores are the most voluminous and densely packed; tubes and some curved cores contain less material, suggesting incomplete packaging. From the tomograms, we measured the surface areas of cores and hence their contents of CA subunits. From the virion diameters, we estimated their original complements of Gag. We find that RSV virions, like HIV, contain unassembled CA subunits and the fraction of CA that is assembled correlates with core type; angular cores incorporate ~ 80% of the available subunits and open-ended tubes, ~ 30%. The number of glycoprotein spikes is variable (~ 0 to 118) and also correlates with core type; virions with angular cores average 82 spikes, whereas those with tubular cores, 14 spikes. These observations imply that initiation of capsid assembly, in which interactions of spike endodomains with the Gag layer play a role, is a critical determinant of core morphology.

Among the very homologous family of K-and L-thionins, known for their antimicrobial activity, the viscotoxin subfamily differs from other members because it is cytotoxic against tumoral cells but weakly hemolytic. We studied the interactions between the most active of these toxins, viscotoxin A3 (VA3), and model membranes made of phosphatidylcholine and phosphatidylserine (PS), the major zwitterionic and acidic phospholipids found in eukaryotic cells. Monolayer studies showed that electrostatic forces are essential for the interaction and are mainly involved in modulating the embedding of the toxin in the PS head group region. This in turn induces membrane stiffening, as shown by fluorescence polarization assays with 1,6-diphenyl-1,3,5-hexatriene and its derivatives. Moreover, vesicle permeabilization analyses showed that there are two modes of interaction, which are directly related to the stiffening effect and depend on the amount of VA3 bound to the surface of the vesicles. We propose an interaction model in which the embedding of VA3 in the membrane induces membrane defects leading to the gradual release of encapsulated dye. When the surfaces of the vesicles are saturated with the viscotoxin, complete vesicle destabilization is induced which leads to bilayer disruption, all-or-none encapsulated dye release and rearrangement of the vesicles. ß

In the present work changes in the adsorption of four 14C-labelled pesticides -diazinon, acephate, atrazine and ethofumesate-on a sandy loam soil, induced by application of anionic, cationic and nonionic suffactantstetradecyitrimethylammonium bromide (TDTMA), sodium dodecyl sulphate (SDS) and polyoxyethylene sorhitanmonooleate (Tween 80)-, were determined using a batch equilibrium method. Three concentrations of each surfactant were used: lower, equal to or higher than the critical micellar concentration. The increases or decreases in the values of the Freundlieh constant K for adsorption of the different pesticides by soil in the experiments revealed that the bebaviour of pesticides in soil-water systems with micelle-forming surfactants mainly depends on the degree of hydrophohicity of the pesticide and the type of surfactant, as well as on the concentration of surfactant in the system.

A lattice model for amphiphilic aggregation in the presence of a structured waterlike solvent is studied through Monte Carlo simulations. We investigate the interplay between the micelle formation and the solvent phase transition in two different regions of temperature-density phase diagram of pure water. A second order phase transition between the gaseous ͑G͒ and high density liquid ͑HDL͒ phases that occurs at very high temperatures, and a first order phase transition between the low density liquid ͑LDL͒ and ͑HDL͒ phases that takes place at lower temperatures. In both cases, we find the aggregate size distribution curve and the critical micellar concentration as a function of the solvent density across the transitions. We show that micelle formation drives the LDL-HDL first order phase transition to lower solvent densities, while the transition G-HDL is driven to higher densities, which can be explained by the markedly different degrees of micellization in both cases. The diffusion coefficient of surfactants was also calculated in the LDL and HDL phases, changing abruptly its behavior due to the restructuring of waterlike solvent when we cross the first order LDL-HDL phase transition. To understand such behavior, we calculate the solvent density and the number of hydrogen bonds per water molecule close to micelles. The curves of the interfacial solvent density and the number of hydrogen bonds per water molecule in the first hydration signal a local phase change of the interfacial water, clarifying the diffusion mechanism of free surfactants in the solvent.

Detergent (pentaoxyethylene octyl ether, C 8 E 5 )-induced conformational changes of Humicola lanuginosa lipase (HLL) were investigated by stationary and time-resolved fluorescence intensity and anisotropy measurements. Activation of HLL is characterized by opening of a surface loop (the "lid") residing directly over the enzyme active site. The interaction of HLL with C 8 E 5 increases fluorescence intensities, prolongs fluorescence lifetimes, and decreases the values of steady-state anisotropy, residual anisotropy, and the short rotational correlation time. Based on these data, we propose the following model. Already below critical micellar concentration (CMC) the detergent can intercalate into the active site accommodating cleft, while the lid remains closed. Occupation of the cleft by C 8 E 5 also blocks the entry of the monomeric substrate, and inhibition of catalytic activity at [C 8 E 5 ] less than or equal to CMC is evident. At a threshold concentration close to CMC the cooperativity of the hydrophobicity-driven binding of C 8 E 5 to the lipase increases because of an increase in the number of C 8 E 5 molecules present in the premicellar nucleates on the hydrophobic surface of HLL. These aggregates contacting the lipase should have long enough residence times to allow the lid to open completely and expose the hydrophobic cleft. Concomitantly, the cleft becomes filled with C 8 E 5 and the "open" conformation of HLL becomes stable.

Vesicles prepared by self-assembly of a hydrated mixture of a cationic surfactant (cetyltrimethylammonium bromide) and a lipid (cholesterol) are studied as potential nanocarriers for the delivery of active ingredients. The understanding of the mechanism of the micelle-to-vesicle transition involved in the vesicle formation appears to be crucial regarding the stability of the vesicles as nanovectors. Here, UV-Vis spectroscopy is used to monitor the phase transition from micelles to vesicles promoted by the progressive addition of cholesterol to CTAB micellar solutions. The employed solvatochromic indicator, pinacyanol chloride (PIN), is a cyanine dye that is highly sensitive to the polarity of the medium. The selfassembly between the CTAB and the cholesterol molecules is investigated by means of turbidity (optical density) measurements as well.

Tetrahydrolipstatin (THL, Orlistat) is a potent inhibitor of gastrointestinal lipases. Using the pH-stat technique we report that, in the absence of substrate, THL (at a molar excess of 100) inhibits rapidly (after few minutes of incubation) human pancreatic lipase (HPL). Bile salts over their critical micellar concentration (CMC) were found to accelerate the inhibition process.

In this work a surface tensiometric method was used to study the effect of the chain length of non-ionic surfactants, viz. ethoxylated sorbitan esters, on micellar composition, critical micellar concentration, mutual interaction parameter (β 12), and activity coefficients of the mixed micelles formed with the cationic surfactant cetylpyridinium chloride at 25 °C. The micellar characteristics evaluated using the Clint, Rubingh, and Blankschtein models deviated significantly from ideality, and were used to ascertain the validity of these theories. Thermodynamic stability in terms of Maeda’s approach and interfacial properties is also discussed.

The micellization of pure monosubstituted sucrose fatty acid esters in water, namely sucrose octanoate, sucrose decanoate, sucrose laurate, sucrose dodec-5-cis-enoate, sucrose myristate, and sucrose palmitate, has been investigated by means of two NMR methods, pulsed field gradient spin-echo NMR (PFGSE-NMR), giving access to the self-diffusion coefficients of free molecules and micelles in solution, and the ERETIC method (electronic reference to access in vivo concentrations) for the measurement of concentrations by external calibration of a synthetic NMR signal. The early micellar regions and, when possible, the premicellar regions were investigated. By this method, we obtained the hydrodynamic radii of micelles, displaying a linear progression in relation to the chain length and an accurate determination of critical micellar concentration (CMC) for each sucrose ester. The effect of the regiochemistry of fatty chain grafting has been investigated, showing special behavior for 1 -O-sucrose palmitate.

Our research group is interested in the study of different technological approaches to treat hospital biofilm as a means to constrain nosocomial-acquired infections. The present work investigated the effect of the incorporation of the antibacterial agent triclosan (TS) into polymeric micelles of poloxamine T1107 (M W = 15 kDa, 70 wt% PEO). The aggregation phenomenon was primarily investigated by means of Critical Micellar Concentration in a broad range of pH. Then, the effect of the polymer concentration on the micellar size was evaluated by Dynamic Light Scattering. Solubility levels increased up to 4 orders of magnitude. The drug inclusion affected the micellization, resulting in size increase and micellar fusion. This phenomenon was only apparent in TS-saturated systems. TS-loaded aggregates proved to be active in vitro against a broad spectrum of bacteria but more importantly, also against two representative clinical pathogens: methicilin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VREF). While the former was sensitive to even very low TS levels attainable in poloxamine-free aqueous media, the later was inhibited only when exposed to higher drug levels affordable exclusively using an inclusion system. These findings indicated the release of the drug from the reservoir. Finally, the activity of a TS-containing 5% poloxamine combination of pH 7.4 was assessed on biofilms of Staphylococcus epidermidis. Results showed a significant decrease (p < 0.001) in the number of Colony-Formation Units when the biofilm was exposed to the TS/ poloxamine as compared to the limited activity of the polymer-free TS control.

Spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion (1) in dichloromethane with added base is catalyzed by cationic surfactants (RNMe3Br, R = n-CsH~7, n-Ct2H25, and n-CI6H33), by EtNMe3Br and n-BuNMe3Br, by RaNBr (R = Et, n-Bu, n-CsH17, and n-CI2H25), and by PhCH2NR3Br (R = Et, n -Bu). The tetraalkylammonium and benzylammonium bromides are better catalysts than the n-alkylammonium bromides. Reaction in Bu4NBr and CTABr (n-CI6H33NMe3Br) is inhibited by water, and conductivity and IH NMR spectrometry show that CTABr plus water form "water pool" reverse micelles. Reaction in the absence of quaternary ammonium salts is faster when the base is tetramethylguanidine rather than Et3N, probably because Et3N+H deactivates 1 by hydrogen bonding. This difference disappears in CTABr, which disrupts the hydrogen bonding. In the absence of water, reaction probably occurs in small ion clusters of quaternary ammonium bromides which are gradually transformed into less catalytically effective water pool reverse micelles on addition of water.